Some questions regarding Sportscar/Le Mans Racing:

I'm fairly sure that turbo diesel engines are not the highest performing engines in motoring at the minute, but I might be wrong. I'm basing this on the fact that Formula 1 engines, and the engines that power all high performance road vehicles are petrol powered, with a trend to small(er) turbo petrol engines from large multi cylinder normally aspirated ones. With this in mind it is therefore somewhat surprising that by far the fastest cars at the Le Mans 24 Hours were turbo diesels (if you kind of ignore the fact that the were the only works supported full prototypes, apart from the tortoise slow Aston Martins). At one point one of the Audi/Peugeots comfortably out dragged one of the petrol powered Rebellion Lola Toyota's on Mulsanne, which prompted the Eurosport commentator to complain re the current equivalency rules twix Diesels and Petrol's.

I'm a bit new to Sportscar racing, so, my questions are:
A) why is this so, do the Diesel's run smaller air restrictors, or is it just because the only 2 'proper' teams happened to be running diesels?
B) what sort of engine size/restrictor equivalency would be fair?
C) does this not require a rethink, you would think Porsche/GM/Toyota/Fiat Group or any high performance manufacturer would be unlikely to build a prototype that will get trounced by family car manufacturers?

Thanks

Bump

The engines in sportscar racing are regulated according to displacement, air restrictors, boost pressure and so on. The idea is to try and make different engine types competetive.
However there is a large group in the sportscar world that beleives that the regulations give a too big advantage to the diesel engines. Indeed this advantage has been reduced over the years, but the diesels are still comfortably ahead. Some of this is undoubtly due to the fact that the only major manufactorers in sportscar racing run diesels, but there may indeed be an inherent advantage of the diesel engines in the current regulation.

The diesel/petrol equivalency is a large can of worms in the sportscar world.

It's as much about torque as horsepower - and a turbodiesel has a lot more than a N/A petrol with the current capacity restrictions.

A turbo-charged petrol car would be closer in torque output, but still not as high, but would produce comparatively more hp due to a higher rev limit.

The other big advantage was the energy density of diesel makes it more efficient for a set weight than petrol - so means either smaller fuel tanks (and less weight) or longer between stops. The regulations have reduced the diesels fuel tank sizes to reduce the latter advantage, but the former still remains.

Finding a good balance on the equivalence would be devilishly difficult but ATM petrol powered cars have absolutely no chance in LMP1. Not withstanding the technical superiority of Audi/Peugot, the tweaks to the rules for 2011 were very small.

Quite how hard the ACO try to find a genuine balance will depend on how much they want an expanded competitive field compared to keeping Audi and Peugot 'sweet'.

The other side of the question would be should the ACO actually try to equalise things? The greater economy of diesel does mean that it is genuinely a superior fuel for endurance racing.

I am by no means an expert on the technical details of engines, and would probably not even qualify as knowledgeable, but with that in mind, perhaps some of these stories linked to below (some older than others) can shed some light on this issue.

One of the main points made in these articles seems to focus on the limitations imposed on both diesel and petrol engines in the regulations.

AutoblogGreen - ACO reveals 2010 Le Mans rules, diesels get more weight, less air (August 2009)
Popular Mechanics - Why Diesels Rule the Le Mans Raceway (June 2010)
Motorsport.com - Le Mans Blog: Juggling Engine Performance (June 2011)

Some related discussion on other forums:

Honda-Tech.com - Diesel Le Mans Prototype -- Why are they faster? (June 2007)
LFS.net - Engines; Normally aspirated, turbo, vs Diesel engines. How to compare? (March 2008)
F1Technical.net - Peugeot diesels, why not in F1? (June 2008)

Edited by Nonesuch, 13 June 2011 - 13:50.

I am by no means an expert on the technical details of engines, and would probably not even qualify as knowledgeable, but with that in mind, perhaps some of these stories linked to below (some older than others) can shed some light on this issue.

One of the main points made in these articles seems to focus on the limitations imposed on both diesel and petrol engines in the regulations.

AutoblogGreen - ACO reveals 2010 Le Mans rules, diesels get more weight, less air (August 2009)
Popular Mechanics - Why Diesels Rule the Le Mans Raceway (June 2010)
Motorsport.com - Le Mans Blog: Juggling Engine Performance (June 2011)

Some related discussion on other forums:

Honda-Tech.com - Diesel Le Mans Prototype -- Why are they faster? (June 2007)
LFS.net - Engines; Normally aspirated, turbo, vs Diesel engines. How to compare? (March 2008)
F1Technical.net - Peugeot diesels, why not in F1? (June 2008)

Thanks!!

The other side of the question would be should the ACO actually try to equalise things? The greater economy of diesel does mean that it is genuinely a superior fuel for endurance racing.

Are privateers able to obtain competitive diesel LMP1 engines for reasonable prices (compared to petrol engines)?

If some, say, Lotus (Judd) LMP1 engine was entered as a customer diesel engine would it be much more expensive than the petrol engines?

