chrisfrost

iTrader: (8)

Hello all , I've got a set of Speed-Pro pistons for My 5.3L that are flat tops .030" over and I went to mock up the crank and 1 piston to measure how much out of the hole it was and it's like right at 0 flush with the deck and this after I took off roughly .010" from the decks ? Anybody else running into this ,,,,,I guess I'll have to use LS1 .041" head gaskets if I want a decent quench .

3rdCoastPowerSports

iTrader: (5)

why did you take .010" off the deck? are the pistons the correct part for your rods and crank?

chrisfrost

iTrader: (8)

They are SLP-H855cp for the 4.8L flat tops ,,,,,,,same compression height as the 5.3L I took material off the deck to clean up the small coolant pits ,,,,,,,,,iron block and My gaskets were .061" or pretty close and the original pistons were out of the hole between .015 - .020" so to end up with .030-.040" quench provided the new pistons had the same compression distance as the factory pistons which apparently is the problem .

malibutwins

iTrader: (1)

I read in a machine shop magazine that they change compression height on oversized pistons to maintain the stock compression. I cant remember what magazine though. So maybe thats what going on?

kossuth

iTrader: (12)

I know I'm dragging this up from the dead, but I'm facing a similar problem finding pistons for a budget 5.3 I'm building right now and I wanted to make sure those of us that build these motors understand what is going on in the aftermarket.

First off the "Help Desk expert" guy for Summit Racing was worthless and didn't seem to care about my concern. Basically his comment was slap it together. Anyways, the 4.8's and the 5.3's if you use the factory crank with factory rods and taking into account the block deck is the factory 9.240" in order for the pistons to be at a theoretical 0 on the block deck you would need a compression height of 1.331" on the piston. That piston you ordered for that motor actually only has a compression height of 1.324" http://www.summitracing.com/parts/SLP-H855CP/ So if everything was right at the factory spec for deck height, rod length, and stroke the piston would be about .007" below the deck. This accounts for why after decking it was flush. Obviously the LS motors are supposed to be out of the hole some.

You should have gotten a piston somewhere around the 1.337-1.340 range if you hadn't decked the block. Or in this case it should have been in the 1.327-1.330 range being you decked it.

I'm looking for the "correct" pistons and I'm having a heck of a time because it seems all the budget piston folks want to neuter the compression on the motor.

chrisfrost

iTrader: (8)

Yes I was just looking at Summit some more and the speed-pro's for standard bore 4.8/5.3L have a pin height of 1.325" and the ones I bought are 1.324" . So at least as far as the Speed-pro's are concerned the keeping the compression stock story does'nt work too well . I kinda doubt You will be able to find pistons that have much longer pin height than pretty close to stock without ordering some custom slugs . Part of the reason I bought the ones I did is because They were under $180 for the set . So once again proven is I'm getting what I paid for ..........Lol Have You seen the Redline pistons for LS based gen3/4 ,,,,,,They look pretty good quality wise and design and They are $220. for a set for 5.3L .