How, exactly, do you get the power from the output sprocket to the wheels? What engine is that? What about reverse? are you using the original chain drive that came with the S600?
First things first. The engine. I knew I wanted to go with a motorcycle engine for two reasons: 1) sequential shifting (side note, why is sequential shifting not a thing on more sports/supercars?) and 2) 12,000 RPMs. I wanted to stick with a Honda engine for the Honda car. I was really leaning towards the 600RR engine to stick with the 600cc format, but I really wanted the extra power. I also considered the Goldwing engine; it would be more suitable for a car because it is made for a larger bike, and the newer ones have a reverse built in (runs off the starter motor). Unfortunately the Goldwing engine redlines at a paltry 6000 RPMs, which is not only less than the 12,000 I was looking for, but 3,000 below what the original engine had. So I went with the only remaining option, the CBR1000RR. Since the original car was a 600cc and called an S600, then my car would ideally be called the S1000RR. Unfortunately, that is the name of a BMW motorcycle, so I just went with S1000.
To mount the engine, I placed it on blocks in roughly the position I wanted it and then cut and welded in some steel tubes to the engine mount points. I considered the torque reaction on the engine and placed the tubes so that the load path would ideally put the motor mount tubes in compression or tension rather than bending. Bending is not a very efficient way of resisting force.
Waterjetting is the way to go here. Find your local water/laser shop and tell them what you’re doing. Tell them you’re making an awesome thing on the cheap and you’re in no hurry and ask them what you can do to make it easiest on them. There are a few free CAD programs out there that you can use to draw up your component, flatten it, and then export the .DXF file. Once you get your metal back, you need to use a metal brake to bend it; you can get a cheap desktop one at Harbor Freight for about $40. It’s not great, but it’ll get the job done. After that, weld up the seams and you’ve got an intake and a fuel tank. I used aluminum but steel will be just as good if you paint it and coat the inside with a sealant. Dont’ forget the baffle in the fuel tank to prevent slosh.
The exhaust wasn’t terribly easy. There are companies that sell lego-style kits that you can assemble to show you what bends and lengths you need, but I didn’t want to spend the money, so I just bought a few bends and straights and carefully cut them up to fit. the collector I bought from someone online, I don’t remember who. The port attachments are from the OEM bike exhaust; I just cut them off and welded new tubes on. It is really tight in the engine bay in that area, so I have a bit of an abrupt change right at the outlet. Not ideal, but it works. after I welded it up, I checked for leaks by sealing the end and filling it with water. No leaks, and it went to my local coating shop for a ceramic coating to help keep the heat in and keep the rust off.
The drivetrain on this thing is kind of a mixed bag. I made the sprocket-to-driveshaft adapter; I pulled off the sprocket and lathed out a tube of steel so that it would center itself on the sprocket. I then waterjet a plate out that would press lightly onto the other side of the tube. The waterjet plate had the bolt pattern of the U-joint of the BMW driveshaft I had planned on using. I clamped it all down and welded it slowly to maintain parallelism and concentricity. The driveshaft is a BMW two piece, used mostly so I could snake the driveshaft down the extremely narrow tunnel. It is offset to the side so that I could keep all the angles, engine to front shaft, front to rear, and rear shaft to diff, as low as possible. Better to have four degrees between all of them than zero on two and 12 on one. Any angle will not only decrease efficiency but will impart a perpendicular load on the ends. The middle of the driveshaft is held with a beefy bearing and a waterjet-and-welded structure that holds it to the frame.
The diff is from an E36 BMW, chosen mostly because it was cheap, had limited slip available, and had the low gear ratio I needed. I ended up taking the limited slip out and putting a welded center in. I was getting more wheel spin than I wanted; the BMW is made for a much heavier car with twice the power. I have waterjet and machined plates on the output that change the bolt pattern from the BMW to the Miata half shafts that I used.
Cooling, Clutch, and Nitrous
Thermal management on this thing was really just a matter of fitting the largest radiator I could, and then plumbing the engine to it. I found an aluminum radiator on Jegs or Summit or someplace like that and cut about 6 inches off the bottom so it would fit. I welded up the bottom and added the right size ports for the engine hoses. The fan is a Spal that is hooked up to the stock ECU and automatically comes on at whatever temperature it is set to (215?)
The clutch was originally the foot clutch from the car hooked up to a Miata master cylinder, but it didn’t match well with the motorcycle slave cylinder (basically it was an on/off switch. Also, I really enjoyed the had clutch from my FSAE days, so I found a stubby motorcycle master cylinder that would fit and stuck it on the shift lever:
I’m only running a 35 shot now, set up with a controller to automatically come on at WOT above 8000RPM. It is, of course, a wet shot, because I’m not an idiot. I usually leave the bottle out when I’m driving on the road because it’s quite conspicuous and seems like one of those things that will be used against me in a court of law.