1st Miata Motor Build/Rebuild
 

Hey all, I am new to this forum but I an an mercedes automotive technician, I tinker with my miata and my motorcycle in my free time. Looking for some more info while I’m getting my new built/rebuilt motor freshly machined. I’m curious what the limitations of the stock ECU are on the 99-00 NB1s. Not concerned with CARB compliance. I want to know what my limitations are for bore/stroke and compression since I am cleaning up the head and block (head had 0.007” taken off and block 0.005” to make both flat). Know between those measurements not worried at all about interference fit, and my ring gaps are gonna be larger for boost so my CR should only sit slightly higher and within stock ECU limitations, but how far can I go if I have this head cleaned up again before the ECU won’t be able to keep up? Will be going with a standalone eventually and have it professionally dyno tuned but right now just doing a stock bottom end rebuild with a fully built head with manley stainless valves and bronze guides. Just want to know how much more I can take off safely if I wanted to get the head decked again when I throw a forged bottom end in my other block and swap it in. Want to be able to run my fully built motor thru the break in period on my stock ecu with no turbo so I can make sure everything is good before I start tossing high horsepower numbers at it later. Gonna be running manley H beams and flyin miata wiseco pistons in the bottom end being built.

Important note, this is a turbo car in progress already have a boundary pump and pretty much all the support systems already there. I am overbuilding the entire drivetrain for way more power than I will be pushing so I can safely run a lower level of power and drive it on the street since this is my daily.

Check out the Spec Miata rules on the SCCA website as to engine modifications. Those all work with the factory ECU. Some head work, like de-shrouding the valves, decking the head and block, over boring to 20 thou on the cylinders and pistons, but no stroker work.
Also, look at the rules for the SuperMiata series, and advice on how to maximize horsepower for that series here on this site. That again uses a stock ECU.
Install an after market wideband O2 sensor and monitor what the ECU is managing to accomplish, rather than depending solely on the wisdom of the internet.

But I suggest you change the strategy a bit, if you are planning to do any of the tuning yourself with the aftermarket ECU.
Put the aftermarket ECU in now, before you do very much upgrading, and learn how to use it on the stockish engine. Get it running right.
Then when you do more engine upgrades you will know your ECU is starting from the right place in terms of most settings, and probably just needs VE table adjustments and maybe some timing adjustments.
Then add the turbo and do it all over again.

If you do the engine upgrades first, swap in the turbo and then change ECU you will be faced with a far steeper learning curve. Although, given you are an auto technician, perhaps the curve will be far less steep than it was for me.

Preciate the info! Definitely will look into those sources, reason as I was saying before is because I want to get my built motor through the break in period first before I try adjusting the tune at all or slap any turbo on it so I can be absolutely sure all the machine work and motor prep is good. I am trying to preserve as much of the stock motor configuration as possible even if I sacrifice power for it. Minimal boring and no head porting and no oversized valves. I want as much of the metal to stay as I can so I have the extra added strength for higher boost numbers over a long period of time, hence why I'm shooting for a motor/drivetrain capable of 500 hp, so I can have a ultra reliable 350 whp street car. Tuning is not my expertise and while I could learn and teach myself, it would arrogant and naive to say that my tuning or any shadetree mechanic's street tuning would be as good or reliable as a dedicated tuning shop's dyno tune, especially on the street with A/C and creature comforts and differing weather conditions.

If you want an engine that runs like stock on an aftermarket ecu you better put in the time to learn to do it yourself. I don't know how any dyno shop could spend half a day with a car and get it to handle things like sub-zero e85 cold starts, reliable idling with a/c, over temp conditions, over or under voltage conditions.

The people with cars that can do those things have dozens of hours in to it.