The Mazda ECU is, in fact, a 6801 series, confirmed via pinouts. I feel silly. I *knew* the Kawasaki was 6801-based, but for some reason I got it in my head somewhere that it was likely to be an Intel design. I only ever muched around with the 8080/A back in the day, and gave up the hardware side of the hobby in the very early 80s. I should have kept up on it!

The Xtal is shielded on the Mazda ECU, but on the CX500T it's 6.00 Mhz.

I suspect you're bang on about the setup on the Mazda being very similar if not identical to the Kawasaki unit. I wish I had a spare Kawi ECU to play with.

The Honda ECUs have similar part numbers on their MPUs and 40-pin support chips, which makes me think the same basic architecture. I need to have a box in my hands to check further, but it sure seems like there are a lot of things that point toward Intel (Vcc and Vss look on the photos like they follow Intel convention, also the traces I can see between CX500T MPU and support chip are the right ones by the look of it to support the 8085 and an outboard EPROM with ports made for it; I really need to get a box and take a closer look.

The Mazda ECU is for a low-cost solution for those who are uninterested in heavy engine mods. Since the cost of just a simple rebuild on a rotary is over $2000, assuming nothing major needs replacement, a lot of people A) don't modify their engines at all, and B) don't have a whole ton of money around for doing anything major to the car. People that want power and handling to be far beyond the 1st gen don't mod a 1st gen, they buy an FC or FD and mod that. It's a much better suspension setup on the later cars, a beefier trans case, and a lot more engine management solutions that are off-the-shelf. I'm merely trying to account for mild changes in porting, using later intake components, a header, a better exhaust, etc. Plus we're talking about sensors and injectors and a fuel pump that are aging and may not be in original spec; and there are people who race them in the SCCA who are not allowed to change ECUs in their class, but CAN change the maps. I happen to own one and want that access, unless it's miserable to make it happen. Someone has already done what I want to do for the early Toyota MR2, and their ECU and MPU both have the same prefix digits as the RX-7 GSL-SE, so I am relatively sure it is possible... It's just matter of how much effort and cost is involved.


On the Hondas, they are liekwise old, and have far fewer miles on them, which means a lot of time sitting. They have become very collectible, and many are out there in excellent shape. I know of at least three people in the US who specialize in restoring them, and they always have at least four or five at their shop undergoing restoration; prices have been climbing, and museusm in Japan have been buying low-mile units to ship back to Japan. Prices for a good used machine are now around $5000; a totally clean, low-mile original 650 can fetch up to $10,000. Many people who ride them want to remove the overboost cut-out, and it is suspected by many that there is room for improvement on the stock fuel maps without risking engine damage (Honda overbuilt these bikes by an incredible margin -- witness all the logic on the 500 ECU, as you mentioned!) They could limp home with a huge variety of sensor failuers, even allowing for multiple failures in some instances. In any case, no one really builds the engines any stronger, as they totally don't need it... Those bikes can survive for years and years being regularly boosted to 19 psi, as long as they don't have to sit for long periods of time and get maintenance when they need it. Some owners want to keep the bike stock-looking but still be able to improve on mapping and remove the overboost cutout. And I'll wager very few of them would want to spend thousands on canned ECUs and then have to build maps from scratch, or buy a Megasquirt and having the fun of being the first one to spec out all the sensors and to make useful maps that won't lunch the forged pistons while working out the fueling (and in the case of the 650, spark as well).

I'm obviously not here to make a fortune at these projects. They are my way of contributing back to a community of like-minded individuals to improve the sport and help us all enjoy the machines a little bit more. Keep in mind that even just the ability to data-log without anything too drastic in terms of wiring harness mods or building and configuring a box will be very useful to anyone who DOES want to go the next step and add an aftermarket ECU and maybe build the engine or change the turbo.

Incidentally, the 500 made over 90 bhp, and the 650 was conservatively rated at about 115 bhp. It is only in the past two or three years that NA motorcycles have achieved the same power per displacement as these unlikely engines (v-twin, 500 and 650cc, pushrod, screw-foot and locknut valve gear, 4-valve) back in the very early 80s. The fact that most of these bikes (the ones that have not been wrecked, or were put properly back together!) are still running strong with lots and lots of life left in them speaks to Honda's quality, and their level of innovation in their designs (the IHI turbo was by far the smallest in the world when the bike hit showroom floors).