I agree with Mc, Above 1 pound is alot ! I would not worry about that ,just the performace increase alot of stock cams have tons of overlap and yours now may not have as much ,so it will not loose the boost ,,,need more data .....

1# of boost is a 15% reduction. Seems significant to me. Probably increased flow#'s about the same amount.

The Whipplecharger is an efficient positive displacement compressor. I don't think it will increase its volumetric flowrate the way a centrifugal compressor does when the discharge pressure is lower. If you are spinning at the same RPM with the same pulleys I would not expect the Whipplecharger to move much if any more air than it did before. Therefore I would not expect the horsepower or speed to change much if any. The only effect of the better heads and cam will be the lower boost observed.

You say that the speed is the same and that makes sense. Do you have some throttle left at 5100? It seems to me that you will need to spin the compressor faster to make more power. This will bring your boost level back up and the better heads and cam should allow you to do all this without having cylinder pressure or detonation problems. What compression ratio do you have now?

BINGO Tomcat.... You are a smart man

These motors stock were carb. 365HP? What carb do you have now? Intercooled whipple manifold?

Stock 365HP x 7lbs/16 = 525HP

New heads and big cam probably lost some TQ but HP ?+40HP increase? 405HP x 6lbs/16 = 555Hp

you made 30HP more and probably the same peak TQ.

Isn't performance boating fun. With engine upgrades it almost never seems to end You are correct if the motor breathes easier (less restriction in and out) you should drop some boost. Which you did and the million dollar ? now is how much boost. A lot of things affect boost. Testing yourself or unless someone has tried your exact set up and changed exhaust I think we will be just making educated or uneducated guess in my case. I am not that familiar with Stainless Marine exhaust and the differences between there models or series. I would call Stainless Marine. How much HP are the Stainless Marine manifold and risers you run rated for? I think I would also call Dustin Whipple he has a real wealth of information especially with whipple applications and is always there to help from what I have seen. Or if you have the $$$$ try a new set of exhaust. Sorry could not be of more help. Sounds like a fun project.

Get the boost back to 7 lbs and you'll see about 405 x 7lbs/16 = 582HP. There is your +60HP increase from the heads and cam.

Thanks for the input guys.

Dustin has been a great help to me all along and I will check with him on it as suggested.

From previous posts/research I had done I got the impressions that with this combination my boost would drop by 3-5# hence the reason I am looking for other reasons for the small drop. I also realize that the Stainless Manifolds that I have are not the ones they recommend for high horsepower motors.

I wonder if there is anyone that actually did a similar swap and what change did they see?