Forged Pistons

[stuart 31 3 Cars]

I'm building a new engine for my rally car and have acquired up to now a big valve head (1mm bigger inlets) with Newman rally cam (PH4 I think) and a pair of nearly new Weber 45's on a Longman inlet.

 

The original plan was to keep the bottom end fairly standard and just get everything balanced and lighten the flywheel but am wondering if it's worth spending a bit more and getting slightly bigger forged pistons to take the capacity as close to 1600cc as possible and also enable me to rev the engine a little more to get the best out of the cam.

 

How much more power / torque would I gain from fitting bigger, stronger pistons though? I'm just wondering if it'd be worth the extra expense or not really.

 

Cheers

Stuart

[James_R 3]

The real gain will be ability to run high CR which you'll be wanting for the cam, rev's wise you'll be about the same.

[stuart 31 3 Cars]

I believe the head has had a pretty hefty skim to raise compression so I'm not sure if I'll need to raise it any more or not by using high comp pistons.

Is there any way of measuring how much the head has been skimmed by?

 

I was just wondering if that cam would work better with larger dia pistons or not really.

 

I'm also under the impression that I'd be really pushing standard pistons to their limits running around 7500rpm for sustained periods so thought that lighter forged ones might be a safer bet and get a chunk more power / torque in the process, or does it not work like that?

[James_R 3]

The power/torque is all in the head, the bottom end is just the bit that pumps the air about, the change of piston won't really effect that. I'm not sure on the maximum ceiling for 1.6 engine's but due to the short stroke it's pretty high next to an 8v engine, which are good to 8k so 7.5 would be with in limits, but worth seeing what others have done.