Dual quad info

-
4spdragtop

4spdragtop

FABO Gold Member
FABO Gold Member
Joined
Aug 28, 2009
Messages
41,785
Reaction score
25,738
Location
Ontario Parts Unknown
Hi all, I have an unmolested Offy DQ single plane and have been doing some reading about carbs and linkages. It's a ways before I will install, but recommendations for fuel supply lines, carbs(Eddy preferred) and linkage are appreciated.
DQ is going on a 70 340, slightly warmed up, 904 auto.
I'm not sure which linkage to look at? My 1st time with multi carbs.
Street car
Thanks
Steve

20221214_223418.jpg


20221220_162656.jpg
 
Last edited:
The old standby was to have the rear carb as primary, front as secondary. "I guess" it depends on how built the engine is, and or how much mileage you expect. Also more barrels with same linkage "ratio" means much harder to control a small throttle change with your great big foot LOL
 
I have mine hooked up 1 to 1 (direct). I'm still using the 2bbl linkage, but it could use more "professionalism" in the looks department on the dual quads :) I'm running off the original mechanical fuel pump. I have had zero issues.
 
Thanks guys, 318WR, can you post a pic or 2 of your setup?
67Dart273 said:
The old standby was to have the rear carb as primary, front as secondary. "I guess" it depends on how built the engine is, and or how much mileage you expect. Also more barrels with same linkage "ratio" means much harder to control a small throttle change with your great big foot LOL
Click to expand...

318willrun said:
I have mine hooked up 1 to 1 (direct). I'm still using the 2bbl linkage, but it could use more "professionalism" in the looks department on the dual quads :) I'm running off the original mechanical fuel pump. I have had zero issues.
Click to expand...
 
Just a FYI post. If you get progressive linkage similar to what I posted, you can make it work 1:1 or progressive. If you get the dedicated 1:1 linkage, that's what you're stuck with. Just more to think on. lol
 
Steve, before you get something, if you want 1:1 linkage, lemmie look out in the shop tomorrow. I think I have a set.
 
If you are doing this for 'looks', fair enough. I ran that intake on a 440 with dual 625 AVS carbs. It's performance was about equal to a T2 intake with a 750 AVS.
 
Did I say it was for looks lol. It was an hour away from me and a great price. So I now have 2 options for an intake for my 340(not 440). Last I checked, options were a good thing??:rolleyes:
Bewy said:
If you are doing this for 'looks', fair enough. I ran that intake on a 440 with dual 625 AVS carbs. It's performance was about equal to a T2 intake with a 750 AVS.
Click to expand...
 
The extra carburetor was good for like 25-35HP on the early Hemis. That's power you can feel. Go for it.
 
Last edited:
I run my dual quads 1:1. Just a simple rod (with rod ends) between the two carbs.Hard to see in the pic - but maybe you can zoom in to see it. Runs fine on the street AND the strip. Remember, the engine will only suck in what it wants / needs. Keep it simple!

Cuda.jpg


Engine.jpg
 
The way I see it is the throttle linkage from the pedal needs to be 1:1 on a dual quad setup. Now the carbs themselves can be 1:1 or progressive or even vacuum operated (AVS or Vacuum secondaries) but from the pedal 1:1
 
The intake I had was beautifully made & finished, fitted perfectly. Every Offy intake I have seen was similar.
 
I bought a length of metal rod from a hardware store and threaded the ends.

The 2 joints, and the 2 piece aluminum parts that screw into each other on the tbs came from summit.

Bolts and nuts from my stash.
I know I reconfigured the nuts/bolts recently, but still very similar to pic.

Works great and extremely inexpensive and strong.

I bought a number of linkages, they all sucked, one bent under the strain of the throttle body springs, which are on the tbs (why carbs haven't graduated to this no idea).

For fuel line, same deal, bought pre-made setups, they sucked, some leaked.
When I went to 600s I made my own hard lines, better, cheaper.

Efi got braided, Fragola, easy peasy, and I would have done this with the carbs if I had known better.

Do not fear dual quad, embrace it.

