1994 Miata MPG project B3 STEALTH MK II

If you’re like me, the first thing you do when you get a new (er) car is tweak it. Sometime just plugs and wires and sometimes a turbo is required. We have all been there and we all do it. This project is bassakwards because I removed the perfectly good 130 HP engine and swapped in a 63 HP engine.

I’m not trying to save the planet…. I am among the sinners.

For those who are not familiar with the story, I started with a 1994 Miata. I swapped out the 1.8 for a 1.3 engine from a Ford Festiva. The SOHC Festiva engine bolts fight up the Miata transmission and the Miata motor mounts bolt up to the Festiva block. I mixed and matched Miata parts and Festiva parts and this is almost a bolt together swap. Minor fabrication to tie up loose ends, but it isn’t like putting a 396 in a Vega.

The transmission was modified by swapping in a RX7 5th gear set. The swap will give you a .697 over drive. The taller 5th gear is a great mod to any street driven Miata. I modified the Miata wiring harness to mate with the Festivas sensors and used a 93 Festiva ECM.

The resulting car is an economy car with front engine rear drive, decent suspension, great brakes ….and fun to drive. It ain’t fast and if you want a fast car, then keep the 1.8 or put in a V8.

The B3 STEALTH name is derived from the fact the car is powered by a B3 engine and doesn’t look like a crappy econobox.

The engine produces 63 HP @ 5000 RPM and doesn’t sound happy when you run it that hard. However you get 75 lbs of torque in the exact RPM range you need it in. The car will grunt along in 5th gear and not complain. Push the car hard and it will give up at 4200 RPM.

Being punished with a neutered car should have some benefits? Right? Well the gas mileage worked out to be 34-37 MPG on the daily commute. Not as good as I though it would be. I did every trick I could think of and this is the best it could do.

So…..I installed an innovative motorsports LC-1 wideband and programed an offset signal to fool the Festiva ECM to run at 15.5 AFR. The LC-1 is pretty cool…. It is a wide band sensor that has programmable outputs. You can program the output for narrow band and then offset the signal to run rich or lean.

The leaner mixture bumped the MPG up to 40-42 MPG. Some minor pinging in hot weather. I put close to 15,000 miles on the car and then upgraded to a Megasquirt II. Adapting the Megasquirt to the Frankenstein electrical system was a snap. The car was back on the road in no time.

Tuning Megasquirt for maximum power on the least amount of fuel is an education in itself. This is my first attempt at tuning from the ground up and is well worth the effort. I spent two months tuning and along the way I have seen MPG numbers as high as 45 and as low as 34.

All the fun came to a halt on December 21st 2012. That is the day it snowed and they put salt on the roads.

The original build thread is http://forum.miata.net/vb/showthread.php?t=441727 The second page of the thread has a fully detailed step by step instruction on how to modify a Miata transmission for a taller 5th gear.

THE NEW BEGINNING

The car is built and has plenty of real world miles logged on it, however the project is not done. My goal is to get an average of 50+ MPG from the car.

The engine has already been modified with an Aspire roller cam, OBX adjustable timing sprocket, MegaSquirt II and a hybrid ignition system.

During the winter down time I pulled the cylinder head and addressed some minor issues.

I had the head shaved .020 for a slight bump in compression.

The intake ports were cleaned up slightly, nothing radical. The exhaust ports were polished and the cleanup was slightly more aggressive.

The correct two stage thermostat was fitted to get operating temperature to stabilize in colder weather.

The intake manifold was also cleaned up internally and was modified for vapor ports. The vapor ports are experimental and will be used to test various myths found on the internet.

Interesting. You could out a stock ALH 1.9 VW tdi motor in that car with an adapter and hit over 50 mpg. Heck, stock Golfs of that vintage that weigh more do it without a problem. Also 90 hp and 150 ft lbs of torque is plenty. Impressive work so car, keep at it!

interesting for sure. welcome aboard!

I like it. If we had a decent 4-seat platform for this, I'd be all over it.

I'm thinking it would be fun to go the other way in my 323 and put in a BP from an escort GT. (I believe the 323 has the single cam 1.6.)

As it is, I drive my '90 323 ~50 miles a day and it turns in 32 mpg reliably...driven as if stolen. (My drive includes a max 65 mph speed limit...so that helps.)

Clem

I hope to have the car back on the road in early to mid March. I guess it depends on the weather more than anything.

I still have to fabricate a new correctly sized exhaust and reassemble the whole mess. I'm also going to drop the car about an inch or so.

I wonder what you would have gotten with that 5th gear and the 1.6l. Or with that 5th, and the much lower final that makes crusing at 70mph 1000rpm lower...

Looking at that chamber design of the head used, I wonder how sensitive that engine is to indexing the spark plug & ground strap shrouding. I wonder how that chamber shape & sizing compares to other heads that are more fuel efficient.

What about tires and aero? Top up driving? If its top down, do you use a tonneau(sp?) cover for the cab?

