54 replies to this topic

[Paolo]

A typical question many F1 enthusiast are asked is "what was the most powerful engine ever in F1".
And the typical answer is "BMW Turbo, 1500 cc, 4 cylinders, mid 80's"

Now... BMW's engine was competing against 6 and even 8 cylinders engines of the same displacement.

Oddly, it was the most powerful of them all, while Alfa Romeo's 8 cylinders was probably the less powerful, together with the underfunded Hart.

It has been said that the reason for BMW's excellence was that its disadvantage in maximum RPM was overcome by an advantage in maximum turbo pressure.

Anyway this still does not explain why a designer should have shoot himself in the foot by laying out a 4 cylinders with the absolute guarantee that, for the same pressure and same design expertise, a 6-8 cylinders unit would have been more powerful. BMW probably had some metallurgical advantage that allowed them to build more robust engines, but why do not apply it to an 8 cylinders?

An inherent advantage of 4 cylinders in maxumum sustanaible pressure? Frankly, I can't see a reason for this.

Engine packaging advantages? Unlikely: BMW's engine was an inline 4 that was even longer than a V6; and these 1500 cc units were on the smallish side anyway.

Less parts and increased reliability? Not enough of a justification, IMHO.

Notwithstanding this, the trend towards 4 cylinders continued; had not the rules changed, in time we would have seen Ferrari and Alfa switching to 4 cylinders; they even ran tests with them.

So, what do you think the advantage of 4 cylinders turbo was?

[rhm]

I'm no expert in engine thermodynamics (to put it mildly), but I'm not seeing what advantage more cylinders would have with displacement limited to 1.5L and revs made largely irrelevant by forced induction.

As for BMWs special metalurgy, I believe the engine not only used the block from a production BMW car, but the actual blocks used were scavinged from used cars with lots of miles on them (heat treated for free if you will).

[Paolo]

Originally posted by rhm
I'm no expert in engine thermodynamics (to put it mildly), but I'm not seeing what advantage more cylinders would have with displacement limited to 1.5L and revs made largely irrelevant by forced induction.

As for BMWs special metalurgy, I believe the engine not only used the block from a production BMW car, but the actual blocks used were scavinged from used cars with lots of miles on them (heat treated for free if you will).

Forced induction does not make revs irrelevant. They are a multiplicating factor.
Supposing they both operate with the same efficiency at top RPM, for the same turbo pressure an unit doing 11000 RPM will have 10% more power than an unit doing 10000 RPM.
Of course efficiency changes, getting worse with increasing RPM and making the gain sub-linear, but still having more RPM is a big advantage.

About BMW blocks: yes, it was recently discussed in another thread (http://forums.autosp...threadid=105343 ), but I don't think this was much of a secret weapon, just good engineering practice for cast iron blocks.

[zac510]

Surely the most efficient were the Honda and TAG/Porsche twin turbo V6s!

The BMW turbo I4 has some kind of mythical status. I think the advantage of the inline 4 was simply that it got into the turbo game and won its races early before bespoke racing engines like the TAG Porsche, Ford and Honda etc joined in and dominated. Renault may have had a head start but we allknow that story. BMW dropped out when the bespoke engines rolled in. They must have known their time was up.
There was definitely some more disadvantage to the I4 too as later in its life they laid it over to decrease its frontal area and rear wing blockage. Then it was completely uncompetitive by 1985s onwards bar two race wins (1 in 85, one in 86). Even then only 4 wins in 5 years after 1983 season.

I'm not saying it's a **** engine, perhaps just not as high and mighty as people perceive it.

[cheapracer]

Originally posted by rhm
.

As for BMWs special metalurgy, I believe the engine not only used the block from a production BMW car, but the actual blocks used were scavinged from used cars with lots of miles on them (heat treated for free if you will).

Indeed they were old blocks and BMW used that fact with pride.

Amazing how looked down at cast iron is and yet engines such as SBC use minimul structure and wall thickness but contain a lot of torque just fine thank you. When Audi went to the Audi Sport Quattro in '84 the aluminium block ended up heavier than the cast iron block after they continued to add ribbing to it to stop it walking about. If they had stuck with the cast iron block they may well have had 1 more WRC up their sleeve.

[cheapracer]

Originally posted by zac510


The BMW turbo I4 has some kind of mythical status.

I'm not easily impressed but I can never forget Picket at Kyalami in qualifying exiting turn 2 sideways and laying 2 wide black continuous strips all the way until he lifted for the turn 3 lefthander - that wasn't myth. I don't know if you watched F1 then but I certainly was totally convinced by the Brabham BMW.

[zac510]

I was watching F1 then but didn't really understand engines! It has its status of the most powerful engine, but it wasn't the most successful. That doesn't take away from your admiration of it.

