David wrote:Thanks for the feedback Simon. I find it quite flattering that it stands up so well to a BTCC engine - my experience is limited at this level and budget is certainly not in the BTCC league. Given unlimited funds, I would be quite happy to play around with exhaust lengths, but the fact of the matter is that they are as good as I'm likely to get in a one-off attempt.
I have always intended this to be a three stage project - engine, exhaust, and induction. I still need to improve the induction - but that won't be this year as the roller barrels are working well enough. The roller barrels are 45mm but the Duratec really needs 48+mm to get above 280BHP. The engine is also soft limited to 8000 rpm so I think there is more to come.
The dip you refer to has been the subject of some discussion, and we feel it is induction. At low RPM the roller barrels struggle with velocity past the injectors and fueling is particularly tricky. Torque actually increases as the barrel closes and we think it this is because velocity past the injector increases due to the geometry of the roller barrel (their shape is like a funnel). The standard fix for this is to move the injector out of the head and further up the induction path (which will be part of the induction upgrade).
David
I'm always totally bewildered when people say 48mm tb or 45mm or what ever - 48mm where?
the trick in induction is mostly length, then airbox volume, then snorkel length [you don't have one] and dia, then throat TAPER -which obviously means a different dia at every point away from valve
also do not believe what you hear about injector position - its much much more complicated than that, - for instance what spray angle do you have? if you have a very wide spray, then at low speeds you are just wetting the tb walls and fuel is dribbling into the cylinder to wash your bores and not burn, at higher gas speeds [higher revs] you will obviously get less wash out, move that injector up the bore where the bore is wider, maybe beyond the butterfly and you will get a better air/fuel mix which will give you a better result on the dyno , on the other hand if you have a pencil jet injector, the reverse may happen. that's why moving the injector about with no other consideration is a nonsense - people who want the best will choose injector and its a surprise to some but choose the right injector and site it properly and there is no disadvantage to two injector set ups which is clumsy and expensive.
secondly I guarantee the low dips have absolutely nothing to do with induction, I've modelled it and played with it a billion times - its all to do with collector shape and volume - not primary exhaust length, not induction length or tb size at all. Careful design will smooth it, but you need to do the software simulation and get the exhaust made as a one off.
Ps the whole BTCC "thing" is a nonsense, my BTCC engine is less TB size, less valve size, less cam, on a plenum, on a wet sump like a stock OEM Honda K20A2 - which shows you what tuning can do - and the exhaust was a carry over from the Judd - I wasn't allowed the time or budget to do my own, consequently it was much too big at 2 inch dia for an 8500rpm engine and I know I could have got another 15brake out of it had I been allowed a smaller stepped exhaust and been allowed to change the induction pipe which was ridiculously too big.
the money in this engine went on making ridiculously heavy one off rods and pistons to meet regs - ie pistons had to be 350gmm - which meant lots of extra ally and a solid gudgeon pin to make the weight - stupid really but those were the regs