20180624_154851.jpg
 
matthon said:
I bought a length of metal rod from a hardware store and threaded the ends.

The 2 joints, and the 2 piece aluminum parts that screw into each other on the tbs came from summit.

Bolts and nuts from my stash.
I know I reconfigured the nuts/bolts recently, but still very similar to pic.

Works great and extremely inexpensive and strong.

I bought a number of linkages, they all sucked, one bent under the strain of the throttle body springs, which are on the tbs (why carbs haven't graduated to this no idea).

For fuel line, same deal, bought pre-made setups, they sucked, some leaked.
When I went to 600s I made my own hard lines, better, cheaper.

Efi got braided, Fragola, easy peasy, and I would have done this with the carbs if I had known better.

Do not fear dual quad, embrace it.

View attachment 1716024816
Click to expand...
Believe it or not that is identical to Harley bagger shifter linkage
 
I would think that to run 1:1,
your engine would need to run a good amount of idle and low-rpm vacuum, which is gonna depend an awful lot on either,
a) your Cylinder pressure/total chamber volume/and intake closing angle, and
b) the stall/and gears, or
c) some combination of those, and, not to ignore,
d) the size and type of the chosen carbs

At my age (69) I wouldn't be excited to run them on a low pressure/low vacuum combo, in 1:1 .
 
4spdragtop said:
Hi all, I have an unmolested Offy DQ single plane and have been doing some reading about carbs and linkages. It's a ways before I will install, but recommendations for fuel supply lines, carbs(Eddy preferred) and linkage are appreciated.
DQ is going on a 70 340, slightly warmed up, 904 auto.
I'm not sure which linkage to look at? My 1st time with multi carbs.
Street car
Thanks
Steve

View attachment 1716024529

View attachment 1716024530
Click to expand...
If new carbs are in order, check into the AVS II 500’s and the Edelbrock linkage Rusty posted up. The Edelbrock air cleaner may not fit since on the Edelbrock intakes, the carbs are super close to each other.

The progressive set up will have the secondary (front) carb come in at a reasonable area and have both carbs fully open by WOT. It’s actually a pretty good set up. You can out around town and drive the high way, to a degree, gear ratio and tire size will have a play in this. But…. If you have 2.94’s and down, you could get on down the road with just the primaries on the primary (rear) carb.
 
Yes, I think the best plan is to go with new carbs. That will be the biggest financial hurdle. At least Summit offers "free" shipping to us Canucks. I'll have to see if there are a "matched pair" designed for DQ.
It would be interesting to put the DQ on the 273 and see what it does, but I think the carb requirements 273 vs 340 would be substantially different?
Be neat to do a comparison.
The reason I mentioned direct 1:1 linkage is it seems the most "headaches" come with progressive linkage? From what I've read. I would imagine that it's a learning curve.
@matthon set up looks pretty damned nice. I havent added up the $$ to see what it cost. The Edelbrock linkage that Rob posted seems like a fair price, but of course that's only if it works.
Air cleaners will need to be figured out also.
The rear has 3:23 in it. With 26.5" tires.
I measured ports and they're all around 0.930 X 1.950 avg.
Thanks for help guys.
rumblefish360 said:
If new carbs are in order, check into the AVS II 500’s and the Edelbrock linkage Rusty posted up. The Edelbrock air cleaner may not fit since on the Edelbrock intakes, the carbs are super close to each other.

The progressive set up will have the secondary (front) carb come in at a reasonable area and have both carbs fully open by WOT. It’s actually a pretty good set up. You can out around town and drive the high way, to a degree, gear ratio and tire size will have a play in this. But…. If you have 2.94’s and down, you could get on down the road with just the primaries on the primary (rear) carb.
Click to expand...
 
My buddy setting up my old set up. 600 x 2 AFB on a 11-1 - 360 w/a solid comp 294S, Edelbrock heads 1-3/4 super comps headers. Minimal tuning, ram very good.

Linkage is the Edelbrock stuff. So you can see you get a reasonable amount of primary throttle before the front carb kicks in. By this time of the rear throttle opening, your moving pretty good to begin with.

 
You must log in or register to reply here.
-

Back
Top