Since then it's continually talked up as the most powerful and the fish gets bigger every time! The engine's success and results don't get any bigger.

[cheapracer]

Originally posted by zac510
It has its status of the most powerful engine, but it wasn't the most successful.

Well thats possibly an oxymoron right there, depending on what you guage success as.

[rhm]

Originally posted by Paolo


Forced induction does not make revs irrelevant. They are a multiplicating factor.
Supposing they both operate with the same efficiency at top RPM, for the same turbo pressure an unit doing 11000 RPM will have 10% more power than an unit doing 10000 RPM.
Of course efficiency changes, getting worse with increasing RPM and making the gain sub-linear, but still having more RPM is a big advantage.

Ok, well they don't make revs irrelevant, but they make them no longer the most important factor. In an atmospheric engine, if you can't increase the displacement, increasing revs is the only way to increase the volume of air pumped. In a turbo engine it's the turbo that determines how much air you pump. Increase the revs without increasing the size of the turbo and you are pumping the same volume of air at a lower density which would be less efficient (as far as I know) due to the higher losses with increased RPM. Of course you could fit a bigger turbo, but that's really the crux of the matter isn't it? These engines were really limited by the turbo-charger technology of the day.

[Paolo]

Originally posted by rhm


Ok, well they don't make revs irrelevant, but they make them no longer the most important factor. In an atmospheric engine, if you can't increase the displacement, increasing revs is the only way to increase the volume of air pumped. In a turbo engine it's the turbo that determines how much air you pump. Increase the revs without increasing the size of the turbo and you are pumping the same volume of air at a lower density which would be less efficient (as far as I know) due to the higher losses with increased RPM. Of course you could fit a bigger turbo, but that's really the crux of the matter isn't it? These engines were really limited by the turbo-charger technology of the day.

An interesting observation, yes: to increase power with increased RPM in a turbo, a greater mass flow is needed.

Now: was an increased mass flow a problem?
I am inclined to answer "no": having more mass flow just requires a bigger turbo, or more turbos.
Bigger turbos cause increased lag, and this is what usually limits their size.
BMW was running a single (big) turbo, while all the others (maybe with the exception of Hart?) had long ago switched to twin units. Had BMW wanted more power without facing an increase in lag, they could have switched to twins; another thing they did not do, for reasons that at the moment I don't understand,

I am aware that a single turbo unit is more efficient than a twin; that is it will give a greater pressure increase for a given exhaust energy.

Yet, to my knowledge, there was a lot of still unused energy in those exhausts: the real limit was that engines broke if too much pressure was applied. That was why a wastegate was present, even in the years before it became mandatory to limit maximum boost.
Quali engines had to be thrown away after a few laps.

Your remark has sparked, anyway, a memory of that era.
I read on Autosprint, in these years, that during quali Ligier (Renault engine) once tried to shut the wastegate closed.

To their surprise they had no increase in power.
So it IS indeed possible that the turbo ability to extract energy from the gas flow was actually a limiting factor....

Waiting for the engine guys to throw their ton of salt in....

[Greg Locock]

I can think of one immediate advanatge of an I4 with a monster turbo compared with a V6 - packaging. The I4 keeps all the hot bits on one side and the cold bits on the other.

Also, there used to be a theory that there was an optimum cylinder size, around 350-400 cc, but that was for road cars.

[cheapracer]

Originally posted by Paolo
.

the real limit was that engines broke if too much pressure was applied.

Ahh nows thats the game BMW played best, they put in a whopping 5.5 bar and knew how to make 'em not break.

[J. Edlund]

As zac510 mentioned, the BMW engine was an early engine and intially it competed mostly against naturally aspiranted engines and later against early versions of turbo engines from competing manufacturers. Compared to later turbo engines it lacked race power and was significantly heavier.

The BMW engine was production based and a development of an engine that had earlier seen use in F2 and IMSA. Later engines from Honda, Renault, Ferrari, TAG and others were clean sheet designs for F1.

Eight cylinder engines was rare, and they were generally unsuccessful. Sometimes they were not even capable to finish races due to their high fuel consumptions and the fuel limits put in place to limit power output. This was a reason manufacturers chose inline fours or V6 engines, a V8 suffers from too much friction to offer a low fuel consumption. Most of the manufacturers ran V6 engine though; I can't recall any other four cylinder turboengine than the BMW, Alfa Romeo, Hart and Zakspeed, can someone else? The Alfa was the only twin turbo inline four but it used by modern standards a rather strange manifold design.