The other side of the question would be should the ACO actually try to equalise things? The greater economy of diesel does mean that it is genuinely a superior fuel for endurance racing.

well, thats part of my question. If diesels are genuinely superior then that is fine. But I would suggest that they aren't seen as they have a 1.7L head start on turbocharged petrol engines, even if nobody bar Aston Martin is running one. If the diesels were easily spanking 3.7L petrol turbo's then ok, but they aren't. I think diesels and petrols should have exactly the same rules, and if Audi/Peugeot can beat an equal sized turbo charged petrol Porsche/Toyota/Ferrari engine in a straight fight then fair play to them, there could be no arguments then. I would suggest the playing field is not level at the moment and Audi and Peugeot aren't proving much other than that they can read a rule book.

Are privateers able to obtain competitive diesel LMP1 engines for reasonable prices (compared to petrol engines)?

If some, say, Lotus (Judd) LMP1 engine was entered as a customer diesel engine would it be much more expensive than the petrol engines?

Yes it would. Not sure on the exact figures but it was suggested in the Eurosport broadcast that the cost would be close to double.

well, thats part of my question. If diesels are genuinely superior then that is fine. But I would suggest that they aren't seen as they have a 1.7L head start on turbocharged petrol engines, even if nobody bar Aston Martin is running one. If the diesels were easily spanking 3.7L petrol turbo's then ok, but they aren't. I think diesels and petrols should have exactly the same rules, and if Audi/Peugeot can beat an equal sized turbo charged petrol Porsche/Toyota/Ferrari engine in a straight fight then fair play to them, there could be no arguments then. I would suggest the playing field is not level at the moment and Audi and Peugeot aren't proving much other than that they can read a rule book.

As a fan, this is what I would like to see but are there any manufacturers who would actually build petrol engined LMP1s to those specs?

well, thats part of my question. If diesels are genuinely superior then that is fine. But I would suggest that they aren't seen as they have a 1.7L head start on turbocharged petrol engines, even if nobody bar Aston Martin is running one. If the diesels were easily spanking 3.7L petrol turbo's then ok, but they aren't. I think diesels and petrols should have exactly the same rules, and if Audi/Peugeot can beat an equal sized turbo charged petrol Porsche/Toyota/Ferrari engine in a straight fight then fair play to them, there could be no arguments then. I would suggest the playing field is not level at the moment and Audi and Peugeot aren't proving much other than that they can read a rule book.

True equivalency has always been almost impossible to achieve, even if it was only between n/a and turbo petrol engines. Look at the 3 litre F1 formula. For years it also allowed 1.5 litre forced induction, meaning supercharged but no-one could build one that was competitive (although I doubt anyone tried). But then Renault tried turbos and quickly the n/a engines were outclassed. Bring is different fuels as well and it becomes even harder. Look at BTCC which had turbo diesels, n/a petrol and n/a LPG engines. One was always better than teh others and whenever they tinkered with the rules it just swung the balance another way. The rotary engine was another problem - the swept volume of a RX7 rotary was only 1300cc but it was generally counted as double that which still gave it a power advantage over standard fourstrokes of the same nominal displacement. It is a hopeless area. As regards Le Mans, ACO will not allow Peugeot to be outclassed as they are French. Audi are just a nuisance for using the same technology and spoiling the show!

The turbo-diesel engined cars are winning for two main reasons:

- Only works teams with big budgets run them, therefore benefit from highly developed chassis'

- Diesel fuel efficiency

In 2009 the Aston LMPs were faster than the Audis in a straight line indicating that they weren't lacking in power at all, but they didn't have the grip or the fuel efficiency to go for the win.

The way I see it, ACO technical regulations for petrol engines is what is killing them. Of course manufacturers can build petrol engines that could give the current diesels a run for their money but the rules won't allow them to. I guess Audi and Peugeot spend alot more than everyone else, which makes the gap even bigger and makes it all seem worse, but alot of that money also probably goes towards lobbying ACO to keep the petrol cars down via technical regulations.

ACO's equivalency target is to have the fastest diesel and the fastest petrol within 2% of each other in performance. I think this target is 'overall performance' as they have further reduced fuel rig flow for diesels but increased flow for petrol, in addition to smaller tank size for diesels and larger for petrol - a bid to negate the economy of the diesel cars. It was interesting to hear one of the GTE Pro teams commenting that the larger sized restrictor specified by the ACO recently did not help them reduce their refuel time significantly because their fuel rig pressures were not meant to support that increased flow.

Certainly a very challenging task for the ACO because in theory you could have equivalency to perfection such that one team runs both a diesel and petrol and finds both cars clocking similar lap times and doing similar number of laps between stints and spend same amount of time refuelling.

But if that team hands that diesel over to Audi or Peugeot, the car starts to go quicker and quicker.. because of the vast resources now available in developing the car. It's a moving target for the ACO because the real disparity is not just in the cars but in the team resources available

Edited by ferruccio, 13 June 2011 - 18:30.

So in a nutshell, for there to be true equivalency, we need a large manufacturer to lobby for petrol engines, preferably Porsche and/or FIAT (Ferrari/Maserati/Alfa/Lancia) for weight of name or Renault for weight of Frenchness?!

The issue is that are just too many rules and regulations instead of just letting natural selection do what it does with road cars.Having rules interfering with the process of letting them all sort themselves out can then just be abused by any group with an interest in whatever type to engineer the result that they want.Which is where we are at the moment instead of seeing a forced induction big petrol V12 Aston battling with a similar powered Merc etc and the diesels where they are in the real world on the road in which eventually the weight/ torque /power /equation beats them just like it does in the real world of really fast road supercars versus trucks.

