19

Project Miatabusa hayabusa engine in a miata wiring

Next up in our pile of partially finished projects is making the Hayabusa's engine harness fit properly in the Miata. The Hayabusa is fuel injected (not always an obvious thing on a bike) and runs a pretty sophisticated speed-density engine management system. Each cylinder is mapped individually to account for the fact that the Hayabusa's cylinders all breathe differently. the center two cylinders have slightly longer intake runners than the outer two, and the 4-2-1 header is actually paired incorrectly, or at least unconventionally. None of this is accidental, of course. Both of these strategies reduce the power peak, but spread the powerband over a wider rpm band, all in an effort to make a 173-hp crotch rocket a little more manageable.

 The service manual shows rough images of each cylinder's fuel map, which gives you a decent idea of how different each cylinders fuelling is.

Miatabusa hayabusa miata fuel maps

 

None of this is relevant at this point, though. All we're trying to do at the moment is get the whole Hayabusa engine management system stuffed into the Miata and working properly. The Hayabusa harness has all kinds of bike-specific traps we're not used to, like kick-stand switches, I-fell-off-my-bike-and-I-can't-get-up switches and nonsense like that.

Rather than figure all this stuff out for ourselves, we shipped the harness off to Peter D. Motorsports, a Dwarf Car shop that deals with bike-powered cars all day long. Peter D. has a harness trimming service that makes the harness car ready for $150. That seemed like a great time saver, and in the end we still think it will be, but naturally, we overlooked some details on this first try.

The physical layout of the Miata engine bay doesn't really agree with the shape of the Hayabsa's harness. Plugging everything in leaves a messy spider's web of wires all over our work of art. That just won't do...

So, the unfinished project this time around is re-re-trimming the harness to follow a Miata-friendly layout. And the first step there is figuring out what a Miata-friendly layout looks like. Where should we mount the ECU, for example? The stock Miata ECU moved around from year to year, sometimes residing under the dash, sometimes under the passenger's floorboard, and sometimes behind the passenger's seat. The Hayabusa's ECU mounted under the seat, sitting in a little ECU-shaped plastic home and secured with a rubber strap. The Hayabusa ECU is at least a generation newer than the Miata's, meaning its smaller, lighter, and much more weatherproof. The connectors are water-tight, and as you can see in the picture below, the whole ECU is potted in a rubbery goo, making it substantially more rugged than the circuit board floating in a metal box that is the Miata ECU.

Miatabusa Wiring

All this compactness and watertightness opens up new mounting opportunities. Similar ECUs are mounted in the engine bay on modern cars, but with the Hayabusa's original mounting in a relatively cool part of the bike, we figured it was safer to keep it away from the heat, just in case some little diode in there was heat sensitive. After jamming the ECU in every nook and cranny we could find, its natural home turned out to be in the cowl, exposed to some of the elements, but in the shade and away from the engine. 

miatabusa instrument cluster before

Swinging the windshield wipers through their travel reveals just how perfectly the ECU fits here. Half the box is thin, almost as if those clever Suzuki guys were thinking they better make sure it clears Miata wiper hardware...

With no mounting tabs on the plastic ECU housing, we'll be mounting it here with industrial strength Velcro.

miatabusa ECU Location

The next mounting challenge is the rectifier. This is the magic box that takes all the AC noise coming from the alternator and turns it into 12V DC. Based on the giant cooling fins, we were also guessing this one didn't want to be anywhere hot. It found a home right next to the ECU.

miatabusa hayabusa rectifier installed in miata

As luck would have it Mazda anticipated this problem and left two perfectly spaced mounting holes in the cowl for attaching Suzuki rectifiers. The hole on the left was filled with a rubber plug, while the hole on the right was used for a plastic mounting clip to hold the clutch line. We replaced the clip with an Adell clamp, and bolted in the rectifier as Mazda and Suzuki intended. Thanks guys!

miatabusa hayabusa rectifier installed in miata

Now, about that wiring harness... Making that spaghetti look clean is actually pretty easy if you tackle the project the right way. My way is to make a wiring harness out of rope and tape, running the rope where you want the wires to go and taping the ends with labels that correspond to each connector.

miatabusa instrument cluster before

 As you can see, virtually every connector is on the same side of the engine, and the harness will be both tidy and tucked away under the intake manifold. Now, this is as far as we've made it on this project so far, but I already did a similar project on the Rally Beater several years ago. The photo below was taken while the old, messy wiring was still in place and the new, clean, rope harness was being laid out.

