what is the cfm size of a stock 4bbl carb on a 86 lg4 ?

 

You can make it flow around 750-800ish.

 

In other words, well more than any 305 would likely ever require, and more than enough for all but the highest RPM 350s. These things used to feed 454s and 455s to 5,000+ RPM with no problems, and did it by the millions. If you want reassurance, just open the secondaries and look at the bore sizes. Then remember that NASCAR engines with restrictor plates have only four 7/8" bores to make 700HP.

 

i guess this is one of those things that nobody knows isnt it ? and here i thought it was a simple question that atleast some one on here had to know

 

Actually it's one of those things that pretty much everyone knows.

The factory never "rated" OEM carbs for flow like the aftermarket manufacturers do. Even in the aftermarket there are variations in testing. Some manufacturers might test wet flow, some might test dry, some might vary the pressure differential, all of which lead to variations in flow.

 

well if its one of those things that every one knows why cant i get a str8 answer ???

 

what does it matter if it is sufficient?

 

because it just happens to be somthing that i want to know right now. and i figured that it would be a quick and simple question that would get a quick and simple and correct answer. but i guess i was hoping for a bit to much

 

If you're arguing with your friends with the hoods up in the McDonald's parking lot, you can tell then "1,080 CFM". That should shut them up.

Beyond that, the total flow has little relevance. Using a "Holley-type" rating is just as insignificant, whether your friends understand that or not. Advertising numbers mean little. Results are king.

If you really want to throw numbers around, the typical post-1972 Rochester 4MV/E4ME (QuadraJet) has a peak primary flow of 161 SCFM @ 1.5" Hg PD, and 760 SCFM on the secondary side. At 3.0" Hg PD the primary flow peaks at 227 SCFM, and total flow with secondaries is 1,080 SCFM.

Comparatively, the ratings of a Holley 1850/4150/4160 are at 300/600 SCFM @ 1.5", and 424/848 SCFM @ 3.0" Hg PD.

Strictly by the numbers, a Holley is generally a big step backward. That, of course, is with no regard to the cool stickers you get with every Holley purchase, and the stigma that surrounds the name - Deserved or not. In primary fuel metering and transition, the step backwards is more along the order of 4-5 times worse than a proper Rochester 4MV.

 

And I thought that "every one" knew about Google...

Perhaps is the words "straight", "can't", and "too" could be typed correctly, a "str8" answer would be forthcoming.

Strange, "isnt it ?"

There's a cool and helpful web address called "Google". The "web?" - You know, that thing Al Gore invented. You can find all sorts of trivial information there, like this:

http://www.mergetel.com/~fraso/RasoE...arburetion.htm

 

 

Is this some kind of joke? good ***, the first reply had the answer:
750-800CFM
Did you miss that or something? Most were "rated" at 750, with a handful out there with slightly larger secondaries putting them at 800CFM....
They're a damn good carb.

 

Well, the stock Q-Jet on my L69 had a tab on the sec. air valves that restricted their opening thus reducing the air flow (CFM) through the sec's. Wouldn't that reduce the CFM rating of this carb say to around 600 cfm?

Auggie

 

Something like that, but it's nothing that can't be removed in a few seconds. That's why in my reply I said they can be made to flow 750 CFM.

 

Exately! We do that when we run a Q-Jet on the dyno and drill and tap a hole just above that removed tab and install an allen head screw. This screw will allow us to be able to adjust the open angle of the sec. air valves.

Auggie

 

The regular 4MV is either 750 or 760 SFCM, depending upon what you read. The HP versions were 800 SCFM or over:

http://www.buickperformance.com/qjet.html

 

Auggie (or anyone else), suppose you have a picture of that tab removal / set screw placement?
I'm just not able to picture it, are we talking about removing the vertical "plate" thats in the secondary air valves (a simple pull and remove), or a tab on the secondary air valve shaft on the outside of the carb? I remember reading about this on the main page, but it was lacking the necessary 1000word picture....
Thanks

 

Sonix, it is the tab on the sec. air valve shaft on the outside of the carb. You will see that that tab prevents the air valves from opening to their 90* max. This limited the 750 cfm Q-Jet to a guess of around 550 to 600 cfm. I use a cut off tool to remove the tab and then locate the allen head set screw just above it so you can make air valve angle adj. I do not have any air valve spring tenision (see pic) because the dash pot controls the opening rate of the sec. air valves which is slow by the way. I have a dash pot from the Carb Shop that opens instantly but that is another story.

Auggie