Edited by Vanishing Point, 13 June 2011 - 19:04.

So in a nutshell, for there to be true equivalency, we need a large manufacturer to lobby for petrol engines, preferably Porsche and/or FIAT (Ferrari/Maserati/Alfa/Lancia) for weight of name or Renault for weight of Frenchness?!

Thats probably one possible way of looking at it.

I do think however that in the beginning when diesels started racing, the regs were clearly in their favour. I think ACO wanted to attract the manufacturers to race diesels and so they were incentivized as the costs for developing a competitive diesel was high and the manufacturers would want some assurance that it would be worth their time.

The performance differential against the petrols were too great and the ACO started culling the diesels performance every year but with some advantage still in place.

However I don't believe that either Audi or Peugeot are committed to a diesel programme more than commercially necessary. Their 'loyalty' is to whatever type of powerplant gives them the best chance of winning. Right now it is still the diesel. Wolfgang Ullrich did hint that when they looked at the new concept to replace the R15, they looked at everything in relation to the ACO regs. not just whether open or closed cockpit but also whether diesel or petrol.. and he said the diesel route still provided the best chance of winning.

the head of lola said there where 5 manufactorers who would like to come in, but wont because of the diesels having the advantage. he said the situation is worse that before now aswell, as the diesels are at 900kg again.

the diesels use the extra power to run more downforce mostly, just like we had in f1 a few years ago

the key aspects are restrictor size, displacement, turbo boost pressure (if avalible)

restrictors limit the amount of air going in, and that effects what revs are most effiecent, which typicaly means low revs

the head of lola said there where 5 manufactorers who would like to come in, but wont because of the diesels having the advantage. he said the situation is worse that before now aswell, as the diesels are at 900kg again.

the diesels use the extra power to run more downforce mostly, just like we had in f1 a few years ago

the key aspects are restrictor size, displacement, turbo boost pressure (if avalible)

restrictors limit the amount of air going in, and that effects what revs are most effiecent, which typicaly means low revs

If I was the ACO - I'd prefer those 5 Manufacturers in - and would cut the petrols some slack. If that annoys Audi/Peugeot - Tough!! Go and play somewhere else. I'd rather 5 (hopefully Sportscar) Manufacturers at the front battling for honours, than 2 family hatch Manufacturers dominating.

Obviously, it's not as simple as that, and there's all kinds of vested interests, politics, etc

The ACO should loby some petrol car manufacturers, preferably Luca de Montezemelo and whichever descendent of Ferdinand Porsche runs the show now, and offer them some incentives to get involved. A race between quicker, more powerful but thirsty hares (petrol) and more efficient, very torquey erm slightly slower hares (diesels) would be well worth watching.

The ACO should loby some petrol car manufacturers, preferably Luca de Montezemelo and whichever descendent of Ferdinand Porsche runs the show now, and offer them some incentives to get involved. A race between quicker, more powerful but thirsty hares (petrol) and more efficient, very torquey erm slightly slower hares (diesels) would be well worth watching.

Well that was what I thought was the plan when the Diesels came in in 2006 - the petrols would go away from the diesels, but they'd come back through fuel efficiency, etc
Sadly, this hasn't happened - the diesels are faster, full stop.

It's as much about torque as horsepower -

Certainly isn't.

The turbo-diesel engined cars are winning for two main reasons:

- Only works teams with big budgets run them, therefore benefit from highly developed chassis'

- Diesel fuel efficiency

In 2009 the Aston LMPs were faster than the Audis in a straight line indicating that they weren't lacking in power at all, but they didn't have the grip or the fuel efficiency to go for the win.

Top end speed is a very minor factor. RLM asked one of the petrol drivers (I forget who) where the diesels got their advantage during qualifying. His answer was that they were able to put the power down faster and stride away. That's all about the torque a diesel puts out compared to a petrol.

It's all very well having a higher terminal velocity, but if you take an age to get there then you're going to be looking at the back of the diesel from almost a standing start.

the head of lola said there where 5 manufactorers who would like to come in, but wont because of the diesels having the advantage. he said the situation is worse that before now aswell, as the diesels are at 900kg again.

He said he had 5 wanting to come in, but the ACO had taken so long to decide the rules that had put them off.

For the future, there are two routes. Either the current 24 Heures du Diesel Marketing continues or complete revamp to the regulations. Fortunately the latter one seems to be what the involved parties are thinking about according to leaked details from a constructors meeting held last year (mulsannescorner.com, go to "7.19.10" "Power: limited by a maximum instantaneous amount of energy that can be used", "Type of engine: All types of engine apart from turbines, reactors and engines using Stirling cycle"...

Edited by Meanstreak, 13 June 2011 - 22:23.

Top end speed is a very minor factor. RLM asked one of the petrol drivers (I forget who) where the diesels got their advantage during qualifying. His answer was that they were able to put the power down faster and stride away. That's all about the torque a diesel puts out compared to a petrol.

It's all very well having a higher terminal velocity, but if you take an age to get there then you're going to be looking at the back of the diesel from almost a standing start.

When your car has adjustable gear ratios, it's a moot point.

The ACO should loby some petrol car manufacturers, preferably Luca de Montezemelo and whichever descendent of Ferdinand Porsche runs the show now, and offer them some incentives to get involved. A race between quicker, more powerful but thirsty hares (petrol) and more efficient, very torquey erm slightly slower hares (diesels) would be well worth watching.

