4.2 Piston Limitations

[redneck truck]

I've got a set of pistons and rods sitting and would like to modify them and install them while the motor is out and I'm installing the Touareg heads and S6 camshafts. This seems like an ideal time, since I'll have good access to everything and won't be laying in/under the engine bay. Before I install them, I'd like to make the most of them. I'm also wondering if it is a good idea to install the pistons/rods with their existing rings and bearings (new), or reuse the ones in my engine, since they have likely worn into the crank and cylinder bores over the past 145k miles. Does anyone have an opinion on this?

As for making the most of these pistons, I'm looking for any and all limitations of the pistons in the belt-driven 40v 4.2 motor. Heat, knock, pressure, speed, and anything else I haven't thought to consider. People seem to be pretty happy with the quality of these pistons and their ability to withstand abuse, and I like that they're light and don't expand drastically with heat. My only concern is that the high silica content might make them brittle.

First, I'd like to install some S6 forged rods, which I recall being slightly longer (hopefully Scotty can verify) resulting in a higher compression ratio and presumably a tighter squish band.

Second, I'd like to remove material from the crowns of the pistons to reduce compression ratio without affecting squish, with increased valve clearance being a positive side effect. However, I do not want to adversely impact crown strength or heat retention/dissipation tendencies.

Finally, I'd like to ceramic coat the crowns so they absorb less heat. Wouldn't it be lucky if the ceramic I added weighed the same as the material I removed?

[Scotty@Advanced]

I've got a set of pistons and rods sitting and would like to modify them and install them while the motor is out and I'm installing the Touareg heads and S6 camshafts. This seems like an ideal time, since I'll have good access to everything and won't be laying in/under the engine bay. Before I install them, I'd like to make the most of them. I'm also wondering if it is a good idea to install the pistons/rods with their existing rings and bearings (new), or reuse the ones in my engine, since they have likely worn into the crank and cylinder bores over the past 145k miles. Does anyone have an opinion on this?

As for making the most of these pistons, I'm looking for any and all limitations of the pistons in the belt-driven 40v 4.2 motor. Heat, knock, pressure, speed, and anything else I haven't thought to consider. People seem to be pretty happy with the quality of these pistons and their ability to withstand abuse, and I like that they're light and don't expand drastically with heat. My only concern is that the high silica content might make them brittle.

First, I'd like to install some S6 forged rods, which I recall being slightly longer (hopefully Scotty can verify) resulting in a higher compression ratio and presumably a tighter squish band.

Second, I'd like to remove material from the crowns of the pistons to reduce compression ratio without affecting squish, with increased valve clearance being a positive side effect. However, I do not want to adversely impact crown strength or heat retention/dissipation tendencies.

Finally, I'd like to ceramic coat the crowns so they absorb less heat. Wouldn't it be lucky if the ceramic I added weighed the same as the material I removed?

Rods are the same dimension on the S6/A6, the difference is the A6 is powdered metal and the S is forged, the engine have the same compression ratio.

Pistons are good for stock but explode when detonation is experienced. i would not cut any part of the piston at all, the piston crown is pretty thin to begin with. nitrous you need a piston with a thick crown to withstand the extra cylinder pressure.

[redneck truck]

Interesting, for some reason I thought I remembered reading that the S6 had a higher compression ratio. Don't remember where, so I can't cite a source. Looks like Nikasil bore plating and generic forged pistons are the way to go, eh?

[Scotty@Advanced]

Interesting, for some reason I thought I remembered reading that the S6 had a higher compression ratio. Don't remember where, so I can't cite a source. Looks like Nikasil bore plating and generic forged pistons are the way to go, eh?

Or just bore the block using the Alusil boring process and use appropriately coated pistons. Pistons/rods are the same dimension across the 40V engines sans the RS6. The power diff is the manifolds and cams.nikasil is an option but it's more costly and another thing to worry about (Nikasil peeling off).