The Honda V6 engine was probably one of the best overall turbo engines, perhaps it didn't have the highest qualification power output but it offered a high race power output (about 1000 hp, around 100 hp more than the BMW) with a reasonable torque curve, a low fuel consumption which allowed the driver to use the power during the race, a low weight (140 kg vs. 170 kg for the BMW), a compact installation (no bulky production based unit) and engine failures were rare for the time. The Honda engine used a cast iron block too, but not a grey iron production block but a thin walled ductile iron block.

Another impressive engine was the later Renault V6. It used an aluminum block for the race, but the qualification engines used a cast iron block. This engine was also the first to feature pneumatic valve return. The qualification engine took many pole positions during 1986. At the end of the season boost pressure up to 5.2 bars were used. Qualification engines ran without wastegates (which was normal practice), the boost pressure is in other words limited by turbine power.

It's also worth to note that the BMW qualification engine that saw 5.6 bars at Monza didn't last the whole lap. It's this run that is the base for most +1300 hp speculations.

[cheapracer]

Originally posted by J. Edlund
As zac510 mentioned, the BMW engine was an early engine and intially it competed mostly against naturally aspiranted engines and later against early versions of turbo engines from competing manufacturers. Compared to later turbo engines it lacked race power and was significantly heavier.

The BMW engine was production based and a development of an engine that had earlier seen use in F2 and IMSA. Later engines from Honda, Renault, Ferrari, TAG and others were clean sheet designs for F1.
.

Mate it beat the Renaults and Ferraris who had track time before BMW and they weren't standing still in their development either, Ferrari even practicing for 1 race with the Comprex (name?) exhaust wave charger. Renault went to twin turbo's quite early as well.

Agreed that BMW had some earlier Turbo experience, I remember a 2002 being raced for a bit many years before, fast as but apparently had horrifying lag.

[Paolo]

Originally posted by J. Edlund
As zac510 mentioned, the BMW engine was an early engine and intially it competed mostly against naturally aspiranted engines and later against early versions of turbo engines from competing manufacturers. Compared to later turbo engines it lacked race power and was significantly heavier.

The BMW engine was production based and a development of an engine that had earlier seen use in F2 and IMSA. Later engines from Honda, Renault, Ferrari, TAG and others were clean sheet designs for F1.


-------------------------------------------

I can't recall any other four cylinder turboengine than the BMW, Alfa Romeo, Hart and Zakspeed, can someone else?

As Cheapracer pointed out, BMW came on the scene years later than Ferrari and Renault and with only months of advantage over Alfa and Honda, and it was more than competitive

Ferrari had a 4 cylinders in the works when a scheme for gradual abandoning of turbos was announced and the new engine was shelved; I think they even tested it at Fiorano, with Arnoux IIRC.

[J. Edlund]

Originally posted by cheapracer


Mate it beat the Renaults and Ferraris who had track time before BMW and they weren't standing still in their development either, Ferrari even practicing for 1 race with the Comprex (name?) exhaust wave charger. Renault went to twin turbo's quite early as well.

Agreed that BMW had some earlier Turbo experience, I remember a 2002 being raced for a bit many years before, fast as but apparently had horrifying lag.

Renault was first with a turbocharged engine for F1 with their EF1 engine, they introduced it in 1977, but reliability was terrible and their car was wasn't good enough to be competitive. Then for 1981 came the Ferrari with its Tipo 021 and Hart with their 415T. 1982 saw the introduction of the BMW M12/13. The BMW engine had however been tracktested since late 1980 and turbocharged versions of the same engine had been around since the late seventies. The real brakethrough for the BMW engine though came in 1983, it started the season with about 640 hp but at round 12 Wintershall started supply a toluene based fuel which replaced the avgas used earlier, now the output was almost 750 hp. 1983 also saw the introduction of the Honda RA163E, TAG PO1 and Alfa Romeo 890T. That year the BMW powered Brabham took the drivers title by just two points ahead of Renault and Ferrari took the constructors championship, the first drivers title for a turbocharged engine but the second for a constructor, with Ferrari taking that title in 1982 too. In 1982 Renault took most poles, but had trouble finish the races on the podium and in 1983 it was the Tipo 021 powered Ferrari that took most pole positions, Brabham-BMW only took 2 seeing itself beaten both by Ferrari and Renault.

1984 saw the introduction of Renault EF4, Ferrari Tipo 033 and the Honda RA164. This year the TAG powered McLaren was the race winner taking 1st and 2nd in drivers and the constructors title. Most pole positions was taken by the BMW powered Brabham team which only managed to finish fourth in the constructors behind McLaren with its TAG engine, Ferrari and Renault, all using turbo engines.

1985 saw the introduction of a new Renault engine, the EF15, a turbo engine from Zakspeed and one from Motori Moderni. Once again the TAG powered McLaren took drivers and constructors titles. Most poles was taken by the Renault EF15 powered Lotus. The BMW powered Brabham team only managed one pole and one win, they finished fifth in the campionship behind McLaren, Ferrari, Honda powered Williams and Renault powered Lotus.

