I bought a 5.3 lm7 and I need to change out the pistons. Can I change to lm4 pistons? What change will they have for compression? Just looking for a little info from someone who knows better then me.

Thanks

 

Anyone have any input?

 

LM4 and LM7 are identical short of the fact the LM4 has an aluminum block. Same pistons from either or. So if you want your stock compression ratio back, use them.

Just get a set from either an LR4 ( 4.8 ) or the L33 (5.3) which are the same piston and flat top. With a 61 cc head you will be in the neighborhood of 10.5:1 with the flat top slugs.

 

As far as I know the other difference is lm7 has dished pistons and lm4 is flat.

 

Ok so l33 are the only ones that are flat top

 

Or the pistons out of any 4.8...... The pin height is identical between a 4.8 and a 5.3 as GM used a different rod in the 4.8 to accomodate the shorter stroke. The L33 was the first engine did from the factory as a 5.3 with the flat top 4.8 pistons. Now all the Gen IV 5.3's are flat tops, regardless of RPO code.

 

These are what I am looking at

 

Looks 4.8 or L33'ish to me. Doesn't have the raised lip along the edge of it like the normal dished LM7 pistons do.

 

so how can you tell if they are 4.8 or 5.3?

 

LM7 is dished, the LR4 is flat tops, the L33 is flat tops. The LM4 only had a aluminum block, not flat tops. If your looking to bump compression, I would pull the heads and just mill them rather then pull the rotating assembly apart. Just find some LR4 pistons for your 5.3, you will basically have a iron block L33.