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Old 12-04-2008, 01:45 PM   #1
m50tech
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lowering compression

i have a question if i build a plate out of aluminum just like a head gasket and put a head gasket on both sides of the aluminum plate and place it between the block and the head to lower my compression will it work on a turbo?:con fused:
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Old 12-04-2008, 09:06 PM   #2
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lol i dont think so !

a mls head gasket is about $250 and you can get them in diff. hights
but the best way is to get fordged pistons like i did
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Old 12-04-2008, 11:51 PM   #3
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i was also thinking about that spacer just in case the timeing chaine snaps the valves dont hit the pistons and nothing happens to either
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Old 12-05-2008, 07:34 AM   #4
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Yes the plate idea would work just fine, although steel might be a better idea. They've been using the plate ideas in Volkswagen's for a long time now. Basically the plate is a copy of the HG, and then there is half of the HG on one side (bottom) and the other half on the other side (top).

Would be far better then an mls I would think, but then again the rules are a little different when you're talking about straight 6's where the head's like to warp and you have sealing issues stock.
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Old 12-07-2008, 04:00 PM   #5
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Like notorious said, steel would def be a better idea because aluminum doesn't hold upto heat as well.
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Old 12-08-2008, 05:23 PM   #6
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Bandaid solution. Forged, low comp pistons and a proper rebuild is the only way to do it without going halfass.
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Old 12-08-2008, 05:24 PM   #7
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Originally Posted by NOTORIOUS VR View Post
Yes the plate idea would work just fine, although steel might be a better idea. They've been using the plate ideas in Volkswagen's for a long time now. Basically the plate is a copy of the HG, and then there is half of the HG on one side (bottom) and the other half on the other side (top).

Would be far better then an mls I would think, but then again the rules are a little different when you're talking about straight 6's where the head's like to warp and you have sealing issues stock.
So they split a head gasket in two? That doesn't make any sense at all. The cost of getting a riser machined properly, within spec, would outweigh a set of pistons.
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Old 12-08-2008, 06:10 PM   #8
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So they split a head gasket in two? That doesn't make any sense at all. The cost of getting a riser machined properly, within spec, would outweigh a set of pistons.

Of course it makes sense. On a metal HG, the top and bottom is all you need (its the parts of the HG that actually have the seal) when you're using a metal head spacer like the OP wants to make. The stuff in the middle of the OEM gasket gets replaced by the metal spacer.

And you're right it will be expensive, although you don't know he knows so he might get it done for free or for very little. Although having someone water cut a piece won't be as much as 6 forged pistons. 6 forged pistons are the proper way to do it.

Regardless, it's known that stock internals of an M5x motor will make upwards of 500whp, so if his goals are around that or under it power wise, it's not a bad idea IMO.
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Old 12-09-2008, 01:07 AM   #9
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i plan to get the plate cnc machined i am going to make a compression ratio test so that i can set the ratio like at 7 of 8 and in case something was to go wrong nothing happens to the pistons and the valves cuz of the spacer. i do all my work and i have takes apart m50s m20 m10 before nothing new.
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Old 12-09-2008, 12:26 PM   #10
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7:1 is too low. Shoot for 8.5:1 or even better 9:1 IMO.

Not sure why you're so concerned about bending valves?
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Old 12-09-2008, 11:22 PM   #11
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my friend has a 87 bmw and he was boosting and piston #3 bended the valve and ever since it has never been the same i just dont want to go throught that with my car i rather do my research right
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Old 12-10-2008, 06:28 AM   #12
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my friend has a 87 bmw and he was boosting and piston #3 bended the valve and ever since it has never been the same i just dont want to go throught that with my car i rather do my research right
you definitly don't wanna go down to 7:1, your car will be a dog. Piston/valve clearance is not really a very good justification for choosing what compression ratio you want to run.
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Old 12-10-2008, 07:51 AM   #13
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my friend has a 87 bmw and he was boosting and piston #3 bended the valve and ever since it has never been the same i just dont want to go throught that with my car i rather do my research right
That has nothing to do with research. And that is a horrible reason to lower the compression of an engine that much.

If everything has been set up correctly, there is no issue with bending valves at all. My friend is making 400RWHP on a stock motor M20. No bent valves.

Just because your friend did something wrong doesn't mean you should sacrifice your build like that and going with such a low CR.

You lower CR to increase detonation resistance under boost. You don't do it to save your valves. If thats why you're doing it, get forged pistons with deep valve reliefs end of story.
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Old 01-04-2009, 05:52 PM   #14
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my friend has a 87 bmw and he was boosting and piston #3 bended the valve and ever since it has never been the same i just dont want to go throught that with my car i rather do my research right
If you lower the compression too much, you'll have no off boost power.
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Old 01-04-2009, 08:42 PM   #15
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