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317 heads on N/A lq4 408 stroker!

This is a discussion on 317 heads on N/A lq4 408 stroker! within the External Engine forums, part of the LSx Technical Help Section category; i have a set of 317 heads and an lq4 block when i build the 408 can i run the ...

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    Member My00Z28's Avatar
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    317 heads on N/A lq4 408 stroker!

    i have a set of 317 heads and an lq4 block when i build the 408 can i run the 317 heads and flat-toped pistons to keep my compression at around 10.19:1 compression?

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    Moderator Firebirdjones's Avatar
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    Quote Originally Posted by My00Z28 View Post
    i have a set of 317 heads and an lq4 block when i build the 408 can i run the 317 heads and flat-toped pistons to keep my compression at around 10.19:1 compression?
    Actually the 317 heads on a stock bore/stock stroke LQ 6.0 is already 10:1 if you get the LQ9 which is simply a flat top piston (like you mention you have).
    It's the dished piston of the LQ4 that gave those 6.0's the 9.4:1 compression ratio.

    With your flat top,,,,plus an overbore,,,,plus a 4" stroker crank to reach your desired 408 cubes,,,,on a stock 317 head your compression would be quite a bit higher than the 10:1 factory rating.

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    ok so running the 317's will keep me above 10:1? even tho its a 72cc(317)vs a 67cc(241) wouldn't the flat tops put it right around 10.08:1 like the LQ9's?

    why do you say it will be higher?

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    Moderator Firebirdjones's Avatar
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    Quote Originally Posted by My00Z28 View Post
    ok so running the 317's will keep me above 10:1? even tho its a 72cc(317)vs a 67cc(241) wouldn't the flat tops put it right around 10.08:1 like the LQ9's?

    why do you say it will be higher?
    It would be higher because you are no longer talking about a stock 364 cubed motor.

    You mentioned building a 408, which is a bored and stroked 364. The bore and the stroke is also figured into the compression ratio, so it will be higher than the factory rated 10:1 LQ9 (364).
    You would have to do the math to figure just how much. Off the top of my head you are probably looking at 1/2 to 3/4 point rise at a minimum.

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    Member My00Z28's Avatar
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    Quote Originally Posted by Firebirdjones View Post
    It would be higher because you are no longer talking about a stock 364 cubed motor.

    You mentioned building a 408, which is a bored and stroked 364. The bore and the stroke is also figured into the compression ratio, so it will be higher than the factory rated 10:1 LQ9 (364).
    You would have to do the math to figure just how much. Off the top of my head you are probably looking at 1/2 to 3/4 point rise at a minimum.
    alright thanks i was worried that the compressioin of the 317s would be low lol less parts for me to have to buy!

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