piston installation

[blckdrgn1987]

I am embarrased to even ask this but here goes.

The last time I had my heads of I noticed the my "reputable" engine builder installed my pistons backwards i.e. the arrow w/ FRONT engraved on the top of the piston is pointing towards the rear of the motor. I have talked to a couple of guys in that are into chevys and they have said that some builders put pistons in backwards for more hosrepower. I do not know if this is true because I am not a builder. My gut says that it is wrong but I don't know if it is something to freak out about.

Thanks for the input

Geoff

 

[cchilly]

I've assembled a lot of motors but none that use pistons that have Front marked on them.

That being said, why would you want to install a piston backwards. The pistons have valve relief pockets machined in them and putting them in backwards would mean the reliefs would not line up with the valve. I think this could possibly lead to the valve hitting the piston if you have a big enough cam.
Most of the engines I work on are pro mod engines and if I put the pistons in backwards you are going to have a very unhappy customer.

Chris

 

[Big Turbo Scott]

The stock pistons have a dimple or "hole" in the piston crown designating the piston is installed correctly. This is because the pin bore is offset to reduce side loads and cold start piston "slap". I mean offset (.030-.040) of the pin bore in relation to the centerline of the piston. Now, im not 100% sure of this in aftermarket pistons. If its a cast piston, Id bet that it too has offset pin bores. A forged piece will almost always square the crown over the pin. My best educated guess is that your engine assembler did this ( if it was intentional) to get the rod closer to vertical when the crank is at 90^. Pros: None im aware of but i can see the argument. Cons: Increased cylinder wall wear because of heavier side loading. Remember that when the crank is rotating, it is trying to push the rod through the side of the piston. In doing so it loads the outer cylinder walls. The greater the degree of rod to piston angle the harder the piston will be loaded. Ah, the benefits of longer rods now come clear...HTH.