Since this thread is about piston-to-wall clearance (or was originally) you should probably mention that those numbers you referenced are not actual clearances, but rather a multiplication factor that applies to ring end gap and not piston-to-wall clearance. As in "to determine the top ring gap you multiply the bore diameter in inches by the appropriate factor." So with an 85.5mm (3.366") bore x .005 your top ring gap would be .017". If some confused ************ sees those factors and thinks they need to run .0065" piston-to-wall in their track raping motor they might not be 100% happy with the result.

 

Thanks for stepping in and correcting this confused ************, so I don't screw up some other confused ************.

 

FWIW the box of FM 2.0L Wieseco pistons come with a spec sheet from Weiseco that says "recommended piston clearance .0030" Seems like supertecs with lower thermal expansion could be tighter.

Bob

 

What would you suggest on a street engine that is going to be running 1.7 bar daily and possibly 2.2 -2.3 bar on meth at the track?

i dont want to go crazy loose and have it be essentially a full blown drag car...

I will be using supertech pistons.

 

30-32 psi? Seriously? You do have a good setup but that 2871 will kinda be falling off the map at those boost levels. My thoughts are that the high hp mixed street/strip Miata engine should be built the same way as a high hp street Miata engine.

 

Not to mention the fact it is going to be difficult to keep it all cool, engine, trans, and diff, at those power levels, on the track. I am assuming by track you mean road racing. Bring lots of $$$

 

Supertech recommends .0028" IIRC

 

the turbo is getting FP HTA wheels. they are efficient to ~40psi.

 

Your fixation on manifold pressure is extremely unhealthy. How much power do you expect to make?

 

would be nice to make 350-400 on a 1.6 at those levels.

 

So you don't need anywhere near 40psi to make those numbers, then. With a good intake manifold and race gas, 400whp is probably doable in the 27psi range on a 1.6 and a genuine 2871R with Garrett wheels. On pump gas for the street, I wouldn't push much past 21psi which will get you right around 320-330whp. If you have E85 available, 400whp is probably doable at ~24psi.

Don't bother with the FP wheel upgrade, keep your Garrett warranty intact since the Garrett wheels are still efficient at 27psi.

 

i was going to get it setup with the current turbo and then get it done later... my brakes need attention before i get a brand new turbo rebuilt.

plus i meant 32psi to make 400... not 40.

i just stated that it is effecient to 40 with FP wheels.

 

Wait, wait. How did nobody else see this?!

Compression is not based on how much air you put in.
If I run my motor super rich, enough to wash down my cylinder walls, my compression doesn't go up. Or down. Or whatever you think.

lololol

Ps, has the motor been built yet?

 

1. Fuel has nothing at all to do with compression.
2. Compression doesn't change with boost pressure.. static compression doesn't. That is determined by the pistons, valves etc. etc. Dynamic pressure does change greatly which is where the force that damages pistons, bends wrist pins, buckles rods etc. comes from.
3. More pressure always equals more heat. If you can make more power on less boost and have an efficient turbo, it's a very good thing.

 

And why are you telling me this?