Okay so Iive got my 5.3 tore down to the short block, going for more cubes. I'm sending it off the the machine shop next week and I'm going to make an iron ls1 out of it. I had never tore into the motor since I've done the genIII swap and to my surprise when I pulled the heads it had flat tops, made me think it was actually a 4.8. So what I did was set the number two cyliner to bdc, took a piece of carboard and measured from the top of the piston to the top of the block. I measured 3 5/8th inches which is like 3.625. The bore for 4.8 is like 3.268 right? Its an iron block so I'm hopin that the guy I bought the motor off of just put flat tops in it. I just need some reassurance before I go any further with this motor, thanks in advance.

 

what year motor do you have? If 07+ genIV its possible to be a 5.3 as they had flat tops, if it has flatops its a 4.8

you can tell by looking at the pin to skirt of the piston as well
if someone swapped pistons you be able to see the marks from them swapping pistons as they are press fit pistons

 

Its an 02 motor, so even though I measured the stroke at 3.625 it could still be a 4.8? The thing has been all the way down to the bare block before I bought it which was why I was hoping that he just put some flat tops in it. I havent tore it down that far yet but when I do I'll look at that too. Could my measurement be that skewed? I measured it about 20 times and came up with the same thing every time, lol. Now that the heads are off is there a better way to measure the stroke then the way I did it? Thanks

 

https://ls1tech.com/forums/generatio...-how-tell.html

 

Yeah I read that thread, the block has been painted so I wouldn't see a painted mark next to either 5.3 or 4.8. It's saying that the stroke should measure 3.622, I measured 3.625 so it should be 5.3 right?

 

Yes...4.8 stroke is shorter than the 5.3

 

Yeah I know, the 4.8 stroke is supposed to be 3.268, whereas the 5.3 is supposed to be 3.622. I measured 3.625, so even though it has flat tops this is a 5.3 correct? Thanks you guys.

 

no stock genIII iron block 5.3 came with flat tops so unless pistons been changed now a 5.3 has a slight dish not very much of one

 

Yeah that's why I was kinda freaking out. I'm assuming they've been changed because i measured the stroke at 3.625. The pistons did have a bit of build up on them but I'm almost positive they're flat tops. I'll check again when I get home, thanks for your help.

 

Issue resolved, its deffinately a 5.3. The flat tops were put in prior to me buying it when it was tore down. Thanks!