I have a 1986 IROC with a 383 swap.

The build on it is basically a 10:1 cr motor with an edelbrock performer RPM intake.

The cam is about 244 int./244 exh. duration at 050.

292 advertised duration, about .501 lift?

I had an old 750 CFM holley with vacuum secondaries on it, but i had some trouble under hard acceleration it feels like it bogs down at higher rpms or when i push the gas down further...

I put a 750 CFM edelbrock on top, and it performs a lot better, but as soon as i open up the secondaries on it, it decides to bog down and not even accelerate, the car just stops and loses power completely. sometimes it happens in first gear too when i'm taking off if i give it too much gas off the line... It does it even when i turn the adjustment screws all the way in. runs great as long as i don't pound on the throttle and open the secondaries. . . .

I also have some work done to my heads, ported and polished, valve job, heavy duty springs.
I have a holley mechanical fuel pump

Is 750 cfm too much for this motor?
I also have a 650 edelbrock.

I know a lot of people are going to tell me to switch to holley, but i've never had any problems with my edelbrock carbs on my 305 and 355.

What carb should i use for this size motor?

 

That 383 should have no issues with a 750cfm. I ran an 830cfm when I was using a blow-thru setup on my 383. It does seem to show the signs of being over carbed though. I ran my 305 a couple times, once with the 830cfm blow-thru, and another with the 105mm TB and 95lb injectors, and both times it did like you're saying where power drops off with WOT but is fine at something like 75% throttle.

 

Make sure your timing is set right. That being said make sure the jets are working all the way through the throttle band without any flat spots. your secondary jets may not be working properly, check it out. 750cfm is spot on with a 383 build I wouldn't go any lower.

You also may be under jetting on the secondary's if the jets are visually working try to go 2 sizes larger then see how it works.

 

Sounds liike you have a restriction somewhere in the fuel delivery system. Clogged filter, weak pump, kinked line- something like that.

Get a cheap remote fuel pressure gague kit and mount the gague somewhere you can see it while driving (duck taping it to the outside of the windshield temporarily is perfectly acceptable). Go make a couple full throttle runs. If you're outrunning the fuel system it will be as plain as the nose on your face- fuel pressure will nose-dive followed shortly thereafter by the engine losing power.

THis definitely doesn't sound like a problem with the carb being oversized. Whatever is wrong is much more basic than that- inadequate fuel supply or inadequate (or improprly timed) spark.

 

I checked the filter... and it isn't clogged, the pump is an aftermarket holley, and i've never had issues with it in the past.. the lines are all freed up and flowing smoothly... I just had the timing checked and reset the other day. . . What should my fuel pressure be at? If the fuel pressure drops like you mentioned then what can i do to fix that? do i need a new pump? it only does it when i open my secondaries. . . .

 

should be anywhere from 5.5-8 best at around 6-7 psi

 

Edelbrock says set pressure at 5.5 psi, don't let it drop below 2.0 psi, don't let it go higher than 6.0 psi.