Quote:
Originally Posted by ElAurens
Interesting discussion Viper, thank you.
I am a mechanic, not an engineer, and I work on vintage/veteran automobiles.
I have always wondered why you never see Brake Mean Effective Pressure used in modern automobile engine specifications. All the old English cars I work on usually have this listed in their manuals, and it is indeed indicative of their maximum development potential. We race a Triumph TR3, and after all the years of development and money spent on this old design, the maximum BHP that they produce now is still just about what tuners got out of them in the 1960s. Just no way to get around that BMEP thing in any meaningful way. The only thing that has changed over the years is the ability to have much flatter torque and BHP curves, so the engines are more flexible and lap times decrease, even if maximum power is about the same.
Sorry to go off topic, but I rarely get to talk about these things outside of our small vintage racing community.
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I think that the people who produce the brochures these days are afraid that BMEP is too technical for their market.
I think that they emphasise peak bhp because it's a nice big number that's relatively easy to massage in order to sell next year's model.
Really of course you get a better indication of car engine performance around a track by looking at the area under the power curve. This is much harder to massage because generally when you start tuning you end up adding to one part of the curve and subtracting from another unless you either supercharge (and thus increase BMEP) or increase cubic capacity; both of these options are obviously expensive.
Of course, if you improve the gearbox then you can win by tuning the induction & exhaust systems and accepting a peakier power curve. But new gearboxes are also expensive.
If you're stuck with the stock gearbox and don't want to supercharge then really all that you can do is blueprint the engine, perhaps clean up the induction & exhaust systems if possible, and obviously take great care with balancing it. All of this was obviously perfectly possible to do by hand and eye back in the 1960s.
This sort of work might allow you to increase the rev limit a little, but unless you start tweaking the valve and ignition timing this probably won't gain you an awful lot; and of course you'll then find that the gear ratios don't necessarily play nicely with the new power curve.
So in the end you're stuck with the fact that the vehicle is a system of systems, and they all have to work together to produce a fast lap; meanwhile the engineers who originally designed the car (and the tuners who first tried to make it go a bit faster) weren't stupid, and so beating their performance isn't going to be easy.
I think that it's probably easier to improve cars of this vintage by making aerodynamic tweaks; I'd be inclined to pay particular attention to the undertray if there are no rules preventing you from doing so, as quite often old cars are quite poor in this area.
If the track is fast you can probably also reduce drag by cutting down on engine cooling intakes, since they tend to be oversized for road use, based upon the worst case hot-weather uphill traffic jam scenario.
Indeed, if the race is short you could potentially win by going to a total loss cooling system.
Likewise, getting rid of engine accessories that you don't need will save both power & weight. You might also replace the original lead-acid battery with a lithium one, get rid of the alternator entirely and run the coolant & fuel pumps from the battery. And of course you can also down-size your spare tyre (or delete it completely if you don't need to remain road legal).
You can also potentially start playing with the weight distribution by moving the battery around.
New wheels can help to reduce the unsprung mass, and this will open up additional options for tuning the suspension.
But once you start down this path, either you'll run into regulations* if you're racing in some kind of vintage formula, or else you'll be in the slightly unsatisfying position of driving a very fast, very new and extremely expensive car with a vintage numberplate...
PS - glad you enjoyed the discursive part of my little rant. I fear I was being somewhat harsh, but from time to time hecklers get the better of me and I bite...
*Of course, regulations in any serious competition are an exhortation to find innovative ways of violating the spirit of the law without transgressing its letter;
if the other teams aren't periodically complaining about aspects of your design then you're doing it wrong.
