4GC was never a spread bore.
Fuel lines and antifreeze
- Thread starter Iowa409
- Start date
Don had recommended the AV2 and there is one in the store right now, 3 blocks away, for $10 less than the on line folks, BUT I want to see this super duper $1500 carb perform, and now its become a mission, I do not care if I take it right back off and put the AV2 on, this SPEAD BORE is going on lol
So all square bores are not created equal, that's the point. The centerlines of their bores, regardless of size, are in a square. The bore size and/or flange bolt pattern may vary, and they do. Thus the 4GC (and AFBs, clones and most Holleys) are square bore. And they may use different gaskets, for sure.
Spread bore, generally Q-jet and replacements, moves the rear throttle bore centerlines out a bit. New ball game.
Spread bore, generally Q-jet and replacements, moves the rear throttle bore centerlines out a bit. New ball game.
Ok That I understand, so if I go with a square bore gasket and spacer it will not line up on my intake mounting bolts? but the spread bore gasket does?
Did your square bore spacer have duel bolt pattern if not then you will need one that is.
This is a AFB with the duel bolt pattern.
This is a AFB with the duel bolt pattern.
Just because the primarys are smaller than the secondaries does not make it a spread bore carb.Get a base gasket for a typical Holley carb and place it on the manifold.The pholic spacer made just like the gasket goes on next,then add another gasket and bolt the carb down,it''ll work.As James said,make sure that the gaskets and spacer have two bolt holes per tab.
Something like this.
https://www.summitracing.com/parts/edl-8722
https://www.summitracing.com/parts/edl-8722
BINGO........thats the problem, my MR. Gasket one I bought was a fixed hole , not options or 2 sets of holes, so I did see some kits out there that offered a aluminum type spacer with dual holes, but it looks like it would lift my carb up a full inch or better, it comes with 3/8 x 16 bolts.
To answer another issue mentioned here, when I measure my square bore (corrected and learned , thank you) it is a square measurement, bolt pattern, same distance between bolts in all directions. I want a gold star or a happy face on my homework today, lol I learned something new, thanks guys.
To answer another issue mentioned here, when I measure my square bore (corrected and learned , thank you) it is a square measurement, bolt pattern, same distance between bolts in all directions. I want a gold star or a happy face on my homework today, lol I learned something new, thanks guys.
No, it has to do with the throttle blade spacing as Dave said.
We've had to use a carb adaptor to mount an Edelbrock carb on a small square bore manifold. I think it was a truck intake. I believe something like this: https://www.summitracing.com/parts/trd-2064
Yes Jim those are required when putting an AFB/Edelbrock/Holley carb on a 250 horse 348 and the truck engines that used the smaller based GC's.The 340 horse carb is a larger based carb .I have the same intake laying here and a 625 Carter afb bolts right on adapter unneeded.
So was there 3 4gc bolt patterns?A buddy has an early olds dual quad that uses the small rochester bolt pattern,and while searching for another carb we were under the impression that it was for 56 or 57 and earlier and that all 58 and later were large base,so did the the 340 use an oddball 4gc that had an AFB pattern or did it have a distinct 3rd bolt pattern,and if so was it used on anything else?Never mind after rereading Don's last post it already answered my question.
So was the AFB pattern 4gc used on other GM engines during this time?Also what pattern carb is Iowa409 dealing with that it won't bolt directly to his 340hp intake,weren't the 340hp rochester carbs bigger bore and venturi's than earlier large pattern 4gc's meaning that it would be a step down performance wise?I was thinking there was a thread a while back that was extolling the virtues of the larger 340hp carb.
He's not having trouble fitting the carb to the manifold just getting the right gaskets and a pholic spacer to put under said carb.The 4gc's on the 340 horse 409 flowed right around 700 cfm.The smaller ones like the 220-230 horse 283,the 250 horse 327 and 348 were maybe 500 cfm.The larger 4gc pattern is the same as the afb/holley ect.The smaller carbs need an adapter like Jim posted if you're planning on running the stock manifold.