There's only one way to find out which would be the winner and that's to allow both petrol and diesel cars to run with forced induction and without fuel tank capacity limits,engine capacity limits,and without restrictors in just the same way that a Ferrari or an Aston customer does'nt have to buy a road car that's been limited in any way to allow a diesel car to look a like a better choice than it actually is.Mercedes already have a road car based engine available in the twin turbo AMG V12 which is known for having enough torque to pull a house down.

The result this year seemed to show that a faster car,which can't run as far on the fuel carried,can still be competitive with a slower car that can run further.It would need a big rule change to allow that to be taken to it's logical conclusion in a real race between the petrols and diesels with both being allowed to use their relative advantages to the maximum.

Edited by Vanishing Point, 14 June 2011 - 01:12.

The ACO are considering reintroducing Group C type rules for 2014 onwards where teams are given a fixed amount of fuel to get to the finish.

gt3 has similer rules to that, and performance balancing.

and to take away fuel tank limits, and let them have monsterously powerful engines is a scary thought.

i think the audi's did 4 stints on a set of tyres (mostly) with each stint being 10-11 laps. pug did mostly 3 stints on tyres. changing tyres aparently costs 30seconds, so audi gained back some time with that.

Top end speed is a very minor factor. RLM asked one of the petrol drivers (I forget who) where the diesels got their advantage during qualifying. His answer was that they were able to put the power down faster and stride away. That's all about the torque a diesel puts out compared to a petrol.

It's all very well having a higher terminal velocity, but if you take an age to get there then you're going to be looking at the back of the diesel from almost a standing start.

This implies that the petrol cars are able to go to full throttle without wheelspin (ie insufficient torque) at any point after the corner apex which is patently nonsense.

i think the audi's did 4 stints on a set of tyres (mostly) with each stint being 10-11 laps. pug did mostly 3 stints on tyres. changing tyres aparently costs 30seconds, so audi gained back some time with that.

Yes, and was quite amazing to see both from day break, both Treluyer and Lotterer stretching their runs to five stints each on one set of tyres... though Lotterer ended up making an unscheduled tyre change due to the puncture

This implies that the petrol cars are able to go to full throttle without wheelspin (ie insufficient torque) at any point after the corner apex which is patently nonsense.

Yes.

Also I think 'top end speed' and 'terminal velocity' refers to the same thing. Certainly not a 'minor thing' at Le Mans because of the Mulsanne straight. It is over 5km long, broken by 2 chicanes. Used to be one long straight until the FIA stepped in.

The ACO are considering reintroducing Group C type rules for 2014 onwards where teams are given a fixed amount of fuel to get to the finish.

Fuel? Leaked minutes on Mulsannes Corner (the link I gave just few posts above) mentions energy, not fuel. Obviously makes more sense with energy recovery systems.

This implies that the petrol cars are able to go to full throttle without wheelspin (ie insufficient torque) at any point after the corner apex which is patently nonsense.

How does it imply that? It implies that the Diesels accelerate much quicker.

Yes.

Also I think 'top end speed' and 'terminal velocity' refers to the same thing. Certainly not a 'minor thing' at Le Mans because of the Mulsanne straight. It is over 5km long, broken by 2 chicanes. Used to be one long straight until the FIA stepped in.

It is important, but if you only get to that top speed at the braking point when a few mph more is not going to make you faster when the other car has been at its top speed for half the straight.

and to take away fuel tank limits, and let them have monsterously powerful engines is a scary thought.

It's no more 'scary' than when a customer buys an AMG V12 Mercedes with the 155 mph limiter deleted and then uses it on the autobahn.It seems ridiculous that theres a situation whereby fast road cars and road car drivers are prepared to accept more risks than race teams if that's what's stopping them.I've got nothing against making cars and circuits as safe as possible but Stirling Moss does have a point in that we can't allow the 'risk' issue to take control over all aspects and there's no evidence to suggest that the old Can Am formula was any more inherently dangerous than overregulated forms of the sport like F1.

Edited by Vanishing Point, 14 June 2011 - 11:09.

How does it imply that? It implies that the Diesels accelerate much quicker.

It seems that a lot of people can't understand the idea of more torque at the flywheel being turned into more bhp at the wheels by being able to pull a higher gear and therefore turn the wheels faster than something with less torque at the flywheel can.

It seems that a lot of people can't understand the idea of more torque at the flywheel being turned into more bhp at the wheels by being able to pull a higher gear and therefore turn the wheels faster than something with less torque at the flywheel can.

Exactly.

Exactly.

That's the secret of the diesels success.However big forced induction petrol engines,(if the rule makers/jobsworths would 'go away' and leave natural selection to sort it out instead) have the advantage of being able to provide both high levels of low down torque at the flywheel and high power outputs by being able to sustain those levels of torque higher up the rev range which means that in addition to being able to pull the same high gearing they also have more outright pace at the top end.It's obvious that the rule makers know all that and that the slow petrol versus fast diesel racing that we're getting is just a manufactured 'result' and I'm surprised that the drivers are prepared to go along with it all as,after all the risks, it seems to me to be a hollow victory.

