[olddog]

Dwight,

First let me tell you I am not an engine builder with lots of experiance. I have built a few hot chevy and mopars but 30 years ago. I have read a good deal and I have friends that race, so I have always had an interest.

I cannot tell you what 70mm is good for.

Since it is a newer block, I assumed it is a roller cam, not flat tappet. The duration you have, if it is a roller, should pull good torque to 6000 rpm. The same durration in a modular pulls to 7000 rpm, but that is a 4 valve OHC engine. Also your torque does not come up until about 2700 rpm, which tells me there is enough overlap to hurt torque down low. More durration will shift that even further up the scale.

That is why I am thinking your air flow is restricted on the intake or the exhaust side. The 1 5/8" headers may be some of the restriction at the top end. Obviously heads are a huge factor in breathing.

If you are running a flat tappet cam, I could be all wrong. The cam may be the bottle neck.