By 1986 only turbocharged engines was allowed, and that year the Cosworth DBA engine was the only completly new engine to be introduced. BMW powered Benetton managed two poles and one win, they finished sixth in constructors. Drivers were taken by TAG powered McLaren and constructors by Honda powered Williams. Most poles was one again taken by Lotus-Renault with its EF15B engine.

In 1987 Honda RA167E powered Williams took both drivers and constructors and also most poles. In constructors they were followed by McLaren-TAG, Lotus-Honda and Ferrari.

By 1988 naturally aspiranted engines were allowed again and the year was a clean sweep for the Honda RA168E powered McLaren which took 15 wins, 15 poles and 25 podiums out of 16 races. Second place in the constructors was Ferrari with just 1/3 of the points, they managed one pole and one win using their turbocharged Tipo 033E engine. BMW didn't supply engines anymore, but the BMW was availible under the Megatron badge. Megatron engined cars only managed one podium though. This also brough the turbo era to an end.

So during the years BMW managed one drivers title, Honda managed two drivers and three constructors, Ferrari managed two constructors and TAG managed three drivers and two constructors. As for most poles, Honda powered cars took most poles in 1988 and 1987, Renault/Lotus-Renault took most poles in 1986, 1985, 1982, 1981, 1980 and 1979, BMW powered cars in 1984 and Ferrari powered cars in 1983. In 1979-1981 Cosworth powered cars took more or an equal number of poles as Renult powered cars, but these were divided among two or three teams.

To sum it up; BMW engined cars had some success in 1983-1984, but it was quite limited. To claim that it beat the Ferrari and Renault is an overstatement. Yes, it beat Renault to the 1983 drivers championship by two points and took most poles in 1984, but in 1984 it was a rare sight to see a BMW powered car finish a race and there is really not that much to brag about compared with what other manufacturers managed to achieve. Overall, I would say that the turbo engines from Honda and TAG were the most successful followed by the Ferrari and then I would say Renault. First after that, I would place the BMW engine.

[cheapracer]

Originally posted by J. Edlund


To claim that it beat the Ferrari and Renault is an overstatement. .

You seem confused, I answered to your first paragraph in post 13 (and I forgot about the Hart too).

[J. Edlund]

Originally posted by cheapracer


You seem confused, I answered to your first paragraph in post 13 (and I forgot about the Hart too).

And you seem to lack knowledge on the subject. Read my post above with the results each engine managed to get. To state that the BMW beat the Renault and Ferrari is an opinion not a fact and you have made no argument to prove your opinion. You could aswell say that the Ferrari or the Renault beat the BMW, which in a way they did, it's just a question on how you measure success. Still, the success of the BMW engine was limited compared to the later Honda and TAG engines (just count the number of championships each engine managed to bring home).

The Ferrari engine also saw track time not that much before the BMW. The BMW engine was tracktested already in 1980, but at the time it was unable to beat the DFV engine in terms of lap times (although, it was most likely more powerful in terms of peak power).

[desmo]

Originally posted by Paolo




Ferrari had a 4 cylinders in the works when a scheme for gradual abandoning of turbos was announced and the new engine was shelved; I think they even tested it at Fiorano, with Arnoux IIRC.

http://picasaweb.goo...feat=directlink

Anyone know what the deal with this 4 banger engine with huge turbo I saw at Maranello is?

[Powersteer]

Originally posted by J. Edlund
TAG powered McLaren

There was a Porsche badge on the black plenium chamber if I remember correctly, a TAG badged Porsche engine I assume.

[Ray Bell]

Originally posted by Powersteer
There was a Porsche badge on the black plenium chamber if I remember correctly, a TAG badged Porsche engine I assume.

...as mentioned in post No 4...

[stuartbrs]

The whole TAG Porsche thing was COMPLETELY funded by TAG... the engine was built to John Barnards ( in effect McLarens ) specifications. There are quite a few pics of these engines with no Porsche badging whatsoever. The first ones, were hugely fond of drinking oil, untill McLaren convinced Porsche that these werent sportscar engines, you couldnt just pull into the pits and give them a drink of oil. They didnt build specific Qualy engines unlike BMW, Renault and Honda.

When Porsche returned to F1 in the 90`s, without guidance from a topline F1 team, they made an utter fist of things, in effect, joining two TAG V6`s together to make a V12, and achieving astonishing weight and little horsepower. A shortfall of cash mixed in with a healthy serving of arrogance made that engine a complete and utter failure. A lot of people want Porsche to return to F1, I for one, hope they stay away. Porsches natural arena is Sportscars, and its a pity Ferrari still wont take them on anymore.

