Thread: dual quads

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i have a sbc 350 that is stock, i was thinking about putting dual 600cfm edelbrock carbs on it. i was wondering if the motor would be able to handle dual carbs.

Edelbrocks have vacuum-operated secondaries, so the secondaries will not operate until there is enough manifold vacuum to open them. Therefore, you cannot over-carburet the motor, even with 2-4 barrels. Most fellows will rig up the throttle linkage so that the motor runs on the primary 2 barrels of the rear carb, then at about 1/2 throttle, the primary 2 barrels of the front carb will chime in. Then, if there is enough manifold vacuum to operate the secondaries of each carb, they will open. The resultant sound is one you will never forget....BA-WAAAAAAAAAAAAA......

Be sure you use enough air filter so you don't choke the motor down.

If I just wanted the LOOK of two 4-bbls, and weren't interested in making max hp, I would probably use an Edelbrock C26 manifold, part number 5425, and top it with an 1803 and an 1804 carburetor, 500 CFM each.

If I wanted additional performance from the motor, as well as looks, I would use the RPM manifold, part number 7525, along with the 1803 and 1804 carbs. The added height of the RPM makes it the best bet for street hp. You may encounter some driveability issues in cold weather with the Air Gap feature of this manifold. Street motors need the heat of the motor to help atomize the fuel/air mixture for a good, clean burn. I thought Edelbrock made a 2-4 RPM intake that was a closed design, not the Air Gap, but I cannot find it now. Maybe they stopped making it. There is insufficient room to use an HEI distributor with the 7525, so you would have to use a smaller diameter distributor body.

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I ran an Offenhauser dual quad manifold and 600 AFBs on a mild 350 Chevy (RV cam and Headers) many years ago. It ran great. Like Tech mentioned progressive linkage is kind of the way to go. You will also probably have to play with jets and step rods a bit to get the mixture right.

Many of the multi-carb intakes can be a bit cold blooded in cool/cold weather until the engine is warmed up. One thing I've found that can really help in those cases is adding an MSD box.


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These posts make the hair on the back of my neck stand up. It takes me back to the days of the Corvette 283/270HP carbs and manifold. They looked great as did the three two setups that several GM engines had from the factory. They won't have any performance advantage over single carb setups, but they add a nostalgia LOOK that Tech mentioned to any engine.

I am currently running the Edelbrock Dual Quad set up on my 327 sbc. To me, it looks great and runs great! MSD ignition helped as well.

The OP asked me a question on PM, but the chintzy PM on this forum allows only 1000 characters, insufficient to answer most any technical question, so I have copied and pasted the dialog onto the OP's original thread.

Originally Posted by hud-49

Hi tech, u suggested 500cfm carbs rather than the 600cfm. would the 500 carbs be better for the air gap intake? an would the 500's have a bit better throttle responce and maybe help the low end torque just a little better than the 600's.I have have another question, i think this motor may have a mild cam in it but is their a way i could find out

Those carb numbers, 1803 and 1804, are what are suggested by Edelbrock and they know a whole lot more about what will work best than you or I do. A 350 Chevy will make the best hp with a 750 CFM carb on a high-rise, dual-plane intake manifold. Two 500's are overkill, but like I said, the secondaries will only open when there is sufficient intake manifold vacuum to operate them. As Mike P suggested, some tuning may be necessary. Jets, step-rods and shooters are available from Edelbrock so that you can dial in your combo. With the proper tuning, throttle response will be outstanding.

You can find out the valve lift and duration by mounting a degree wheel and pointer on the front of the crankshaft and a dial indicator on the valve spring retainer and turning the motor over. First you must determine top dead center of number one cylinder (front cylinder, driver's side).
http://www.crankshaftcoalition.com/w...op_dead_center
You cannot accurately time the motor with a light until you do this. It is also necessary to have TDC located to check cam timing. Once you have TDC, you can mount a dial indicator on the valve spring retainer of the intake and exhaust valves and find the valve lift and cam timing.

If you want to know only the valve lift, view this video beginning at 3:45 minutes. It shows the mounting of a dial indicator on an assembled motor. Never mind the checking springs shown, it works equally as well with the springs and retainers that you now have on your motor. sorry, lost the video, cannot find it.

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My sedan has a 327 with the 1803 & 1804 (500cfm) carbs. 1803 is a manual choke (front carb choke wired open), 1804 is electric choke (rear carb). The rear carb is the primary carb and the electric choke works great. It has progressive linkage to the front carb and is adjusted as tech advised. Someone told me I needed to set the linkage non progressive periodically to keep fresh gas in the front carb, I told them my foot does that automatically.

The kit I purchased came with darn near everything you need to install it (sans an air cleaner). The carbs were pretty closely tuned right out of the box, only needed minor tuning (Edelbrock tech will help you with that). Be sure to install a good fuel regulator and set it at 5.5lbs max or the floats will leak (even with a stock mechanical pump). My carbs perform real well, you kick it a$$ and the mouse gets angry quickly! MDS ignition made mine run even better, as did re-curving the distributor's mechanical advance to come in a little quicker.

The only other issue I have had is the alcohol blended gas is real hard on the rubber parts, ate up the mechanical fuel pump's diaphragms (twice, a year apart). I installed an electric pump (my mechanical was real hard to get at) and now use a fuel stabilizer, it seems to lessen the rubber deterioration.

My recommendation, if you like the dual quad look go for it, you won't regret it! Once tuned they are set! GOOD TO GO!

I have a blown 350, 5 lbs boost with 2 - 500 cfm Edelbrocks on it, can't remember why but the Edelbrock guy told me no to a progressive linkage on it, adjust both evenly and its been on the road since 2000 with no changes. One thing I might add is the Edelbrock tech when asked about chokes said, "man you have 2 500 carbs and you think you need less air & more fuel" and recommended against it, though I don't have any chokes the motor needs it, when its cold out at night she's running lean with the dense air and pops. Yes on the rejetting and rod changes, especially if you are not running progressive linkages. I know a guy running 2 Edelbrocks normally aspirated with progressive linkages and the motor is running leaner on a few cylinders and rich on others and not running right, I would say manifold selection is critical to keep from having that happen, I believe he was trying to do that on a single plane tunnel ram setup. Best of luck it will look cool. Matthyj

I can understand the non progressive linkage on a blown motor, the last thing you want with a blower is too lean.