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93gmc 10-06-2012 02:39 PM

377 carb choice
My dad has a 93 gmc Sierra 1500 with a destroked 400. Has double hump heads with a 2.02 intake valve. What would be a good carb to run on it.? It is mostly street driven.

vinniekq2 10-06-2012 03:03 PM

750 cfm would be a good size.What type of carb depends on the owner and how its driven,IE: not everyone like double pumper carbs.

techinspector1 10-06-2012 03:34 PM

Manual trans or auto with 3000+ converter I would use a pumper. Otherwise, I would use a vacuum secondaries carb.

93gmc 10-06-2012 10:47 PM

It has a 600 cfm on it now. Would this not be big enough to feed it on the top end?

xxllmm4 10-06-2012 11:12 PM

What kind of cam? Intake manifold? Headers? Exhaust? Stock heads or ported? What kind of RPM's are we talking about for the top end? You kinda need a real good idea of the combo to actually recommend a carb.

93gmc 10-06-2012 11:15 PM

I have no clue what cam it has. It was in it when he bought it. It has a holley contender intake. Stock manifolds for now but he will be getting headers. Has double hump heads. Stops gaining rpm at 6000 rpm. From what I have read the 377 should be good for 7500-8000 rpm.

DoubleVision 10-07-2012 12:19 AM

While you've read the 377 can rev high, the cubic inches and the bore and stroke have nothing to do with how high it will rev. Rev is controlled with a iron fist by the valvetrain. If the cam runs out of breath at 5500 RPM, valve float will only be maybe 1000 or less RPM. Not just the cam plays the role, the valve springs play a huge role. Lets say you have a cam that says it's power band is 2000 - 6000 RPM. That means that it will effectively stop making power around the 6000 RPM range. However if you were to take a engine and slap a cam and valve train in that would rev to 8000 RPM, the next thing you have to consider is will the rods, crank and pistons hold up at that high RPM. Since it's got a contender intake which has a spread bore carb flange I would go with a Quadrajet.
Summit racing carry these carbs. Jet has a excellant line of Q-jets as does Sean Murphy Induction. When you have a good Quadrajet you get the best of both worlds. It's small primaries make for sensitive fuel injection like throttle response and good fuel economy. The massive secondaries are there when wide open throttle performance is needed.

xxllmm4 10-07-2012 02:49 PM

The 377 is typically a high RPM engine but without knowing the cam, and valvetrain specs its hard to say what the RPM range should be. unless your willing to disassemble the engine and check it out, along with looking at the connecting rods and pistions I personally would never try and rev it to 7500-8000 rpms.

First thing I would do would be add a quality set of long tube headers, and a good high flow exhaust system. Stock manifolds will kill upper rpm performance. On an engine like this I think the Q-Jet would be my choice, just make sure you have it tuned to your engine. That's the real trick :mwink: 10-07-2012 03:09 PM

Q jet.
Just remember there are also different size Q jets like any other carb, but still stick with a 750 size. Or big block carb.

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