(19-07-2012, 05:48 PM)Ruan Wrote: It's really a myth that an engine needs backpressure to make *power*... It needs the least amount of backpressure to make it's *PEAK* power - wherever that is in the RPM band, but as always with engines, it's a compromise, you want the backpressure there to prevent the valve overlap from sending half the mixture out the exhaust at low RPMs to keep up the midrange torque, but unrestrictive enough at high RPMs to allow the valve overlap to keep gas velocity up to let inertia keep pulling the gasses out the cylinders after TDC combined with the pulse tuning of the exhaust.

(19-07-2012, 06:13 PM)ginge191 Wrote: I now know the fire ring is still decent; the back box had come off along time ago and leaking into the cabin; we must have broken it when we changed the turbo

(19-07-2012, 10:04 PM)Ruan Wrote: Oh no absolutely, I was more referring to petrol engines there... Diesels really don't suffer from valve overlap, however, if they have a restrictive exhaust, they cannot get the gas out fast enough... The more you de-restrict the exhaust, the more power you'll make... I was pointing out that on a Diesel, it really won't make any difference.

The only time you'll see gains is if you tune the exhaust so that at a certain RPM it'll help pull the gasses out - just like blowing over a bottle, you can tune it to a certain frequency... Same as the inlet... But naturally this is ALL pre-turbine wheel...