29scarab

Engine is torn down to the block with a bad piston. Most of the underside of the pistons are black. My engine builder said it was from too much heat on the face of the piston. The #4 is cracked and has to be replaced. He said they were forged pistons, but they were not good for a blower application.

What type of piston is good for a Whipple with stock heads?Whats a good recommended compression ration? I would also like to upgrade the cam also. I heard of a cam at one time that was a good one for a whipple application.

Any help on this would be appreciated.

Thanks,
Shawn

articfriends

iTrader: (1)

I'd use a j/e piston set,they make a sportsman racing piston that is a drop in on 502's with heavy honing. I ran a set in my 502 with no problems. They are so close in wght to originals you could get away without re-balancing if your motor was original. The regular j/e is better yet if you want real good pistons,thats what I'm running in my 540. Flatlander racing has better prices than anyone ive ever seen on J/e pistons. I thermal barrier/ceramic coated the top of mine this time to prevent burn thru and keep exspansion down BUT it takes so long to have swaintech do it that you'd miss the rest of summer,Smitty

Turbojack

My opinion is to go lowest compression you can get easiest 7.5-8:1. Then make up the low compression with the blower. You will be able to build more HP on the same grade of gas with lower compression & more boost then with higher compression & less boost. With the Whipple you build boost almost instantly so that will not be a problem. I think you can find some off the shelf pistons around that compression fairly easy.

29scarab

Will burn through on a piston hurt?? I'm not familiar with the term or familiar with cause an affect long term?

Could you shed some light on it for me Smitty? My mechanic said the cylinder was a lil' scarred but he thought he could hone it and go with a piston a few thousand bigger and not have to replace the rest of the pistons.

Any pro or cons on doing this?

Thanks

Turbojack

If Owen says the pistons are not good for blower motor then why not replace all with new pistons. I know the $$ comes to mind but over the long run I think you will be happer you did. Labor cost to put back together with old or new pistons is going to cost about the same. I believe federal has off the shelf pistons with the dish.

cstraub

If the pistons are black on the underside then they have been subjected to enough heat that the aluminum in now brittle and will crack. You need to replace all the pistons. I would definiately run coated pistons and run a piston with a full skirt.

If it is an Iron head engine I would run around 7.5 to 1. If it is an aluminum head engine no more then 8.5 to 1.

Chris

articfriends

iTrader: (1)

When i said burn thru I really meant what happened to your pistons,they got hot from being lean and one failed,the others were probably not far behind.The ceramic coating i had put on the top of my pistons is supposed to help keep the heat from expanding piston as much witch will cause them to scuff or become weak like yours did. 2 Stroke pistons sometimes burn right thru the crown if ran lean,four strokes usually become brittle and break. My motor was set at around 11.4-11.6 a/f ratio wide open on dyno,it doesen't make as much power BUT it helps cool the pistons if you run wot for a long time. The ceramic coating on top is insurance in case it goes a little leaner. Smitty

29scarab

Thanks for the info Smitty.

I'm going to need all the help I can get on putting back together a good solid motor.