Posted by Dave Speed on Tuesday, July 05, 2005 at 10:37PM :
In Reply to: Re: 251 dual carb set-up performance? posted by Garrett Mayer on Tuesday, July 05, 2005 at 11:09AM :
Generated HP is more a function of cubic feet of properly charged air in (and out) than just cc of gasoline per second. Big jets just make it too rich.
I have never seen any dyno numbers on these, but I'll inquire next time I talk to the "boys". The stock dual manifolds were on the heavy trucks for added power.
While the "truck" carbs had relatively good flow compared to the smaller car carbs on the mopar flatheads, these engines were limited by their ability to push air in and out - poor flow and low rpm.
On advice from George and others, I started with the 'short stroke' 251 (4 1/2"!) for higher RPM, added a cam, 30 overbore, dual intake and exhaust manifolds and opened up the intake/exhaust passages about .1" to match the manifolds. Also static balanced the engine to 0.1 gram (dynamic was not readily available and outside my budget)and milled the head 30 thou.
I'm expecting a 20 - 30 (+)% gain in power with premium fuel.