[Henri Greuter]

Originally posted by desmo


http://picasaweb.goo...feat=directlink

Anyone know what the deal with this 4 banger engine with huge turbo I saw at Maranello is?

I forgot the exact year but Ferrari, then still under Mauro Forghieri had wanted to use a fourcylinder, probably inspired by the success of BMW. I never saw a picture of that engine and eventually it was never used.
But this could have been that particular rumored engine.


Foghieri was promoted away and Ferrari stuck with the V6 concept after all.
If my memory serves me well, they did introduce a new 90degree V6 in 1986 or 1987 to replace the original 120degree engine debuted in 1980.


Henri

[mariner]

Funnily enough the Turbo Offy was a 4 cylinder and matched V-8's until the boost was limited and it was BIG 4 banger at 2.7 litres.. I think the "old fashioned" head plus barrels layout helped as there was no head gasket but maybe there are some subtle benefits in having only four exhaust ports to feed the turbo.

Incidentally whilst revs are important if you read the Tony Rudd book "It was fun" he explains how when at Rolls Royce in WW2 they struggled to teach the pilots that high revs and fine prop pitch was the wrong way to save fuel and have the engine last till you got home. The optimum way with the Merlin was lots of coarse pitch to really load up the enine then heavy boost at low RPM to get the BMEP and hence fuel economy up whilst limiting RPM based engine stress. Not exactly as per F1 but you life as a bomber crew did depend heavily on such things!

[McGuire]

Originally posted by mariner
Funnily enough the Turbo Offy was a 4 cylinder and matched V-8's until the boost was limited and it was BIG 4 banger at 2.7 litres..

I think that's mainly because the V8 in question, the DOHC Indy Ford, was so unsuited to turbo conversion. It had enormous intake ports for 255 CID and when it was reduced to 161 the guts were cut out of it. Typical Ford of the period, more is better. They necked it down twice, once NA with injector venturis and again with port sleeves as a turbo. Also, due to the central intake/high exhaust port layout it was a plumber's nightmare in turbo form.

[Henri Greuter]

Originally posted by McGuire


I think that's mainly because the V8 in question, the DOHC Indy Ford, was so unsuited to turbo conversion. It had enormous intake ports for 255 CID and when it was reduced to 161 the guts were cut out of it. Typical Ford of the period, more is better. They necked it down twice, once NA with injector venturis and again with port sleeves as a turbo. Also, due to the central intake/high exhaust port layout it was a plumber's nightmare in turbo form.

Curiously, the Ferrari CART engine, built in 1986 but never raced also had the exhausts within the V and the turbo above the gearbox. Intake was on the outside of the engine, where the opposition had the exhausts.
Very much like they were used to with the 120 degree V6 F1 engine from 1981 till 1984.

As of why the Offy was so much better than the Ford, I also think that the Offy having no head gaskets but integral cylinderheads was a big advantage. Once they knew how and had the fuel pumps that were able to supply that amount of fuel required to cool the thing down too, it could take massive boost levels much better than the Ford ever could.
Besides that, I wonder how much the pedigree of the Ford V8 (stock block Fairlane crankcase origins for example) was a factor that limited the power it could generate and withstand.

Henri

[McGuire]

No doubt about it. When the Ford DOHC Indy V8 was developed the possibility of a forced induction version was never considered. Of course, that is also true of the Offy. Its integral head/cylinder block and barrel-type crankcase are a historical accident as much as anything. Vestigal features for a 1960s engine, you might say. If the Offy had been redesigned between 1930 and 1960 by any sensible engineer, those features would have been dropped. The Offy was like a shark -- an atavism, 50 million years old and still the deadliest thing in the water.

EDIT: all that said, once a proper modern racing engine came along -- the Cosworth DFV/DFX V8 -- the Offy was finished. But 50 years is still a hell of a run.

[Henri Greuter]

Originally posted by McGuire
No doubt about it. When the Ford DOHC Indy V8 was developed the possibility of a forced induction version was never considered. Of course, that is also true of the Offy. Its integral head/cylinder block and barrel-type crankcase are a historical accident as much as anything. Vestigal features for a 1960s engine, you might say. If the Offy had been redesigned between 1930 and 1960 by any sensible engineer, those features would have been dropped. The Offy was like a shark -- an atavism, 50 million years old and still the deadliest thing in the water.

EDIT: all that said, once a proper modern racing engine came along -- the Cosworth DFV/DFX V8 -- the Offy was finished. But 50 years is still a hell of a run.

historical accident or not: the feature forgotten to drop (integral cylinder heads) was pretty much the thing that saved the Offy. It was the key feature that enabled the thing to withstand the (for the time) incredible boost levels that enabled it to outperform the more modern, and theoretically superior V8 design of the Ford Quadcam.

