Is it ok to use the petcock drain hole plus the plugged hole on top GMC head near the 3rd intake port as in/out water ports for carb heat. Both holes are close to the carb location and on the same side of the engine.

The only other hole available is on the passenger side of the goose neck leading to the radiator. top. That would take a long run of hose to get back to carb on the driver side. But, water circulation might be better.

Engine is a mild GMC 302 with a Holley 390 CFM 4 barrel. Having trouble with carb bogging so I'm adding heat.

Your lower therm housing should have a threaded port on both sides. If it does not, find a lower gmc them housing that does. Run the water from the driver side lower them port to the bottom of intake and bring the return back no tee it into the heater hose return.

Did you up the squirter size of the Holley significantly? Works for me and others. For some reason 390s seem to have this problem.

You can use the petcock hole from the block for one of the lines - but to mdonohue's point you need to get the other line from the input side of the water pump in order to produce flow:



Keep in mind that the water pump impeller is pushing coolant into the engine - with no flow out of the block until the thermostat opens. If you tap into just the block for both lines you will likely have limited flow (when the thermostat is open - best case) or no flow at all.

The pictures above ended up being a mock-up on my 216. FTF warned me about using brass - so I re-did them in galvanized steel painted the same color as the engine.

This routing produces constant flow regardless of whether the thermostat is open or closed - essentially a bypass loop running through the intake.

I have to bigger squirters. Just receives a 121-131 and -135 in the mail and will try them out this week.

Also played with higher vacuum power valve. I'm up to 8.5 in hg now. Tried 9.5 in hg, but made little difference.

Still have stumble on normal takeoff in traffic. It goes ok if I rev it up and slip the clutch. Seems ok on fast takeoff and when floored thru the gears.

Has anyone ever tried to wrap copper tubing or wire around one siamese header pipe, then coil it under the intake manifold/carb and finally coil it back around the other siamese header pipe? Sees like that might transfer more heat to the intake manifold than a water system. Headers is 500+ deg. and inches away from the intake/carb..

I'm planning to go to the LA Antique Drags at Fontana next Sunday,May 13th,- to see if the car goes better with 4 barrel. I run in the Street Legal Inline/Flathead class. Best so far is 89 mph and 15.9 sec. over about 10 years. Winner of class in 2015.

Frenchtown Flyer- you were correct. Went up to 0.035 squirter today and stumble disappeared. Thank you for the advice.

Will be trying out the Holley 390 at Fontana tomorrow. It feels stronger than my 3 - 2 barrel Webbers setup.