Boost didn't drop?
 

I have a pair of 1997 454 magnums with with Whipple superchargers. I replaced stock rectangle port heads with Dart Pro1 heads and a 632 lift 256 duration cam but my boost didn't drop like expected (with same pulleys), I suspect that my Stainless Marine Hi-torque (basic, not Gen III) manifolds and risers may not be able to flow enough.
1) Has anyone else had this problem?
2) Any recommendations on manifold for a supercharged application like this?

Ian T.

I have stainless marine on my whippled 502's No problem here. 502MPI's about 5 PSI 700HP.

Your probably right... Exhaust will limit the benifits of cam and intake mods on Whipplecharged motors. Time for some Stellings.....

Could be exhaust but I think we need more info. What cam were you running before and do you have the cam cards on both cams. Need to know specs as they will make a difference. Why did you think your boost would be lower now then before changes. How much boost are you running?

Paradigm,

I was running the stock cam before and the new one is 632 lift, 256 duration with 114 lobe separation. I was running 7# boost before and now seeing 6#. I have significantly increased the flow with the heads and cam which should drop the boost. I have read posts from JimV, Dustin and others that all suggest that with the changes I have made I should see a drop of at least a couple of pounds maybe as much as a 5# drop.

You lost a pound of boost.
That IS significant.

(I would have guessed 2, though).
Exhaust is really the ONLY place for a noteworthy restriction since the whipple uses its own intake manifold.

Did you notch the bores when you did the head swap? (would have been helpful).

What did you pick up in speed & in acceleration? That is the most inportant question.

What if you need more prop because the added HP? When I put my whipple on I didn't have a new prop yet and was running a 24p bravo and if I hit the throttle the boost went up to 9-10, not sure because it scared me and I backed off.
Like mcollinstn stated, 1 lb. of boost is significant.
If you need to change props I would do that first because I can change my boost using different props; 28, 28lab, 30 , 30lab. In fact I have tried 2 lab 28Bravos labed by different shops and have 1lb boost difference between the 2. What rpm's are you turning now?

Acceleration (more than I can use) and speed are about the same as before, speed within 1mph.

I am still running the labbed 30p Bravo 1 prop at about 5100 RPM however with this cam and heads I am looking to turn about 5500 - 5600RPM and will prop accordingly once I get the boost sorted.

Thanks for the input guys.

Call Dustin!!!!!!!