I am considering changing the current carburetor on my LS6: Holley list 4780-3 800cfm DP to a more street friendly-cruiser carb. Would a 650cfm meet the needs of the engine and be more friendly?
Heads are rectangular port, open chamber 166cc, 2.19 intake and 1.88 exhaust valves.
Trans is a M20 4 speed.
Intake manifold is a High Rise-duel plane for rectangular port heads. It also has a electric fuel pump Holley "Blue" set at 6 1/2 psi. With this set up I am getting less than 7 mpg. And performance "bogs" off the line...…
If anyone has suggestions or insights.....I would appreciate the info. Thanks! Craig
Your current carb should run fine on an LS6. The factory carb was a 780 vacuum secondary which is very similar to your 800 mechanical, and they run beautifully.
What cam is in the engine, what does your entire ignition system consist of (base and total timing), how do the plugs look, and what rear axle ratio is in the car?
I have a good friend who has been running a 3310 on his L88 since the late 70's. Car performs great and he knows it could go better with something bigger but for the street you can't beat it. New gaskets every once in a while and a clean up and they will run forever. I have 2 of the Demon VS, never tried them on a street car but maybe next year I will give one a shot.
FWIW, these engines came with 780 cfm from the factory and there would be no reason to install anything smaller than 750 cfm
It will be down on HP and torque without a doubt with anything smaller.
and he may not ever notice it, an assumption. Another assumption is that he doesnt want to tinker with it and learn how to dial it in. Which is fine, but a limitation.
Step #1 is to set floats while HOT, and I would recommend you at the least do this.
Thanks....for the info. I am going to try the timing solution.....first. But keep this carb info due to the responses received about it...and the performance. Thanks!
That 830 is a race car carb, will get single digits gas mileage. they're pig rich in the idle transition because they were originally designed for racing use where there was no expectation of street use.
there's no adjustment for this, you have to take the carb completely apart and start drilling orifices.At minimum, to get this carb to a reasonable facsimile of a street car carb, you would have to change the Idle feed restriction, the idle air bleed, the accelerator pump squirter and restrict the fuel to the idle transition slot.
Truth is, you'd better buying a new Holley like the one linked to in Post #2. Beware of any local "Holley experts", they're not. Bigger is not better with carbs, especially with street cars. Chevy sold those engines in cars with a warranty, they had a 780CFM carb with vacuum secondary. The difference between 750 and 780 is piddling.
Correct me if wrong Tom, but believe mr 4 speed indicated the difference is shaved butterfly screws, etc to get an additional 30 cfm out of that GM hipo carb. Also, the OP's carb is a standard 800 cfm DP with downleg boosters. A bit of a orphan, but not a race carb, is it?
doesn't matter much about the details of the calibration, it's still a 60's DP. expect single digits gas mileage.
Last one I checked with an WBO2 meter was in the mid 12s AFR at cruise. Those carbs are good with drag racing or oval track usage though. the 830 was the NASCAR speedway carb of choice for many years.
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