So I've got this spare engine...
 

Being not insane, I picked up a spare engine from a friend not long ago from his engine swap car. Here is what I know about the engine:

It is not original to his car

• It was installed by a Mazda Dealer as a replacement after they botched an oil change

It was built for a spec miata

• Apparently Mazda Dealer didn't have or couldn't get one so they bought one from a local SpecMiata builder here locally (Hartzel Automotive: Service and Repair - Spec Miata), installed it and then warrantied it.

Its a BP4W, but its a combination of things from various places

• NA part number on the oil pan, BP4W head, CA-Emissions dipstick, etc. Pulling the pan revealed BP6D oil pump, stock rods and stock pistons.

The documents that came with the car included the invoice from the Mazda Dealer purchasing the engine from Hartzel

• I know exactly when it was installed and how many miles are on it (still has less than 40-50k :fawk:)

It runs fabulously :greddy:

• I got a chance to drive and ride in the car before the engine was pulled. No leaks, no funny noises, far more power than my original BP4W, basically exactly what you want from a used engine.

My brain damage:

I originally bought it to build it, but this engine is literally "too good" to mess with so I'm going to leave it alone. If something was going to go wrong with this engine, it would have happened already. I've done HPDE events with the PO of the engine and it performed flawlessly. I will be boosting it with my puny 2560 but there are certain things I don't actually know:

94-00 or 01-05 head gasket?
compression ratio?
head or block decked changing compression?

I'm nervous running boost + CA91 with an unknown compression ratio. Its got so much more N/A power (lol) on the stock ECU than my shagged out 120k BP4W does that I can't chalk it up to better internal condition (valves sealing better, less cylinder wear, etc.)

I plan on running my M-Tuned coolant reroute on this "too good" engine, but not knowing what head gasket is on the engine sounds like a recipe for disaster. I could totally see the SpecMiata guys running the later head gasket that Mazda changed for "better" coolant flow, but this will screw me with the reroute.

The Questions:

Should I pull the head and install an OEM 94-00 MLS head gasket just to be sure?
If I post pics, can the compression ratio of the pistons be identified visually by one of you geniuses?
Are the SpecMiata guys aloud to screw with swapping stock pistons to change compression ratio?
Do they regularly do things like cut the block and head to the FSM "minimum" to get "a little more" out of these engine builds?
Am I Hustlering this to death? Should I just run it and not worry about it?

(While this engine is in the car, my OG sloppy 120k BP4W will be getting filled with forged goodness)

Educated and experienced opinions are welcome, thanks guys :party:

Sounds like a really really nice engine that you could sell for way more than a random core bp6d to rebuild.

94-00 gasket
9.5:1
if you're not sure, yes
yes

Should toss some rods in it ;)

Drop new engine into car NA. Build the block currently in your car. Swap in built engine and sell spec miata engine for moneys.

nvm missed the part where forged goodies were going in the engine currently in your car.

What's the problem with running it NA? You're currently NA right? And the new engine makes more power than your current one? Just antsy?

https://www.miataturbo.net/attachmen...ine=1399495744
But that's just like, your opinion, man.

I already have it, I'm keeping it, its the no-cost no-hassle option right now. In fact, it'll be in the car before the end of the month. I see no reason to buy a BP6D of Dubious Origin to rebuild when I already have a BP4W of known origin in my car that is a perfect candidate for a rebuild.

Plus there is a complete BP6D head in my garage so I don't need another one should I decide I need/want VeeVeeTees :party:

Agreed. Ordering gasket today.
Not so sure... if the bottom was built for a 01+ Spec car, wouldn't it be 10:1? It has a VVT pump in it after all. :dunno:
I'm not sure about a lot of things so not sure what this is in response to :rofl:
Agreed, assuming you mean I'm worrying too much.

Again, original engine is getting the big beef injection of hot forged goodness. You forget that I'm in California and we keep all our stock, unmolested parts out here. This includes engines. 18psi knows what's up.

No problem running NA, except I have all this turbo shit sitting here, forever mocking me. So yes, antsy :)

Run <10psi with NONEOFIT timing, or keep it NA. When do you expect the engine build to be complete? Worth it for an engine you may be able to sell to some SM schmuck for $3k (pulling that number out of my ass but maybe there's someone dumb enough to pay it since it was "built for SM")?

if you run no more than 10psi and keep timing at peak at like 10-14* I think it should survive, even on CA 91 garbage.

Although my green one had this same combo and would ping on a bad batch of fuel, even n/a.....so....uhhh....I dunno

I changed the order of the questions in the OP, just to confuse everyone in the future :rofl:

Former was the initial plan, starting to think the latter is a better idea all things considered.

I want it complete, installed and tuned before Miatas @ MRLS in September.

I honestly don't think its worth that much, plus I don't know what all is in it. I'm not sure the SM guys would be willing to buy a mystery motor that's possibly built outside the ruleset.

but now that I'm thinking about it a little more, I may be able to contact Hartzel and see if they have any documentation for this motor and find out exactly what's in it.

Though I don't expect much from Hartzel. I've contacted him in the past looking for service (timing belt/water pump service, valve train check and possible shim juggling) and he basically shoo'd me out the door. :jerkit:

Wanna tune it for me when I eventually get it running? :party:

If you track . . . a LOT . . . you go through engines. They're a consumable.

Have one in the car and one built and pickled on the stand ready to swap in. Taking a 2 month track hiatus because you don't have that spare ready to go sucks. I'm doing that now. Never again.

I've been "off track" for 14 months. I'm pretty sure everything I learned in the previous 2 years is gone. :cry:

Ok, so with the head gasket ordered I'm on track to make that happen. I'll probably start a new thread when I get pics of the pistons and I can go from there.

As for the boosts, jury is still out. I'm really jonesing to drive the Miata with 100+kpa again but that might have to wait until after I get my daily driver situation figured out. Actually, thats probably the smartest thing I can do right now.

Swap engines & drive it N/A > resolve DD situation > build motor > swap engines again > boost.

Is that kinda what I'm getting from this?

G I had the same experience the first time I checked out Hartzel, you pay a arm and a leg for service at this place... do you recall what he quoted you for the "timing belt/water pump service, valve train check"??

Actually, we never got to that point. I had just purchased the car but had no records about timing belt or shim adjustment so I was trying to find someone locally who had Miata specific experience, and someone mentioned him on NCR (minime maybe?) so I gave him a call. We spoke on the phone and once I said I wasn't packing SpecMiata or RACECAR money he got kinda dismissive and recommended I find a local independant to do it for me. I got the distinct feeling from him that he felt like I was wasting his time. :dunno:

I can understand telling you to find an independent for the TB/WP job, any Joe Schmoe can handle that. But for the valve shims? Good luck finding an independent who will want to tackle that mess. Most won't have the shim tools, so will want to pull the cams, then reinstall to check specs, then remove to change shims... all the while charging you $80+/hour. When someone with the right tools and a shim kit can check your specs, pop out the offending shims, and pop in the right spec shims in like, an hour.

In the Taurus SHO community, we had a shim kit that you could rent from one of the (few) parts suppliers that included the tools. You paid for the new shims you took, put in your old shims (one side is still good) for others to use, and returned the tools for like, a $40 charge, IIRC.

Exactly! At this point I can (probably) handle it myself with a set of feelers and pulling the cams, but I was completely happy to pay someone who knew what the hell they were doing. Too bad Rosenthal does not list the shims anymore

Rosenthal still lists shims. Bought a couple last month. ??

Do a search on "shim." They should popup.

Sanp! The last time I checked they were not listed? That'll come in handy later.

You got a second engine? Dual engine Miata.