Being a Novi adept I have difficulties to `cope` with the normally aspireated Offy's but I do respect the engine quite a bit. That I admire the Offy however is largely because of the achiements with the turbocharged versions. The Offy remains a milestone engine in every aspect.


Now I would love to see a picture of a turbo Ford/Foyt Quadcam, all derssed up and standing next to it, a Cosworth XD all dressed up.
Just to see the differences in size and shape in one sight....



Henri

[gruntguru]

A typical question many F1 enthusiast are asked is "what was the most powerful engine ever in F1".
And the typical answer is "BMW Turbo, 1500 cc, 4 cylinders, mid 80's"

Now... BMW's engine was competing against 6 and even 8 cylinders engines of the same displacement.

Oddly, it was the most powerful of them all, while Alfa Romeo's 8 cylinders was probably the less powerful, together with the underfunded Hart.

It has been said that the reason for BMW's excellence was that its disadvantage in maximum RPM was overcome by an advantage in maximum turbo pressure.

Anyway this still does not explain why a designer should have shoot himself in the foot by laying out a 4 cylinders with the absolute guarantee that, for the same pressure and same design expertise, a 6-8 cylinders unit would have been more powerful. BMW probably had some metallurgical advantage that allowed them to build more robust engines, but why do not apply it to an 8 cylinders?

An inherent advantage of 4 cylinders in maxumum sustanaible pressure? Frankly, I can't see a reason for this.

Engine packaging advantages? Unlikely: BMW's engine was an inline 4 that was even longer than a V6; and these 1500 cc units were on the smallish side anyway.

Less parts and increased reliability? Not enough of a justification, IMHO.

Notwithstanding this, the trend towards 4 cylinders continued; had not the rules changed, in time we would have seen Ferrari and Alfa switching to 4 cylinders; they even ran tests with them.

So, what do you think the advantage of 4 cylinders turbo was?

I just discovered this thread and it got me thinking. There are two advantages for the 4cyl configuration that occur to me.

1. Combustion chamber surface-area/volume ratio will be lower for 4 larger cylinders. This will mean less heat rejection to chamber surfaces. This is a limiting factor, especially for high boost turbo engines.

2. Turbocharger efficiency increases with turbo size, so one big turbo is better than two small turbos. Although blowdown energy can still be harnessed on a V6 with a single turbo and divided exhaust housing (blowdown criterion is a maximum of 3 even-firing cylinders per turbine nozzle), the long exhaust runners would lose more heat and be too long for wave tuning - not to mention packaging difficulties. So V6 engines tended to go with twin turbos and V8's cannot utilise blowdown energy with a single turbo anyway.

Of course two small turbos provide better throttle/lag response so the possible power advantage of a 4 cylinder package has its downside too.

[Paolo]

I just discovered this thread and it got me thinking. There are two advantages for the 4cyl configuration that occur to me.

1. Combustion chamber surface-area/volume ratio will be lower for 4 larger cylinders. This will mean less heat rejection to chamber surfaces. This is a limiting factor, especially for high boost turbo engines.

2. Turbocharger efficiency increases with turbo size, so one big turbo is better than two small turbos. Although blowdown energy can still be harnessed on a V6 with a single turbo and divided exhaust housing (blowdown criterion is a maximum of 3 even-firing cylinders per turbine nozzle), the long exhaust runners would lose more heat and be too long for wave tuning - not to mention packaging difficulties. So V6 engines tended to go with twin turbos and V8's cannot utilise blowdown energy with a single turbo anyway.

Of course two small turbos provide better throttle/lag response so the possible power advantage of a 4 cylinder package has its downside too.

I noticed gruntguru's answer a bit late... it is possibly a good explanation, I think.
If I understood what he means, to use the same boost pressure on a V6 (compared to an I4) you need larger radiators and, providing you're on a single unit, a larger turbo.

Should the V6 use its rpm advantage, turbo and radiators must become even bigger to allow for higher mass flows.
Therefore more weight, drag and lag.

Those disadvantages possibly outweighed the theoretical higher power output of V6.

Possibly...


I am curious anout the "blowdown energy" "blowdown criterion" bit, anyway, and would be glad if someone expands on it.

Edited by Paolo, 18 January 2011 - 12:32.

[MatsNorway]

good work Paolo and grunt. I liked those posts very much.

The problem with the BMW was allways lag not power..

Edlund what track did BMW win and took pole on? in 1985? Fast track? = there ya go.. Legend status right away.

Was it hard to drive Yes! = legend status.

http://www.gurneyfla...bof1engine.html

Edited by MatsNorway, 18 January 2011 - 18:19.

