4x2 2x3 intake.........mileage? ....impossable? - Team Camaro Tech
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post #1 of 11 (permalink) Old Jul 26th, 01, 06:24 PM Thread Starter
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is it possable to get mileage from a multi carb setup? it will be on a sbc400 mild cam 700r4 3.08 gears thanks for the help
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post #2 of 11 (permalink) Old Jul 26th, 01, 06:41 PM
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Sure- just keep your foot out of it!
Seriously, a friend had a 6 pack setup on a V-8 Vega with an old Offenhauser manifold and 3 450 cfm 2 barrel Holleys, and it would stumble like crazy off the line because of all the fuel dumping in at once. An older guy at a car show clued us in to set up the linkage so that the outer carbs came in later, much like a mechanical secondary 4 barrel. Ran great after that, and the bonus was amazing mileage.
I would imagine you could do the same with a 2 x 4 setup, with the front carb being the primary.

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post #3 of 11 (permalink) Old Jul 26th, 01, 07:23 PM
 
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couldnt you use two 390 four barrels? i think what your going for is the look of a dual quad but not the mileage killer correct? its hard to obtain that, but w/ two 390's it shouldnt be horrible mileage. the 700-r4 must really help out.
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post #4 of 11 (permalink) Old Jul 26th, 01, 08:37 PM
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What is the advantage of two small carbs compared to one good big one, why go through all the trouble and expense? also usually a dual carb setup would need higher compression, a big cam, steep gears and so on, doesn't it?
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post #5 of 11 (permalink) Old Jul 27th, 01, 12:05 AM
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have both a X-1 Edelbrock 6x2 which has be put into a 78 Chevy stepside which we have the 2 middle 2bbls running full time with the outer carbs running a progressive linkage setup and they run fine. will be putting a Offy crossram on my Camaro with the two 390's and toying around with them. Got to say the milage isnt all that great but if you want something different either one will do. Athough the multi carbs systems might not be the best set up on the street
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post #6 of 11 (permalink) Old Jul 27th, 01, 06:28 AM
 
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dual quad system spreeds the fuel/ air mixture across the entire 8 cylinders, this makes the engine believe the entire world is a mixture of air and fuel. its a very effective system apposed to just one carb, and if you put it on a tunnel ram you'll have alot of high end power, not so muh low end torque though
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post #7 of 11 (permalink) Old Jul 27th, 01, 05:07 PM
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Dual quads make a great sound and look great at a car show, but they're pretty inefficient and get poor mileage. I have them on my '57 270 Vette with the two stock Carter WCFB's (385cfm each); dual quads work progressively, with the rear carb as the primary and the front carb comes in at about half-throttle. With the rear carb as the one that works alone 99% of the time, mixture distribution is lousy to the front four cylinders. You'll have much better throttle response, driveability, performance, and fuel economy with a well-designed dual-plane single 4-barrel manifold. If 3x2's or dual quads were better power-producers, ZL-1's and L-88's would have had them - there's a message there. Cross-rams are the same - look good at car shows and run great over 4500 rpm at wide-open throttle (which is all they were designed for), but are a tuning and driveability nightmare on a street-driven car due to the huge open plenum passages and low air velocity which creates lousy metering signals.

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[This message has been edited by JohnZ (edited 07-27-2001).]
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post #8 of 11 (permalink) Old Jul 27th, 01, 10:50 PM
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Gene Chas from the Chevelle site is getting 17mpg with his tripower L88. I want one for my Camaro.

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post #9 of 11 (permalink) Old Jul 28th, 01, 01:45 AM
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? for John Z/// John like most on this site if not all your input means alot to us. They alsway say the stupid ? is the ? not asked. I have the X-1 running pretty good, it was put in a 78 stepside on a 350. The other question i would like to throw out to you is I also have come across a Offy Crossram (dual quad top). You post above says there poor runing do mostly to the air velocity. Would Adding one if not two prochargers kicking up the velocity improve the mixture and response at lower RPM's?
as always thanks
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post #10 of 11 (permalink) Old Jul 28th, 01, 10:43 AM
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Jeff -

Prochargers are a great power-adder on port-injected cars, as all the intake system has to handle is air, and fuel metering (pulse-width of signals to the injectors) is handled by sensors and a computer. Adding them to carbureted cars is a whole different world (like the old factory McCulloch blowers on '57 T-Birds), as they have to blow through the carb, which meters fuel based on vacuum signals, and there is no vacuum with a blower running. As a result, the carb has to be completely sealed inside an enclosure to equalize the pressure inside and outside the carb, and that's only the beginning of the grief. That's why 99% of blowers for carbureted cars are downstream of the carb, not upstream like a Procharger.

Air velocity is everything to a carb in order to meter fuel properly and have good throttle response, but it's a function of how much air the engine is drawing in (it's just a big air pump) and how large the orifice/restriction is that the engine is drawing it through (the carb and intake manifold). The smaller the hole, the higher the air velocity, and the better metering signal the carb gets, which results in better fuel atomization, more accurate metering, and crisper throttle response. It's all basic physics, and you can't fool the physics involved; that's why cars don't use carburetors any more - they couldn't meter fuel accurately enough to meet reduced emission limits and increased demands for fuel efficiency - too many variables involved for a mechanical device to respond to, although GM tried with the "electronic" Q-Jets before fuel injection and computers took over.

You can't "have your cake and eat it too" with carburetors - they have operating limitations based on physics, and there's always some compromise you have to make for "all-around" performance - that's what "tuning" is all about.

There are no "stupid questions" - that's how we all learn

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[This message has been edited by JohnZ (edited 07-28-2001).]
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post #11 of 11 (permalink) Old Jul 28th, 01, 12:09 PM
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John Z, Thanks and Mahalo for your time and reply. If the Team Camaro Members can count on one thing its you and your expertise and when provided its in terms that all can understand.
Again Thanks
--Jeff 67/68 & 69 RS's
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