# Machining Pistons



## I-Rocco2 (Dec 8, 2003)

Has anyone machined the top of the pistons to lower compression? I dont like the idea of thicker head gaskets. It should work if everything is rebalanced? http://****************.com/smile/emthup.gif http://****************.com/smile/emthdown.gif


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## bobqzzi (Sep 24, 2003)

*Re: Machining Pistons (I-Rocco2)*


_Quote, originally posted by *I-Rocco2* »_Has anyone machined the top of the pistons to lower compression? I dont like the idea of thicker head gaskets. It should work if everything is rebalanced? http://****************.com/smile/emthup.gif http://****************.com/smile/emthdown.gif









sure, but you need to consider the thickness of the piston crown. I wouldn't go below .300" on a FI car, .350" if it is going to be a high boost application.


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## I-Rocco2 (Dec 8, 2003)

*Re: Machining Pistons (bobqzzi)*

I wanted to lower to around 7-6.5.


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## wootwoot (Sep 21, 2003)

*Re: Machining Pistons (I-Rocco2)*


_Quote, originally posted by *I-Rocco2* »_I wanted to lower to around 7-6.5.

you mean thats the compression ratio you want???


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## I-Rocco2 (Dec 8, 2003)

*Re: Machining Pistons (wootwoot)*

Yes


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## bobqzzi (Sep 24, 2003)

*Re: Machining Pistons (I-Rocco2)*


_Quote, originally posted by *I-Rocco2* »_Yes

what is the compression ratio of the pistons you are starting with?


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## BubonicCorrado (Jul 24, 2003)

*Re: Machining Pistons (bobqzzi)*

by the time you get the pistons machined, have all the parts nessary to run the machined pistons, and have rebuilt the engine, you might as well have spent the extra 200 bucks and gotten the forged pistons cutom made


_Modified by BubonicCorrado at 5:05 AM 6-7-2004_


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## I-Rocco2 (Dec 8, 2003)

*Re: Machining Pistons (bobqzzi)*

Probably JE Pistons 9:1


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## I-Rocco2 (Dec 8, 2003)

*Re: Machining Pistons (I-Rocco2)*

I am also a Machinist


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## bobqzzi (Sep 24, 2003)

*Re: Machining Pistons (I-Rocco2)*


_Quote, originally posted by *I-Rocco2* »_Probably JE Pistons 9:1

unlikely you could take that much materila out. Can't see why you'd want such a low comp ratio


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## wootwoot (Sep 21, 2003)

*Re: Machining Pistons (bobqzzi)*

yea, i see absolutely no point to run such a low compression ratio. any reason why?


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## BubonicCorrado (Jul 24, 2003)

*Re: Machining Pistons (wootwoot)*


_Quote, originally posted by *wootwoot* »_yea, i see absolutely no point to run such a low compression ratio. any reason why?

Absolute stupid amounts of boost... I.E. 45-50 + psi is the only reason I can see


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## ErosNJ (Oct 21, 2002)

*Re: Machining Pistons (I-Rocco2)*

http://www.ffp-motorsport.com/...x.php
Read his story and macine at your own risk


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## kimosullivan (Aug 12, 2002)

*Re: Machining Pistons (I-Rocco2)*


_Quote, originally posted by *I-Rocco2* »_I am also a Machinist

Then mill out the head. Increase the volume that way. You'll probably need a combination of methods if you want to avoid custom length connecting rods.
For my Ghia's new motor, I have: shorter rods, copper head gaskets, short pin height pistons, and cylinder spacers. Current CR is 6.8, and I can swap head gaskets to raise or lower that quickly.


_Modified by kimosullivan at 4:15 PM 6-7-2004_


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## I-Rocco2 (Dec 8, 2003)

*Re: Machining Pistons (kimosullivan)*

I was planning around 7.5-1 at first and was worried about detonation problems. I was planning around 35 - 39 PSI. I would like to run no head gasket and stainless o-rings that is why I wanted the lower compression. I have built supercharged V-8 that have taken more pressure than this. Looking at the pistons this cannot be taken off them. I would like to experiment with how much HP can be produced?


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## MKII16v (Oct 23, 1999)

*Re: Machining Pistons (I-Rocco2)*

Just use and 8V block and save all the headache


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## Angular (Mar 12, 2002)

*Re: Machining Pistons (I-Rocco2)*


_Quote, originally posted by *I-Rocco2* »_I was planning around 7.5-1 at first and was worried about detonation problems. I was planning around 35 - 39 PSI. I would like to run no head gasket and stainless o-rings that is why I wanted the lower compression. I have built supercharged V-8 that have taken more pressure than this. Looking at the pistons this cannot be taken off them. I would like to experiment with how much HP can be produced?









Is this a 16V motor? You'll never get CR that low by machining stock pistons. Mine are dished down to 9.3:1 which was as far as [email protected] wanted to go to avoid weakening the piston. Note that the machined area goes nowhere near the edge of the piston or the ring lands.








If I were you and wanted low CR on the cheap, I'd get a early ABA bottom end (like everybody else! haha...) and smack a 16V head on it. You'll get approximately 7.9:1 CR.


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## I-Rocco2 (Dec 8, 2003)

*Re: Machining Pistons (Angular)*

Excellent I have a 8v block here out of my old GTI I rebuilt for my daughters car. I didnt even thing of that?







Thanks!


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## wootwoot (Sep 21, 2003)

*Re: Machining Pistons (I-Rocco2)*

also what was said about the pistons. you would want to "dish" them or dimple them to make it proper. i wouldnt take more than .09 off. thats just me though, i wouldnt want to accidently throw away that much money. maybe just sell the pistons and use the money to throw down towards the new custom set? thats if you diddnt just solve it with the block idea


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## I-Rocco2 (Dec 8, 2003)

*Re: Machining Pistons (wootwoot)*

Thanks guys!


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