CFM of QJ

I have a QJ question! Are all of these carbs built after 1970 800 cfm? I was given a 1978 QJ that was used on a Chevy 454 truck but I have no way of knowing if it is 800 cfm. 17058213 is the # on the side.
RW

 

Some are 750s.

 

Pretty sure after a certain point they were all 800. Not as early as '70 though.

 

The only way to know is to LOOK at the primaries.

 

On the left picture... notice the "bump" at "8 o'clock' position.. thats a 800 CFM

 

Jim is correct, some were 750's, however, ALL front inlet Buick, Olds and Pontiac models (non computer controlled) were the larger castings after 1974. Some side inlet models after 1974 were still the small castings.

FWIW, we have customers running into the 9's with the smaller castings. My own 600hp engine only shows a few hundreths of a second and less than .5 mph difference between the larger and smaller castings on back to back dragstrip runs.

Basically, no need to run out and get a larger casting for most applications. One item I do find with the larger castings on large cid engines, is that you have more cfm available on the primiaries for "normal" driving. This shows up as improved heavy/part throttle driving, climbing steep grades, higher top speed on the primaries only, etc.....Cliff