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Posted by StangerMach1 (Member # 3677) on :
 
i have a 351 clevland with an edelbrock performer RPM manifold, keith black 10.5/1 compression pistons, bored .030 over, mild crane cam. unilite igniton (mallory). do you think a 750 holly double-pumper is too much, i have it on there now, and it seems to be bogging and not having a crisp throttle responce.


im thinking a street avenger 670 or demon carb would be better??

anyone know?

[ December 11, 2004, 12:04 PM: Message edited by: StangerMach1 ]
 
Posted by Wolfie351 (Member # 651) on :
 
Are you sure you have a Performer RPM intake? Don't tease me now, I've been waiting for Edelbrock to make that for YEARS. Anyways, I'll assume you have a regular Performer manifold. With that intake and a mild cam, I don't think you'll see much gain over 6000rpm. The 750dp will give you a higher peak hp number, but the 670 will give you a much more broad torque curve. I have a 750dp on my 351C but it has 4v heads, a decent cam and pulls to 7000 rpm. If you were in the process of putting together the motor, I'd say get the street avenger. But, since you already have the 750, I'd save your money and just try to get that to work. Since your hesitation comes right off idle, I'd first try going up one size on the shooters. Here's a Holley tech page that will give you an idea on where to start.

http://www.holley.com/HiOctn/TechServ/TechInfo/TI-221.html
 
Posted by StangerMach1 (Member # 3677) on :
 
yea its just a performer i guess

it says performer 1b then some numbers, so thats just a regular performer


now on the freeway at about 3500rpms, if i accelerate it will hesitate and stutter (not extreme but it feels like its struggling to go faster) until 3700 then it will pull hard.

can that be the carb?
 
Posted by Wolfie351 (Member # 651) on :
 
Oh, it stumbles at speed...yeah, that would be a sympton of overcarburation. Has it always done this, or is this new? Go through all the trouble shootings steps before you shell out $$ for a new carb. Make sure the fuel filter isn't plugged, fuel pressure is good, no vacuum leaks, etc. If it's an automatic, it would probably be a good idea to go with a vac secondary carb. If it's a manual, you can get the double pumper to work.
 
Posted by StangerMach1 (Member # 3677) on :
 
Yea it has done this but its only on the freeway, i can rev it past this with no hesitation, and can go in first past this with no hesitiation.

yea its an automatic, i replaced the fuel filter but havnt had a chance to drive it yet,

thanks a lot for the tips.
 
Posted by talaposa (Member # 2460) on :
 
My little black book of formulas indicates that at 100% efficiency (seldom achieved) your engine would neet 689 CFM. Years ago I ran a 750 cfm double pumper on my pumped boss 351 and had the same problem. The double pumper takes a lot more dialing in than the vacuum secondaries because the rear plates open whenever your foot tells it too. When you tromp on it all of a sudden sometimes the stock carb out of the box doesn't have enough fuel to compensate for the sudden air rush. Holley makes different squirters and cams...even 50cc pump. You probably have the .025 or .028 squirters on the back side. I'd go up a size or so and experiment with different cam rates.

I wouldn't worry about the CFM. The carb should do well once its dialed in.
 




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