I have an 84Z28 with a 355sbc. with a 600 Holley an edelbrock performer intake,Dart Sportman II heads,crane roller rockers,crane cam(.454,216@50int. .480,228@50exh.),1 5/8 hedman shorties,true dual exhaust. It dynoed at 227hp@5500 and 265lbs/ft@3600 My buddies car is a 96 firebird formula with a cold air intake,slp headers borla cat back and 1.6 roller rockers His car dynoed at 300hp@5500 and 317lbs/ft@4000. Everyone tells me the 600 holley is too small.I already bought a used Dart Sportman II intake and I am looking at a 750 holley to go with it.I know it is not going to give me 75hp.,but it should help.I was also wondering if the 1 5/8 headers are hurting me. I really don`t think he should be that much more powerfull than I am.Please let me know what you think

It shouldn't hurt too much. Maybe at higher rpms above 5k. Search the carb board there is a formula to determine how much cfm you need.

It's engine cid*max rpm/3456 IIRC. Maybe someone can confirm this.

if that formulas right, for my 350 .060 over (360) with 5500redline i would only 572cfm....so a 600 should be about right?

Go here and look at the Cubic Feet per Minute. There are three formulas that are listed.

Theoretical CFM

Actual CFM

Carburetor CFM

According to the Carburetor CFM formula, you will need a 631 CFM carb. That's at 90% VE. That's a good ballpark VE for a modified street/strip engine.

But as you said earlier, it won't make a huge RWHP diff. You're not that far off on CFM.

Your problem lies somewhere else. I suspect it's the intake/head/cam combo you have. Those are VERY high RPM heads, IE they flow a lot. You have a relatively mild cam, and a very mild intake compared to those heads. Mismatched parts will do that.

You won’t see any huge gains unless you increase the cam duration and lift and move up to AT LEAST a Victor Jr. Intake or equivalent, like the Dart II intake. But then you’re going to need a 750 CFM carb.

So it looks like you’ve got 2 of the problems covered. Get that cam changed!!! Otherwise you’re still going to have similar problems.

Don’t forget to change TQ stall speed to match the combo as well as the rear gear ratio. Those will determine if you get the power to the wheels.

AJ

I think a big restriction is the intake and the intake lobe of the cam... But the cam isn't THAT bad... It just seems like something's wrong there. Those heads flow like nuts. Even with a Performer intake, it just seems like he should get a bit more. If this is gonna be a street car, he should get more out of even a Performer RPM. <shrug>

There's something else wrong with your motor... even with the small carb, your peak torque at the rear wheels should have been around 80-90% of the CID, which would be around 300-320 ft-lbs. Just for reference, my 305 (that's right, the 0 comes before the 5) dynoed at 208 HP and 245 ft-lbs at the rear wheels the other day, with the stock intake, stock CC Q-Jet carb, stock air cleaner, stock cat and exhaust, all emissions devices installed and operating (cat, AIR, EGR, etc.); the only things that are different are the heads which are 186 casting, the cam which is a Comp XM264HR-12, and the exhaust which is Edelbrock TES but stock behind that. There are a few other details but you can see the overall picture I'm sure.

I think something is broken about your motor; blown head gasket, rolled cam lobes, something like that. It's sick somehow to put out torque numbers that low. You don't need to be worrying about carb CFM yet as the cause for poor performance. I personally would be extremely disappointed if I had as much money in a motor as you have in that one, and got those numbers.

you should be putting a lot more out than that. those are great heaqds and that cam is not too small. you definately have something not setup right, what is your timing set at? you should have dynoed at about 260-280 horsepower at the wheels and right around 300 for torque. check your timing and do a tune up and run it again. try different timing advance amounts with the different dynos.

The funny thing is that it runs fine,I really doubt it has a blown head gasket or a dead cylinder.The dyno guy said by the shape
of the tourqe curve it wanted more fuel.The carb was rebuilt and works great on regular driving so I thought rejetting it may help
some, again there is no 75hp. there.How much hp. should I have.