If those rule makers would just do as I'm politely suggesting and just 'go away' and let the engineers and drivers win races not the rule book I'd prefer to either win or lose fair and square with an unlimited diesel or an unlimited petrol car depending on which one wins on it's own merits not on what the regs say.My suggestion of a petrol V12 AMG twin turbo Mercedes and Aston powered LMP cars versus V12 diesel Peugeots and Audis would be something worth seeing next year. But just hope it stays dry and warm for the race.

Torque is everything. Yes, the absolute horsepower of the diesels is slightly higher than the best petrol cars, say 630HP to 570HP, but the torque advantage is huge, which as others have pointed out leads to the mid range (100mph-180mph) acceleration in a diesel LMP being much, much quicker than in a petrol car. Yes, the Aston Lola had lots of power and a slippery body so it peaked at an equal speed to the diesels, but off the corners it struggled and the Aston team chose to run much less downforce than the Audis and Pugs so that they could have such a high terminal velocity while the diesels absolutely destroyed the Aston Lola in the Porsche Curves where downforce is everything. For an idea of the torque advantage, here is a news brief from Mike Fuller's excellent website, mulsannecorner.com-

"So how much torque are the current generation diesels making? We'll be using the Peugeot engine as the basis, but ultimately we're generating data for a "generic" diesel. Stephen Knight, "knighty", suggested this first method (and guided us through the second), simply pro-rata the the torque of the previous 5.5 liter engine to 3.7 liters. We're going to use the official figures for the 908 HDi FAP's torque, 1200 Nm, though we understand this is about 15% too low. Reducing that figure by 32.7% (the difference in capacity between the 5.5 and 3.7 L) gives us 807 Nm of torque for the 3.7 liter. OK, so that's a bit of a ham-fisted way to estimate torque, but it gives us an initial figure.

So we've previously calculated a power output based on top speed and drag estimates of between 609 and 594 hp for the "908". Taking an average, 601.5 hp, we can calculate for torque using the formula:

Power (bhp) = (Torque(lb/ft) x RPM) / 5252

multiply by 1.35582 for Nm

Plugging in 601.5, and using an rpm range from 4500-2500 RPM (remember, diesels rev much lower), and solving for torque we get and torque range of between 952 and 1712 Nm. Obviously it's very RPM dependent. But more importantly, we're calculating torque at peak power and this isn't accurate. The torque peak is going to occur a bit below the RPM for peak power, and therefore the power at that RPM is going to be reduced as well. And obviously power varies with RPM though we're going to keep it constant throughout our 2000 RPM ranges (for all our cases, see below) as we haven't a way to predict the relationship (or, plot the curves) in our fictitious diesel engine. So we're going to have to make some assumptions. Let's assume that at peak torque RPM the engine is producing 75 hp less than what it does at peak power RPM. Therefore we'll use 526.5 hp. Plugging that back into the same RPM range gives use between 834 and 1500 Nm . Averaged, that's 1167 Nm.

So now that we have a rough figure for the diesel, what does the opposition generate?

With a calculated 570 hp, the gasoline powered Judd 3.4 liter, using similar methodology (knocking 75 hp off peak power, but using an RPM range from 10000-8000), generates between 353 and 441Nm of torque (397 Nm averaged). So between 42 and 29% the torque of the diesel. The high revving nature of the normally aspirated engine simply kills torque production.
So what about a gasoline powered turbo engine? At the moment we really don't have reliable figures for the Aston Martin in the power department. But let's just assume a solid 600 hp at peak power for a "generic" gasoline powered turbo. Using an RPM range between 7000 and 5000 RPM (gas turbos torque peak won't be as low as a diesels) gives us 534 and 748 Nm of torque at 525 hp (641 Nm average).

So it's pretty easy to see that the torque figures for a normally aspirated gasoline power engine are not even in the same ballpark. The gas powered turbo has a better chance, but there isn't even any overlap if you look at best case (for gas) vs. worst case (for diesel). Admittedly there is a lot of fudge in our factoring, but there's really not enough to turn a 64% difference into a 5% difference.

With the ACO giddy to add hybrids to the line up, and the manufacturers waiting in the wings having designed their new cars around such systems, the performance balance is simply set to go from poor, to ridiculous. And the ACO has only shown hesitancy in addressing the issue."

Torque is everything. Yes, the absolute horsepower of the diesels is slightly higher than the best petrol cars, say 630HP to 570HP, but the torque advantage is huge, which as others have pointed out leads to the mid range (100mph-180mph) acceleration in a diesel LMP being much, much quicker than in a petrol car. Yes, the Aston Lola had lots of power and a slippery body so it peaked at an equal speed to the diesels, but off the corners it struggled and the Aston team chose to run much less downforce than the Audis and Pugs so that they could have such a high terminal velocity while the diesels absolutely destroyed the Aston Lola in the Porsche Curves where downforce is everything. For an idea of the torque advantage, here is a news brief from Mike Fuller's excellent website, mulsannecorner.com-

"So how much torque are the current generation diesels making? We'll be using the Peugeot engine as the basis, but ultimately we're generating data for a "generic" diesel. Stephen Knight, "knighty", suggested this first method (and guided us through the second), simply pro-rata the the torque of the previous 5.5 liter engine to 3.7 liters. We're going to use the official figures for the 908 HDi FAP's torque, 1200 Nm, though we understand this is about 15% too low. Reducing that figure by 32.7% (the difference in capacity between the 5.5 and 3.7 L) gives us 807 Nm of torque for the 3.7 liter. OK, so that's a bit of a ham-fisted way to estimate torque, but it gives us an initial figure.

