forged pistons clearances

[Aries_Turbo]

Hello All,

I am finally building my 2.5l T2 motor for my k car.... What are people running for piston clearances. I have a set of .020" over JE's and the .004" cyl wall clearance seems a little tight as far as forged pistons go. From what i hear, .0006" is the clearance for the pin, and .017-.021" top and bottom ring end gaps are ideal. Thanks for your input.

Brian

[Aries_Turbo]

anyone?

.004 is OK for forged, Chrysler specs .0018 on cast as a max, they like tight clearances on turbo motors, I would run no tighter than the .004 on the forged though, they expand a lot more than a cast piston. I run .0008 to .001 on my pins, no tighter.

[Aries_Turbo]

really? .0008-.001" on the pins? that seems alot tighter than what i heard for a JE.

Brian

[Reeves]

I ran .005" with the JE's...but I'd say .004" is probably OK...not sure.

I ran .020"/.020" top/bottom ring gaps. I used to run .016"/.014" and had a ring butt, blew the top off the piston. Then I tried .018"/.016"....did the same thing. Then tried .020"/.020" and had sucess for a long while, until it started making too much power for the stock fuel rails and fuel lines, then is went kapllooee.

With my new forged pistons, I'm running a gap of .028"/.025".

What pin specs do you guys speak of?

[Mike B.]

No instructions with your pistons? There should be unless you bought them used.

[CSX321]

Quote:

Originally posted by Reeves With my new forged pistons, I'm running a gap of .028"/.025".

Likewise. I'm running .005" and .024"/.022" gap with Venolias.

[Aries_Turbo]

no i bought them new. the sheet was misplaced when they were reboxed for shipping. well for JE's gary says he ran some at 3.5 thou, danny fazzina tells me 3.2 thou, and ned from rolling thunderz tells me 4 thou @ .5" up from the bottom of the skirt. i hear that JE usues a different alloy that doesnt require as much clearance due to less expansion. i know that venolias expand more. but as far as ring gap, from what reeves, my machinist and ned at rolling thunderz says 20 thou on both rings should be fine i suppose. reeves, did yours blow cause you ran it lean, not cause of ring butt?

anyone else have anything to add about the pin clearance?

thanks for the input.

Brian

[Reeves]

Yeap, all times blown were due to leaness. With the smaller ring gaps thou, when it ran lean, it butted. Granted, it shouldn't have been that lean, but it shouldn't have butted either.

The two last times I blew, it damaged the #1 and #4 piston. The last time caused a ton of damage on the #1 piston and head. I suspect the stock fuel rails and stock fuel lines to be at large...especially since the last cylinder to get it's fuel by the stock fuel rail design is cyl #1.