I have a coupla small Carter 4661 and 4663 AFBs (which I think flow about 380-400cmf of air) on an Edelbrock C-26 manifold sitting on top of a '70 Corvette 350 with stock guts and heads and an RV-2 Comp camp, T-400 ******, 3:70 **** gears in a highboy 30 coupe. Carbs have hot tube chokes, gas inlets on the same side as the linkage. (See the pictures). This is a street motor, and not intended for stoplight racing...well...except when that ricer pull up alongside and revs up his Buzzer-mobile... My questions are: (1) would I be better off with straight linkage or with progressive and why? Spacing of the carbs over the engine using this manifold seems to me like the back cylinders would be richer than the front cylinders at lower rpms (if the rear carb is used as the primary carb) til the front carb comes on...using progressive linkage. seems like straight linkage would be better in that respect...wouldn't I have to jet down the primaries with straight linkage? (2) if I was to keep my loudpedal foot under control on the freeway, and I was using straight linkage as compared to progressive, would there be any noticeable change in gas mileage, given everything inside the carbs being the same? (3) can these 'climate" chokes be converted over to electrics? (If so, I need a source) and which carbs should get them: both? just the primary? neither? I live in Oregon about 630 feet above sea level. Damn...I aint been this awake this early in a long time...but I guess the juices are flowing today...so gotta take advantage of them at my age!!! Thanks.
I would run progressive linkage and run on the back carb for street cruising and low highway speeds. Then at about 3500 or whatever rpm you want you can have the front carb start to tip in. You will probably use more gas with a direct linkage hook up and some say they prefer it, others say it is kind of scary!! Forget about the chokes as both carb's idle circuits will be giving you a little richer mixture. If you find that the rear carb is a little lean for street cruising you can fatten it up. There is not much of a leaner mixture because of the rear carb location. The driver side intake runners feed cylinders #1.4.6 and 7 and the right intake runners feed 2,3,5,and 8 on a dual plane intake. I have checked the plugs on my dual four setup on my 65 GTO and they all burn the same. I run 2 600 cfm edel. carbs on a edelbrock p65 intake with progressive linkage set up as stated above. Good luck.
I noticed about a 5% - 10% improvement in highway gas mileage when I went from dual 500 cfm Carters on a medium riser Offenhauser on a 462" Buick to a 750 cfm Carter on an Edelbrock performer in a 32 roadster. At the same time the big cam was pulled in favor of a milder one. I'm guessing the cam change made the most difference . . . especially in city driving. I ran straight linkage on the dual quads and one thing I noticed was it doesn't take much of a throttle depression to make the car pull strongly since you're getting twice as much throttle opening as you would with a single four barrel - ***uming the same amount of throttle pedal deflection. Especially in an off-idle maneuver in a parking lot. It's not a problem and you get used to it pretty fast, but be careful if you let someone else drive the car . . . especially if that someone is an Econo-Box driver who floors the throttle for most any in-traffic situation. Far as progressive goes, the front two barrels of the rear four barrel are very close to the center of the engine so there's no real problem with cylinder to cylinder air/fuel ratio changes within the manifold due to any cylinder can draw from the plenum.
I meant to comment on chokes. When I installed the dual quads, I couldn't find any information about whether or not to make both chokes operative. I set up both chokes to operate off one cable. Engine started up like right now and it was no problem to back the roadster out of the garage and down the street in 37 degree weather. Since then I've found that factory dual quad choke installs utilize the rear choke only. Haven't tried it yet, but I have a pair of 750 Carter's with electric chokes and making only the rear one operative will be an interesting experiment. Chokes make life easy . . . even in hot rods....
I've got 2 600 edelbrocks on an offy intake on my mild 355 running only the rear electric choke and carb until my linkage tips in at around 1500 its early but gave the best performance I get around 12 mpg and can put tires up in smoke at will This thing starts no problems and as C9 stated it moves out a little quicker than a single 4 barrel so be careful because my light coupe will blow the tires off it and go sideways scary as hell till you figure the car out and learn how to get around that and still get the car moving.All my plugs read a nice amberish color and the motor sits at 12.5-13.5 A/F ratio per bank as I tuned it with a wideband O2 sensor.I have however rejetted my carbs with .089 primary jets and .098 secondarys in the rear carb and .093 primary and .098 secondarys in the front carb. Both have 3in.hg step up springs and .045x.070 metering rods.Hope this helps as it took me awhile to figure out my best setup and this is it.Good luck,Paul
thanks for the very informative post here....I would be interested in reading that air-flow and jetting article. I made my mind up yesterday to do the straight linkage and leave the jetting alone as I think the stock setup for these smaller AFB carbs including the metering rods and springs will be ok with the RV2 camshaft profile. I dont think it will make a hill of beans difference in the mileage, and I can have some fun with the throttle response when I feel the urge. Just gotta get used to driving with an egg under my foot! I am also interested in your reasoning on the vacuum distributor with dual fours... Where on the Edelbrock manifold is there a port for the full vacuum connection? Comment? THANKS AGAIN!!
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