I was talkin with a knowlegable buddy of mine about my ever-changing build and he informed me that a problem I'd run into with a forged rotating assembley is piston slap, which would greatly reduce engine life due to cylinder wear. Anything I can do about this or...is this just one of those tradeoffs for performance?

 

Forged pistons expand more than cast pistons and therefore must be installed with more clearance than cast designs.This causes the increased noise levels.The company that supplies your pistons can tell you the proper amount of clearance you should have when installing theie products.When ordering your parts don't just say the cilynders were bored "twenty over".Actually measure the bores and give the supplier this measurement.I would callthe eventual piston maker first and see what size to have the cylinders machined to make sure they have a piston that will fit.A water cooled engine will soak up a lot of the extra noise inherent in the extra clearances involved.

 

Well I'm not concerned about the noise, I'm worried about the wear on the cylinder walls. Doesn't that cut down engine life?

 

There's a crap load of stock cars out there with forged Al. pistons from the factory.

If you get a quality piston, and take the block to a GOOD machine shop, you shouldn't have any issues with durability.

Probe pistons seem to have a fairly tight clearance...

jason

 

Increased piston wear isn't a big problem when using forged pistons if they are sized right for the cylinders.One thing you don't want to do to ANY engine you care about is to abuse it while it's still cold.If you take it easy on the car or let it idle for a few minutes befrore you start driving and take it easy until the temp. gauge is getting close to the normal driving range the pistons will last the life of the car.

 

Just a little clarification...

The pistons are never re-sized to fit the cyl bore.
In reality, your machine shop will hone the cyl bores to the exact size needed for the pistons you bring them.

Any decent machine shop will not hone a cyl wall without first having the pistons in hand.


jason

 

Thanks for the info guys, this will certainly help alot....if not just cost more money.

 

Might cost more money now, but it'll save you thousands down the road.

Are you doing a forged V6 assembly?

 

As most have said...."piston slap" is from / controlled by piston to wall clearance. Now, there are more variables in this.Piston manufacturers call for different clearances depending on the amount of different materials in the pistons. JE pistons for example, does like to run allot of clearance with their pistons. Wehave been usingProbe pistons for years with great success. Probes can be set up tighter....no slap. Also, just so you know, piston slap is usually onlyheard when the engine is cold. Once heated up...pistons expanded, etc. it goes away.Oh, and another thing about clearances....depending on how the engine is going to be run....n/a, forced induted, nitrous will play on how much you set it up at.

Casey

 

As most have said...."piston slap" is from / controlled by piston to wall clearance. Now, there are more variables in this.Piston manufacturers call for different clearances depending on the amount of different materials in the pistons. JE pistons for example, does like to run allot of clearance with their pistons. Wehave been usingProbe pistons for years with great success. Probes can be set up tighter....no slap. Also, just so you know, piston slap is usually onlyheard when the engine is cold. Once heated up...pistons expanded, etc. it goes away.Oh, and another thing about clearances....depending on how the engine is going to be run....n/a, forced induted, nitrous will play on how much you set it up at.

Casey