So we've previously calculated a power output based on top speed and drag estimates of between 609 and 594 hp for the "908". Taking an average, 601.5 hp, we can calculate for torque using the formula:

Power (bhp) = (Torque(lb/ft) x RPM) / 5252

multiply by 1.35582 for Nm

Plugging in 601.5, and using an rpm range from 4500-2500 RPM (remember, diesels rev much lower), and solving for torque we get and torque range of between 952 and 1712 Nm. Obviously it's very RPM dependent. But more importantly, we're calculating torque at peak power and this isn't accurate. The torque peak is going to occur a bit below the RPM for peak power, and therefore the power at that RPM is going to be reduced as well. And obviously power varies with RPM though we're going to keep it constant throughout our 2000 RPM ranges (for all our cases, see below) as we haven't a way to predict the relationship (or, plot the curves) in our fictitious diesel engine. So we're going to have to make some assumptions. Let's assume that at peak torque RPM the engine is producing 75 hp less than what it does at peak power RPM. Therefore we'll use 526.5 hp. Plugging that back into the same RPM range gives use between 834 and 1500 Nm . Averaged, that's 1167 Nm.

So now that we have a rough figure for the diesel, what does the opposition generate?

With a calculated 570 hp, the gasoline powered Judd 3.4 liter, using similar methodology (knocking 75 hp off peak power, but using an RPM range from 10000-8000), generates between 353 and 441Nm of torque (397 Nm averaged). So between 42 and 29% the torque of the diesel. The high revving nature of the normally aspirated engine simply kills torque production.
So what about a gasoline powered turbo engine? At the moment we really don't have reliable figures for the Aston Martin in the power department. But let's just assume a solid 600 hp at peak power for a "generic" gasoline powered turbo. Using an RPM range between 7000 and 5000 RPM (gas turbos torque peak won't be as low as a diesels) gives us 534 and 748 Nm of torque at 525 hp (641 Nm average).

So it's pretty easy to see that the torque figures for a normally aspirated gasoline power engine are not even in the same ballpark. The gas powered turbo has a better chance, but there isn't even any overlap if you look at best case (for gas) vs. worst case (for diesel). Admittedly there is a lot of fudge in our factoring, but there's really not enough to turn a 64% difference into a 5% difference.

With the ACO giddy to add hybrids to the line up, and the manufacturers waiting in the wings having designed their new cars around such systems, the performance balance is simply set to go from poor, to ridiculous. And the ACO has only shown hesitancy in addressing the issue."

There's only one way to go for those who are'nt happy about the direction of where the ACO wants to take the 'race' and that's to boycott it.It's happened a few times in the past when the regs have been found to cause obvious disadvantages to some competitors in,what should be,a type of racing based on the logic of the free choice criterea which apply when buyers choose their road cars.

There's no engine capacity or induction limits when a buyer enters the showroom to choose between buying a diesel Jaguar XF or the forced induction petrol 5 Litre XFR version for example and the same applies when choosing wether to buy that 6.5 Litre twin turbo V12 AMG Merc.

Those figures above seem to be more of a reflection on the disadvantages of using relatively small capacity high revving petrol engines instead of large capacity ones more than any reflection on the ability of petrol engines to close the deficit.When the capacity of petrol engines is increased to more realistic levels the torque/power equation starts to look a lot more attractive versus diesel which is why Jaguar went for that idea with the XFR and Mercedes with the AMG V12 not big diesels instead.

Torque is everything. Yes, the absolute horsepower of the diesels is slightly higher than the best petrol cars, say 630HP to 570HP, but the torque advantage is huge, which as others have pointed out leads to the mid range (100mph-180mph) acceleration in a diesel LMP being much, much quicker than in a petrol car. – –

The torque difference doesn't matter at all...* Torque is totally insignificant and arbitrary number we should completely ignore. I can't realise why people dig it up over and over again. Torque is strictly related to angular velocity of the engine an for example a steam engine has a lot of torque...

All* that matters when conserning a RACING ENGINE is POWER, power and nothing else.

In SI units: POWER = TORQUE × ANGULAR_VELOCITY.
Which means that: POWER = (2PI / 60) × TORQUE [nm] × FREQUENCY [rpm].

And of course the most important of them all: TORQUE × LEVERAGE = FORCE = MASS × ACCELERATION, which means that ACCELERATION = TORQUE × LEVERAGE / MASS.**

But this torque is measured at the wheels not at the engine! And if we have a car moving at a certain velocity, then the angular velocity of its wheels is FIXED to ANGULAR_VELOCITY = VELOCITY / LEVERAGE . That is TORQUE = POWER / ANGULAR_VELOCITY.

If we combine them all we get: ACCELERATION = POWER / (VELOCITY × MASS). No torque here... and from this formula it's evident why we should always employ the engine at maximum power revs, not maximum torque revs... It also explains why the acceleration of a car slows down as the speed increases (even in frictionless vacuum)...

*ignoring the possible changes in driveability, size, weight, rules or fuel consumption of engines... Of which I now little.
**assuming no air resistance, or other friction effects for that matter. They would add unneccessary complications to the system.