Might be time for a turbocharger... (<- thats the evil mpgs emoticon)

Very interesting!

Just read the thread. Very interesting and wonderfully documented. Great fab skills, really liked the heater pipe build. Looks factory!

A while back, I looked into putting the DOHC head on one of those Fiesta motors. Unfortunately, it wouldn't fit. I was thinking of a small displacement turbo engine for efficiency. I think we've still got the engine around somewhere...

RossD wrote: What about tires and aero? Top up driving? If its top down, do you use a tonneau(sp?) cover for the cab? Might be time for a turbocharger... (<- thats the evil mpgs emoticon)

Additionally what weight are you at now, any weight savings to get you over the hump.

Also what tires are you running, I have seen boosts moving to a ecu tire more then a few times. With the power that you have sticky tires are not doing you much good.

Sweet build. I would like my r package miata to get better mpgs

Keith Tanner wrote: A while back, I looked into putting the DOHC head on one of those Fiesta motors. Unfortunately, it wouldn't fit. I was thinking of a small displacement turbo engine for efficiency. I think we've still got the engine around somewhere...

Again, the question of what makes 15-30 hp more efficienty at 3500rpm is a question to ask.

Smaller is always assumed to be better, but it's also matched with whole powertrain work to be correct. The Miata is originally geared to have a specific acceleration potential at various speeds without downshifting. So far, the only action is to change 5th gear.

If you changed the whole gearbox (IIRC, there's a gear set from a RX7 of that trans family that works nice) AND the final drive (again, from an RX7)- you can almost match the overall ratio between 1-3, and have 4 taller, and 5 a LOT taller. Like 25% less rpm for a speed taller.

At that point- 70 mph moves from 4k to 3k, and then ask- which engine would produce the power needed to move the car at that speed- the 2V 1300 or the 4V 1600? It's not an easy answer.

Good questions, Alfa. That's the right way to look at it, really. But when you've got a 1.3 sitting around the shop, the immediate question seems to be "hmm, would that head fit on it?" Answer: no. End of "investigation".

In reply to wearymicrobe:

The '94 Miata is at about stock weight. I made no attempt to shed any weight off this project.... yet.

The car is equipped with power steering and a fully functional air conditioning.

The power steering was kept so the air conditioning would still work. I have run the car with the power steering belt off for a few thousand miles and it appears the power steering has little or no effect on gas mileage.

No aero mods yet, although I am actively looking for a hard top.

Neat project. I had this same thought with the new Fiesta 1.0L if there is a crate version.

So...are you going to plop the Miata engine into the Festiva?

Ok, so its early March and the car is still sitting in the cold garage. One medium cup of Tim Horton’s coffee and a 5hr energy and I find my motivation.

I got a lot of oddball ideas and fixes in the works, but first I need to get the car running again. Last fall while I was experimenting with tuning the megasquirt I noticed slightly better MPG numbers with an elevated fuel pressure. So I got an ‘El Cheapo FPR on ebay for an experiment.

In order to make this Ebay FPR work I had to hack up the original FPR that is mounted on the fuel rail.

The hack was basically just cutting off diaphragm section and pulling the guts out of the Festiva FPR. I then machined a new cap on my Smitty lathe and had a local welder TIG weld the unit back together.

This is the original FPR, It was gutted and welded shut

I mounted the FPR on the firewall and plumbed it . Interestingly there is no documentation included with the El Cheapo regulator, nor is there any info on the web. The best guess is the fuel comes in from the side and exits the bottom.

As a bonus, the El Cheapo regulator came with “high pressure fuel hose”. Ummm …no thanks. I would rather not see the impending fire. I got some real high pressure hose and proper clamps locally. Six bucks a foot!

With the fuel pressure regulator mounted and the battery fully charged, I jumped the fuel pump relay and started the fuel circulating. With no vacuum at the port, I adjusted the regulator to 42 PSI. I then put some vacuum to the port and noted the regulator leaked vacuum like a sieve. I took the regulator apart and Teflon taped the vacuum port and put some Teflon tape around the adjustment screw. The adjustment screw has an O-ring to help seal the threads but it was ineffective by itself.

Ok, try again and this time the regulator holds vacuum and I get it adjusted for a baseline of 38 PSI with vacuum and 42 without. I shut off the fuel pump and notice the regulator also doesn’t have a check valve and the pressure drops to zero in about a second.

'El Cheapo FPR with vacuum leaks fixed

‘Ya know you get what you pay for, I don’t recommend these ‘El Cheapo regulators and I’ll probably go ahead and buy something better, but for now it will work.

almost ready to start!

Hope it starts up again soon! The project is an interesting exercise in parts swapping.

In reply to Nitroracer:

I have about 3-4 hours of assembly to go before I can turn the key.... so results will be coming soon. Once the car is running again I'll fabricate the new exhaust.

According to info I gleaned off the web, the current exhaust is to big. I need to decrease the pipe size by a quarter inch. Sounds counter productive but remember this engine is only 63 HP and the Miata exhaust was sized for 125 hp. Apparently the velocity produced by the smaller pipe will keep things in order.

