Erotomania

I'm about midway through my 1.6 rebuild and I'm having the crank turned and about to send the block on its way to the machine shop but I've been getting some mixed input from builders as to what clearance to aim for on the bottom end. I've been told to put it at .0012, then I've been told to run .0025 and I've been told "middle of the road" which would be .0019...This motor wont see any more than 250hp and will be a weekend warrior mountain run car mostly with some track days here and there.

It'd like to have a solid idea of where it needs to be so I can have the block line honed in addition to the crank being reworked If I need to create clearance. My personal unexperienced but somewhat educated guess would be to aim for the rods at .0015 and the mains at .001.

lordrigamus

iTrader: (14)

I'm not sure about the rods but .001 sound a little tight for the mains. You want it loose enough to spin freely but tight enough to retain oil pressure in the mains. IIRC, mine are .002-.0025. I believe I used the factory specs when assembling.

neogenesis2004

iTrader: (12)

For that little bit of power I would do 0.0015" on the rods and mains. That will give you cushion but will provide plenty of support to have long term reliability.

As for p-w clearance, I saw no mention of what pistons you will be running. If stock, I would use stock spec + 0.0005" since they will not expand much. If forged, I like the rule of thumb of 0.001" for every 100HP. It will keep you safe.

lordrigamus

iTrader: (14)

It depends on the silicon content. More silicon= less expansion. Stock piston( high silicon) .001-.0015. Wiseco(low silicon) .002-.0025. No silicon(JE piston) .003-.004.

Erotomania

I've got factory auto pistons with thermal coated tops set with sealed power premium chromoly rings to go on M-tuned rods. If the machine shop can't hone the bores true without removing too much for the factory piston I'll more than likely get the 78.5mm 8.8:1 supertech pistons. Forged pistons would be nice regardless but for my power goals, I think stock pistons would hold up w/ good tuning so we will see once the machine shop does their thing.

Thanks for the good info guys.

BTW factory specs for b6 oil clearance
rod- .0011-.0027
main- .0009-.0017
Quite a range move around in.

If I do end up going the forged piston route, I'd probably build it with more power in mind. I'm only looking at running 250hp because I really can't afford to support any more than that(college) at least for a little while. With more power, to keep reliability what clearances do you look for then?

neogenesis2004

iTrader: (12)

At 250whp I don't think any piston in existence is going to need 0.003-0.004", period.

With what you just posted, using stock pistons, I would personally do exactly what I said above. That will be reliable, DDable, and HPDEable. Not sure if it would withstand a Sav-like track abuse, but it should...

Erotomania

Yeah...even at low boost I plan on running individual port water meth...Not to run higher boost really, just to keep overall temps down. Mountain runs=thin air+lots of load...I should be able to achieve my power goals on 93 without water meth so it'll only be there for det. prevention and overall cooling efficiency.