[DEEZPAZ]

I'm looking at a carb for a 455 Olds but I wasn't sure if it was a 750 or 800 cfm. Is there any way to tell by the #'s on the carb?? It it a Rochester carb and has the following #'s on the carb: 7043251 RB 0533. Any ideas??

Also, can someone tell me what cfm means and whats the difference between 750 and 800?

[camerjeff]

cfm = Cubic Feet per Minute of air flow at wide open throttle

The easiest way to tell them apart is an 800 cfm Q-jet has larger primary bores, so large in fact that they protrude into the carbs fuel bowl area, so both primary bores have a bump or protrusion in the primary bores if you look down from the top of the carb and open the choke and butterfly valve.

here is a link with a picture of both style primary bores

http://dyeager535.topcities.com/qjetidentify.html

If your carb does not have those bumps it is a 750 cfm carb. FYI I have found very few 800 cfm carbs were made 1970-1974, Pontiac 455 HO's, some Buick and Caddy, I don't know about Olds. From 1975 on very few 750 cfm Carbs were made. They seemed to standerdise on the larger casting size.

Hope that helps

[DEEZPAZ]

Thats some good info and the pix are very helpful!!