Have 2 non running answers, need 1 running one - help me figure it out.

About a month ago I picked up a white 95 with what the PO said was a blown headgasket  at 190k miles. (He's a pretty good mechanic so I don't have any reason to doubt him)  The plan was to do an LS swap with my son. it already had FM vmaxx suspension.

Since I'm now hooked on facebook classifieds I had a search saved for miatas.  Low and behold a rough black 94 automatic with 170 k miles showed up with an OEM hardtop.   I picked it up for $350.  The engine was in the trunk.  The PO had started the rebuild.  He had it bored, and bought some cheap ebay pistons, and has all new bearings.  He left the stock rods in.  He said the next thing he was going to do was get new valves and valvesprings in it then put it back together.  

So now the plan has changed, I'm going to take one and get it back up and running, and eventually add boost via either a rotrex or FM turbo.  This will serve as a fun weekend car, plus occasional commuter, with lots of AX and a little track work.  I want it to be anvil like in its reliability.  

I'm trying to figure the best way to put this back together.  If I'm targeting a "safe" 240-250 hp on the turbo, a little more on the super, is there anything I should do with the head since it's already off?  I've seen them as cheap as $450 at oreilly's.  Would I be money ahead to just buy a new one?  or would I be better served rebuilding?  what parts and pieces should I throw at it right now to get it up and running before I megasquirt then boost it?

Get the 95 running first.  Then the 94 gets fully pulled apart and prepped for the LS swap.  

(I read this as you've ditched the LS swap idea and want to go forward with getting one running with the intent to add boost)


If you're keeping both Miatae then I would assemble everything "as is" in the '94.  Do a quick valve lap, and make sure the head is true (cannibalize any parts you might need from the '95 since I think that one is more likely to have a damaged head).  Do the absolute bare minimum to get it reliable and then drive it while you create a plan to add forced induction to the '95.


Then I would get a parts list together and order everything needed to do the '95 "the right way" all in one go. 

I'm admittedly NO Miata expert but at 240-250hp you're talking about 80% more output from the engine through forced induction and I just dont see that being "anvil like" on e-bay pistons, stock rods, assembled by who knows...  Plus the '95 already has good suspension and probably isn't automatic so I'm thinking it's a better jumping off point for your go fast machine.

(if you're only keeping one Miata, then I'm leaning '95 all the way.  Take the hardtop and whatever's good off the '94 and sell it to someone with a locost project.  Buy new pistons and rods if you're going to use the bottom end.  I wouldnt bother.  Just snag the head if the one on the '95 is damaged)

And now for the obligatory Greatful Dead quote:



 

I'm making 245whp on my Rotrex supercharged Miata. It has a rebuilt junkyard 2000 1.8L that's bored 0.010" over (more because of rust in the bores than performance) with Mazda Motorsports stock-style pistons. I did throw ARP head and main studs in it (not necessary, just seemed like a good idea), and set the ring gaps to the max spec to keep them from butting. The only real power mods are the Racing Beat header, Techno Toy test pipe and Good-Win RoadsterSport3 exhaust.

Track Dog says that their C30-84 kit will make 240whp on stock internals and no upgrades are necessary other than fuel pump and injectors. The Mazda BP engine isn't the most advanced or refined engines out there but they have a ton of beef. The block and crank is good to 500+hp. Rods are good to 300+hp (just watch the engine speeds). the pistons have oil squirters, which help keep them alive. My only regret is that I I did not upgrade the connecting rods while I was in there, as I have been warned to keep it under 7500rpm in boost by Gary at TDR. Granted, the stock BP-4W camshafts run out of breath at 7000rpm, but if I ever swap them out, I'll need to tear it down and upgrade the rods.

I commute to work in my car, go on roadtrips, made a bunch of dyno pulls and have autocrossed the hell out of it this year on some very long, very fast courses and I have not had an issue. It's tame on the street under light throttle, and an absolute rocket ship at wide open throttle. It's outpowered every turbo Miata I've personally come across by a good margin.

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NickD said:
The Mazda BP engine isn't the most advanced or refined engines out there but they have a ton of beef. The block and crank is good to 500+hp. Rods are good to 300+hp (just watch the engine speeds). the pistons have oil squirters, which help keep them alive.

Good god man! 

Whelp, today I learned: "there's overbuilt and then there's Miata"

Hungary Bill said:

NickD said:
The Mazda BP engine isn't the most advanced or refined engines out there but they have a ton of beef. The block and crank is good to 500+hp. Rods are good to 300+hp (just watch the engine speeds). the pistons have oil squirters, which help keep them alive.

Good god man! 

Whelp, today I learned: "there's overbuilt and then there's Miata"

BP Performance Specialties has a number of turbo Escort GTs with ~400whp on stock block, rods and cranks. They have a drag Festiva with 740whp on a stock crank and block. They have a couple dyno pulls of ~300hp stock internal 1.6Ls that have supposedly been up and running for several years and still have A/C and power steering.

Hungary Bill said:

NickD said:
The Mazda BP engine isn't the most advanced or refined engines out there but they have a ton of beef. The block and crank is good to 500+hp. Rods are good to 300+hp (just watch the engine speeds). the pistons have oil squirters, which help keep them alive.

Good god man! 

Whelp, today I learned: "there's overbuilt and then there's Miata"

Yeah, the whole BP series was based around the 323 GTX (80s AWD turbo car), so you know how old school engineering went.

"Hey Ron, how thick do ya think we need to make this part to survive?  .125"?  Okay, I'll just make it .25", then."

WonkoTheSane said:

Hungary Bill said:

NickD said:
The Mazda BP engine isn't the most advanced or refined engines out there but they have a ton of beef. The block and crank is good to 500+hp. Rods are good to 300+hp (just watch the engine speeds). the pistons have oil squirters, which help keep them alive.

Good god man! 

Whelp, today I learned: "there's overbuilt and then there's Miata"

Yeah, the whole BP series was based around the 323 GTX (80s AWD turbo car), so you know how old school engineering went.

"Hey Ron, how thick do ya think we need to make this part to survive?  .125"?  Okay, I'll just make it .25", then."

No kidding. Also, the block was designed for use in diesel purposes as well. So you can bore them 2.5mm (~0.090") over easily and just use a broached head gasket to make a 2.0L on bore alone. 

Look at the amount of material between the bores on my engine, and that's with a 0.010" overbore.

IIRC there is some discussion re the overbore - a lot of people seem to believe that most, but not all blocks can take a 2mm/0.080 overbore for non-boosted applications. 0.090 might be pushing it.

In reply to BoxheadTim :

Yeah, I was just using the 2.5mm overbore as an example of why the block is so strong. I would not recommend punching one all the way out and then boosting it. I did consider the 2.5mm overbore with the 2.5mm stroker crankshaft with ITBs and 11.5:1 compression and the goods, but realized that would be really pricey and make less than a supercharger kit