Carb CFM ques

[CorvetteOnWater]

What CFM is the carb on an 85 mercruiser 5.7 260?

 

[180shabah]

Re: Carb CFM ques

I would guess about 700CFM, but that is just a guess.

Check out the adults only sticky and download the FSM for your engine, it should answer all of your questions.

 

[Bondo]

Re: Carb CFM ques

Ayuh,... If it's the old Rochester,.. It's known as a variable venturi carb, that'll flow up to about 750cfms...
But,...
The motor will only move around 550cfms at WOT anyways....

That makes the 650cfm Edlebrock the Perfect Up-grade...

 

[JustJason]

Re: Carb CFM ques

If it's the old Rochester,.. It's known as a variable venturi carb

Whaa?? What am I missing here Bondo. I was always taught (and I have so passed on) that Rochesters, Holleys, Edlebrocks.... every sterndrive and every OB carb was a fixed venturi. The diameter of the bore (venturi) is fixed.

Now motorcycle and dirtbike carbs (and alot of off road stuff) Have actual variable ventris because the slide opens and closes (or makes bigger and smaller) the size of the bore. I guess one could say the throttle plate in a standard carb does the same thing. But it really doesn't.

What am I missing here?

 

[Bondo]

Re: Carb CFM ques

I was always taught

Ayuh,... I was taught that the air door on the secondaries is in effect a variable venturi...

Maybe I'm the 1 who's Wrong here, or maybe it's My vocabulary that's Wrong...

 

[JustJason]

Re: Carb CFM ques

Hmmm.... I need an opinion on this one. I just don't want to be spreading the word out there if my word is wrong.

 

[dan t.]

Re: Carb CFM ques

q-jet carbs came in 650 and 750 configurations, the 750s were mainly found on big blocks, (over 400 cid), the secondary air valve is exactly that, a q-jet doesnt have venturies in the secondary side, it is known as a pull over system

 

[ScottRogers]

Re: Carb CFM ques

Correct, I like Q-Jets, they have small primaries for great off idle response, and man hole size secondaries that flow whatever the engine will take in. Just expensive to replace though.

 

[dgopetactical]

Re: Carb CFM ques

my Holley 4bbl is a 600
....I remember last year I did tons of research and I was told 600....also called Holley direct and thats what they recomended.
Denny

 

[mkast]

Re: Carb CFM ques

This might help:

http://www.hemmings.com/mus/stories/2005/01/01/hmn_feature21.html

http://www.carburetion.com/Rochester.asp

http://www.carburetion.com/Questions/QandA.htm

http://cars.rasoenterprises.com/Carburetion.htm