head gasket ?'s
03-24-2010, 08:35 PM
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head gasket ?'s i have an lq9 and i was wondering if i change my headgaskets to thicker gaskets ( say...0.065 or 0.070) will i need longer pushrods? and what will my compression ratio be or how do i calculate my new compression ratio?
03-25-2010, 12:09 AM
#2
Push rod lengths come in increments of .025 from what I have seen. If your wanting to keep the pre load just as it was before the head gasket swap, you would need to measure the actual length of the stock push rods, and then add the difference between the stock gaskets and the new gaskets to the push rod length and this will tell you what your new push rod length should be.
The stock push rod while called a 7.400 actually measures less than that, I do not recall the exact amount, but it is less. With that said, a set of chromemoly 7.400s could wind up being just what you need, as they will measure longer than the stockers, which is what you need in this case.
One good thing about hydraulic lifters is you do have a range that they will operate in, and somewhat of a "cushion" on pre load. If your off .010" one way or another, you should still be just fine.
I have to ask though, why would you want to go with a thicker gasket than stock? If it's to reduce compression, keep in mind this also will make your quench larger, which isn't as effective at warding off detonation as a tighter quench is.
As far as your new compression ratio, what's the bore, stroke, head gasket thickness, deck height, piston top volume, and combustion chamber volume?
The stock push rod while called a 7.400 actually measures less than that, I do not recall the exact amount, but it is less. With that said, a set of chromemoly 7.400s could wind up being just what you need, as they will measure longer than the stockers, which is what you need in this case.
One good thing about hydraulic lifters is you do have a range that they will operate in, and somewhat of a "cushion" on pre load. If your off .010" one way or another, you should still be just fine.
I have to ask though, why would you want to go with a thicker gasket than stock? If it's to reduce compression, keep in mind this also will make your quench larger, which isn't as effective at warding off detonation as a tighter quench is.
As far as your new compression ratio, what's the bore, stroke, head gasket thickness, deck height, piston top volume, and combustion chamber volume?
03-25-2010, 02:48 AM
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this is for my turbo'd lq9......ive completly screwed up the threads on one of my spark plug hole's so i figured if im going to remove the head anyway i might as well change the gasket in an effort to reduce compression. Judging by your post im assuming its a bad idea...lol, as far as the engine specs go, im not really sure of all of the measurements you asked for but it is a stock 03 lq9 which if im not mistaken is 10 to 1 with the stock mls headgasket(0.051 i think) and my options are 0.065 and 0.074. bore and stroke 4.000 x 3.622 with 317 heads