hi,

I am tearing down my '90 5.8l motor. I am putting together my shopping list but am stuck with the pistons.

The stock pistons have the oval shaped dish that is .110 deep. Looking at Summit & Jegs the only ones like this are the expensive forged type. All the hyper or cast either are .140 or .190 deep.

I t is a sd efi motor am I not doing a radical rebuild so What do I do?

cheers

 

Get the hypher tech pistons. They are a flat top piston with the 4 valve relief. If your not building a race motor then I'd leave the forged pistons alone.

 

Nominal CR on a stock '90 5.8 was only about 8.8:1 which means the motor will run without detonation on the cheapest crap gas you can find, so you have some room to bump it up a little without risking the need for higher octane. My 5.8 has those flattops with 4 valve reliefs and it ran great.

 

The cast replacement pistons usually have a slightly deeper dish to keep the compression ratio at or near the same with an oversize piston. The .14 dish will be fine.