New pistons application

[assault187]

My nightmare continues from those who saw my Teardown Diagnoses thread a little while back....

I just got word from my machinest that my PTW clearance on my setup was .009" on my my Ross pistons, thanks to some hack machine work by the original party. Ross recomends .005-.006 PTW clearance I believe, so my choices are to pay for what was done to this block, pick up a new block, have it go 20 over then re-use the already scored pistons

OR

Keep this block, go 30-40 over and pick up new pistons and be happy. I'm leaning towards this 2nd option. This motor will see 30-40 PSI off my HX-40 pro so I want somthing that will take the constant abuse from the daily driving too. I wanted to stick with Ross, but are stronger wrist pins needed for 40psi? Ross offers .20 and .30 over @ 8.3-1 compression, Wiesco offers their stronger HD pistons for 20,40, and 60 over @ 8.5-1 compression ratio. The Wiesco's were recomended to me for the higher boost application but it says they're rated for 350+hp per cylinder which is over kill but offer the upgraded wrist pins. My other concern was going 30- 40 over on the cylinders, Will this lead to any over heating problems due to the thinning of the walls?

Lend some input for making a decision?

 

[spendone]

I would say new pistons and block. Unless you go .30 over.

 

[TOONAH]

I have read that any make of piston can slap around with 0.006" PTW clearance.
I had my machinist set up my block for 0.0015" PTW for my Mahle pistons. I guess I'll find out if Mahle's claims about the expansion properties of their piston alloy are correct. They
had better be!!

 

[Got Grip]

With your goals, now is not the time to be taking shortcuts. On a street driven car, .006 PTW will need to be warmed up before you go anywhere. It will be noisy at startup and will hate the cold weather.

My previous motor was a .030 over Ross motor with .006 PTW. I cracked my block at ~36 PSI after a serious amount of abuse. This motor had been in my car for about 3 years of continuous abuse so they can take it, but it will eventually fail. I was sure to warm up the car before ever driving it and before it went, the piston slap at cold start was VERY bad.

If I were in your situation, I'd locate another block and get the Wiseco HD's. They allow you to run tighter PTW clearances which will be better for a street car and the HD pin will help out with your 40 PSI goal. If you don't have the money for this option, eat Ramen noodles for a few more weeks and save the money, it will be worth it. Another option is to have custom Wiseco HD's made to your specs. They cost more (and probably even more than finding a new block and getting shelf wiseco's) but then you can get the exact piston you want, even to go into your .029 oversized bore.