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Old 01-07-2011, 02:22 PM   #1
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Default Aftermarket pistons

I tried to search but wasn't finding anything relavent. I was wondering if, on a healthy motor, it was reasonable/possible to install aftermarket pistons in a motor with no engine work? The most basic requirements for an aftermarket piston install so to speak.

Every build thread I see looks like the motor was bored, but I see that a few companies make 83mm pistons and was wondering if this was a reasonable option for a budget-ish built motor. If it is not advised, what would be required in order to properly install these stock sized pistons? Obviously rods, bearings, and gaskets would need to be changed as well, just curious specifically about the pistons mating to the block.
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Old 01-07-2011, 02:28 PM   #2
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You must hone it at bare minimum, that's not optional. If the pistons you bought are the correct size to produce correct wall clearances with your motor, then you can drop them in with just a hone - that assumes the clearances are perfect within about .0005". (three zeros there.)

In reality, this is never the case, and you're going to be boring the motor. It's really not a big deal, it's like ~$200 at any competent machine shop - you're going to spend at least 8x that in seals, gaskets, bearings, rods, pistons, head gasket, valve guides and seals, etc.
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Old 01-07-2011, 02:41 PM   #3
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Thanks for the info. I was kindof assuming that if everyone does it one way, that's probably the way it has to be done. Guess I've got to decide if I want to take that plunge or try to enjoy 200whp.
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Old 01-07-2011, 02:58 PM   #4
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um dude after market rods before pistons if your tune is decent pistons should not be a problem at all. But rods on the other hand fold like a cheap map.
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Old 01-07-2011, 03:09 PM   #5
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^ I know, new rods will definitely go in. I was just unclear on what was required to do pistons as well. I really wish the NB motor was a 9:1 compression like the NA, I'd feel a lot better about just throwing rods in w/ stock pistons.
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Old 01-07-2011, 03:33 PM   #6
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You would be taking a risk in assuming the bore is true and the same size as stock after 1xx,xxx amount of miles. You're also assuming the pistons are exactly 83mm.

You might get lucky, but chances are you'll either get blowby, slap, or the skirts will collapse.

It's good insurance on what will probably be the cheapest part of your build to take it to a good machine shop.

Buy the pistons first and have them size the bores.
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Old 01-07-2011, 08:29 PM   #7
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Quote:
Originally Posted by pdexta View Post
^ I know, new rods will definitely go in. I was just unclear on what was required to do pistons as well. I really wish the NB motor was a 9:1 compression like the NA, I'd feel a lot better about just throwing rods in w/ stock pistons.
The .5:1 difference is nothing to be concerned over.
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Old 01-24-2011, 08:34 PM   #8
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Question, is stock compression good enuff to make 300+ whp at low boost?
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Old 01-24-2011, 09:18 PM   #9
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On the 1.8l there is also a big reason for people skipping 20 over and going 40 over. The reason it helps to deshroud the valves for better flow and hp.
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