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Only Tonic is Chronic
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1,549 Posts
Discussion Starter #1
I want to bore out my Project Engine to 3.1 Now, Correct me if I am wrong, but I wont be able to use any stock pistons right? So, what pistons should I use to keep the compression at Atleast 8:1 ..stock vr4 compression. Thanks

Dave
 

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Senior Fanatic
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6,011 Posts
You will need a custom 0.075" overbore piston that reduces compression. The overbore itself increases compression some. You really don't need to worry about it. My 0.050" overbore (3.056 L) increased CR to 8.2:1. A 0.075" might go to 8.3 or 8.4:1. Seriously, it does not make a difference.

Also remember that a 3100 cc engine is only 4.3% larger than the stock 2972 cc engine. That's like 13 HP from the displacement increase. Not a big deal. At 0.050" you can still bore out twice more. At 0.075" over, there are no more overbores.

My piston upgrade guide.

http://www.geocities.com/lutransys/jlucius2/j2-2-pistonguide.htm
 

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Only Tonic is Chronic
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1,549 Posts
Discussion Starter #4
Thanks for the Info Jeff. The reason I thought about doing a Bore on the block is because it is Seized, and dont you have to do somne sort of bore anyway to smooth up the cylander walls? I figured the 3.1 wouldnt increase the HP that much, but it was just a nice number to shoot for. I will be ready to do this project as soon as I find a vr4/TT with a blown engine. This will Involve a rebuild of the block w/ forged aluminum Internals and port and polish of the Heads..but First I need to find a car w/ a blown engine.So if anyone knows of one On or near the East Coast give me a hollar. Right now I am just in the Information collection process.

di93es..I will keep you in mind when I am ready to start collecting parts.
 

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Senior Member
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4,613 Posts
go with a .050" overbore that is what I decided too it is nice to have a little more room and you wont notice a hp increase... all my engine and head work is about $7000 so to give you an idea if you do the work yourself thats about what you should spend.... that also includes clutch and flywheel, motor mounts, precat eliminators..
 
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