The Stovebolt Site Forums The Shop Area Engine Shop Which Carb to use (1970 350)

I rebuilding the 350 out of my '70 CST/10 for my engines class at college heres the specs first of all its a '70 350 bored .030 over (355) i'm going to be running a Comp. Cams magnum cam hydraulic flat tappet(operating range (1800-5800 rpm, 270 degree duration, 224 degree duration @ .050" lift, valve lift w/1.5 rockers .470"), Roller Rockers, double roller timing chain, Ignition will be MSD Pro Billet Distributor, MSD Blaster 2 coil, MSD 6 AL Ignition Box, Superconductor 8.5 Spark Plug Wires. Intake is a Weind Action Plus aluminum 4 barrel intake. heads are stock with 1.94 valves i'm thinking of running a Holley Double Pumper Classic (mechanical secondaries, and manual choke) and i was wondering what CFM to go with that would give a happy medium of power and fuel mileage (i know it wont be that great anyway but every little bit counts) also transmission is an SM420 3.42 rearend gears, and 32x11.50x15 street tread tires on the rear which will put me right around 2 grand at 60 if anyone has a better choice for a carb for this aplication i'm up for ideas but i'd like to stick with mechanical secondaries and manual choke

thanks
Nate

I like the Q-jet for street use but you have quite a bit of cam there. I think a performer (AFB type) or holley about 650-750 CFM. would work best. The performer is more reliable & easier to tune.

I've had a lot of luck with the Edelbrock 600cfm carb on both by GM crate motors (350ci/330hp). They are smooth, reliable, easy to adjust and my MPG was much better than the comparable Holley (although the Holley provided a bit more zip).

thanks for the input a kid i went to highschool with had an 86 GMC 3/4 ton with a 350 he tried a holley one it and it had some big power but he got like 2-4 mpg out of it with a stock Q-jet
Nate

"i'm thinking of running a Holley Double Pumper Classic (mechanical secondaries, and manual choke) and i was wondering what CFM to go with that would give a happy medium of power and fuel mileage "

"Holley" and "fuel mileage" in the same sentence???????

While I would certainly agree with the manual choke.

Most enthusiasts utilize mechanical secondary carburetors ONLY on dedicated race vehicles, NOT street vehicles.

What carb you use is much dependant on the configuration of the intake; but if the intake is set up for a spread-bore (best for street), I would suggest either a Rochester Q-Jet or Carter TQ. Either will give you as much power as the Holley, and a BUNCH more fuel economy. Both are "on demand" secondary carburetors.

As a general rule, the TQ would give about 3~4 percent more HP and fuel economy than the Rochester, but parts are more difficult to find. The decision probably comes down to which of the two you (or your tuner) would be more experienced in tuning.

Now, if this is a dedicated race only vehicle, I might have a different suggestion.

Jon.