392 pistons, D indent or full flat top?
- Thread starter MrWolf
- Start date
jauringer
Member
Mr. Wolf, the contoured piston engines have a different cylinder head chamber design. If you want to go to flat top pistons, you'll need to find the appropriate heads to go with them. These engines are also referred to as non e (non-missions) by the way.
As a side note: increasing compression on a contoured piston engine is a little different than the standard flat top setup. Piston to valve clearance is your limiting factor.
Ie: the most I could get out of my 304 was 8.9 cr with a net of .030" off the heads/deck. Left me with about .080" piston to valve clearance (deflection included) doubt this will directly translate to the 392 but it should at least give you a better feel for the situation.
Jason
As a side note: increasing compression on a contoured piston engine is a little different than the standard flat top setup. Piston to valve clearance is your limiting factor.
Ie: the most I could get out of my 304 was 8.9 cr with a net of .030" off the heads/deck. Left me with about .080" piston to valve clearance (deflection included) doubt this will directly translate to the 392 but it should at least give you a better feel for the situation.
Jason
Robert Kenney
Super Moderator
The d is not the only concern, the compression distance is just as big...
If I recall correctly the 345 and 392 are both 1.904 (compression height) from the piston pin cl to the top of the piston... The d relief is 10cc...
If you can get totally flat (no d) 392 pistons at the height of 1.904 you'll bump the cr about .5 points then add 0 decking you should add another .5+. You need to do the calculation with your own chamber volumes to fine tune the ultimate compression ratio.
Don't worry about valve to piston clearance as you'll never have an issue with a flat top IH sv engine.
Ok. I thought from the pictures that IHPA sold full flat 392 pistons. I'm after the.06 oversized. 0.5 increaseease ease in cr would be nice. I'm currently at .03 below deck with the d's so I have something to gain there. The guy I got the engine from told me he had built several 392's with pistons protruding.01-.02 above deck to gain proper compression ratios. Got very nice results power-wise. We started one up and ran. I don't know so I seak knowledge here before I try to order
To be clear the pictures we have posted on our online store represent the various types of pistons we have available. Which set of pistons you need varies on your application. All 392(and 196) with flat top pistons will have the 'd' recess in them. That is how they all come. The pistons you see in our pictures that are completely smooth are for the 152/304/345 engine. Hope that clears things up.
Robert Kenney
Super Moderator
ok. I thought from the pictures that IHPA sold full flat 392 pistons. I'm after the.06 oversized. 0.5 increaseease ease in cr would be nice. I'm currently at .03 below deck with the d's so I have something to gain there. The guy I got the engine from told me he had built several 392's with pistons protruding.01-.02 above deck to gain proper compression ratios. Got very nice results power-wise. We started one up and ran. I don't know so I seak knowledge here before I try to order
I will try to elaborate on these bits of knowledge later tomorrow.
Robert Kenney
Super Moderator
I don't see how you could run the piston proud .010-.02. The head gasket would be .040 and for a piston clearance like the sv .035 quench is a min...
Racing you can play around with close quench distances like.03 but in a street application no way!
The only way to get a d-less 392 piston is to have them custom made..... $100/hole
Racing you can play around with close quench distances like.03 but in a street application no way!
The only way to get a d-less 392 piston is to have them custom made..... $100/hole
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Thanks for the replies Robert!
I have done some diesel engine rebuilding and there the pistons would sit a little above deck, so I didn't think that would be a problem for gas engines either. The guy I got the 392 from must be playing it pretty tight, I'll have to ask him again, I might have gotten it wrong as well.
Until now I really didn't know a lot about quench, so thanks again. I see most piston producers advice a quench distance no less than .035-.04 in line with your recommendation, so I'll try to get it dialled in towards that distance when I get the pistons here and mocked up for measurement. Anyway now I know which type to order.
I have done some diesel engine rebuilding and there the pistons would sit a little above deck, so I didn't think that would be a problem for gas engines either. The guy I got the 392 from must be playing it pretty tight, I'll have to ask him again, I might have gotten it wrong as well.
Until now I really didn't know a lot about quench, so thanks again. I see most piston producers advice a quench distance no less than .035-.04 in line with your recommendation, so I'll try to get it dialled in towards that distance when I get the pistons here and mocked up for measurement. Anyway now I know which type to order.