[Tom Vaught]

The Offy dual quad intakes had two different carb height pads for the intakes.
Sometimes the lower height pad will package better under some hoods.

Tom V.

[blueghoast]

I'm running the offy right now there the best of the two
And i've run 600-Holleys and 600 edelbrock carbs and they work good two
right outa the box but I run them where there both hooked together.
Don't try and run on for cruising and the other comes in later.
I also run 750 carters to but it was a little fat for the street.
I also get decent mileage too even with both carbs hooked direct.

GT

[carbking]

Originally Posted by 61-63

Jeff Chmura Stray Cat makes a good point. If you go looking on ebay, craigslist, and other places for a used offy intake be sure to get one with the adapters already on it. You will see them offered without the adapters and you don't want that because the adapters will cost you almost as much as the intake new and they are almost impossible to find used. Just keep looking and one with adapters will turn up.

Bill I've only done sets using the original AFBs so can't help with your question. Perhaps carbking can.

I don't have access to a dyno, which is why I normally post in the "street" section. My "dyno" is happy customers.

So I cannot tell you from experience if (2) genuine Carter 625's will support 469 HP, but Carter literature suggests they will.

Far easier to make any carb race well (WOT consideration only) than perform well on the street (idle, off-idle, various values of vacuum, transition, etc., as well as WOT).

Personal experience, with a LOT of testing:

I currently have two vehicles with performance engines: (1) Pontiac 350 with 850 CFM single spread-bore Carter carb, and (2) Ford modified 390 with two heavily modified Carter aftermarket 625 AFB's (similarity to Bill's question).

When I first put the two 625's on the 390, as always, I built them bone stock. They ran, actually pretty good, and many would have been happy. I wasn't satisfied. So I found a pair of 430 Lincoln AFB's, and transferred primary clusters, secondary clusters, auxiliary air valves, primary jets, secondary jets, step-up rods, and vacuum springs. MUCH BETTER, but still not happy. Changed the mid-range vacuum step on both step-up rods to eliminate a mild surge at cruise. Now it runs the way a carbureted engine should run; and a youngster (then about 25) insulted me by asking what fuel injection unit I was using!

Tom S. made the comment that the imitation AFB's race better than street use. The aftermarket Carters with which I started fit that description, because Carter calibrated them for Chevrolet. The calibration curve for Chevrolet is totally different than the curve for Ford, or Pontiac. If fact, the Ford curve is very close to the one for Pontiac (the Chrysler curve is even closer to Pontiac).

So your 625 Carters will probably race well as is, better with minor tweaking, but will require surgery to run well on the street. But "running well" is a subjective term, different folks will have different tolerances.

For street use, we generally suggest using a couple of original Pontiac single AFB's as the calibration curve is close, and only minor tweaking is generally necessary. Doesn't really matter which Pontiac AFB, as long as the two are the same. We generally suggest either 3300s or 3326s (these two MAY be mixed or matched), as they are relatively easy to find, and relatively inexpensive.

Jon.

[Skip Fix]

My 409 I jetted the E 600s one step leaner than stock and made 600 HP

[PAUL K]

With the exception of the Grocery Getter Guys does anyone have any experience with track testing the Offy manifold??

Maybe I'm missing something but I've ran them several times on different applications, all three square bore versions and a low rise dual Q-jet and never noticed any kind of gain over a single four barrel other than the Offy liked to RPM a bit more. The best set up was welding the rear halves of two manifolds together to get rid of the big bend in the front runners.

Back in the day my buddy went back and fourth between the Offy 2x4 and his tri-power and they seemed very close in performance. The tri-pwr seemed to have more mid-range and the 2x4 rpm'd a little higher.

A guy that works for me runs one on his Olds because they look cool but pretty sure his four barrel set up is faster.

[61-63]

Can't answer your question re track testing but I've had more than one person tell me they could get rubber in third gear after installing the offy dual quad setup, where they couldn't with the tripower setup they replaced with it.

