Jayclay
Jayclay None
9/30/19 9:02 a.m.

 I am looking for some input for the best bang for the buck with my 1990 Miata, I come from the FWD turbo camp so I am not sure what the best route would be.  

 

The car is a 1990 N/A Miata 1.6L stick car with 220K miles and a worn out engine (low compression cylinder #1) that still drives ok, the brake and suspension are well sorted and need no real work. The car is only driven in nice weather (parked inside most of the time) and is not my DD and used for Auto-X and track days, and the car has almost zero rust.

 

So with the car needing an engine/ overhaul I got to thinking, more power? Don't mind if I do. But how?

 

A few weeks ago my co-worker crunched his 1999 NB (1.8 stick) with about 200K miles on the factory engine, unopened. The powertrain survived without any issues. I picked (drove it onto the trailer) the car up cheap as he knew about my issue and decided to give me first crack at it.

 

So, now the question is how best to proceed?  I have a few ideals that I would like some input on.

 

A few things before we get to far, no forced induction, no emission, I can get race fuel at the local Sunoco station, I am fine with spending money on this project, maybe 200 HP, I have lots of skills, tools and work space. Last thing is I would like a driving car by Spring of next year so this could be done in steps.

 

A) Drop (reseal) the 1.8L in and use the factory ECU.

  Cheap and the fastest.

 

B) Re-build the engine using factory spec parts.

More time and money but should be easy.

 

C) Re-build and raise compression.

This would cost more.

 

 

This is the part where I am not sure about.

 

 

D) Stand alone ECU? How much real power by brand or do they all have the same limits? I  am sure I would need this for the high compression option.

 

E) Individual throttle bodies, they sound great (pipe dream). How much real power?

 

F) Ported head, now or later? I was thinking after the bottom end is sorted, maybe next season.

 

Since this is just a working ideal I am interested in hearing from the hive on this project.

 

Thanks Clay

Keith Tanner
Keith Tanner MegaDork
9/30/19 9:59 a.m.

If it's in good shape, do a complete rollerskate swap. You'll get a better diff, bigger brakes and a better rack and it's easier than pulling the engine if you have a lift. I've done it in an evening with the help of friends. Then drive the car and evaluate.

200 whp naturally aspirated just isn't going to happen. You'd be far better off accepting your lord boost right from the start. 150-ish wheel hp, sure. I've had a Miata making about 180 rwhp naturally aspirated but there was at least $15k in that engine not counting time. Maybe more. Alternately, drop in a Honda K series. The Miata engine is a strong little bugger but it's not good at making naturally aspirated power. The head just chokes off.

If you really want to do a naturally aspirated 1.8 Miata engine, get the VVT head. It'll fill in a bunch of torque although it won't change your peak.

d) As long as you're not scrabbling around in the cheap end of the spectrum, the quality of the tune is going to be more important than anything else. And max power is the easy one. How do they deal with cold start, hot restart, AC compensation - that's all the stuff that's a lot harder to do and most DIY tuners will skip.

e) they can make more power. They'll also make a bunch more noise and will make idle a lot harder unless you do the plumbing. A set of ITBs on a high compression engine have a hammering sound that will impress your friends and sound racy and make the car painful to drive as a normal car.
Dyno chart

f) port the head when you have the engine apart, because there's no point in pulling the engine apart and not doing the valves on a 200k engine.

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