Carb too big??Now what?

[The_Dealer]

Well i bought a holley carb from a buddy, he told me it was a holley 350cfm, and reading the numbers and matching them up in my summit book, i actually got a holley 500...ok so thats way to big for my 2.8 to utilize. So the question is, what is the difference between the 350 and 500? is the body the same? i know the 500 has 50cc accelerator pump. basically can i rejet my 500 to work like a 350 on my motor? i would like to keep the carb because when i go to do my 5.0 swap i can put it on that motor too.

basically what im asking is what can i do to run my already bought used holley 500cfm 2bbl on my 2.8 durasparked?

 

[adsm08]

basically what im asking is what can i do to run my already bought used holley 500cfm 2bbl on my 2.8 durasparked?

Go faster!


Seriously though, I know diddly about carbs. I'd guess that using the smallest jets available would help, but I'm assuming that it fits the manifold. I don't know that for sure.

 

[The_Dealer]

it fits the manifold, its a 2bbl, and the same series as the 350cfm everyone is using

 

[mn_smokeater]

jetting down will help im sure long but thats long as you dont run too lean...

something to restrict the flow of fuel would too.

 

[adsm08]

I'd get the lightest jets you can find. It might suck for mileage for a while, but it should work.

 

[kimcrwbr1]

I hate to tell you a 350 is pushing it for the 2.8. The difference is 150 cfm and you will never be able to get the air fuel right with a 500 you will either be running to lean or dumping too much fuel in there that it can burn. You can try it just be careful you dont fry the valves (lean) or wash out the rings and score the cylinders (rich).

 

[martin]

Carburetors use venturi effect to draw fuel into the air-stream. Without getting into a crap load of typing, the 2.8 will not draw enough air through fast enough to make it viable. Don't waste your time trying to achieve the impossible.

 

[Young_unn]

in reality no matter how hard you try to fanagle a big carb to work, your usually going to dump more fuel that you need and lose gas mileage and performance.

yes you will be able to get it to work, but never as well as the right one will, and unless your running as stock 5.0 500 cfm is a bit light.

The math formula is CARB CFM = CU.IN. X Rpm divided by 3456 X VE%

Rpm is the max Rpm you would run the engine to, ie if you usually shift at 5k racing thats your rpm, even if it will rev a little higher.

Volumetric efficiency (VE%) is never 100% usually on a stock car its roughly 70% a performance engine usually 80-85%

hopefully my blathering of numbers will help. you can always make an engine run on the wrong size, but it wont run right

 

[Nhaz]

I hate to tell you a 350 is pushing it for the 2.8. The difference is 150 cfm and you will never be able to get the air fuel right with a 500 you will either be running to lean or dumping too much fuel in there that it can burn. You can try it just be careful you dont fry the valves (lean) or wash out the rings and score the cylinders (rich).

X2

The carbs venturi is simply too wide for the fuel being drawn into the engine to ever mix with the air right. The 2.8 cannot drawn enough air across the venturi of that carb to properly atomize the fuel. smaller jets won't help. its a matter of air speed not fuel so much.

So the effect is, either too rich or too lean. It will never run right. You can fiddle with it forever.

it WILL run but not well. You can get a restriction plate made up. but honestly I would just get the right carb.

 

[LIMA BEAN]

Clamp the fuel line a little and put duct tape over half the airhorn, that's how the big boys in the hood do it.

 

[The_Dealer]

wow i did the formula for my 347 and i wont be able to use that either...going on 80% VE ill need around 520cfm. so i guess im gonna have to sell it

 

[adsm08]

This is why I say to carbs and to EFI.

(yes, I know your truck came stock carbed)