I need to make some decisions on which parts to use in my engine build.

I have two sets of pistons.
The right one is a smooth type which has smooth crowns (x5e) with very slight machining marks, while one has deeper machining grooves (t5b), this set is 1 gramme lighter.


What are the differences between them? Should one be preffered?

Also. Is there a way to check if enough of the coating is intact? I'm not sure I like the gray colour of one of the sets. It has been ultrasonically cleaned but I fear the solution has damaged them.


Finally I have two sets of rods. One sintered set which comes from a low mileage undamaged engine and one foreged set which comes from a en engine which has been through a snapped timing belt. I expect both sets to be fine, but the sintered set has already been balanced. Is the benefit of the forged seg great enough to warrant sending a second set off for balancing? I'm guesstimating my engine to end up in the 300-320 RWHP range.

 

I can't speak on the pistons since I don't know, but if I were you I'd definitely spend the money to get the forged rods balanced and use those. 300 rwhp isn't a ton of power, but I'd want the strongest bottom end I could build if you're already going through the hassle of building a motor. It'd really suck to button it all up and run it for some time, and then chuck one of those sintered rods through the block.

 

FYI... Porsche thought the forged rods were better for the turbo... YMMV.

For the pistons, I'd be more concerned about matching the tolerance group to the block you're going to use. Also, I'd check for scratches on the sides of the pistons.

 

Thanks guys. All the pistons are group 1.

The cast rods are the originals from my 62k miles 1990 turbo so they must be strong enough for Porsche. Are the cast rods known to cause trouble? I'm asking out of curiosity as I'm leaning towards the forged rods myself.

 

Cast rods plenty strong enough for 250 bhp...

 

Has anyone even bent a stock rod without some sort of engine trauma going on?

 

I havent heard of any rod problems fordged or not

 

Me neither...Still, I might as well go with the cast rods if they check out fine.