Any one know the cfm of the stock carb on the 91 502 mag. motor.How much horse power will this carb support?

750cfm
I've been told if you find the right guy to tune it, 425-450hp

Payton is correct. They can be a very good carb.

I thought it was 850 cfm while the SBC's ran a 750 cfm??

I was told from way back from the folks at Jomar Engineering in the Detroit area that "Rochester carbs only come in TWO (2) different CFM sizes; 780cfm and 800cfm---period!" -----But I am not going to stake my life on what I was told so, take the info I have just given as you may.

But the real question that i've asked a hundred times is, how do you identify what size the carb is, based on looking at it?

I have a 1991 boat with a 502 mag. When i run the s/n of the motor by mercruiser they say it's an MPI motor, a '94. But it's carbed now, and i don't know what size the carb is.

What's the number on top of the carb on you're 91 502, nordic95?

I dont have them right now.They are at the engine shop.I was just wondering if I could get them to support 500 to 550 horse.I spent a lot of time at the drap strip years ago and some of those guys were running 650 hp and more on 850 cfm quadrajets.

1-3/32 in venturi (primary) 750 CFM
1-7/32 in venturi (primary) 800 CFM

So if I have the 800 cfm ,how much horse power can this support?