[gruntguru]

If I understood what he means, to use the same boost pressure on a V6 (compared to an I4) you need larger radiators and, providing you're on a single unit, a larger turbo.

More important
- a single turbo is more efficient than two turbos with exactly half the capacity each.

I am curious anout the "blowdown energy" "blowdown criterion" bit, anyway, and would be glad if someone expands on it.

When the exhaust valve first opens there is still a lot of pressure in the cylinder which is basically "free" energy - if we can harness it in the turbine rather than expand it in the exhaust manifold, it will not increase the average exhaust backpressure (which would increase the work done by the pistons during the exhaust stroke). To achieve this we must duct this pressure pulse directly to the turbine wheel, during a period when no other exhaust valves connected to that manifold are open (otherwise the pressure pulse will affect the flow from that other cylinder and increase its backpressure.) The maximum number of cylinders that can share a manifold without such interactions is three - and they must be evenly spaced in the firing order. Some turbochargers have a twin entry turbine which keeps two exhaust streams seperated all the way to the turbine wheel. This allows three evenly spaced cylinders to be used on each entry port so 4 and 6 cylinder engines can use a single turbocharger and still harness the blowdown energy.

Edited by gruntguru, 19 January 2011 - 11:20.

[Wuzak]

More important
- a single turbo is more efficient than two turbos with exactly half the capacity each.

Is that always teh case, or is there a crossover point?

[Wuzak]

When the exhaust valve first opens there is still a lot of pressure in the cylinder which is basically "free" energy - if we can harness it in the turbine rather than expand it in the exhaust manifold, it will not increase the average exhaust backpressure (which would increase the work done by the pistons during the exhaust stroke). To achieve this we must duct this pressure pulse directly to the turbine wheel, during a period when no other exhaust valves connected to that manifold are open (otherwise the pressure pulse will affect the flow from that other cylinder and increase its backpressure.) The maximum number of cylinders that can share a manifold without such interactions is three - and they must be evenly spaced in the firing order. Some turbochargers have a twin entry turbine which keeps two exhaust streams seperated all the way to the turbine wheel. This allows three evenly spaced cylinders to be used on each entry port so 4 and 6 cylinder engines can use a single turbocharger and still harness the blowdown energy.

Does that work over the entire operating range, or only at specific points?

Does it require the turbine to be as close to the ports as possible? Presumably the mainfold has to be equal length?

In a turbocompound engine would it be better to use this energy for compounding and use the exhaust for turbocharging, or vice versa?

[GrpB]

I'm not easily impressed but I can never forget Picket at Kyalami in qualifying exiting turn 2 sideways and laying 2 wide black continuous strips all the way until he lifted for the turn 3 lefthander - that wasn't myth. I don't know if you watched F1 then but I certainly was totally convinced by the Brabham BMW.

Last I saw, an IMSA 320 version of this engine (David Hobbs, et al), sits on a stand in the far corner of McLaren Engine's waiting room, a relic from the past. Those that remember the program dwell not on the prodigious output, but rather on the nasty, toluene based fuel required to run it, toxic fumes and all. Ironic that something like this would come back specifically to emulate a more ecologically friendly (efficient?) engine package.

For 'new' LMP, which requires production based engines, ok, but for F1, why??? There is never 'free' energy anywhere, at anytime. If there seems to be, the engine, regardless of configuration is far from optimised.

[WhiteBlue]

In a turbocompound engine would it be better to use this energy for compounding and use the exhaust for turbocharging, or vice versa?

There is only one energy in the exhaust. You can use it for the compressor or bypass it to the crankshaft. Once it is used it is gone. In a turbo compounded engine we simply do a higher boost and extract more energy from the exhaust gas than a turbocharger would do.

[bettonracing]

This is a rudimentary perspective, but it is very possible that the BMW engineers traded "ultimate potential" with a new engine for development time with an old engine.

More food for thought:

• Within reasonable limits & constraints (e.g. bore/ stroke/ valve diameters/ bearing sizes/ etc), a 4cylinder will typically have lower friction than an equivalent displacement 6cyl or 8cyl.
• The reduction in valve curtain area when compared to an equivalent displacement V6/ v8 can be accomodated with additional air density (aka boost pressure).
• With [relatively] unlimited plenum pressure, a turbocharged engine has more potential to gain peak power from pressurized inlet (aka ram air inlet) than a naturally aspirated engine.
• A 4cyl will generally consume less fuel on the overrun than a 6cyl or 8cyl.

Regards,

H. Kurt Betton

[gruntguru]

Is that always teh case, or is there a crossover point?

It is a general rule that applies across all size ranges. There will be exceptions of course.

