[knighty]

I worked on the BMW-M5 Ascari 4.0 LMP900 twin turbo engine - we originally started with a cross plane crank and it gave reasonable power - about 580bhp if I remember correctly (audi had about 650!).........we had a flat plane crank made with new cams to suit and it did not make any more power.......but the race drivers liked the flat plane engine because the transient response (snappiness!) of the engine was much better - it revved with a much greater urgency. the engine was always going to be poor on power, as it ran a 5.5 litre BMW-M5, de stroked to 4.0, with a wide valve angle head, a 93mm bore which required a filthy great piston intruder to get a sensible compression ratio - which kills power in any engine - especially a turbo engine......if it had something like an 86mm bore it would have been a cracking engine - but not so.

I also heard Cosworth did a similar evaluation project for a possible Aston Martin LMP900 sports car project back in 2001 ish - they did the same flat/cross plane comparison and also found there was no power benefit of either.

BUT - believe me - a flat plane crank weighs about 25% less than a cross plane crank and due the the flat plane exhaust pulses being even.......the flat plane is the way to go........if I was designing an LMP1 normally aspirated V8 sports prototype long distance race engine, I would go for a low revving 6 litre, with flat plane crank, and with twin counter rotating balancer shafts in order to dampen out the horrible unbalanced 2nd order horizontal shaking movement, which rattles the drivers fillings out, and generally shakes the car to pieces as said above. hope that helps.