[tom s]

Paul,did not do any back to back on the Dport engine but did do a RA V engine with a factory dual plane,a single plane and a dual quad low tunnel ram.Results are on this site somewhere and I think Stan posted it also.Prostocks run duals for a reason!Tom

[Bill Eveland]

I can get a couple 3651 AFB also, from a 64 421. How does the Doug Nash measure up to the Offy intake?

[Mike Davis]

There is nothing wrong with the Carter Competition AFB carbs that start with a 9000 number. I have heard for years they are junk. My experience says different. Even the E carbs are not bad. I run the Carter Competition 9755 AFBS on my 66 since 2005. SMALL CID stock block with a Wenzler intake. Car weighs 3750 with me in it, Stock suspension, full exhaust and has been the best of 9.79 in the 1/4. I also street drive this car and have never had a problem with idle. Drove it 30 miles to eat lunch with my daughter the other day. 60 miles round trip with quite a few red lights. No issues, no rich exhaust fumes etc. ANY carb needs tuned to the combo.

The Offy intake was .4 tenths faster than the Edelbrock P65 on my car. The Wenzler was .3 tenths faster than the Offy. Both intakes were ported to a 1233 gasket.

As far a carbs go, I have run the Carter Comp 750's and the E-800's back to back. Only .04 difference. The E-600's were bout .15 slower.

[jeff chmura]

Guys...all good info...
I'm 98% sure I have 2 '65 GTO AFB's. One for sure.
Just an FYI....
I'm running a Brawler 850 on a performer RPM right now and I can't get the carb set up right
I'm rich at idle,lean at cruise, and I'm so disgusted that I'm either going with the 2x4 setup (mainly for the cool factor, plus I already have carbs,),or EFI, which it going to be more $$$.
Damn hobby......lol

[Mike Davis]

Originally Posted by jeff chmura

Guys...all good info...
I'm 98% sure I have 2 '65 GTO AFB's. One for sure.
Just an FYI....
I'm running a Brawler 850 on a performer RPM right now and I can't get the carb set up right
I'm rich at idle,lean at cruise, and I'm so disgusted that I'm either going with the 2x4 setup (mainly for the cool factor, plus I already have carbs,),or EFI, which it going to be more $$$.
Damn hobby......lol

The 2- 65 carbs should work really well with that set-up.

[michaelfind]

Originally Posted by 61-63

For a 462 cubic inch engine start with .092 primary jets, .073 secondary jets, and .050x..060 metering rods, or .094 primary jets, .073 secondary jets, and .062x.068 metering rods. Actually you can use any size metering rods and use piRsquare to determine primary jet size, just have an 8-10 size difference between the small and large diameters on the metering rods.

This is great information from everybody. I'm reading through it trying to figure out what to do with my set up. I have a new 467 stroker with the Edelbrock P65 manifold and two 600 cfm edelbrock carburetors on it. It runs OK, but I'm having a hard time getting it dialed in for optimal performance. It sounds like I need to go more lean than stock settings since I'm running two carburetors. Is that generally correct?

And as far as the original question goes, I opted for the Edelbrock P65 because of the dual plane design and I was looking for more low end torque than high RPMs. I wish it looked more factory original but it is what it is.

Thanks in advance.

[61-63]

You can pull the tops off of your carbs, with the carbs on the engine, and use pin gauges or small drill bits to determine jet sizes, and a dial micrometer to determine the diameters of the metering rod steps, and go from there. It may be that you can reach the calibrations I suggested for the primary jets by changing your metering rods alone? I don't know what you consider "optimum performance" or why you feel you don't have it but the best way to check for it is by using a wide band air/fuel ratio gauge, and after that just reading your plugs. If your engine is falling on it's nose shortly after you put your foot all the way into it your problem is most likely float level.

