Backwards Pistons?

[97imprezaobs]

So the other day I was talking with my boss at the shop and he was telling me about these 101 HP upgrades he used to do on mk1 rabbits. Part of the upgrade included removing the pistons and instaling them backwards. If you look at a piston the hole for the gudgen pin is a little bit of to one side. This so after combustion the piston isnt pushed straight down on the rod it is pushed off to the side a bit. Well in VW motors if the pistons are reversed it makes that angle bigger so the piston is pushed down much easier.

Does anyone know if this may work on a subaru motor?

[evolutionmovement]

You would theoretically mechanically be able to bump out some more torque, though you will be getting more piston slap in return. The issue more specific to this engine is that the piston face is asymmetrical. The first thing is that the valve indents on the piston face will be wrong, with the intake valves receiving too small an indent. Being non-interference, how much of an issue this would be, I don't know, but even aside of hitting the valves, there's the question of the effect on combustion chamber dynamics. Beyond the valve indents, is the differing quench area (the intake side has a flat spot where the exhaust side is a rounded cutout). How much that would affect the swirl of the air into and out of the cylinder, I don't know, but I can't imagine it not having some effect, an effect that may offset any gains from the change in mechanical leverage and then some. You could get custom pistons made with a reverse offset, but IMO you'd get better results keeping from just bumping up the compression instead.

[Lunatech]

I have read that there are right and left side pistons, however when I rebuilt my '90 2,2 n/a, I used after market ones made by rock. They were all exactly the same. I fretted over that for a while and even got the mic set out and checked them they were all perfectly even, including the ones I pulled out of it to start with. I'm not sure if it is because they were after market or the n/a just wasn't built that way or it's a later model enhancement or what.

So, maybe I am enjoying something half way between.LOL.

[evolutionmovement]

The N/A are offset. I'm looking at one now and I'd say it's 1-2mm by eye. Piston face aside, 0 offset shouldn't cause any problems other than the potentially reduced time between rebuilds and possible increased noise.

[Lunatech]

I have experienced no problems. Well, there was the delay due to confusion and worry over not having the right parts in the middle of a rebuild that had to be done in 36 hours. But other than that no problems over the last 100k miles.

[gijonas]

Wieseco pistons have the offset in them,most aftermarket pistons do not.