Chevy 350 Dilemma - The 1947 - Present Chevrolet & GMC Truck Message Board Network

UntrustedAlly · 11-01-2018, 11:50 PM

I bought my 1968 GMC C2500 with a non-running Chevy 350 swapped in. The previous owner provided little information on the engine and truck, so I have figured out what I could and have done some work to the engine myself.
Engine/Truck Specs:

~1976 truck block, intake, heads - all stock as far as I know
Holley 570 Street Avenger, rebuilt
Aftermarket cam installed by previous owner, audibly bigger than stock (unknown specs)
New Street Fire (MSD owned brand) distributor
New plugs and wires. I don't think I've run the truck enough for the plugs to have showed fowling as I have not noticed raw fuel or buildup of any kind
Aftermarket headers, appear to be Hooker or similar
Engine vacuum is erratic, jumping between 8" and 16", possibly too bad to run the advance
Compression test: 70psi across the board with the choke and throttle mistakenly completely closed - no blow-by, oil usage, or smoking, however
Rocker press-in studs are bad: some are stripped, one is stretched. None of the rocker nuts screw in without an unreasonable amount of force.
Rockers are in good condition, pushrods straight
New fuel pump, intake gaskets, carb baseplate gasket
Timing chain and sprockets gone through
All vacuum ports plugged except for the vacuum advance
SM465, Dana 60, 4:10 gears - 60k miles

Additional Details:
The truck starts, idles, and revs without issue. In gear 1/2 throttle+ or high RPM makes the engine stumble and sputter but I have driven up to 60mph being light on the throttle. The truck was originally a V6 so I believe in addition to the heads needing work the fuel lines might be too small. Truck constantly lunges when idling in 1st gear, no issue when throttle is applied. Cylinder #3 which somehow got 0psi compression though the cylinder's plugs are fine and the headers get just as hot as the other cylinders. I'm assuming user error on that.
I believe new or reworked heads would solve the majority of issues.

Dilemma:
My goal with this truck is to make a solid 350-400HP on 91 octane or E85. Possibly more HP in the future. I'm aiming for a fun street rod. Budget wise, would I be better off fixing and building up my current 350 or should I consider an LS swap? The engine obviously needs a lot of work but I have access to machine shops and I am willing to put in some man-hours. Budget accounting for ECU's, transmission adapters, high pressure fuel pump, etc.

11-01-2018, 11:50 PM	#1
UntrustedAlly Registered User Join Date: Nov 2018 Location: Rapid City and Yankton, SD Posts: 7	Chevy 350 Dilemma I bought my 1968 GMC C2500 with a non-running Chevy 350 swapped in. The previous owner provided little information on the engine and truck, so I have figured out what I could and have done some work to the engine myself. Engine/Truck Specs: ~1976 truck block, intake, heads - all stock as far as I know Holley 570 Street Avenger, rebuilt Aftermarket cam installed by previous owner, audibly bigger than stock (unknown specs) New Street Fire (MSD owned brand) distributor New plugs and wires. I don't think I've run the truck enough for the plugs to have showed fowling as I have not noticed raw fuel or buildup of any kind Aftermarket headers, appear to be Hooker or similar Engine vacuum is erratic, jumping between 8" and 16", possibly too bad to run the advance Compression test: 70psi across the board with the choke and throttle mistakenly completely closed - no blow-by, oil usage, or smoking, however Rocker press-in studs are bad: some are stripped, one is stretched. None of the rocker nuts screw in without an unreasonable amount of force. Rockers are in good condition, pushrods straight New fuel pump, intake gaskets, carb baseplate gasket Timing chain and sprockets gone through All vacuum ports plugged except for the vacuum advance SM465, Dana 60, 4:10 gears - 60k miles Additional Details: The truck starts, idles, and revs without issue. In gear 1/2 throttle+ or high RPM makes the engine stumble and sputter but I have driven up to 60mph being light on the throttle. The truck was originally a V6 so I believe in addition to the heads needing work the fuel lines might be too small. Truck constantly lunges when idling in 1st gear, no issue when throttle is applied. Cylinder #3 which somehow got 0psi compression though the cylinder's plugs are fine and the headers get just as hot as the other cylinders. I'm assuming user error on that. I believe new or reworked heads would solve the majority of issues. Dilemma: My goal with this truck is to make a solid 350-400HP on 91 octane or E85. Possibly more HP in the future. I'm aiming for a fun street rod. Budget wise, would I be better off fixing and building up my current 350 or should I consider an LS swap? The engine obviously needs a lot of work but I have access to machine shops and I am willing to put in some man-hours. Budget accounting for ECU's, transmission adapters, high pressure fuel pump, etc.



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