Back to flow testing 3900 heads.

[SappySE107 WOT-Tech Find all posts View Profile Close SappySE107]

Posting from my phone, so this is interesting. Can it handle the picture I took?

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Manifold porting first. +10 cfm at .500" bolted to a stock head.

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Ported manifold set on a stock head.

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Tidbits of info that might relate. The piston dish is 18cc. Compression is 10:1 from measurements. Intake valve has .120" lift before it clears the deck surface (stock). Exhaust valve has .160" lift before it clears the deck surface.

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Flowed the exhaust port stock, with the stock exhaust manifold (rear middle port, probably the best or near the top flowing for stock exhaust. Then with a 1 3/4" header stub, and then ported with the stub. I am going to try the 3500 LX9 exhaust valve job to see what that does, and go from there.

LZexhaustflow.jpg

[niceguy Find all posts View Profile Close niceguy]

So what do you conclude from this so far? Not alot to improve on from factory without adding a cam, etc? I've had an Uplander van with an Overkill PCM and TCM tune for about 6+ years now and aside from the very aggravating (and expensive) minor oil leaks, I love the LZ9. Smooth and punchy, even in a 4500lb lwb cargo van with a 4sp auto. Can't imagine how this engine feels in a small sporty car like some have done.

[1QUICKHATCH Find all posts View Profile Close 1QUICKHATCH]

Was the rear manifold the van or G6 style?

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I want to finish my new testing before I comment on the value of porting. 10cfm from porting the manifolds so just need to test that on the dyno to see what it means for power. Testing valve jobs now since porting the intake side was always a loss other than 1 spot...and the exhaust was as you can see. The exhaust manifold is the crossover style, not the G6.

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Modified the intake valve, modified it some more, then some more, and then the last one is a stock intake again modified in reverse order with only what helped. None of it helped. Id be modifying valves if they helped, but since they don't, ill share that the stock valves are best left alone

20230721_052834.jpg

LZValveMod.pdf