CFM-stock carb size? cant find answer anywhere

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bitchin_buick

Cragar Keystone Klassics
Joined
Nov 11, 2008
I have searched high and low to no avail.......... I have the 2barrel stock 231 cant find anywhere the CFM for my carb or the CFM for the 4barrel used on the 231turbo & 252 (4.1liter) I have tried beforeblack.net- G.M. sites - quadrajet sites, summit, jegs, holly & eddlebrock......
CFM ---2barrel stock ????
CFM ---4barrel stock ????
 
The flow at 1.5" pressure drop is 161cfm for a dualjet which is the stock carb on all NA 3.8's from 79-87. Most q-jets flow 750cfm at 1.5" pressure drop and some flow 850. I believe the ones on turbo engines flow 850. Not sure though. Its been a long time.
 
Maybe I can find out by calling the parts department at a buick dealership... I want to get a new carb but dont want to do so untill someone can tell me the CFM of the stock2 barrel carb I have already. Just want to go slightly larger than what came on it. cant go to large or it will just bog my non turbo 3.8 down ( too much gas).... CFM 2barrel stock on the 3.8 non turbo ??????
 
bitchin_buick said:
Maybe I can find out by calling the parts department at a buick dealership... I want to get a new carb but dont want to do so untill someone can tell me the CFM of the stock2 barrel carb I have already. Just want to go slightly larger than what came on it. cant go to large or it will just bog my non turbo 3.8 down ( too much gas).... CFM 2barrel stock on the 3.8 non turbo ??????
Click to expand...

Did you read my post:rolleyes: ? It was post #3
 
Check for Doug Roe's book on rochester Carburators. I think it says what the cfms are for the different ones.
 
I have both the FSM and a Rochester Carb Manual, I'll look and see if it's in there when I get home tonite.
 
my bad bison--- Read it too fast and missed that. thank you guys for your help.??? Bison???? 161 CFM seem really low, was that a typo??? thanks again u lucky bastards with your kick ass turbos. LOL. fast or not, G-bodies kick ass!!!!!!!!!!!!!!!!
 
My manual lists the following:

Rochester Carburetor Flow Ratings

DualJet (2M Series)

1-3/32" venturi = 230 cfm
1-7/32" venturi = 285 cfm

Quadrajet (4M Series)

1-3/32" venturi = 750 cfm
1-7/32" venturi = 800 cfm

Greg
 
As mentioned in a previous post all Quadrajets are 750cfm or 800 cfm. The 800's came on the 455's from 71 till the end in 76. You could also find them on the big caddy's, Olds and Pontiacs, but I'm fairly sure you couldn't find them on the big Chevys.

Q-jets are air on demand carbs so putting a big carb on a small motor isn't really a huge problem. The only problem that I could see is with the idle circuit. I tried putting my 72 800 cfm Q-jet on my stock 70 GS 350. I couldn't get it to idle less than 1200 rpm. If I had a larger cam things may have been different.

When I decomputered my 86 Regal with the 3.8, I swapped the intake to a 4.1 style and used a 73 Q-jet from a Pontiac. I also set my timing to about 18 degrees initial (this was the only timing I had since the advance was adjusted by the computer...and non-computer controlled HEI's for the 3.8 are like hens teeth in my part of the world). By doing this swap I went from getting around 21 or 22 mpg to 24 mpg.
 
Thanks everyone for your help. NOW THE ? IS---what would compliment my motor the best : KEEP IN MIND I HAVE THE NA-3.8 (non turbo!!!!!!!!!!!!!!!) currently the stock CFM is 230-285( thanks morbid
HOLLY 350 cfm (2 barrel) ?
HOLLY 500 cfm (2 barrel) ?
HOLLY 390 cfm (4 barrel) ?
 
I haven't looked at any Holley's but I'm sure you know the Stocker is "Feedback" meaning it interfaces with the CCC system. If you change the carb you'll need to figure that in.

You may also need to change the intake manifold or use a adapter to get one of the other carbs to fit.
 
Eddlebrock has a manifold that im looking to get. it fits the turbo 3.8 and the 4.1liter, as well as mine. have to lie and say mine is a 79' (non emmisions) to get it! LOL!!!!
 
Is it goin to matter if I get rid of the emmisions crap on my car???? I have heard from some it doesnt effect much on my older 82' (non turbo) as it would a newer car. and I have also heard I should keep it. If I keep it that limits what i can do as far as a new intake and carb! Thanks again for all your help....
 
Is this a track car or a street application? If it's a street car depending on your state you may not be able to pass inspection without the proper emissions.
 
street application. called summit and found that the carb and intake I plan on getting they can sell me & I didn't even have to lie! so that was cool. I live in ohio and they dont do any emmisions inspections on cars here. Not yet anyhow! thanks again 4 your help.
 
bitchin_buick said:
my bad bison--- Read it too fast and missed that. thank you guys for your help.??? Bison???? 161 CFM seem really low, was that a typo??? thanks again u lucky bastards with your kick ass turbos. LOL. fast or not, G-bodies kick ass!!!!!!!!!!!!!!!!
Click to expand...

Not a typo. Thats at 1.5 inches pressure drop. At 3.0 inches pressure drop i believe its 227cfm. Most listings for carbs list air flow ratings for 4bbl carbs at 1.5inches pressure drop and 2bbls at 3.0 inches pressure drop.You gain a lot more on a NA application by removing the exhaust restriction in the manifolds by replacing them with equal length headers even if the carb is way too small. I have heard of super stockers that are forced to run small carbs that actually pull upwards if 6 inches of vacuum at the top of 3rd. Thats about an 80 hp loss on a 650 hp engine. I ran a q-jet with a 4.1 intake on a 3.8 and couldnt tel a difference vs the 2 bbl.
 
Dual jets:
Model 200-1977: 1&3/8 bore
Model 210-1978: 1&7/32 bore

Quadrajets:
4m-4mc-4mv-Air flow @90degree air valve opening-Primary size 1-3/32=750 cfm
M4M-m4mc-e4mc-Air flow @ 90degree air valve opening-Primary size 1-7/32=800cfm
The exception is the opening of the rear butterflys. Rochester changed the angles of the rear butterflys to reduce the amount of air flow going into the carb for each engine. The lower rear butterflys never open fully if the carb is set up properly. They only open to meet the metal spacer in the rear two barrels. The upper butterflys may not be opening all the way either. The part that sticks up should be at a 90 degree angle to be fully open. The restriction is designed to reduce the total cfm. There are also other ecceptions to this rule. The 86 gmc I had with the 4.3 used a restriction just below the venturies cast in that reduced the cfm to 630. Hope this helps.
 
i am looking to replace my quadrajet M4ME. it is leaking air around the primary linkage shaft. i was going to get an edelbrock 1403 carb putting out 500cfm but after reading this thread i am worried that it won't be enough carb. i have a 1982 3.8 v6 turbo in my sandrail. leaking air into the carb is real bad in the sand. Can someone tell me what carb would work well for my application?
 
Nothing better than a Q-jet.;)As said the rear air door rate effects the flow capacity.Do not look at flow ratings only when comparing carbs,our q-jet will run with the best Holley's and give way better fuel mileage:D

Kevin
 
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