Hot Rod Forum banner

what Rochester carbs for tri-power

13K views 7 replies 5 participants last post by  Centerline 
#1 ·
im looking for information on what carbs i need to put together a tri-power for my sbc. i want to use an offy intake. Stromberg's cost to much for me, a guy told me to use Rochester's but i know nothing about them i've seen a few one 70's Chevy's but thats it.

thanks
 
#3 ·
What are commonly used are Rochester 2GCs but you can't use just any 2GCs for the system to work correctly. If you can't find the correct outboard carbs you'll have to have a couple modified to remove the idle circuits and they'll also need to have the butterflies changed so they seal completely. Some people run them without these mods but the engine won't idle right and will run rich most of the time.

If you're lucky you might be able to find a complete set on e-bay like I did a few years ago that came off a factory setup. GM had them on some late 50's 348's and of course the GTO plus a few others so they are out there. A word of warning though matched sets with the correct outboard carbs aren't cheap. I think I paid around $600 about 5 years ago for my set that came off a factory '58 348 tri-power setup.

Good luck.
 
#6 ·
1957plymouthhemi said:
Not sure I buy into the changine the butterflys, but they will generally need to be centered into the bore.......
On standard Rochester 2G and 2GC carbs the butterflies have fixed idle air bleed holes. Two little holes in each butterfly which provide air to the idle circuits. The outside carbs on a factory tripower setup have thicker butterflies with no bleed holes. You can get away with using stock butterflies but if the holes aren't plugged they create a small vacuum leak plus the correct butterflies have a slightly different angle on them so when closed they completely seal out air. Again if they didn't it would create a small vacuum leak.

A lot of people run standard carbs front and back with just plugged idle circuits and their engines run fine, but that's not the way the factory did it. Once I get all my stuff unpacked (in a month or so) I'll take some pics of the differences in the butterflies so everyone can see.
 
#7 ·
It's not uncommon to find the bleed holes on the Large base 2Gs, but you almost never see them on the small base carbs that are most commonly used for the outboard carbs. More common to find on the small base carbs are butterflys that rivited rather than retained by screws. I normally avoid these as too much of a PIA to drill tap and counter-sink for screws and I have a good supply of bases with screws.

The standard butterflys however are usually NOT centered in the base. This is normally not a big deal when used in a standard set single 2BBl application as the throttle plates are held slightly open all the time. By loosening the screws that hold the butterflys the plates can be centered and create the seal necessary to prevent vacume leaks.

I've seen and read about the plates before but have never really felt a need for them (at least for me). I currently have 3 Tri-Power set-ups, all have stock plates which have been centered and they all idle fine.
 
#8 ·
1957plymouthhemi said:
............................. I've seen and read about the plates before but have never really felt a need for them (at least for me). I currently have 3 Tri-Power set-ups, all have stock plates which have been centered and they all idle fine.
Like I said a lot of people don't run them and everything works just fine but "factory" setups included different butterflies. The 2 GC in the center had butterflies that were 3/32" thick while the 2G outboard carbs butterflies were 5/32" thick. That's a pretty big difference. Now, how many tripower setups out there are running with these?? Probably not many more than were originally produced by Rochester, but that is the way the factory did it.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top