Question for 750 CFM Carbed 5.0 owners here please

Uber5.0 · Apr 3, 2005

This is related to a thread I posted a couple weeks ago about people running carbureted 302's which looks like it might be lost. I've decided to go with a Holley 4150 HP Model, but I am still trying to choose between the 650 CFM and the 750 CFM units.
Okay, here's the question: In general, has anyone had trouble or had to make adjustments to their setup to accomodate a 750 CFM carb? Is it reasonably streetable? I know it's going to get crummy fuel economy, but if you can give any input regarding your experiences, that would help making the last decisions before buying & building.
As always, thanks in advance!

EMW150 · Apr 4, 2005

Really, it depends on the combination. For most street applications a 650 is right where you want to be. Give us your engine and cam specs , and intake, and I can give you a better idea.

bluevenom867 · Apr 4, 2005

What EMW150 said,and also if its a auto or a stick,what converter (if auto),and rear gear.

The Fox · Apr 4, 2005

I have some decent mods and the 750 was too much for it. I also don't know what I'm doing as far as tuning. Now I put my 600 back on and it gets not enough fuel. But I think, once again, I don't know how to tune a carb other than idle to save my life. I think I'll just get a predator 670 and call it a day.

I can't say my post will help to much but that's my experience.

Boss 351 · Apr 4, 2005

I don't know some people tell me my 650 (bought used and was on a chevy 400ci) is waaaaaaaaaay too much for my engine yet my spark plugs are perfect (not too much fuel, not running lean)? I'd be game to try a larger carb on my 302...

I guess it depends how it's jetted. Do a search on the net for 302 carb setups and find someone that has about the same specs and jet the carb like theirs? Or if you can get an O2 sensor and air/fuel gauge so you can tune the carb yourself?

donsbad68 · Apr 4, 2005

speed demon 650..........750 is too much carb for a street car.

NosPony · Apr 4, 2005

When i ordered my motor from DSS about 2 yrs ago they told me to run a 750 dp on it out of the box. They said i would have no problems and that is what they run on the same motor combo i bought.

I got a pro bullet 306 world products windsor jr heads, victor jr. intake, x303 cam. (all the other minor stuff)

So far so good.

90NotchBack · Apr 4, 2005

I had a 750 DP on my 302. Here was my combo The short block is out of an 88 Mustang. I have 68 302 4V heads with 49cc chambers and 1.94 / 1.60 valve. Cam Dynamics Roller Rockers. Harden pushrods. Luntia Cam 221/232@50 .526/.530 lift with 111 lobe sepration and 106 center line. Cobra Intake with a 750 Double pumper. The carb was stock out of the box. Just set the idle and floats. Worked great. It's my daily driver. I'm running the saem carb on my 351W know.

Uber5.0 · Apr 4, 2005

The main relevant specs for the car are currently as follows:
stock shortblock, TFS Twisted Wedge heads, 1.6 RRs, E303 cam, Mac longtubes, ORX pipe, Flowmaster catback, WC T5 tranny, 3.55 gears, Aeromotive A1000 fuelpump. The intake will probably be Edelbrock RPM AirGap, and the carb is yet to be decided, of course.

fly4spd · Apr 5, 2005

this is close, most everyone runs to large of a carb.
this is the equation i got out of my engine building book.
(VE x CI x Max RPM)/3456

VE = volumetric efficiency ~ for most street cars about 75 to 80% or .75 - .80
CI = cubic inches (ex. 302, 289, 331, 347...)
Max RPM = i use the highest the car will ever see (redline)
3456 = magic number (too bad i can't use this in my engineering courses

of course the more you mod your engine the higher the VE so adjust accordingly
with a 302 @ 6000 RPM (VE= .8) you only need 419 CFM so you would probally
only need to a 450 or 500. the larger the carb the more top end you'll get, the less low end torque you'll get.
good luck (by the way IMO 750 is way too big)
-aj

EMW150 · Apr 5, 2005

Uber5.0 said:
The main relevant specs for the car are currently as follows:
stock shortblock, TFS Twisted Wedge heads, 1.6 RRs, E303 cam, Mac longtubes, ORX pipe, Flowmaster catback, WC T5 tranny, 3.55 gears, Aeromotive A1000 fuelpump. The intake will probably be Edelbrock RPM AirGap, and the carb is yet to be decided, of course.

650 double pumper would be perfect. The E cam's power range is not high enough where a 750 would benefit you.

Uber5.0 · Apr 5, 2005

A quick related question, someone was telling me that nitrous increases volumetric efficiency, even beyond 100% overall. It kind of makes sense, but can anyone verify? I'd hate to run too lean and kill the motor.

jackchan · Jul 4, 2006

hey Eric did you ever swap cams? if so do you want to sell the N-111 anderson cam?
thanks
Ben

R2D2 · Jul 4, 2006

it comes down to the heads being used

dragnazz5.0 · Jul 4, 2006

Uber5.0 said:
A quick related question, someone was telling me that nitrous increases volumetric efficiency, even beyond 100% overall. It kind of makes sense, but can anyone verify? I'd hate to run too lean and kill the motor.

with nitrous or a blower you can make it to 100% VE, but you will never make it to 100% thermal efficiency simply because of the fact that all the metal in the engine absorbs so much heat from the combustion...which makes you wonder if you are really making the VE 100% also.

EMW150 · Jul 5, 2006

jackchan said:
hey Eric did you ever swap cams? if so do you want to sell the N-111 anderson cam?
thanks
Ben

I am still running the N-111. My car hasn't seen the track yet this year. Just finally got tires last week. Baby #2, is here,etc and I haven't had the funds or time to get the new solid roller combo finished yet.

85_SS_302_Coupe · Jul 5, 2006

The problem most people don't understand about carb size is the number is the cfm that the carb flows, and you really need to think about what that means.....if you don't have enough engine under a 750, then chances are pretty good that it's going to run rich and you'll have to play with the jets to bring it down, but then it's going to pull way too much air, and somewhere in the power band no matter how you tune it, you're leaving something on the table because you either have to tune it rich to prevent it from going lean, or tune it lean to keep it from running so rich.

rd · Jul 5, 2006

I have a Holley 80457 vacuum secondary 600 model 4160 on my 82. I jetted up to 68's in front, have not touched the secondary metering plate, and put the lightest spring in the spring kit in the secondary diaphram.

It seems to work fine. Starts, idles, runs 12's on motor, etc, and the electric choke still works.

This is with nearly stock iron GT40 heads, a 4.64 lift/270 cam, and a C4 with a 10 inch TCI converter and 4.10 gears. I flash launch it, so I am most concerned about a quick move into the 3-4000 rpm range.

When I get time and back to a track, I want to try more jet to see if theres more up top.

Advise from the Holley people at FFW's seems to lead me to believe that perhaps a double pumper mech secondary 600-650 might be a bit better.

The main thing I am looking for is a stronger launch right now. Given this, I would think a 600 or so should work just fine on a 302 sized engine. 331 or bigger may need the step up.

Killer50stang · Jul 5, 2006

donsbad68 said:
speed demon 650..........750 is too much carb for a street car.

?? Could have fooled me, my 750 runs perfect with my setup.

dastang2 · Jul 5, 2006

Killer50stang said:
?? Could have fooled me, my 750 runs perfect with my setup.

hmm lets see, maybe since you have a blower on top.

Question for 750 CFM Carbed 5.0 owners here please

Uber5.0

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EMW150

bluevenom867

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The Fox

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Boss 351

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donsbad68

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NosPony

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90NotchBack

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Uber5.0

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rd

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