REDUCING airflow in a 500 Holley....

[sc2dave]

I have a 500 cfm Holley on a 194 '66 ChevyII. This one has been drilled and tapped air bleeds,pvcr too. I want to tune this carb.I know it's big and ,NO, I don't want to put a v8 in it and ,NO, I don't want to put a different carb. Can I put a sheetmetal restrictor under the carb to cut down flow?

[peejay]

The only problems that "too big" carburetors have is insufficient speed through the venturis and switching over from idle circuits to mains. Sticking something under the carb will solve none of that.

That said I don't think a 500 is too big for a 194. If anything it might be too small, the fewer cylinders an engine has the more it "likes" a larger carb.

[sc2dave]

I forgot to mention that I also had annulars installed and the engine has dual headers, cam, Offenhauser intake. so I'm good on the carb?

[DaveMcLain]

If you put annular boosters in a 4412 you most likely made it smaller anyway.

[MadBill]

If it's a 2 bbl. 4412, remember that such carbs are rated at 3.0" Hg. pressure drop vs. 1.5" for 4 bbl., so a '500 CFM' 2 bbl. flows the same as a 353 CFM 4 bbl.

[Diodedog]

If it's a 2 bbl. 4412, remember that such carbs are rated at 3.0" Hg. pressure drop vs. 1.5" for 4 bbl., so a '500 CFM' 2 bbl. flows the same as a 353 CFM 4 bbl.

The one I had on my flow bench flowed 394 CFM, many car people don't know that the 2 and 4 barrels were rated at different pressure drops.

[peejay]

The clue that they are measured at different pressure drops should be that a 500cfm 2-barrel has the same size venturis and throttle bores as a 750cfm 4-barrel. Half the carb should flow half as much, no?

My statement still stands - a 500cfm 4-barrel should be just peachy on a 194 six.

[sc2dave]

Great! Thanks.

[MadBill]

Just for the record Dave, how many barrels does your carb have?

PS: Also for the record, a restrictor can do nothing but worsen the effects of a too-large carb, by further reducing the air velocity through the venturis and so hurting atomization.

PPS: Theoretically, CFM varies with the square root of the pressure drop, so √(1.5/3.0) = 0.707 x 500 = 353. A number of real world factors can somewhat affect the actual values.

[sc2dave]

2bbl, 4412 Holley

[sc2dave]

So where's a good write up on tuning the 4412? Thanks in advance!

[sc2dave]

So where's a good write up on tuning the 4412?

[pamotorman]

I would start by putting all the calibrations back to stock and start from there.

[Geoff2]

Er, limit throttle opening so that the blades only open 3/4 - 7/8 of full open.

[bigfoot584]

I would start by putting all the calibrations back to stock and start from there.

That won't work he changed to annular boosters already.