Oversize Pistons - How big would you dare?
 

I am looking at some time in the future, building a 1.8. On my list of things to do is oversize pistons. I am looking at increasing the displacement as much as possible on the stock stroke so I was thinking 1.5mm oversize (84.5mm) JE pistons as you can buy them off the shelf. I see that you can buy up to a 2.5mm oversize piston from Supertech and am curious to know if anyone has taken a stock block out that far? I want to do this to a stock block ie. I don't want to sleeve it.

So how far has anyone taken out a stock block without troubles and does anyone know the limit?

Cheers,

Tim

http://www.mccullyracingmotors.com/i...s/Page1100.htm for reference

I remember seeing this recently, it was 1mm oversize on 23 pounds boost:
https://www.miataturbo.net/engine-performance-56/cracked-engine-block-d-58823/

:bowdown:

Wow, thanks for the useful responses. I think I might stick to 1mm after seeing that. Maybe 1.5. Sleeved block is a bit outside my budget.

I am sure I have seen a couple people on here running 1.5 over, can anyone own up to having gone 1.5 over? And has anyone else seen any issues like the one in that other linked thread?

Cheers,

Tim

Sleeves... how much is THAT going for? I'd legitimately be interested if/when I kill my block..

Click the link and read :facepalm: Anyhooters, add says price is not finalized, but it will be in a $3-4k range. Not bad really :dunno:

sonic test the cylinders

If you're serious, you sonic test.

I wouldn't bore a stock block 2.5mm over for forced induction use.

I'd assume that's for an assembled engine. Not just getting the block sleeved. If I'm wrong then it's a terrible price. Reading the description though it sounds like it includes rods and pistons, etc... assembled. The price isn't all that bad if you consider that it normally costs at least $1k to sleeve other motors where it's more commonly done in addition to the cost of the core and the other parts involved.

They refer to a "drop-in" short block for that price. I assume, yes, it is assembled. I'd like to see a list of part...

WOW! If they can deliver a $3500 2.0 sleeved built motor, that sounds like a helluva deal.

If they can deliver a built short block for 3500 I agree that it would be a pretty good deal. Unfortunately living on the other side of the world has it's drawbacks and I am sure freight would blow that right out of the water even if I could stretch my budget for the block.

Think I have to try and find someone here that can do sonic testing.

I sonic checked a 2001 block that was at 85.5mm, had less than .050 wall thickness in one spot and was under .070 on every cylinder. Thin spots were near the top of the bore right under the deck (worst possible place). I will say that the fronts of the cylinders were much thinner than the backs, which could have been bad machining, or equally likely to be core shift in the casting process.

Unless I sonic checked the block, I wouldn't go over 84mm.

^^^ This was my block. It's now taking up space in my garage, along with some supertech 85.5mm 11.5:1 pistons. I went with 84mm per Rennkafer and Savigntons suggestions.

One of my buddies has built several +2.5mm NA motors that have been pretty successful. He has the local marine machine shop that we use sonic check the blocks before punching them that big, but he's never had will thickness issues. I'm thinking your block had some serious core shift, Rennkafer. The bore centers are located based on the mains during manufacturing, not the other way around, so if the cylinder section of the block mold shifted rearward, they would just all be thin at the front.

As I said before, could have been core shift or could have been mismachined.

The block front walls were ~.060" and the rear walls were ~.220", if you had that perfectly centered you'd end up with ~.140" wall thickness which would be fine. That's why I'd suggest sticking with 84mm unless you have the block sonic checked and KNOW what you're dealing with. If we'd built Dstn2bdoa's block and boosted it, it would likely have failed in short order, an NA engine "might" have lived for a while depending on how you built it (ie what kind of cylinder pressures you're seeing).