jimmymtfan19

What carb is everyyone running. Ive looked at a few builds and guys seem to be pulling vacume at higher rpms on their builds on the intake. Even with an 850 cfm carb. Do u guys think a 950 cfm will be slow at part throttle on more normal street driving. Im doing a e85 12:5:1 aluminum head. 2800 stall 461, 522 544 lift 232 244 duration not sure whether to run an 850 or 950

droldsmorland

Using some math... 461 CID engine x 6,500(guessing) max rpm = 1,952,500
Take 1,952,500 x .85 = 1,659,625
Then 1,659,625 ÷ 3456 = 737 CFM

Sooo...950 is likely too big IMO. Most people tend to over carb. Do you have a 750 or 800 you can bolt on and try?

Firewalker

Depending on weight and gears shouldn't slow you down at all. It still only gets what your foot feeds it, and wide open shouldn't be a problem then either But you have to ask yourself what you would actually gain, and I would guess not much.

jimmymtfan19

I ask because, from what i understand if its pulling vacume. At wot. The carb is too small

cutlassefi

What intake will you be using? Are the heads ported?

Firewalker

That's what some believe, but there is little to no differences in ETs or power normally from bigger carbs, because the higher the vacuum the more CFMs will flow from the same carb. A 500 CFM 2 barrel, for example at 3 inches, only flows about 350 CFM at 1.5 inches. The same happens with bigger carbs and multiple carbs.

Take dual four barrels as another example. Each carb flows less, because each sees less vacuum and flows less CFMs. Fuel distribution is the key to dual fours along with double the fuel in the float bowls.

When a bigger carb shows any real gain it is usually because of better fuel metering than the smaller one had rather than higher CFMs. Change the fuel metering in the smaller carb to what the larger carb has, and then the gain with the larger carb all but vanishes.

I have seen an Oldsmobile 350 with a two barrel and wheels up outrun a 454 Camaro, with an 850 double pumper, by over 20-30 car lengths.

I am not against big CFM carbs at all, but not really needed to win the race regardless of what you hear.

shiftbyear

A lot has to do with the efficiency of the engine, on the dyno I've seen 750 carbs pull 800 cfm on a race engine. Of course the people to ask are tech reps from Holley, Willeys, Cliff Ruggles, or other race carb specialist. Good luck.

Firewalker

The greater the vacuum/suck, then the higher the CFMs it can and will flow in CFM's. Calling a carb salesman gets you to buying a carb or book usually. Thats what they do for a living. Like guys with dynos dyno. But it doesn't mean any of them know squat about going faster.

droldsmorland

All good info here. But the math(data) generally doesn't lie. It will put you in the ballpark. IMO...750-850 Ebrock, Holley, Demon, Quick Fuel, Qjet et al...It just needs to be super tunned for the application.

cutlassefi

I couldn't disagree more. A lot has to do with the plenum, intake, heads etc. that's why I asked the op what he was using.
I did a test a couple years ago and posted it on here. A BBO with a 750 and then with an 850. It contradicts your statement with dyno proof in HP and Tq and the subsequent curves. Check it out.

Rallye469

Call quickFuel. Tell them what you have they'll build you a carb to spec for less than an out of the box Holley.

Firewalker

Two different fuel and power curves shows different fuel meterings coming from the carbs tested, and if I remember right they did not show the same AFR either. Thats not a carb CFM test, but which is tuned to the closer to the correct fuel supply needed for that combo.

RocketRonnie

Try this site it will do the math for you, https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.gtsparkplugs.com/CarbCFMCalc.html&ved=0ahUKEwjUy-ihh4LTAhUN3mMKHXtpDk0QFggaMAA&usg=AFQjCNEssK_6AmNS roF0i1cNQPfUXZr3pw

or this http://www.gtsparkplugs.com/CarbCFMCalc.html

jimmymtfan19

Mondello posiflow. And pro comps with minor cleanup and 5 angle valve job

cutlassefi

Air/fuels and timing were nearly identical. Check out the difference when a spacer was added to an intake with a smaller plenum.
With all due respect you mention a lot of different thoughts on here but we dont see any proof on any of your statements. Can you supply us with any of that? I've posted numerous dyno sheets on various different builds. Just asking for some sort of backup to your statements, time slips with the details etc., something.

Thanks in advance.