I'd seriously rethink the dual quad setup. Even at 1000cfm, that's way too much for that motor. With the double pumpers, I'd be surprised if it doesn't bog and lose horsepower. If the 500's have a vacuum operated secondary, you'll just engage the primaries and the secondaries will never come in. I think a single Holley 750cfm vacuum secondary 4-barrel would be immeasurably better than that dual quad setup.

If you have your mind made up to run dual quad, look at this carb. It is a Holley 390cfm, vacuum secondary carb. With two, you'd get 780cfm. That'd be plenty for your motor, and should give good driveability and responsiveness.

Keep in mind, with 2 carbs, there's twice as many things to go wrong and plug up.

 

that is very true rusty! i can't argue with you there ! but i had a 750 speed demon on my truck already, and it was too small. i know i could not believe it myself ! i was told to get a mighty demon carb. i've tried to run a vacuum sec carb, it didn't work properly with the nitrous, the secondaries would not come in until almost 90 mph. all this testing and tuning was done by a very repitable shop, p and j speedshop. basically i just want the dual quad set up for looks. i'm pretty sure i can get it to work right. i will take a peek at the 390 holleys though.

 

What spring were you running in the secondary diaphram? I always used the purple or yellow spring.

FWIW, I find it hard to believe that the 750 was too small. Having too large a carb can cause the same symptoms as having one too small. What have you got in that motor that takes so much air? Aftermarket heads, cam, what?

 

i had the light yellow spring in the carb. my motor had edelbrock heads that were ported, 284/296dur, 584/588 lift cam, 4.56 gears, 10-1 comp, 2500 stall. i shouldn'y say it was too small, the demon carbs are set up inaccorence to cam specs. i basically needed a race carb because i pull very little vacuum. they told me to get a 750 mighty demon, or a 800 holley double pumper.

 

Yeah, the steel crank might be the best bet. I really think a 390 crank would hold up but I would hate to be wrong. The scat cranks are cast iron just like the "2T" crank you have in there now. Keeping the crank in the block is what your goal is going to be but I think it should be okay.

 

i have to get a crank anyways now, i still can not believe they stuck a 360 crank in my motor, hey, for a 360 though it really hauled **** !!!! i want my 390 back !!!!!

 

I don't know if I could handle being cheated like that man! He probably screwed up your 390 crank and saw a 2T laying around and said "2T, 2U, what's the difference?" Maybe it was an honest mistake but I doubt it. I would make him cough up a freshly machined 390 crank though on the house!

 

i would love too !! there selling the place. i don't know if they are going out of buisness or moving ? they build lots of people race engines too !! i wonderif i was the first to get the shaft from them?

 

Agreed. Make him give you a new one.

Maybe this is the time to trade up to a 428 crank? Just an idea.

 

just a question ive been running crank dyno's since this thread and was wondering how many rpms an FE crank can handle at 600 hp or less. It seems that with the smaller stroke like a 360 crank you can make high hp in say the 8,000 rpm range "theoretically" but only 6,500 with the 390 or 428 cranks. granted less hp and tq. but ultimately longer rpm band, or am i just reading these things all wrong?

 

You could build a high rpm screamer 360. It's entirely possible to do. However, when you start pushing things much above 6000rpm, particularly with an aftermarket cam, keeping the valvetrain together becomes a huge headache. This is the advantage of longer strokes and increased displacement, you can make your power and torque lower in the rpm range and not have to stress out your valvetrain.

As for how many rpms before the stock FE crank explodes, I have no idea. My guess is that it would be some high number, something that none of us will ever see. This is because (428 cranks and some FT cranks excluded) it's internally balanced and very stable.

 

by keeping it togeather do you mean constantly adjusting to stay in spec? Would those erson rocker assemblies remedy this problem?

 

By keeping it together, I mean not having rocker shafts break or valves pull through their keepers. I haven't run the ersons, maybe someone with some experience with them will chime in.

 

right on, id love to see 7 or 8k that would be the goods!

 

theoretically your right. thats why a small block will rev to the moon, and a big block doesn't need to because of its bore and stroke creates enough low end power were it doesn't need to rev as high. for example the chevy 383 stroker isn't suppose to be taken over 5200 rpm's because it has a long stroke. it makes all of its power around 2500-3500 rpm's.