[michaelfind]

Originally Posted by 61-63

You can pull the tops off of your carbs, with the carbs on the engine, and use pin gauges or small drill bits to determine jet sizes, and a dial micrometer to determine the diameters of the metering rod steps, and go from there. It may be that you can reach the calibrations I suggested for the primary jets by changing your metering rods alone? I don't know what you consider "optimum performance" or why you feel you don't have it but the best way to check for it is by using a wide band air/fuel ratio gauge, and after that just reading your plugs. If your engine is falling on it's nose shortly after you put your foot all the way into it your problem is most likely float level.

Thanks for your reply.

What is in there now is more rich than the original settings I believe. The front carburetor has .100 jets in the primaries and .098 jets in the secondaries. The metering rods are 075 x 047 with orange springs.

The rear carburetor has .101 jets in primaries and .098 jets in secondaries. The metering rods are 075 x 047 with orange springs.

I did check and reset float levels last week. They were a little off but not much. It is not falling on it's nose at WOT, but just not what I imagine should happen with all the extra air/fuel flow that is available when I get into it. I had a couple of single four barrel 400s over the years that would really pull strong, so my expectations are relative to those days. I'm expecting a bit more out of a stroked 467 with head work done. I was previously running stock 62 heads.

This is strictly "seat of the pants" judgment of performance. I don't have access to a dyno. I have considered a wide band AFR but I believe to get meaningful information out of it, that would need to be a permanent installation rather than the kind you hang in your exhaust pipe while not driving. Is that correct?

[61-63]

I think you would be way rich with those jets and rods when you get into it. I would have to do the math and see your net flow area to make a comment re cruising on only the front holes of the rear carb. Is your linkage progressive? What color are your plugs? Here are some calibrations I did for people years ago who have engines close to your cubic inches, and they never changed their calibrations. 462cu .094/.073 jets .062x.068 rods, 472cu .097/.074 jets .058x.068 rods, 480cu .095/.069 jets .058x.069 rods.

We're kind of stealing jeff chmura's thread here.

[michaelfind]

Originally Posted by 61-63

I think you would be way rich with those jets and rods when you get into it. I would have to do the math and see your net flow area to make a comment re cruising on only the front holes of the rear carb. Is your linkage progressive? What color are your plugs? Here are some calibrations I did for people years ago who have engines close to your cubic inches, and they never changed their calibrations. 462cu .094/.073 jets .062x.068 rods, 472cu .097/.074 jets .058x.068 rods, 480cu .095/.069 jets .058x.069 rods.

We're kind of stealing jeff chmura's thread here.

Yes, I'm sorry about that. Hopefully it is helpful information for him and everyone else who reads it.

I'm running as non-progressive linkage, they are opening up together. Plugs are dark but not wet or fouling (yet). Thank you for the recommendations. I will try those soon.

[carbking]

I would agree with 61-63 about way too rich with those numbers.

But even if you get the numbers dialed in, EXPECT hesitations on the street at various RPM's with the imitation carbs when the secondary(2) try to engage because of the wrong auxiliary air valves for Pontiac use. If drag racing and you leave the line at 6000 RPM, the air valves won't be a problem

Jon.

[Tom Vaught]

I have driven my 64 GTO with a couple of single 4 BBL PONTIAC AFBs.
What I mean by that is one carb on the engine but two different physical carbs.

In BOTH cases, the Pontiac AFB carb was seamless in acceleration performance once I had it dialed it. None of that TRI-POWER sudden secondary acceleration.

But I have driven a Tri-Power Car/Engine for over 50 years. So it is what it is.

Pontiac & the Carter OEM Engineers really had their act together on the Pontiac AFB carbs.

Just my opinion on the subject of a dual quad street AFB application.

Tom V.

[jeff chmura]

Guys, I'm following along with all the great info.
I'm sure that after I get the manifold squared away, I'll need some carb info also.
Thanks. jeff

[tempest1964]

John Reeder wrote an excellent 2 part article in Smoke Signals magazine. On how to clone SD Carter carbs for a dual quad. The article is actually available on their web site now. It is very in depth with both text and photos.