The torque difference doesn't matter at all...* Torque is totally insignificant and arbitrary number we should completely ignore. I can't realise why people dig it up over and over again. Torque is strictly related to angular velocity of the engine an for example a steam engine has a lot of torque...

All* that matters when conserning a RACING ENGINE is POWER, power and nothing else.

In SI units: POWER = TORQUE × ANGULAR_VELOCITY.
Which means that: POWER = (2PI / 60) × TORQUE [nm] × FREQUENCY [rpm].

And of course the most important of them all: TORQUE × LEVERAGE = FORCE = MASS × ACCELERATION, which means that ACCELERATION = TORQUE × LEVERAGE / MASS.**

But this torque is measured at the wheels not at the engine! And if we have a car moving at a certain velocity, then the angular velocity of its wheels is FIXED to ANGULAR_VELOCITY = VELOCITY / LEVERAGE . That is TORQUE = POWER / ANGULAR_VELOCITY.

If we combine them all we get: ACCELERATION = POWER / (VELOCITY × MASS). No torque here... and from this formula it's evident why we should always employ the engine at maximum power revs, not maximum torque revs... It also explains why the acceleration of a car slows down as the speed increases (even in frictionless vacuum)...

*ignoring the possible changes in driveability, size, weight, rules or fuel consumption of engines... Of which I now little.
**assuming no air resistance, or other friction effects for that matter. They would add unneccessary complications to the system.

That sounds like the formula that the ACO must be using .

BHP is just torque multiplied by engine speed (or wheel speed).If you've got more torque at the flywheel then you can pull higher gears which means more power (speed) at the wheels.If you don't think that torque matters just put an old spec turbocharged 1000 + bhp F1 car up against a 1000 bhp + big supercharged V8 powered dragster on the exit of a bend and then swap the engines,together with the respective gearing,and see which one is faster afterwards.

Edited by Vanishing Point, 14 June 2011 - 15:54.

That sounds like the formula that the ACO must be using .

BHP is just torque multiplied by engine speed (or wheel speed).If you've got more torque at the flywheel then you can pull higher gears which means more power (speed) at the wheels.If you don't think that torque matters just put an old spec turbocharged 1000 + bhp F1 car up against a 1000 bhp + big supercharged V8 powered dragster on the exit of a bend and then swap the engines,together with the respective gearing,and see which one is faster afterwards.

You don't just seem to get it.

At any given speed maximum possible torque at the wheels depends only from the maximum engine power not the (engine) torque. So if the engine has less torque but equal power output then it will always be revving higher and thus it will have equal torque at the wheels. Which is what matters.

And for having two different engines with identical peak power the one with wider power peak will be marginally faster (so yes, in reality having more torque leads often to a marginal gain ;) )* (in case of conventional gearboxes; with a variable gearing they will both be identical as both keep revs constantly at maximum power revs during the whole acceleration).

Yours,
an university physics student.

*if we ignore the fact that building equally good gearbox is harder with more torque...

Certainly isn't.

This debate can go on forever. Not so much because both arguments have merit, it's really pretty much all about horsepower, but because people who believe in the magic of torque just can't be dissuaded of their misconception for whatever reason.

As for the thread question, the reason is simple: ACO regulations are designed to make diesels win. It has been that way for a number of years.

Torque is everything. Yes, the absolute horsepower of the diesels is slightly higher than the best petrol cars, say 630HP to 570HP, but the torque advantage is huge, which as others have pointed out leads to the mid range (100mph-180mph) acceleration in a diesel LMP being much, much quicker than in a petrol car. Yes, the Aston Lola had lots of power and a slippery body so it peaked at an equal speed to the diesels, but off the corners it struggled and the Aston team chose to run much less downforce than the Audis and Pugs so that they could have such a high terminal velocity while the diesels absolutely destroyed the Aston Lola in the Porsche Curves where downforce is everything. For an idea of the torque advantage, here is a news brief from Mike Fuller's excellent website, mulsannecorner.com-

"So how much torque are the current generation diesels making? We'll be using the Peugeot engine as the basis, but ultimately we're generating data for a "generic" diesel. Stephen Knight, "knighty", suggested this first method (and guided us through the second), simply pro-rata the the torque of the previous 5.5 liter engine to 3.7 liters. We're going to use the official figures for the 908 HDi FAP's torque, 1200 Nm, though we understand this is about 15% too low. Reducing that figure by 32.7% (the difference in capacity between the 5.5 and 3.7 L) gives us 807 Nm of torque for the 3.7 liter. OK, so that's a bit of a ham-fisted way to estimate torque, but it gives us an initial figure.

So we've previously calculated a power output based on top speed and drag estimates of between 609 and 594 hp for the "908". Taking an average, 601.5 hp, we can calculate for torque using the formula:

Power (bhp) = (Torque(lb/ft) x RPM) / 5252

multiply by 1.35582 for Nm

Plugging in 601.5, and using an rpm range from 4500-2500 RPM (remember, diesels rev much lower), and solving for torque we get and torque range of between 952 and 1712 Nm. Obviously it's very RPM dependent. But more importantly, we're calculating torque at peak power and this isn't accurate. The torque peak is going to occur a bit below the RPM for peak power, and therefore the power at that RPM is going to be reduced as well. And obviously power varies with RPM though we're going to keep it constant throughout our 2000 RPM ranges (for all our cases, see below) as we haven't a way to predict the relationship (or, plot the curves) in our fictitious diesel engine. So we're going to have to make some assumptions. Let's assume that at peak torque RPM the engine is producing 75 hp less than what it does at peak power RPM. Therefore we'll use 526.5 hp. Plugging that back into the same RPM range gives use between 834 and 1500 Nm . Averaged, that's 1167 Nm.

