build question

sneakypete

sneakypete

Regular Member
Jul 18, 2007
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Central NJ
in my current build, but i have .020 over probe forged pistons. my machinist said that the tolerances listed on the spec sheet are between 2 thousanths and 6 thousanths. the block i bought its overbored and the clearances are in the 5 thousanths range... close to the extremes. he said that he usually tries to machine right in the middle of the tolerances.
i was wondering what kind of drawbacks i could experience if im that close to the max clearance? im aiming for around 600whp for my build and dont want to take any chances. should i just get another set of pistons .040 over and call it a day? id rather not but i dont want to take any chances.

thanks
-pete
 
jdub

jdub

Official SM Expert: Motor Oil, Lubricants & Fil
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Feb 10, 2006
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Valley of the Sun
That's what I was referring to as well...with my Ross pistons at 5 thou, I experience piston slap when the engine is cold. It gets better when it warms up, but sounds like a diesel until it does. It's going to depend on how long the skirts are on the Probes.
 
jdub

jdub

Official SM Expert: Motor Oil, Lubricants & Fil
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Feb 10, 2006
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Ross are good, but heavy...JE's are light, but the skirts are fairly short requiring a fairly tight piston to wall tolerance. I just purchased a set of CP pistons...ceramic coated tops, coated skirts, double forced pin oiling. CP's are a little heavier than JE. Probes (IMO) are a good stock replacement piston.

If you are shooting for a 600 HP build, coating is going to add a margin of safety for you...it's not cheap. It will also allow you to drop your piston to wall tolerance to about 3.5 thou.
 
jdub

jdub

Official SM Expert: Motor Oil, Lubricants & Fil
SM Expert
Feb 10, 2006
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Pics of the CP pistons:

p1058220_1.jpg


p1058220_2.jpg


p1058220_3.jpg



And a link to the website:
http://www.cppistons.com/products/sport_compact/
 
jdub

jdub

Official SM Expert: Motor Oil, Lubricants & Fil
SM Expert
Feb 10, 2006
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Doing well...it's just hot as hades in Phoenix right now ;)

Coating pistons is not something I want to invest the time in...it would drive me nuts and if you screw-up, a lot of $$$ too. The coating is a factory option when you order these...in fact, each order (other than the .040 over) are custom made. These are .020 over and I opted for the upgraded wrist pins. What really got my attention is the double forced pin oilers...should be a very good upgrade.
 
jkbmkiii

jkbmkiii

Supramania Contributor
Nov 24, 2005
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Castle Rock colorado
jdub;1058229 said:
Doing well...it's just hot as hades in Phoenix right now ;)

Coating pistons is not something I want to invest the time in...it would drive me nuts and if you screw-up, a lot of $$$ too. The coating is a factory option when you order these...in fact, each order (other than the .040 over) are custom made. These are .020 over and I opted for the upgraded wrist pins. What really got my attention is the double forced pin oilers...should be a very good upgrade.
Click to expand...


Thanks for the info! Hell it was hot a mile high today! Phoenix= To hot !
 
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