510 rally beater hayabusa miata wiring miatabusa

Zip tying the rope to a chunk of pegboard makes an easy template for trimming the harness. Just zip down the ECU connector at one end, un-wrap the harness, and start laying the connectors down in their new homes. This breaks down a big, confusing wiring job into easy steps on a nice, convenient table. Since all you're doing is lengthening or shortening wires, there is little opportunity for mistakes.

miatabusa raly beater miata hayabusa rope wiring harness board

Once we're done making this harness, the plan is to send the ropes over to Peter D. so he can offer his harness trimming service in a Miatabusa-specific way.

 

 

 

link to miatabusa home page
Back to the rest of Project Miatabusa

 

Bookmark and Share
Comments
Nick
Nicklink
Sunday, September 19, 2010 11:11 PM
Using rope to mock up the wiring harness is a great idea! I think I'm going to be borrowing it from now on :-P

And I'm guessing you posted the bit about the fuel maps up because there's not need for you guys to retain the factory compromises in the motor anymore. Sweet >:D
8695Beaters
8695Beaterslink
Monday, September 20, 2010 5:30 AM
I like the rope ifea too. We're probably going to rewire my dad's 1953 Morgan in a year or two, and this will make the job a dozen times easier. On mounting the ECU, you guys should try servo tape from the local hobby shop. Nice and strong, leaves no messy residue, and is foam padded to protect the ECU. It should handle the heat, though I'm not sure when it starts to melt (it has no problems holding down my 150 degree ESC, so on the cowl it should be good).
8695Beaters
8695Beaterslink
Monday, September 20, 2010 8:23 AM
That reminds me, are we going to see any updates with the Rally Beater? I loved that little car, and would love to see at least an overview of what has become of the car (similar to how you went over Project Silvia a year or so ago).
saturn racer
saturn racerlink
Monday, September 20, 2010 10:39 AM
+1. and what about finishing the articles on the lemons car. you really need to write a lot more.
8695Beaters
8695Beaterslink
Monday, September 20, 2010 11:06 AM
Agreed, I'm looking forward to see how two different cars were welded together.
dj06482
dj06482link
Monday, September 20, 2010 11:46 AM
On the velcro-mounted ECU - could you install some small straps or even zip-ties as a fail-safe?

Love the rope idea for wiring!
Dave Coleman
Dave Colemanlink
Monday, September 20, 2010 8:25 PM
You guys sound like Kojima, always nagging me to write more!

Wait a minute... Mike, how many logins do you have?
pcruz
pcruzlink
Monday, September 20, 2010 8:56 PM
Dear Dave:

You are the man!
8695Beaters
8695Beaterslink
Tuesday, September 21, 2010 7:15 AM
Hi my name is Dave, and I'm a Colmea-holic.

Seriously, how can you NOT want to read more of this? No lie Dave, I constantly look back to Dear Dave, project Silvia, etc. in reference to my own projects and my friends. Reading what Mike and Eric write on the site is always a treat, but they usually play with race cars and a lot of high-end toys. Projects like the Miatabusa or the rally Beater or the Frankenmiata show what you can do with all that high end thinking with a shoestring budget. It's some inspiring shit.

Okay, I'll remove my lips from your butt now.
rsmotors
rsmotorslink
Tuesday, September 21, 2010 10:35 AM
I gotta agree with everyone here you MR. Dave where the reason I bought SCC back in the day, damn I miss that mag. And the monthly Dear dave fixes!
Post Comment Login or register to post a comment.

MotoIQ Proudly Presents Our Sponsors:

© 2014 MotoIQ.com