Anyhow, the always excellent Mulsanne's Corner had an interesting tidbit several weeks ago.
Yesterday brought a bevy of interesting emails into our inbox.
Seems a few of you have been reading our series that is stepping through the methodology of predicting engine power outputs. Now, power is one thing, and as we've been showing, the outputs between the gasoline powered cars and the diesels aren't too dissimilar. At least it seems to be much closer than in years past.
So how can the large performance deficit between the two "categories" be explained? Simple, torque. As one of our Industry Experts let's on, "I have done a lot of simulation work for Le Mans...torque is way more relevant than anything else. By a big bunch." Le Mans has what amounts to five long straights; from Tertre Rouge to the first chicane, from the L'Arche Chicane (first chicane) to the La Florandiere Chicane (second chicane), from the La Florandiere Chicane to Mulsanne Corner, from Mulsanne to Indianapolis, and from Arnage to the Porsche Curves. Think of these as five drag strips. What's more important on the drag strip, power or acceleration from torque? So check this out, our Expert tells us a 10% increase in torque can amount to, wait for it...upwards of a 3.7 second decrease in lap time. A similar percentage increase in power only drops lap times at Le Mans by around 2.6 seconds. Furthermore, a 10% increase in downforce is only good for a 1 second drop in lap time. So of course the manufacturers have gone the technical route that leads to the easiest way to decrease lap time. They aren't stupid after all and they have a lot of Boffins running the numbers. Says said Expert, "Two mph faster out of the chicanes is 10-12 mph faster at the end of the straight--even gas turbos can't make up for the 22 to 26:1 compression ratio of a diesel. All that BMEP just shoves the car down the track, out of each corner." And it does that five times with consequences each lap. Stephen Knight, "knighty" on the 10-10ths forum, relevantly relays, "I remember Peter Elleray once said that during the Bentley LMP900 development they actually realized, via many track simulations, that torque was of more importance than power at Le Mans...hence they increased the 3.6 liter Audi engine to 4.0 liters, the net result being slightly less power but a lot more torque, which gave them a significant acceleration advantage, much like the diesels have..."
und
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.
We end with a final word from an anonymous source:
The diesels need to be slowed down. We saw a 4.3% lap time difference between the quickest gas and diesel at the Le Mans Test and the diesels lapped under the 3:30 target in the first year of a supposedly "fixed for 3 years" set of regulations. We don't agree that Manufacturers should have a 2% advantage over the rest of the competition (as is implicitly acceptable in the regulations), their strength in depth and resources should be advantage enough. It is unreasonable to place the burden of any change in terms of costs and workload upon private teams, especially when their cars are performing above the target lap time at Le Mans of 3:30. Instead, the Manufacturer teams should shoulder the impact of any changes, it is the diesel cars that should be slowed down, not the gas cars that should be changed to go faster. Halving the size of the diesel car fuel tanks would allow us to play on a level field, that gives the real scale of the difference in performance. Perhaps the diesels should "drive through" every lap instead of crossing the start/finish line? If there was true equivalence between the engines, why did both Audi and Peugeot decide to build diesel engines for the new regulations, coincidence, marketing? Or because there is still a rich vein of performance to be mined from improvements in diesel technology?
Gas on the right, brake on the left. No bumping, no swerving. When you see one finger in the air that means one lap to go. When you see the checker return to the pits. If you come to a stop at any time stay in the vehicle until an attendant can help you.
Let's get it on!
But some rules might need to be changed a bit to sway the bias away from diesels.
