I was talking with one of my friends today who is building up a big block for his '67 Mustang. Its a 428ci engine, and its gonna be really hot. He's putting two 4 barrels on top, which got me thinking....

Is it possible to wire up two stock CC carbs (ie. L69 carbs) so that both carbs are computer controlled?

I do not plan on doing this with my car because i've seen the kind of tuning hell that multiple carbs can be, not to mention the cost.... but I've been thinking about this all day.

Can this be done by sorta "splitting" the connectors that go to the carb so that there is a second connector for the other carb, etc etc.... you see were I am going with this....

Is this possible? Its does not sound to me like it can't be done...

 

Not sure you'd have enough power (voltage*current) out of the ECM to drive two MCS's.

And, all CC carbs are q-jets, which I've never seen nor heard of being used in a dual-quad setup. Dual quad square-bore manifold with square-to-spreadbore adapters ---- sounding pretty ugly to me.

 

Hmm... never thought of that.

But, after reading that, got me thinking again... if the computer sends "X" amount of voltage to the carb to put "X" amount of fuel into the mix, wouldn't that voltage have to be about half anyway? Because even with two carbs, the amount of fuel the engine needs should still be the same right? So each carb would be only putting in half the fuel that it would if it was alone on the engine.

I'm still kinda unfamiliar with multiple carbs, which is probably obvious by now, lol, but is what i said right (at least about the two carbs putting in 1/2 the fuel they would if it ws just one)?

 

It's a nice thought, but that's not the way it works. The computer controls the mixture by sending pulses to the MCS, not a certain voltage. If the solenoid is on, the primary metering rods are pulled into the jets to lean out the mixture via a plunger that goes through the solenoid and a series of springs. If it's off, the rods are at their highest (richest) position. The mixture comes out as an average of the amount of time it's on compared to the amount of time it's off.

You would want to hook the solenoids together in parallel so that they receive the same signal from the ECM, which would change the amount of current going to each solenoid. The reason you'd have to check to be sure enough power is going to each solenoid is that if you have too little current running through the solenoid, it may not be able to pull the primary metering rods all the way down into the jets. Also, the voltage would not be half of the original voltage.

I think you're confusing amount of fuel with mixture. The amount of fuel going into the engine is a function of not only the mixture but the amount of air flowing through the carburetor, which the computer does not measure or take into account. The engine can take in the same amount of fuel by splitting the airflow through each carb, and not necessarily requiring a change in mixture. Isn't the whole idea of dual carbs to get more airflow than with just one, which would increase the amount of fuel the engine gets (assuming mixture does not change)?

Someone correct me if I'm wrong somewhere, I've never had experience with dual carbs.

 

Dual carbs (or multiple carbs, for that matter) were the way to increase air flow when available carbs were small (300-400 CFM). A small benefit was improvement of flow path to each cylinder, although that would apply more to race-only engines than to street-driven.

FWIW, dual quads typically operated with the rear carb as the primary, with the secondaries of that carb and the front carb only coming in under high throttle application. This improved throttle response and kept fuel economy in the somewhat acceptable range.

Hot Rod magazine had an article on carb/manifold choices last year, keeping the engine the same and varying the induction. A single 4bbl carb made more torque and HP, with a broader torque band, than any multiple carb setup they tried.

Dual CC q-jets doesn't make much sense, since each one will flow between 750-795 CFM, which is more than enough for most any street engine. Dual quads are typically 450-500 CFM each at most.

 

Oh yea, i agree Five7... Qjets are way too big to have more than one. And i thought the carbs were CC by the amount of voltage?

 

Nope. Controlled by pulses, amount of time energized per pulse. Voltage applied is intended to be the same for each pulse.

 

Even if it were possible on the carb side of things, which it might be with some additional electronics to get mor current to the second M/C solenoid, you'd then have to look into the distributor. The large cap, integral coil distributor that came in most (all?) CC carb vehicles would most likely not clear a dual carb intake. Any dual 4 BBL setup I've seen has had to use a small cap distributor such as a points unit, usually converted to electronic.

It is something neat to think about stuff like this, and it may even help understand how some things work, such as how the M/C solenoid works!

 

Smaller distributor cap for a dual quad? Are you sure? I've never seen or heard of that before...

And what do you mean by smaller anyway? width, height, etc etc?

 

I'm pretty sure the large diameter HEI would be too big, but I suppose it would depend on your intake selection, etc. When they make room on the intake for the second carb, they have to mount the rear one back pretty far and usually interferes with the Dist. I have a friend that was putting a dual 4 BBL on his Olds 455 (huge engine, more room for this than a SBC!) and that was one of the issues.

 

Interesting... never thought about that before.