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Buddy of mine just got a V6 and he wanted to know something about rasing his compression ratio and what should he expect from swapping to an aluminum flywheel. He just got out of the import tuning thing. I didn't know how to answer him so I was hoping someone could help me out.
 

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raising the compresson can be done 2 ways. one way a lot safer than the other.

unsafe way - milling the head to take a little off. This raises the compression a little bit. Also getting a thinner head gasket will raise the compression.

safe way. -- buy new pistons


alum flywheel. It will make the revs go up quicker, but will lose speed a lot faster. It is a never ending battle about that. Tell him to get 3.73s (since he obviously has a manual) and an alum driveshaft. That will be more bang for the buck and will give more of a feel for what the alum flywheel will feel like.
 

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well raising the compression will help for a N/A motor if he ever deicides to go with a blower he will want low compression... aluminum heads like high compresson and if he wants a n/a motor i would buy a 4.2 crank and rods and get pistons set up for what ever compression he wants then go with ported/polished heads and intakes and finish up with a cam and a dyno tune (bolt ons of course)

raising the compression ratio is alot of work... if he is going to do that he needs to get the motor built while he is messing with it. i wouldnt raise it much though....

an aluminum flywheel is nice but... its not going to to much of anything major.... its worth it but i wouldnt rip my tranny out just for that... maybe if i was replacing the clutch.
 

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Monkey said:
raising the compresson can be done 2 ways. one way a lot safer than the other.

unsafe way - milling the head to take a little off. This raises the compression a little bit. Also getting a thinner head gasket will raise the compression.

safe way. -- buy new pistons


alum flywheel. It will make the revs go up quicker, but will lose speed a lot faster. It is a never ending battle about that. Tell him to get 3.73s (since he obviously has a manual) and an alum driveshaft. That will be more bang for the buck and will give more of a feel for what the alum flywheel will feel like.
I wouldn't say it's unsafe as long as you know what you're doing. Milling the heads like .030" is perfectly safe as long as you don't go too crazy w a big cam and a larger RR ratio. If he goes this route, he'll need to buy some play-doh. What you do is put the play-doh in a ball on the piston and rotate the engine manually. The piston will crush the play-doh between the head and piston and you'll see the clearance you have or don't have.
 

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I didnt mean that it is complete unsafe, but it unsafer than getting new pistons. Plus new pistons can make your compression whatever you want. Milling the heads, will only raise the compression by little amounts
 

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stock compression is fine unless you're building a beast of an N/A motor.
 

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9.0-9.5 I would say is optimal. If you go bigger, then you're forced to stay N/A. My 4.2 is 9.3 and I could still supercharge mine but i'd have to be a little wery about going with lots of boost.
 

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If you're going to throw boost out the window, shoot for a 10:1 CR hell see if you can go with a 10.5:1. But remember he's the guinea pig here. I personally like to play it safe for the most part.
 

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Dom said:
But where would he get the pistons from? I know he doesn't make much money so he would probally want just cast pistons.
Mabey a call to Marrona Racing in Canada will help you. Boost increases the compression as boost increases. New pistions run that higher compression all the time. marrona raciing may have a block all done you can buy. A matching set of heads would be nice.
 

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Well if money is an issue, then I would scrap the project. These kind of projects should be left to people that can afford the lost if the motor goes haywire. The Best I can recommend then would to stroke the engine to a 4.2 and if you use those stock pistons, you'll have a 9.3:1 from a 9:1 CR But parts are still going to be around $500-$1000 and then you still need to do the work. My advice, just still with bolt on for now.
 
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