[Ali_G]

Another point to note using an I4 is that Brabham were forced to have a frame for the rear of the car.

Car with V6 engines could use them as a stressed member.

[gruntguru]

Does that work over the entire operating range, or only at specific points?

Works everywhere although the effect will vary.

Does it require the turbine to be as close to the ports as possible? Presumably the mainfold has to be equal length?

No - although excessively long runners are generally undesirable due to heat loss and possibly loss of pulse amplitude.

[WhiteBlue]

Another point to note using an I4 is that Brabham were forced to have a frame for the rear of the car. Car with V6 engines could use them as a stressed member.

There are simple ways to design adaptor arms to the cylinder head and the engine block to avoid a sub frame. The L4 engine block is plenty rigid to act as a stressed member.

[desmo]

How exactly do you quantify "plenty rigid"?

[Kelpiecross]

How exactly do you quantify "plenty rigid"?

I think the BMW F1 turbo engine actually used a cast iron block from one of their production cars.

[Wuzak]

There are simple ways to design adaptor arms to the cylinder head and the engine block to avoid a sub frame. The L4 engine block is plenty rigid to act as a stressed member.

That helps with the connections to the chassis and the gearbox, but what about transverse bending through the engine and torsional loading? Won't the engine have to be heavier than an unstressed 4?

[Paolo]

There are simple ways to design adaptor arms to the cylinder head and the engine block to avoid a sub frame. The L4 engine block is plenty rigid to act as a stressed member.

Brabham used a subframe, the BMW engine alone was not stiff enough.

[Magoo]

This is a rudimentary perspective, but it is very possible that the BMW engineers traded "ultimate potential" with a new engine for development time with an old engine.

More food for thought:

• Within reasonable limits & constraints (e.g. bore/ stroke/ valve diameters/ bearing sizes/ etc), a 4cylinder will typically have lower friction than an equivalent displacement 6cyl or 8cyl.
• The reduction in valve curtain area when compared to an equivalent displacement V6/ v8 can be accomodated with additional air density (aka boost pressure).
• With [relatively] unlimited plenum pressure, a turbocharged engine has more potential to gain peak power from pressurized inlet (aka ram air inlet) than a naturally aspirated engine.
• A 4cyl will generally consume less fuel on the overrun than a 6cyl or 8cyl.

Regards,

H. Kurt Betton

That's it in a nutshell.

Now, a properly done 6 will actually have lower fhp than a 4, while the breathing advantages are obvious. But both are easily overcome if you can reliably run more boost than the other guy. The great equalizer, like the Colt revolver. God made men and Sam Colt made them equal, etc.

The perfect example is the turbo Offy. It wasn't a very good engine by 1970s standards; it just happened to be better than anything else sitting around at the time. But as soon as the dollars were lined up to do a 2.65L turbo conversion of the Cosworth DFX, the Offy was toast.

[WhiteBlue]

There are simple ways to design adaptor arms to the cylinder head and the engine block to avoid a sub frame. The L4 engine block is plenty rigid to act as a stressed member.

That helps with the connections to the chassis and the gearbox, but what about transverse bending through the engine and torsional loading? Won't the engine have to be heavier than an unstressed 4?

There are F3 and F2 engines that show how it is done. The blocks are rigid enough to support the forces.

[WhiteBlue]

An F3 engine isn't build for 600 hp either. They will simply build the engine to do what it needs to do. A turbo engine will have a more rigid block anyway. I was just pointing to the Japanese F3 engine as an example that there are well known design methods for stressed L4 engines. There should be little doubt that they can be applied to F1 as well.

[J. Edlund]

good work Paolo and grunt. I liked those posts very much.

The problem with the BMW was allways lag not power..

Edlund what track did BMW win and took pole on? in 1985? Fast track? = there ya go.. Legend status right away.

Was it hard to drive Yes! = legend status.

http://www.gurneyfla...bof1engine.html

In the latter years BMW lacked power compared to the other engine manufacturers. They also lacked driveability.

What track did BMW win and took pole on in 1985? The correct answer is none. They won the 1985 French GP, the only win that year, but it was a Honda powered Williams that took pole and fastest lap. In 1986 BMW had also one win, in Mexico. BMW wasn't really that competitive after their 1983 drivers title (when Ferrari took the constructors title). Essentially it was only downhill after that.

I think the BMW F1 turbo engine actually used a cast iron block from one of their production cars.

Production based grey iron block yes.

Honda, Ferrari and Renault did use cast iron blocks too in some of their engines, but these were designed for racing. Hondas block was a thinwall nodular iron casting which is much stronger than regular grey iron.

[cheapracer]

Oh this thread, never did finish our debate on BMW engines JE - as Arnie says - "I be bark".