NightmareTA

iTrader: (20)

Hey all. Recently cracked a few pistons in my turbo 5.3, so I went and picked up another short block to pull a few pistons out of. After seeing that some 5.3's came with normal smooth top dished pistons, and some came with the "cross" top dished pistons, it got me thinking....anybody know what the heck the difference is, or WHY they came with two types of pistons??

My original 2005 5.3 had the smooth top dished pistons, and the 2006 motor I just picked up has the cross on the tops. So now I am in the debacle of whether I should throw 2 cross top pistons into my motor with 6 normal pistons, or replace all pistons for the cross tops. Anybody got any input??

DAMN you GM for always having to change dumb things!!!

killernoodle

If you have some measuring tools, you could compare the thickness of the ring lands, the thickness of the crown, etc and figure out which one has more meat in the best areas?

I've got some 5.3 pistons in my garage, can't remember which kind, maybe I'll take some measurements.

lavoy

iTrader: (2)

older 5.3 had press fit pins and newer are floating and coated skirts. not sure if the cross has nay thing to do with this

NightmareTA

iTrader: (20)

I'd be really interested to know. I compared the two types I have side by side and the rings are all identical in terms of spacing, thickness, etc. Obviously not an exact measurement, but by eyeballing it, that's what it looks like. They are physically identical after looking them over except the top design. There's got to be a reason for it.

Yea, found that out a while back, but both my motors are the newer style with the floating wrist pins and LS2 style rods....only difference is that they have 2 different types of pistons.

a4ls2goat

Their the same thing.

Sarg

iTrader: (6)

Or you could just swap entire short blocks....might be easier than swapping all the pistons.

NightmareTA

iTrader: (20)

Not exactly the same. I'm sure they both give the same compression ratio so I'm not worried about mixing them, but the ones with the cross on the top have a rough finish, and the ones without the cross are smooth as glass.

Wish I could, but the block sat for a while so a bit of moisture got to the cylinder walls and surface rusted them in a few areas. Also pulled the rods/bearings out and they are in pretty shitty shape with some scars on them...I'm guessing again from sitting and moisture. Wouldn't feel safe using the new shortblock over my current one.

831jd

iTrader: (3)

So i have a 2003 5.3 with the cross on the pistons are.they the same? Or are they weaker

Forcefed86

iTrader: (4)

Put a stone ball hone jobber on the swapped cyls and run it!

The "cross" is a casting mark. Diffent factories used differnet molds/dies for casting pistons depending on the year. They are the same dimensions. I ran into the same issue with my motor. Tossed in 2 used "cross piston" assys ($25 shipped ) and am making 800+ flywheel in my 5.3. I'd try not to mix flaoting and pressed pin assys. But I've seen that done as well. Motor still ran and made great power. (bit of a weight diffeerence though, not good for high rpm)

Heres my $220 JY turd... 2003 pressed pin assys (the "weak ones") all around. 20lbs of boost thru an S400 75mm. The original pistons were not broken by me. Thats how the motor was when purchased.

NightmareTA

iTrader: (20)

Forcefed, my motor now has 3 cross style pistons in it and a new rod due to a recent wastegate line blowing off lol. Still runs like a top though, and it just gave a modded 600 a real tight run.

Just curious too, what do you run for fuel in your setup? pump + meth, race fuel, E85? I'm on straight 93 pump gas only and am around 540 rwhp with 11 PSI. I'd love to go more but I'm just not sure what the motors will take safely on only pump gas.

Forcefed86

iTrader: (4)

I run e85, it's cheap and everywhere in my town.

Tough to say what any motor will take. Alot depends on compression, timing, cam, and RPM.

I'm running the 317 heads with the dished pistons. (around 8.6:1). I think you could get away with close to 20psi on my setup with 93 octane and low timing. I plan to turn mine up to 28+. I'm sure it will let go but that will give me something do do this winter.

Denmah and those guys push 19-20lbs with alky injection (windshield washer fluid) and 91 octane on OEM compression 5.3's/4.8's. Usually run timing down in the 10-12* range though. I'd toss on a progressive ALKY kit and 2 10gph nozzles. Keep timing down low, and crank it up. They were pushing right around 680whp on several different JY motors. Usually bent rods when they tried to push beyond that. I think RPM plays a bigger role than most believe too. Keep it under 6k and it should live much longer. I cross the traps at around 5700 at 148.