Here's my setup:

-Vortec heads which were mildly ported and polished
-Performer RPM intake
-XE268H cam
Hydraulic flat tappet
Basic Operating RPM Range: 1,600-5,800 RPM
Intake Duration 050 inch Lift: 224
Exhaust Duration 050 inch Lift: 230
Duration at 050 inch Lift: 224 int./230 exh.
Advertised Intake Duration: 268
Advertised Exhaust Duration: 280
Advertised Duration: 268 int./280 exh.
Intake Valve Lift with Factory Rocker Arm Ratio: 0.477
Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.480
Valve Lift with Factory Rocker Arm Ratio: 0.477 int./0.480 exh. lift
Lobe Separation (degrees): 110

-10:1 C.R.


The deal is, that i have a 600cfm edelbrock and a 750 edelbrock carb....the 600 is on there right now but isn't tuned right so i don't know its optimal power yet......but the thing is, that i haven't used the 750 and i was wondering what you guys though....should i try it or should i return it since it hasn't been used, and then spend the money on other go fast parts??

also, i did the whole CFM calculation and it comes out that the 600 would be ideal, since i only wanna rev it to 5500-6000 tops......


Anyone out there with similar setups?? any suggestions?....btw i also have a 600 holley...and if i do end up returning the 750 i will probably rebuild the holley then try to tune it to see if it would be better than the edelbrock......

thanks!

 

A larger carb than the equation calls out is typically beneficial with dual plane intakes.

Whether to go with another Edelbrock, I'll pass on that.

 

yah i've noticed that about 90% of the guys on here are holley guys...and i have no problems going with a holley, its just that....that is what i have so that is what i was thinking of going for.....actually what i was thinking....was return my 750 edelbrock and get the 670cfm holley street avenger?? good or no? or should i just go all out and get a double pumper??

 

my understanding is, the diff between the big and small
Edelbrock is, the size of the primaries.
If too big, drivabilty suffers.

Is this car for racing?, does one-tenth sec
in the 1/4 mile mean anything?
If not, you should consider keeping the smaller Edel.

Do you have some reason to think that
the WOT jetting of your carb is incorrect?

Owning a car that once had a grossly overhuge Holley DP,
and then swapping to a reasonable Carter AFB,
{a lot like a Edelbrock}, I like the Carter.

 

well i bought the 600 off a friend of mine that has a 84 S10 with a 355, and it ran pretty good on his truck so i dont think that it is off by too much.....but if i do decide to keep this 600 i definately wanna get the tuning kit so i can try to make it run the best.......

 

You've got a very similar setup to mine. I've never ran the 600cfm carb, only the 750.

Once I got the 750 tunned, it ran great with my motor. I personally would never go with a 600, after having this 750 on.

 

I say stick with one of the 600's.

 

lol actually i ended up taking back the 750 and paying the diff for a holley 670 street avenger......haven't put it on yet but i cant wait to see if there is a big diff......

 

You shouldn't compare a new carb, to one you bought used.

 

i have a very similar setup to yours. when i first got the motor running i had stumbling problems when i would mash the gas from a standstill(completely stalling out sometimes). I had a 750 edelbrock on it and i first thought it was to big of a carb so i put on a 600 but still had the hestitation.
After many timing changes and what not i got frustrated and threw a old holley 750 double pumper and sure enough it took away the hestitation. The car launches from a dead start like no other. All the techs at the dealership i work at, said a 750 was way to big. It really surprised them. the vortecs really flow well!

 

Did you play with the step up springs, the ones the carbs come with are based on a mild cam.

 

750holley DP.... you wont be sorry, i tried the smaller carb thing on my motor.... no good.

 

A 750DP is too big for most small blocks. It was too big for my motor i found the 650DP to have excellent responce and works great. When i ran the 750 it would bog when you floor it and felt like it lack power through the rpms also between shifts it would bog when you hit the gas in the next gear. Put the 650DP on and it woke up and no hesitations. I also had a 670 street avenger and it was by far the worst of the 3 carbs.

 

Since the originator has an automatic transmission, the only issue with a 750DP on a 355 is keeping the stall (minimum RPMs at which you go WOT) above the "bog line" http://www.holley.com/HiOctn/TechSer...nfo/P225A.html .

For a 355 with a 750, that's about 1500 RPMs. If it bogs under those conditions, it's improperly tuned.