To me a Quadrajet with 2 big bores and 2 small bores is the only true spreadbore. They look very different from any other carb and only came out about 1965 or 1966.
The 4GC came as a small square bore and a larger square bore, the 4 bores were pretty much the same size in each individual carb. The small ones were for 283’s and low hp 327’s.
The 4GC in the 409 was the large square bore and is pretty rare and it was only used on the 340hp 409, it’s the same size gasket wise as an afb, edelbrock, and Holley.
The above only relates to chevies, lots of other gm products and other brands used a quadrajet and a 4gc. Some look the same as the Chevy stuff, but they are different inside or outside.
Does your 4gc have the original aluminum tag with the model number? That’s the only way to know what you have. It may be off an olds or Buick etc.
A correct 409 gc is as rare as a correct tripower 2gc carb.
The 4GC came as a small square bore and a larger square bore, the 4 bores were pretty much the same size in each individual carb. The small ones were for 283’s and low hp 327’s.
The 4GC in the 409 was the large square bore and is pretty rare and it was only used on the 340hp 409, it’s the same size gasket wise as an afb, edelbrock, and Holley.
The above only relates to chevies, lots of other gm products and other brands used a quadrajet and a 4gc. Some look the same as the Chevy stuff, but they are different inside or outside.
Does your 4gc have the original aluminum tag with the model number? That’s the only way to know what you have. It may be off an olds or Buick etc.
A correct 409 gc is as rare as a correct tripower 2gc carb.
ok guys just got home from work, I can get my carb base number (I already looked it up when I bought it, shows 63-64 auto tranny, 409) the intake is already listed above, I cancelled the JEG insulator for spread bore, I picked up a new one to look at tomorrow, that was available, but I do not like it, ?I see no value other than a spacer, its aluminum Edelbrock 2696 Square bore to Q-Jet adapter. I tried to order the one mentioned above but everyone I spoke to at the parts house said the number is not valid, but its right on the web site advertising it.
Someones looking out for you.You didn't want that one anyway as it wouldn't work.Please forget about anything spread bore related.It simply does not apply.A part that you should be able to get locally is the Edelbrock plastic spacer that they make for their carbs.This is the one that you want.The Edelbrock part number is 8711.You'll need a 4 hole gasket and if you got a carb base gasket with that freshly rebuilt 4gc use that under the carb and you'll need 4 longer carb ounting studs as this is a one inch spacer.They useed to make one about 1/2 inch but I only see that in wood.What you don't want is anything metal because we are trying to insulate the carb from heat.Aluminum spacers in this type of applicationn where we have and need manifold heat have a opposite effect.
I got an idea...........lol I am going to save this 4GC for a swap meet this summer, I am going with the AVS1906, electric choke, Edelbrock.
I spoke to them earlier, they say I will still need an adaptor to get back to my intake, which is odd, it comes with two sets of holes for mounting. I think they were referring to the insulator block and they said they do not make one, but referred me to a company call Transdapt.com they have some cool looking stuff for adaptors. heres the carb choice (Thanks Don)
https://www.edelbrock.com/avs2-650-cfm-carburetor-with-electric-choke-in-satin-non-egr-1906.html
The next step will be to sort out vacum',s and my draft tube connection/brake booster connection, but I think this eliminates alot of issues.
One of the best parts is this is a $350-380 c arb, but with the sale at Napa right now, my cost $291.00 so thats a win.
I spoke to them earlier, they say I will still need an adaptor to get back to my intake, which is odd, it comes with two sets of holes for mounting. I think they were referring to the insulator block and they said they do not make one, but referred me to a company call Transdapt.com they have some cool looking stuff for adaptors. heres the carb choice (Thanks Don)
https://www.edelbrock.com/avs2-650-cfm-carburetor-with-electric-choke-in-satin-non-egr-1906.html
The next step will be to sort out vacum',s and my draft tube connection/brake booster connection, but I think this eliminates alot of issues.
One of the best parts is this is a $350-380 c arb, but with the sale at Napa right now, my cost $291.00 so thats a win.