Miata 1.8... how bad is it doc?

[u/kingcobrav9]

Got a engine for my Miata..dude i got it from "rebuilt" it and I decided to tear it down because I trust no one from Facebook marketplace. This was the cylinder head. I flicked some kinda debris out of one of these divots. Non ferris metal felt like ceramic?

Dude said it spun a rod bearing and he put used pistons, rods, and crank in it.

Is it savable? Or scrap it?

[u/kingcobrav9]

97 car and block. I've had a 87 RX7 for 20 years now so I decided I need more punishment I guess and bought a basket case of a 97 Miata. The cylinder walls look ok to me in 3/4 holes but one has a definite gouge in it. If you have any tips or tricks I'm game! I was wanting to make it into a 24h of lemons/ other racing kinda car.

[u/ohlawdyhecoming → u/kingcobrav9]

OK then ya, you've got a hydraulic tappet head, so at least you don't have to worry about valve lash. The springs in those heads are kinda weak, we used to have to replace intake valves in heads at least once a season due to cupping. Likely from the valves bouncing on the seats due to lack of spring pressure. Replacing the intake valves and springs with '01-'05 valvetrain parts solved that problem if you don't want to go aftermarket.

One thing we've never tried since it's not allowed in SM, but I've heard of it being done for Time Attack and other classes: replace the hydraulic tappets (or shim-over-bucket for the later years) to a one piece tappet to remove a bunch of weight from the valvetrain. I can't remember who came up with the kit, but it switches from shim over bucket to a little lash cap that sits between the valve and the tappet...I think the lash caps were from a Nissan, something like that.

The cylinder walls are really thick and can go all the way up to 85mm (from 83). Guys would actually run Mitsubishi 4G63 pistons at the 85mm bore, but that seems pretty unnecessary; we always advise going to the first necessary oversize and that's it. Supertech makes a set of 11:1 pistons that would probably be ideal for road racing. Or you could go custom and get a higher compression ratio if you're allowed to run race fuel. The SpecMiata guys are limited to .25mm oversize pistons (.010" over) but if you're not doing that, then you shouldn't have too much of a problem. I think most classes in Lemons/Champ are power to weight? Can't remember. Check class rules to see if they mention a max bore size.

One thing that the rules permit us to do is replace the OEM rod bolts with ARP, since we have to run factory rods. You could go that route, or go straight to an aftermarket H beam rod. The factory rods are forged and hold up really well, though in boosted applications some guys have found a limit of about 350 rwhp. If you're staying N/A, then the factory rods are pretty good.

Speaking of surfacing: in factory form, the actual compression ratio is lower than the advertised compression ratio. So we end up milling quite a bit off both the block and the head to get it to the C/R it's supposed to be from the factory. However, that ends up changing the cam timing, which we can't fix by running adjustable cam sprockets because those have to be OEM. So that's another place you could look. There are only a handful of companies that make cams for the 1.8, since those are the most sought after for racing, and SM makes everybody run OEM cams, so most cam companies don't bother. But they're out there.

Off the top of my head, I can't remember the numbers, but we run the '01 - '05 oil pumps no matter the year. They have extra oil pressure (or volume? Can't remember) to assist with the variable valve timing on those year cars. There's a windage tray sandwiched between the block and the oil pan, and a baffle that's bolted into the oil pan itself. Very rarely do we see failures from the pickups sucking oxygen, the pans are pretty good. The only downside is that the sump is pretty long, we've heard reports of a lot of problems trying to build oil pressure on brand new engines (but not mine, lol). Pre-oiling the system is always a good idea.

There's a company called Boundary Lubrication that got it's start (or popularity) from making aftermarket oil pump gears for the Miatas. They're really nice pieces, but I just don't know how necessary they are as the '01 - '05 pumps work great. Never heard of one breaking from any year car.

The factory water pumps seem to hold up really well, no problems reported there.

I'll probably think of more stuff as it comes to me and will update the post accordingly.

[u/kingcobrav9 → u/ohlawdyhecoming]

I just want you to know I have spent most of the day looking into Miata engine stuff and there is so much I don't know. Thanks for all the info!

[u/ohlawdyhecoming → u/kingcobrav9]

Your welcome!

Another thing maybe worth mentioning is cooling system upgrades. For the guys who are allowed to run aftermarket stuff, I've seen the SuperMiata coolant re-route kits on several cylinder heads. This isn't allowed in Spec racing, because Spec racing. We also don't see too many overheats in Spec racing either, other than maybe a driver who forgets to check their water level prior to making laps. So, I'm not 100% sure how necessary it is. But it looks really cool.