Stephen...you say that 280bhp is widely accepted as the ceiling on turbos
One of the main factory tuners (Danielson) could not break the 280bhp ceiling on the A610 even by adding twin turbos. They had set what they believed to be an unambitious target of 300bhp which suprisingly they could not achieve and that is the reason why there was no A610 Danielson or Danielson II.
The most powerful GTA with original manifolds in this country is probably the ex Prima car with 500+ NM torque. We have now seen the power plots and there is a freefall in the power curve again at 280 bhp.
You say that 330bhp is possible on the atmo....what you mean is the factory team acheived this....when you say mega bucks you may well mean it!!!!!
Probably but still mostly basic mods that could be carried out by most 'old school' tuners. Bigger valves, porting, raised compression and crappy Lucas mechanical injection.
If I had limitless money to spend on the turbo engine I'm sure that an engine builder could come up with the necessary manifolds, race cams, football sized turbo and other add ons to acheive well over 330bhp......
Yes that is probably true. The Danielson guys admit that with revised turbos and manifolds they could have achieved the 300bhp target. However they decided that the necessary development and parts costs would be uneconomical. I suppose the proof of the pudding will be Tony Smiths output from his 3.0 turbo and whether he can break the 280 'limit' retaining the existing manifolds.
I think that most people would agree that the best way to obtain big power on a PRV is to dump the existing manifolds and fit twin turbos, preferably starting with the 24V engine. The engine management is also a big deciding factor. This would have been a very costly barrier in the late 80's and early 90's and is now easily and relatively cheaply achieveable.