Stay tuned!

I know of a cheaply priced hardtop that needs some work; if you are interested hit me up!

I pretty much finished the car last Sunday afternoon. I went into the house to check my email and cruise the web for a min to warm up a bit. Saw the box flare thread on GRM and 3 hours later I finished.

Kept say’n to myself……just one more page.

I think if I pack correctly and drink lots of coffee I can make it through the hot links thread in one weekend. I know for a fact that at least one of my cars is being made fun of.

Just a quick shout out to Chandler. Thanks for all the hardtop leads! Unfortunately I still haven’t gotten one. Timing and distance is not my friend. I think I’ll start trolling the Chicago CL when the weather gets a bit better. I hate driving to Chicago in the winter.

Michigan…. A water- winter wonderland…the water part is fine, but I’m about done with winter. Alas spring is legally here but winter has decided to stay. Time to get ‘er done… to hell with winter.

I was not looking forward to an extreme cold start on the fresh engine…. Especially with the megasquirt. Fortunately I engineered the electrical system to quickly revert back to the stock Festiva ECM. I think this was the best way to go.

Reassembly was somewhat tough for the reason that it has been months since disassembly. I have been poking away at this and that over the winter and eventually the final bolt was jammed back into the engine and the only thing left was to turn the key.

The bad news is the car didn’t start, the good news is I got the oil circulating and saw pressure register on the gauge. The no start was alarming because I was pretty sure I got everything right. The culprit turned out to be the fuel pump relay was disconnected a few weeks ago when I installed the pressure regulator.

This time when I turned the key, the engine jumped into life and settled down to a nice purr. The new lifters were ticking madly but the engine was rock steady. The Festiva ECU has a proven cold start algorithm that is hard to match with Megasquirt. I’m sure someday I’ll get the megasquirt to do cold starts, but for now I’ll give credit to the factory ECU.

After about an hour the lifters finally quieted down. For some reason this engine has a tough time pumping up the HLA’s. As I recall, this happened last year on the first start. I figured the new lifters would resolve this issue. Bargain ebay lifters for $39.00 plus shipping may have something to do with the longer than expected noise.

The B3 lives again! I installed the MAF and the Festiva ECM for the cold start. I'll switch back to Megasquirt when I establish some new baseline MPG numbers.

The next step is to fabricate the smaller diameter exhaust.

Hurr! Smaller pipes is better???... that is what the book says. I have two Yoshimura slip-on mufflers with slight road rash, but one should be enough?

I waited for it to rain and wash the salt from the roads. After about ten minutes I decided I had waited long enough. I jumped in the Miata and took her for a ride.

Spring is here and it’s time to hit the open roads in a sports car. Zoom Zoom Zoom and all that.

….Grrrrr… this ain’t a sports car.

Its times like this I hate what I have done to the poor girl. Even I’m a hater sometimes.

Anyway, it handles nice.

I put down about 40 miles in the first ride. The next day I finished up with 120 on the odometer. Feels good to be back in my little car again. My Saturn is a depressing car….. It’s lived a hard life.

The math works out to 37 MPG, Not too shabby when you consider I was driving it like a sports car. This is out of the box numbers with no tuning or fiddling with the AFR. I ran the car another 120 miles and got 32 MPG with more conservative driving.….

The car seemed happy to run 75 MPH on the freeway. I had to keep pulling back the throttle to keep from hitting 80. I seem to recall the car liking to run 65-70 ish las year. Could be psychological or I have actually improved performance. Either way , I’m happy.

With the long weekend, I figured I might find some time to get the exhaust sorted out. The current exhaust is a relatively new system and is remarkably quiet. I know from past experiences that I prefer quiet over loud. But right now I think this car need some attitude. I’m sure things will change.

My plan is to construct an exhaust system from the head to tail pipe. The newer exhaust will be 1.5 inch in diameter. Yes, 1.5 inches in diameter. This is one of those projects that may or may not be the right thing to do.

Fabricating exhaust systems suck. If given a choice I would rather spend a day with my x-wife and the madness that surrounds her. Since I lost her number , I decided to forge ahead on the exhaust.

I knocked out the basic system in a few hours, but things really slowed down with fabricating the hangers. I used all the stock Miata hanger locations to eliminate any rattles.

The Yoshimura slip on muffler was too long to fit under the car and still exit at the stock location. I did some surgery on the Yoshimura and wound up with a very nice stainless steel glass pack.

Weld, cut, curse, weld some more. Finally it was done!

This is the head pipe I fabricated last year, Its too big in diameter according to the book. The VHT paint has held up for 15,000 miles!

this is the new head pipe. 1.5 inch diameter!.... Seems like the wrong thing to do.

new exhaust with modified Yoshimura muffler

hangers were made from super long 3/8 bolts. I cut the hex head with the lathe to form a taper

tailpipe in stock location..... nothing to see here officer

sub frame thingy hits the muffler. I can fix this! [\b]