This is a bit of a follow up to a thread I started a few weeks back regarding forged pistons and rods.
https://grassrootsmotorsports.com/forum/grm/learn-me-miata-pistons-and-rods-for-rebuild/188854/page1/#post3376000
I got into the block and did some measuring. All my pistons are worn beyond spec, all my cylinders are tapered, out of round, and out of spec. So I'm getting a .020 overbore and some forged internals. Long story short, I would like to know the current consensus on keeping the oil squirters with Wiseco forged pistons. It seems that at one point you couldn't keep the squirters due to the piston skirt making contact, which appears to have been addressed in the piston design. But many people also say that the cooling and lubrication provided by the squirters is unnecessary with a forged piston and the improved oil pressure from blocking them off is a plus. I've ordered up some regular Wisecos, not the super cool FM variety as my horsepower goals are modest.
I've read a dozen different threads on the subject, but many of them are quite old. At this point I'm leaning towards blocking them off.
Are you having issues with low oil pressure? If not, I'd clean the squirters, notch the piston skirts, and retain them. Any piston cooling is going to help raise that detonation threshold.
I'd keep them as well, my oil pressure thus far has been fantastic with turbo and squirters.
I'd also buy the strongest internals your budget can stand because boost is addictive and I already regret not building the bottom end of my Miata. (if 250 hp is good, surely 400 is better RIGHT?)
At one point only the FM Wisecos had the piston squirter clearances in the skirts, but it's been a while since I looked into it and maybe they fixed it in the normal ones too.
If you're going forced induction, I would (and did) keep the squirters.
What are you doing for rods?
+1 for keeping them, you can shim the oil pump relief valve spring to boost oil pressure.
In reply to codrus (Forum Supporter) :
I'm following the fairly standard recipe of Manley H-Beam rods, Wiseco pistons, ACL bearings, ACL studs, BE oil pump, sintered water pump, and I'm considering an oil baffle just cuz it's cheap and I'm in there.
Keep the squirters, I've never heard of low oil pressure as an issue on a turbo Miata unless the block was already vented to the atmosphere
The FM pistons don't allow for the squirters because the strutted design puts big chunks of structure in the way. Haven't had any reports of problems that I'm aware of.
Shimming the relief valve only increases peak oil pressure, it won't increase oil pressure when everything's hot.
Seems to me they did not put a lot of things on the NA that were superfluous, in the interest of cutting weight.
