brc told me set em up at .008 but mine are at .010 to .011, i took all my parts back from godwin singer machine in st, pete ,thank god i did they didn't have enough clearance for the pistons to clear the crank so it would have come unglued on the dyno... my bores are too loose and the motors haven't even been together. i guess measuring pistons and cylinders is difficult, its hard to figure out how to work a micrometer... i have some brc blower pistons for sale and now need to bore my new never run block and buy another 2200 bucks worth of pistons. perrrrfect... mark at mer said it looks like a blacksmith worked on my new billet keith black cranks. i have some brand new 6.535 oliver billet rods i'lll let go cheap, as mark wants me to run an ever longer rod in my combo. run like h*ll from the butchers at godwin singer they are the worst of the worst. the thing thats amazing is the think the methods they use are ok... truly scary people.run run very far away if you value your motor.they botched almost every thing they did im waiting for mark to tell me if the decks they cut are even square. if they are then 1 thing was done to borderline at best. mark will probaly cut em again just to get a smoother surface anyway .

ok guys, whats the most clearance you or someone you know has run?

It depends on the pistons, A SRP comes standart with .0035-.004, a JE is about .005-.0055. JE recomends adding .001 for a marine engine. The furthest I have ever used is .007 on a JE.

A .01 will work and the engine would run. The Piston will wear premature on the side rails from all the rocking. Oil rings will have some huge gaps and it would use more oil than normal.

I would not run a engine with that much clearance. It goes back to following manufacturers recomendations. Follow them, and you should have a sucessful engine. A .400 long rod won't work? ???

I took my engines apart this fall due to excessive blow by issues out of the breathers. My piston to wall clearance was around .010 with SRP pistons. Yeh, they were running but I don't think I would recommend it.

Ratman Last year I added blowers to a set of 540,s. Replaced pistons with Ross
Slugs. They were the exact replacements. other then they were a flat top to
bring my cr down to 7.9 to 1. Even the weight was within 4 grams per piston.
The finished bore size would yield .010 to .011. This was measured under the pin on the
Ross. I was skeptical in putting it together this loose. I ended up calling Ross. Believe it or not on these slugs they wanted it loose. Well 10lbs boost later and 60 hours of lay down
throttles. It worked fine. Its all in the type of (Expansion rate) Aluminum used in different piston manufactures. JE calls for .007 to .008. Call your Piston Manufacturer.

Gerry

I built a sweeper with parts in my shop.The piston to wall was .010.The motor runs great.It has more blowby than i desire.I put sae40 weight in it and it cut most of the blowby down.If i recall they were BRC pistons.

It is not uncommon for a Supercharged or Turbo Charged engine to have .008 - .010 of clearence. The piston alloy's will vary a little from all of the different manufactures. A Hi Performance Marine engine will have very low water temps, anywhere from 100 to 140. The block will not expand as much at this temp. The piston needs to be clearenced for the lack of exspansion.

Piston "coatings" may be a option for you.

Gerry

Are they forged?... How much taper and cam grind do they have?... Is the engine going to be supercharged?... What pressure?... Are the wrist pins offset?... Are you planning on racing or just cruising?.... If the engine is going to be boosted to 9 or 10 lbs... and you are planning on running it hard and hot... then .010 would be ok... but I think more like .005 would be best. It's all subjective to what the piston design is also... How long are the skirts?... what is the clearance 1 inch under the wrist pin?..

How many cubic inches are you running???? My motors are 580" and have 6.700 rods. What are they recommending?

I guess the longer rod helps rod-stroke ratio but also puts the pin way up into the piston. I just got done waiting 8 weeks for custom pistons........