BigKID

iTrader: (5)

What is the max piston to bore clearance you would run on a street/strip, ~750whp, supercharged setup with 2618 pistons?

BigKID

iTrader: (5)

Maybe a little more info will spark some responses. Pistons are Wiseco 4.035 bore with coated skirts. Wiseco tech recommends .0040 for my application, which is also their min clearance. The piston is designed for this .004 clearance before the skirt coating, which is ~.0005, so piston should measure 4.0320 assuming +.5 thou for coating on each skirt.
Onto my measurements: Piston = 4.0320 with outside micrometer; With bore gauge zero'ed at 4.0320 with same micrometer, I get .0065-.0068 clearance across all 8 bores. Machinist said the clearance was .0050 when I picked it up.
Block was honed without torque plates. My measurements were made without the mains or heads torqued, ie bare block. Cylinders were round with the exception of a slight hourglass shape on the pin side of the pistons of -.0005.
Wiseco tech didn't come out and say to add any additional clearance above the min .004 for my 15psi of boost but agreed that .0050 would have been ok but .0065 would have ring flutter and wear badly. However, other piston manufacturers, such as Diamond and JE, clearly state on their spec sheets a min .0040 clearance and additional .001-.003 for boosted applications on their similar 2618 slugs.

So... cliff notes... is .0065 too much clearance for a 2618 piston that will see 15psi of supercharged boost and make ~750whp?

MPFD

iTrader: (5)

Thats too much, it will be noisy and it will wear out faster. I'd go with the minimum spec.

BigKID

iTrader: (5)

Update: Over the weekend I torqued the mains, took measurements then torqued the heads and took another set of measurements. I was getting hopeful after the mains as the clearances were getting better but got worse after the heads. Here are my results...

kevinsmachine

It's a tough call, the clearance sounds like a lot until u enter the supercharger to the equation , might get a little skirt rattle on cold startups, just let the internal engine parts get good and warm , you should be fine , I have run more clearance than that , but at customers request and they ran great , lower coefficient friction is the theory, skirts and ring lands wear out faster

BigKID

iTrader: (5)

Based on the torqued head measurements I got, I didn't feel comfortable with the clearance or the distortion so I took it to another shop last Friday. They are going to sonic check the block and determine how much we can go out to get the cylinders straight and order a custom piston. I am hoping 4.040 will get it.

I sure wish I would have known about you guys two months ago. I asked a lot of people locally about shops in Tally or Dothan and came up with nothing. Do ya'll do a lot of LS stuff?

kevinsmachine

Oh yeah, I love the LS's , make some good power, we r doing a big bore 5.3 right now , I'm sorry too, we are just south of Tally in Crawfordville , but do a lot of work for people in Dothan , surprised my name or Randy Castle's didn't come up

TURBHOE

iTrader: (4)

By faster do you mean 50,000miles or 100,000 miles? My bores needed .007 total clearance to be cleaned up. I ordered the wiseco's before I knew the bore was ruffed up on the one. It will be boosted for sure, daily 10psi 15psi when I want to have fun. Also would running a cooler thermostat help keep the block "small" while keeping the pistons big? Giving a tighter running clearance.