Loose pistons?

[88BB8B]

Hey everybody. I just got my super tech 9.0:1 pistons in. The machine shop said my std bore cylinders looked good after a honing and measured just within spec (PTW) against the stock pistons. So I decided on some standard bore forged pistons. I measured my cylinders about 2"down with a telescoping bore gauge against the micrometer and my pistons with the same micrometer. I don't have the most experience making precise measurements and am a little worried about trusting myself, but here are my PTW numbers.

#1 0.0042"
#2 0.0035"
#3 0.0037"
#4 0.00365"
I'm planning on making ~400hp initially and possibly pushing it as high as 650 with future upgrades.

Should I maybe hone the 3 cylinders to get closer to #1? Is 0.0035 gonna be too tight at ~600hp? Keep in mind these pistons are made with the same alloy as mhales and don't expand quite as much as weisco's etc. The manufacturer gave a rough table to calculate clearance, but it doesn't go over varying power levels like that.

Also, maybe just my paranoia but the pistons (which didn't come with rings) feel rather loose in the cylinder. I would expect 0.0035" to feel like a fairly tight fit, but can you guys wiggle around your ring-less forgies in the bore a little?

 

[DSMPT]

You can set to the biggest bore to make all clearance equal, if you are comfortable with it. But you can also send it like that. Probably it wouldn't be a problem. As you mentioned that Supertech pistons are 4032, not 2618. With 4032 you don't want clearances as much as 2618. If you go larger clearance you would lose one of pros of 4032 pistons.

 

[88BB8B]

You are right. I would like to keep them as close as possible and since they're already honed I might leave them as they are as long as #1 being that much bigger isn't an issue.

I measured my cylinders parallel to the rotarional plane. They are a thou or so out of round so they're a little closer at the pin. Do some more experienced people think this is okay? First time.

 

[DSMPT]

I used to run 4032 pistons with min .0025" to .max 004" clearance. I have had both Supertech and Mahle and was boosting 35-40 psi range. I hadn't had any issues. Tuning would be more critical than the material.
As I mentioned above, it's fine if you would run like that or you would set all clearance to the largest one. You wouldn't probably notice the difference. This is all about how much perfection you want. But just don't over hone, don't go more. .004" is already more than the usual clearance for 4032 pistons. 4032 pistons are weaker against piston slap.
Are those numbers with a torque plate or without it? If it's without it, you would easily see different numbers from the numbers with a torque plate.
What I meant above is you probably selected the 4032 piston on purpose, I guess the same reason as the most of people who go with 4032 pistons. They want the tighter clearance for quiet operation, less blow-by etc. So if you hone more, then you would get less benefit from the 4032 pistons.

 

[1990TSIAWDTALON]

Check your ring gaps. I deem them more important to keep a eye on than the PTW (which yours are fine). The more HP, the bigger ring gaps you will want to run. More BOOST = More Ring gap to prevent butting under high cylinder pressures. I do agree with @DSMPT on his comments, very good info!

 

[88BB8B]

Thank you. That is great info. I'll definitely keep them as they are then. I plan to use this car as a semi daily and you're right, I definitely to want to maintain the benefits of the 4032. (That is why I picked them.)

As for the rings, I haven't got em yet. I'm a little disappointed by the vendor I got them from. They clearly stated that they would be included but they were not. So a set is on the way and I got a feeler gauge set so I'll definitely make sure to set those correctly.

 

[DSMPT]

Generally Supertech piston kit comes with only wrist pins. Ring set is sold separately. Maybe the vendor didn't know that when he listed.