the only tinkering we did was on vp import. it is not easy to get this fuel to det and we only bumped up timing after 5500 rpm (it was on 2.0L, green and revolvers) incrementally while always listening with det cans.

 

What was the max ignition used on vp.

Mark

 

oh it was a paltry 20 deg after 7K and 1.7bar that was the highest it ever saw on vp import. look there is no doubt it could have been more conservative, but we were at the track. we checked for det and heard nothing. intake temps could have been lower as they were at 150F. mark what you probably have forgotten is that while you were here and did the pump gas tune, which is all the motor ran from new at that point, and the wrong springs stuck the valve open and bent it we took the head off and there was already signs of scuffing you could feel with your finger nail. so there was already a problem.

 

The motor wasn't always ran on VP Import, was it? Those pistons look like they've seen some lower octane fuel abuse. The rod bearings look to have some wear from either detonation or just too much timing on a good fuel.

The pistons look to be Wisecos, but I'm not very familiar with Arais pistons and could easily be wrong.

 

Yes about 2 years of the equivalent of 91 octane at around 26-28 psi of boost. But not driven all that many miles.

What is the recommended clearance for a run of the mill 85 mm Wieseco piston?

 

2200 miles to be exact.

 

Yes I remeber, I still think the guy who biult it bodged it.

Mark

 

Then I think we are exonerated and we will get back to our tinkering!

Isn't 4 thou a little tight for piston to wall clearance for a high boost motor?

 

I run 3.5thou on all my big boost engines.

Mark

 

....

 

i guess all this tolerance talk is a little vague until we know what piston it was and what the manufacturer suggests.

 

If they are Wiseco pistons, they recomend like 6 thou on an 85mm piston for high boost.

Other pistons are fine with tighter tolerances though.

 

It looks like a wisceo as they are the only ones I have seen with a dot on the crown.

Mark

 

come on 94awdcoupe... you built the motor, you know what you put in it. come in here and give us the details?

 

crcain, I doubt that 20 degrees of timing at 25psi on Import was the problem. Maybe if the 20 degrees was sooner than 7000, but not from 7k up. I would have been more worried about the 150 degree intake temps, combined with timing.