q-jet modifications.

[cdwelch]

 :)i had a few modifications done to my q-jet by brad urban from the carb shop back in the mid eighties. he bored the primaries oversize along with a rebush job and claimed it flowed about 45 more cfm on his flow machine. also opened up the secondary well slightly and tapped the secondary for screw in jets. at that time i did not do anything with the air bleeds. it was a 78 170 series 750 and i put it in the garage for about the next 30 years. last summer i put it on a stock (about 220 h.p 350) and hooked up the wide band to tune it. at 2200 rpm (3.73 rear) it's at 15.00 (little lean) and when you nail it it goes to about 10 to one. throttle response is great. i plan to install the throttle plate on my 170 series 800 and se how it runs. have a 388 sbc with a 225 at .50 cam just about ready for it then i'll tune with the wide band.  any thoughts or advice.   thanks guys    denny

[Cliff Ruggles]

To this day I don't see how installing larger throttle plates can improve cfm, as that area is already larger than the restriction above it.

Anyhow, 388cid with a 225 @ .050" cam isn't going to need that much cfm anyhow.  In addition, not all throttle bodies are fully interchangeable, what are the carburetor numbers that you are doing the swap on?

As far as airbleeds are concerned, I'd need carburetor numbers and what size they are now, and jets/metering rods being used, to be able to provide any guidance in that area.......Cliff

[dwelch]

thanks for the reply cliff, i appreciate it. back then i was going for the rebush job and they talked me into the larger bores. back in those days my friends were putting big cams in and getting mad at their q-jets cause they didn't know the ways to fix that, so i ended up with about a dozen q-jets for free. i wanted to run this q-jet befor i'm in the grave (just turned 67). my race buddies liked the throttle response this carb had. i'll get the numbers this weekend on both carbs. i made my first pass at pacemakers in 1963 and my last one in 2008 in my 70 chevelle.  thanks,   denny

[cdwelch]

 :)the carb. with the modified throttle plate is 17056202. the main bodies that i would like to swap it on are 17059247,17057204 and 17058204 (carter). thanks

[Cliff Ruggles]

Those baseplates are interchangeable with very minor differences, so good to go there.....Cliff

[cdwelch]

 :)thank you very much