aero_ub

Hi all,

I have a new set up 4.065" LSA/LS9 specific pistons. I was a little unsure of what clearances would be best for my situation. So, I called Diamond to discuss and was pretty annoyed by the useless response. To keep it short, I would like to get opinions on some others here, along with an interpretation of their own recommendations.

New Aluminum LSA Block
Street car mostly, maybe a strip once in a while.
Plan to run it < 7000rpm (likely 6500-6600 shifts)
~16lbs of boost with my setup.
I don't have a problem taking it easy on the car until it's up to temp.

Below is the piston spec card with Diamonds own recommendations below it.





As you can see from the spec card, the base piston to wall clearance is 0.004". Then, that number is adjusted to your specific use as you can see from the note at the *. So, I look below that and the suggestion for street and strip boosted is to add '1 to 3' thousandths extra clearance! I thought this was crazy, up to 0.007" clearance?

Then, I noticed what I have underlined towards the bottom and the suggestion is '1 to 3 thousandths LESS' for an aluminum block. I assume this applies to my aluminum LSA with the cast iron sleeves.

So, my assumption is that these two underlined recommendations pretty much cancel each other out and maybe I would go a touch extra. I'm thinking 0.0045" piston to wall clearance for these pistons in my situation.

I would love feedback from others with more experience with this situation though! Thanks!

KCS

iTrader: (20)

It doesn't look like you're going to have much of a choice. Pistons are usually machined with the minimum clearance for the intended bore, meaning that these pistons are probably about 4.061" already. When you put the block in the hone, the machinist probably won't be able to hone just .0005" out and clean up 100% of the cylinder. They definitely won't be able to if the machinist uses a torque plate.

aero_ub

KCS, thank you for responding. I've read a lot here over the years (not so much posting!) and always appreciate your input, even if it's not direct towards me!

I didn't go through and methodically measure all pistons but I did pull out one or two of them and I was measuring at least 4.0625" and close to 4.0630" at the widest spot I could get to.

Measuring the bores on my new block (with the ARP main studs in but no torque plate) with the dial bore gauge set to 4.0650", I'm getting the vast majority of readings a 1/4 to 1/2 thou under with several readings right as 0. Only two out of 32 readings above and only a 1/4 thou over at that.

So, I believe I have a solid 0.002" (at least before torque plating!) to work with if I were shooting for 0.0045". With that said and assuming that's the case, where would you think you'd ideally put these at, clearance wise?



Thanks again!
Ken

KCS

iTrader: (20)

Thanks for the kind words. I haven't really used Diamond pistons very often, mostly Wiseco, so I'd probably want to err a little loose. I think .0045" would work well, but if you use the oil squirters in the LSA block, you should be able to get away with a little tighter. With the squirters, I'd be comfortable with .0035-.004".


Good Luck,
Kent

aero_ub

Thanks KCS.

I do plan to use the oil squirters, these diamond pistons are made specifically for the LSA/LS9 so that they can be used and not have to worry about notching out for them like some others.

I definitely feel better about it then. I'll talk to my machinist and tell him 0.0040-0.0045" then, assuming he can keep them to that once the torque plate is on.