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Old December 8th, 2021, 02:24 PM
Prowbar Prowbar is offline
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Join Date: Dec 2020
Location: Friesland, the Netherlands
Truck: 1965 GMC 1500, 478 V6, SM420
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Default Re: The fuel efficient GMC V6

Quote:
Originally Posted by James View Post
Stock rod length: 7.17825" C-C;
Piston Deck Height 0.000"
Not for sure on the Piston Dished Volume but I believe it is around 10CC.

Plans for my 305:
To increase the compression ratio I am planning on offset grind the crankshaft to increase the stroke, going from stock journal size to 0.030" undersize. Then mill the head of the piston (will be 0.030" oversize) to get it back to a zero deck height, this will remove most of the dished from the head of the piston.

Also in the works I have been flow testing the heads to improve the flow. Been getting mixed results from this. Still in progress. I will be targeting high swirl and all the flow I can get. Stock head has no swirl and badly shrouded valves.

I had already modified the intake manifold to be equal to the Magnum engine and had installed the Holley 2 barrels carb. I need to schedule time on the chassis dyno, this will show the change from the totally stock dyno reading.
Thanks James. What would the compression ratio be after you've performed the modifications? How much displacement do you gain?

Looking at a picture, indeed, those valves are shrouded pretty bad. Should be better on the larger bore engines, if they have larger chambers?

Custom pistons are expensive, but do you see any gains in my idea? Maybe it is possible to modify a standard piston by machining to up the compression and reduce friction.
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