DD Built-Engine Longevity - Advice on Pistons and Other Bits
 

Long story short, I bought an MSM with a built engine and shortly after I took possession of the car it dropped a valve, destroyed the head, a piston and one of the cylinder walls. Since that block is already at 84mm and piston choices are slim in 84.5mm, I'll probably be salvaging what's left inside that block (Carillo H-Beams and ARP studs) and having machine work done to a 190k 99 core that I've got laying around.

Could I use the crankshaft from the built block in the 99 block if it was in better condition? I.E how interchangeable are cranks and blocks? Obviously it'd have to be mic'd and plasti-gauged, but just out of curiosity. The 99 thrust bearing issue concerned the crank tolerances or block tolerances?

I'd like some feedback as to what sort of lifespan I can expect from a built engine using new 9:1 cast pistons, 2618 pistons, and 4032 (Supertech) pistons. I'm running an FM2 kit, and I plan to beat on the car quite regularly in DD use and during trips to the mountains of western NC. I want it to hold up to abuse, but also last a LONG time. Not too much to ask, right?

I'd like to have the extra headroom and safety of Supertech pistons over cast pistons, but not if they're a large detriment to longevity. 2618 are overkill for what I need, but I figured I'd throw them in the discussion anyway.

Assuming 250-275whp
Cast - 150k miles ?
2618 - 50k-75k ?
Supertech - 100k-125k ?

I have an ATI crank damper already, stock oil pump or go BE street/strip?
-Sidenote to that, will a BE pump last as long as an OEM pump?

What bearings would be recommended for longevity and abuse? Clevite, OEM Mazda?

There's three Spec Miata shops in my state, Race Engineering, Ti-Speed, and Rossini. There's also 42 Autosports, which does a little bit of everything. I'm somewhat concerned that a Spec Miata shop might be out of their element on an F/I build. Is this a valid concern?

Can anyone recommend any of those shops for machine work and/or possibly assembling the short-block?

Since when are piston choices slim in 84.5mm? I just got a set of wisecos for about 450 in that size.

It should last forever unless one of a million things goes wrong. My pauter/wiseco build lasted over 10 years of abuse and finally died from an oil squirter falling out and destroying a piston skirt which is one of those random things that "never happens" until it does. Plenty of people here have lost motors from other causes. Over enough time, shit just happens.

Also, assuming 250-270whp, I wouldn't expect cast pistons to last at all and if something goes wrong, you can have a rod go through the block. When my wiseco piston lost a skirt, the entire remainder of the piston (including even the rings) was still there holding the rod in place.

There's nothing special in terms of building a block for FI that I'm aware of, at least not at that power level. Just stick with low compression pistons.

You should be able to get any piston available in any size, except for some of the proprietary FM stuff. My tuner said my engine would last forever if nothing goes wrong and I run Wiseco pistons. FM builds their engines almost exclusively with the softer FM pistons. Most of your wear will be on cold starts, which is why they have the skirt coating. You can send any pistons to Swaintech and get the skirts/tops coated. It's hard to say how much you'll get out of it not knowing exactly how you drive, what the clearances will be, the oil you'll be using, among a million other factors.

Supertechs allow tighter tolerances and theoretically improved wear
Wisecos allow looser tolerances so theoretically more wear

However, theories don't always translate to real life. My expectations of my engine were 50,000 miles. Seeing Always Broken's 10 year build makes me hopeful for more than that.

My real life experience. Supertech > Wiseco

Though this motor has only about 4000 miles on it, it's lasted far longer and has made more power than my previous before pistons bits met with turbo bits and blew it out. The machinist was a bit weary about the p2w tolerances I asked him to use, but it's worked out so far.

That being said, ymmv and there are enough people that subscribe to both camps that have had great results. If you are keeping it moderate like it seems, just choose whichever one is on sale, and go nuts. At that point it'd seem like reliability falls on the machinist and tuner.

When I looked into it, 84.5mm pistons were available, but cost enough more than 84mm supertechs that it was cheaper to just machine a new block.

Where are these $450 Wisecos? I assume they're not the ones with all the FM fixes in them?

--Ian

Honestly, unless you are pushing the car super hard for long periods of time or doing ragged edge tuning, you should be fine so long as you keep up with regular maintenance and there aren't random catastrophes.

One thing that doesn't get mentioned a lot is that you need some sort of noticeable alert system for high coolant temp, high oil temp and low oil pressure. Either something that puts your car into some sort of blatant limping mode so you notice immediately and pull over or something that sets off a deafening alarm. Your engine will not snap a water pump belt or burst a coolant hose or lose oil pressure when you are expecting it. It will happen when you're puttering along at 45 mph, with nothing having gone wrong in months. Your mind will be on work or that thing your wife asked you to get at the store or you'll be thinking about a funny meme you saw. Then suddenly you'll notice that your oil temperature is at 300F because you haven't had any coolant for the past 5 minutes.

The wisecos were 84.5mm 8.5-8.8:1 units. Basically just a .5mm oversize version of what I ran for 10+ years. No FM ceramic coating on them but my car was fine without the coating so I'm not inclined to spend 2x as much money for no benefit.

For the record, 6,000+ miles on my Wiseco build with loose 4 thousandths p2w. Blackstone results are very good and show no abnormal wear. Has a few solid hours of tuning and hooning, with a bunch of regular driven miles. Making 330whp and using minimal oil as well. Bearing clearance .020 on rods and mains

Assume you mean 0.002" on rods and mains?

Sorry I always mix that up. Point being the engine overall is built looser than factory and has done fine. I think all things equal, if you were just using a stock non turbo miata for a daily, and then one with a well built engine (with any of those pistons) for the same daily, and performed the same maintenance on both, they would both run for a very very long time. It's when you add the heat of turbos and extra pressure that things break because of a number of perhaps outside factors. I'm not sure how someone can really say which piston lasts longer than which because no two engines are the same, and I'm pretty sure nobody has tested them all on an even playing field with the proper controls in place to really know. People can speak from experience to which takes detonation better perhaps, things like that, but I've never seen results from any kind of real comparison for the sake of longevity.

My impression was that there were a bunch of improvements in the FM wisecos, not just a ceramic coating. I dunno details though.

--Ian

Use.

Stock.

Pistons.


That is all. They are way stronger than 99.5% of people need and work awesome.

Agreed. When I built my motor in 2006 I had reliability concerns as well. I went with stock oversize Mazda pistons, and had them ceramic coated and cryo treated for piece of mind. It is N/A, but far from stock otherwise. I've since put about 30k miles on it and it still runs great. You don't hear too often of built motors lasting that long, but in my opinion, unless you have some other requirement, keep stock pistons and careful tune if the goal is <300 horsepower. Any more than that, or plans for extensive track driving, then go forged pistons. Forged rods though, are a no brainer for any build these days.