So now that we have a rough figure for the diesel, what does the opposition generate?

With a calculated 570 hp, the gasoline powered Judd 3.4 liter, using similar methodology (knocking 75 hp off peak power, but using an RPM range from 10000-8000), generates between 353 and 441Nm of torque (397 Nm averaged). So between 42 and 29% the torque of the diesel. The high revving nature of the normally aspirated engine simply kills torque production.
So what about a gasoline powered turbo engine? At the moment we really don't have reliable figures for the Aston Martin in the power department. But let's just assume a solid 600 hp at peak power for a "generic" gasoline powered turbo. Using an RPM range between 7000 and 5000 RPM (gas turbos torque peak won't be as low as a diesels) gives us 534 and 748 Nm of torque at 525 hp (641 Nm average).

So it's pretty easy to see that the torque figures for a normally aspirated gasoline power engine are not even in the same ballpark. The gas powered turbo has a better chance, but there isn't even any overlap if you look at best case (for gas) vs. worst case (for diesel). Admittedly there is a lot of fudge in our factoring, but there's really not enough to turn a 64% difference into a 5% difference.

With the ACO giddy to add hybrids to the line up, and the manufacturers waiting in the wings having designed their new cars around such systems, the performance balance is simply set to go from poor, to ridiculous. And the ACO has only shown hesitancy in addressing the issue."

You're making a classic mistake of ignoring torque multiplication that happens between the flywheels and the wheels, and how it's going to be different for different engines. Petrol engines rev much higher, and thus have much higher torque multiplication than low-revving diesels, so the actual torque at the wheels is not as mismatched as you make it sound. Of course, people who know their physics don't even bother with trying to keep flywheel torque and torque multiplication in synch when doing the comparisons, they're just using power curve figures which negates the need for dealing with two variables at once.

Edited by Dmitriy_Guller, 14 June 2011 - 17:38.

You don't just seem to get it.

At any given speed maximum possible torque at the wheels depends only from the maximum engine power not the (engine) torque. So if the engine has less torque but equal power output then it will always be revving higher and thus it will have equal torque at the wheels. Which is what matters.

And for having two different engines with identical peak power the one with wider power peak will be marginally faster (so yes, in reality having more torque leads often to a marginal gain ;) )* (in case of conventional gearboxes; with a variable gearing they will both be identical as both keep revs constantly at maximum power revs during the whole acceleration).

Yours,
an university physics student.

*if we ignore the fact that building equally good gearbox is harder with more torque...

Perhaps that's the reason why the petrol engine entrants don't stand a chance because they're using too many university students instead of real car nuts with a mis spent youth around drag strips and race circuits like Carroll Shelby etc who showed how to beat a powerful high revving Ferrari engine with a torquey pushrod Ford V8.For your information,as those university lecturers seem to be having trouble explaining it all,torque and power outputs are mathematically related.There's no such thing as a 'wide power peak' as peak power is related to the torque curve.The longer and higher up the rev range an engine can sustain torque the higher the power output at the flywheel will be.However the fact that power is related to torque means that you can make a lot of power (at the flywheel) by multiplying a lot torque by a relatively low engine speed,which is what forced induction diesels and big forced induction petrol engines are good at.Or you can make a lot of power (at the flywheel) by multiplying a low amount of engine torque by a lot of engine speed.Which is what relatively high revving smaller capacity race engines do but those engines are a one trick pony in only being able to provide much effort at the upper end of the rev range which provides them with a headline grabbing peak power output but which is about as much use at Le Mans as an F1 car ould be.However the difference between diesels and larger capacity forced induction petrol engines is that diesels are the reverse of small capacity petrol engines in that they are just a one trick pony,because they are'nt any good in combining the ability to sustain large amounts of engine torque (therefore power) at relatively high revs,with their ability to provide relatively large amounts of engine torque at relatively lower revs,whereas large capacity forced induction petrol engines have the ability to provide large amounts of torque at both relatively lower revs and sustain it up to relatively higher revs.So in addition to having diesel like qualities of low end torque they've also got the ability to sustain relatively large amounts of torque at relatively higher revs so they've got the advantage of both large amounts of torque/power at relatively low engine speeds and high 'peak power' outputs.

It's only having established those basics that you can throw gearing into the equation and it's that which determines the amount of power actually available at the wheels.The anomaly in the present ACO regs is that the diesels have more torque than the small capacity petrol cars have and after the gearing has been taken into account the end result is that the small capacity petrol cars have less power available at the wheels than the diesels do regardless of what the peak power figures at the flywheel state.

But if you really think that it's power that matters not torque maybe you'd like to do an acceleration comaparison between an F1 car and a truck tractor unit,both running at an equal weight,although the truck has a lot less power (at the flywheel) than the F1 car.

Edited by Vanishing Point, 14 June 2011 - 19:02.

I can make more torque than any engine ever with my bare hands and a long bit of metal.