 

I think that if you can tune the carb yourself go with the 750. If you can't take it back and get a street avenger. It'll run best right out of the box. Get rid of the 600. As far as a DP goes it's like anything else if it doesn't fit your package it's not going to perform right. A DP is going to be best with a loose converter or a manual trans.

 

i got the 670 street avenger....took back the old carb and returned something else and it ended up only costing me 70 bucks.....so i was pretty happy...havent put it on yet though.....soon!!

and also i need to swap my spark plug wires.....i ended up running a 13.8 at the strip like it is now with the 600 and it was popping and stuff at upper rpms and it is fine at lower..... i checked the wires and a couple of them have laid against the header and got burnt though a little......so hopefully with the carb swap and wireset swap i will be into the mid 13's.....

 

The 750 is going to make more power than the 600.
it's not too big. The accelerator pump will need fine tuning either way. I have a 750 edelbrock and and few holleys and have used them on a very simular vortec 350. The 750 edelbrock works just fine. I use out of the box jetting and rods.

The carb selection formula assumes you want a intake manifold vacuum of 1.5" while at max power at WOT.

Carbs are rated at 1.5" vacuum. This is not the ideal for max power. Max power is achieved with a carb that typically results in a .75 to 1" manifold vacuum reading while at max power and WOT.

A 750cfm rated carb does not flow 750cfm on a motor AT WOT when the guage reads .75 to 1" it flows about 550cfm.

Hook up a vacuum guage to your motor and go for ride with a friend. have him read the vacuum guage while at WOT max power rpm. A 600 will read higher than a 750.

As long as the carb that gives a .75 to 1" manifold vacuum reading at WOT is resonably responsive at the low rpm range that u use, It is the right carb for best over all performance. A 750cfm carb that is tuned in right is usually the best carb for a high performance 350 overall. Usually a motor with a dual plane fully devided plenum like the performer RPM can use a even larger carb.

Lots of people just don't know how to tune in a carb well, or care to so a smaller carb works easier for them. ( a smaller carb is naturally more responsive to throttle movement. But they are giving up power and performance on a good 350.

 

I went from a 625 Carter AFB (basically an Edelbrock) to a 750 Holley VS.. HUGE difference, even tho it is running pretty rich right now. My engine specialist told me he may downjet me some, but in any case, im really happy with the 750.. so much better response than the carter...

 

Rabbitt, what do you mean by 'response'?

a long time ago, what other people called 'response',
I would call, the 'one-fourth throttle - same a full throttle' effect.
People were impressed by getting full power with
slight throtttle movement. Unfortunately,
these cars were tiresome to drive on the street,
as it would be difficult to get a certain speed
on a city street. beccause slight throttle changes made for
big speed changes.

 

i mean if i would hammer on the happy pedal with the carter, my car would not go for half a second or would bumble then go.. with my holley, it reacts quicker to throttle movement.. i dont mean that a little pressure on the throttle does a lot, but i do mean the carb's response was quicker to cable movement on the holley than the carter

 

the cpmbo you are running is the same exact one I had, and now it resides in my friends car. I sold it to him about 2 years ago. The only diff inyours and mine is I hd the roller version of the 268 it has the same duration, but with a little more lift on the cam. its called the 274h.

I had a holley 750 on mine and it ran good! then I got a proform mainbody and picked up almost 3 tenths!!!!!!!!!!! in the 1/4 so I guess you could say more air is better! I then sold my carb and bought a quickfuel 750 and got even better reults with better idleing and it was not so cold natured. SO stay away from a 600 with your setup.

Also to let you know how good the quickfuel carbs are, I called them about a carb for my racecar which has a 406cid in it. They asked me everything about the motor and the rest of the setup as far as drivetrain, exhaust and gears. The built me a carb and when I got it I went to the dyno. After the first pull the guy asked me who had been tunning the car. I told him this is hte first time out with it and it has zero carb tunning. Well the a/f ratio was 12.8 from the minute I hit the gas untill I let off!!!!!!!!!!!! you want to talk about amazed for a carb that was built to spec!!!!!!!!!!! I mean damn we left everything alone and only tried playing with the timing a little.

 

Do you have a link for those QuickFuel Carbs?

 

http://www.quickfueltechnology.com/

 

hmm.....well i think im still going to keep the 670 for now cuz i wanna see how it will do......went back out to the strip this weekend and pulled off a 13.6@101mph and had some tire spin and couldn't floor it off the line because i was afraid i would break loose with my street tires.....