GM 350/290 Head replacement advise - Team Camaro Tech
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post #1 of 5 (permalink) Old Dec 11th, 16, 08:53 AM Thread Starter
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Andrew
 
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GM 350/290 Head replacement advise

I have a great running crate 350/290 motor in my 67. I also have a 700r4 overdrive transmission which is a smooth 2200 rpm at 75mph.

I replaced the carb and intake with Edlebrock RPM performer intake and holley 650 to give it a bit more bolt on power, and replaced the factory intake with full headers and 2.5" flowmaster exhaust with "H" pipe.

These are upgrades that typically are the way to go. But now my exhaust sounds like a "trumpet" when stoping on the throttle, and the the motor just sounds lazy. I have spoken to a bunch of people and researched online to find that the incredibly low compression of this rate is most likely why the motor sounds lazy.

I cannot see spending $3k on a top-end kit for this car. If I am going to spend that kind of money, I'd just buy a 383. But since this crate motor has a pretty beefy cam, and because I think the issue is the low compression, do you guys think I will solve the riddle by simply upgrading the heads to lower CC aluminum heads? I was looking at JEGS Performance Products 514002 Cylinder Heads (JEGS Performance Products 514002: Cylinder Head Small Block Chevy | JEGS) with the following specs:
- 180cc Intake Ports
- 64cc Combustion Chambers
- 2.020"Int./1.600"Exh. Valves
- 1.250" Valve Springs, .525" Max Lift
- 3/8" Rocker Studs
- Straight Plug

In case you are not familiar with the GM 350/290, here are the crate motor specs:
350/290 HP Engine Specifications
Displacement:..................350 cubic inches
Bore x Stroke:..................4.00 inch x 3.48 inch
Compression ......................8:1 nominal
Block:.....................Cast iron, four-bolt intermediate mains
Cylinder Head:..........................Cast iron
Valve Diameter (Intake/Exhaust):...................1.94"/1.50"
Chamber Volume:....................76cc
Crankshaft: .......................Nodular iron, 2 piece rear seal
Connecting Rods:.......................Forged, powdered metal, 3/8" bolts
Pistons:.........................Cast aluminum
Rings: ..........................Cast iron
Camshaft: ........................Hydraulic flat tappet
Lift: .......................450" intake, .460" exhaust
Duration: .........................222 intake, 222 exhaust @ .050" tappet lift
Centerline:..........................114 ATDC intake, 114 BTDC exhaust
Rocker Arm Ratio: ......................1.5:1
Timing Chain: .......................8 mm single roller design
Oil Pan:........................4-quart
Oil Pressure (Normal):.......................20 psi @ 2000 RPM
Recommended Oil:.....................10w30 synthetic motor oil (after break in)
Oil Filter: ......................AC Delco part # PF454 or PF1218
Valve Lash:......................1/8 turn down from zero lash
Fuel:.......................Regular unleaded - 87 (R+M/2)
Maximum Engine Speed: .....................5100 RPM
Spark Plugs: ..................AC Delco part # R45TS
Spark Plug Gap ......................045"
Spark Timing:..................32 maximum @ 3000 RPM

Again, keep in mind I am looking for a easy option to increase the compression, thinking that will wake up the motor and get rid of the lazy sounding exhaust.

Your thoughts? Will going from 76cc to 64cc make a big difference?
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post #2 of 5 (permalink) Old Dec 11th, 16, 12:54 PM
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Re: GM 350/290 Head replacement advise

You may gain a half point in static compression until the pistons have been changed to flat tops from dished.
Use a steel shim head gasket and 'hone' the block and head with a new Norton honing stone and WD40 for lube on the stone.
Better if you remove the block dowel pins.

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post #3 of 5 (permalink) Old Dec 12th, 16, 05:36 PM
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Re: GM 350/290 Head replacement advise

Check out trickflow. They make a 56cc head with 175cc intake runners.

1969 Camaro 350, Trickflow heads, ST-10 4spd, Hotchkis suspension, Baer SS brake kit, moser 12bolt
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post #4 of 5 (permalink) Old Dec 12th, 16, 06:13 PM
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Re: GM 350/290 Head replacement advise

Going to 64 cc isn't going to do much IMO

You're compression is perfect for a blower.

I'd add a Procharger and leave the heads alone.

Or hit it with Nitrous. Yeah
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post #5 of 5 (permalink) Old Dec 12th, 16, 08:01 PM
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Bobby
 
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Re: GM 350/290 Head replacement advise

Those cam specs look similar to the 151 cam.

Did the engine sound lazy before the bolt-ons?

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