I got an idea... (High revving, rear/mid engine miata content)

D2W wrote: If mid-engine is your desire, and if there is enough room to mount the motor in front of the rear axle I would take out the differential. The dif is going to cause a fairly large power loss from the right angle gear drive, and its heavy (weight is your enemy). A better solution is to use a spool with a sprocket on it and drive from the output shaft of the motor straight to the spool. You will need to suspend the spool from the chassis on bearings of some sort and then attach it to the axles. I have seen guys who took a differential out of its housing, found a way to seal it to keep the oil inside, and then put a sprocket in place of the ring gear. This way you could have an open rear end, or one with a limited slip.

Yep, but conveniently, if you replace the diff unit in the stock diff housing with a spool, you can keep the housing and dump the ring and pinion gear. Input can go to either side (to match the output side of your motorcycle gearbox), and voila - you have factory engineered bearings, supported in a perfect location for the factory engineered IRS and axles, etc.

When it comes to bike engine swaps I always arrive at the gearbox.

Even though the bikes have huge power numbers, have you seen how small the gears are in a bike transmission compared to a car transmission? If such small gears are adequate, why do car gearbox designers make everything so big by comparison?

The fear I have is that the bike engined cars are going to be eating gearboxes due to being outside of the designers weight envelope.

In reply to NOHOME:

I think you are right, eventually the bike gearbox (or really many other pieces) could be a failure point. But I also don't think I will want to DD my bike engined car for 100k miles.

I wonder what the turbo-nitrous-big slick drag bikes do for transmissions?

Robbie wrote:

D2W wrote: If mid-engine is your desire, and if there is enough room to mount the motor in front of the rear axle I would take out the differential. The dif is going to cause a fairly large power loss from the right angle gear drive, and its heavy (weight is your enemy). A better solution is to use a spool with a sprocket on it and drive from the output shaft of the motor straight to the spool. You will need to suspend the spool from the chassis on bearings of some sort and then attach it to the axles. I have seen guys who took a differential out of its housing, found a way to seal it to keep the oil inside, and then put a sprocket in place of the ring gear. This way you could have an open rear end, or one with a limited slip.

Yep, but conveniently, if you replace the diff unit in the stock diff housing with a spool, you can keep the housing and dump the ring and pinion gear. Input can go to either side (to match the output side of your motorcycle gearbox), and voila - you have factory engineered bearings, supported in a perfect location for the factory engineered IRS and axles, etc.

I hadn't thought of that, and to save even more weight you could just use a splined coupler between the axle shafts. You could probably even shave more weight by removing unneeded parts of the dif housing.

NOHOME wrote: When it comes to bike engine swaps I always arrive at the gearbox. Even though the bikes have huge power numbers, have you seen how small the gears are in a bike transmission compared to a car transmission? If such small gears are adequate, why do car gearbox designers make everything so big by comparison? The fear I have is that the bike engined cars are going to be eating gearboxes due to being outside of the designers weight envelope.

Somewhere I saw someone who had done a bike engine conversion for use in endurance racing and was having problems with gear failure. His solution was to remove all the gears from the transmission except the final drive and run through a regular car transmission. But that was a front engine rear drive combo.

If you stay with the bike tranny soft launches are your friend.

Bike engines have big HP numbers but much less impressive torque ratings. When a bike motor moves a 600 lb bike like a rocket, it may seem a lot more relaxed saddled with 1,700 lbs.

You could hit 1500 lbs easily.

That's still 2.5X as much weight as the Busa is used to pushing around, and it has no torque.

If you can make the Busa sit amidship, then the obvious answer is AWD with a second Busa up front!

SVreX wrote: You could hit 1500 lbs easily. That's still 2.5X as much weight as the Busa is used to pushing around, and it has no torque.

The good news is the superbikes redline in the 12-14k rpm range, and go almost 200mph, so you can gear down to literally double or triple the torque.

SVreX wrote: If you can make the Busa sit amidship, then the obvious answer is AWD with a second Busa up front!

Or run an 'offset' v with one engine chained to one output flange of the diff, and the other to the other. Run zero guts in the diff, but retain power to both wheels in all situations.

2 busa motor/trans combos is still probably lighter than most 4 cylinder + trans car powerplants.

SVreX wrote: If you can make the Busa sit amidship, then the obvious answer is AWD with a second Busa up front!

Oooh! That might not be completely impossible!

Robbie wrote:

SVreX wrote: You could hit 1500 lbs easily. That's still 2.5X as much weight as the Busa is used to pushing around, and it has no torque.

The good news is the superbikes redline in the 12-14k rpm range, and go almost 200mph, so you can gear down to literally double or triple the torque.

That's what I was thinking. I haven't looked at all the gearing yet, but between the "front" and "rear" sprocket, and whatever ratios for the diff I'm sure it could be geared to top out at like 120, and have some great acceleration. It would be more shifts, but if it has to use solenoids anyway, they're going to be fairly quick at shifting.

I need to find a cheap cheap Busa so I can bring something to the challenge... Anyone got one laying around?

Good luck on the busa. Since it is kind of "king" they tend not to be cheap (if you find a source for less than $1000 let me know!!!).

600s, 750s, and for the most part 1000s are chump change though.

The kawi 1400 might be another consideration.

The first thing we do on the bike transmissions is to undercut all the gears both up and down shift.

Second is billet output shafts. I have blown stock output shafts on my Busa with just minor engine mods and sticky tires.

I put a turbo Busa engine in a Legends car for a guy to drive on the street. They can take it for a while but the weak point in them is the case where the output bearing is pressed in. They have kits that extends the shaft so you can run it on the outside of the frame for wider wheel/swingarm setups, it has a bearing on the end to help support it, it would be good to use this if you have the room.I like using the rubber coupler from a newish GTO to help with the cushioning on the driveline. without it you will munching the trans of the bike engine.

An external GEO metro alternator is a good idea if you are running a bunch of electronics.

I have used the Roadstercycle reverse box in a couple Busa/GSXR sandrails And will be putting one in the Legends car in the next couple months when we pull the engine for a reseal. https://www.youtube.com/watch?v=PzvNpv_J0A4 Its a pretty good unit, they clain 500hp. I will be testing the limits since the car engine had 575hp when it was in the bike.

There was a guy here in Burbank Ca that was building subframes for smartcars to put bike engines in them, I think he closed up shop and went back to england. http://www.extreme-engineeringuk.com/the-story.html

And after all of that, the best "car" engine I have used was one from a Suzuki Bandit 1250. It has the Tq numbers down low, The busa is second, The GSXR1K would be my last choice due to very thin cases and they dont make much power down low.

Robbie wrote: In reply to NOHOME: I think you are right, eventually the bike gearbox (or really many other pieces) could be a failure point. But I also don't think I will want to DD my bike engined car for 100k miles. I wonder what the turbo-nitrous-big slick drag bikes do for transmissions?

Did the bandit have a more durable output? I am just curious why it is better than the busa? I get the down low power is likely better do to not being a high horsepower engine but it seems to me that the extra 80 hp might make up for that.

The 1250 still would need the upgraded output shaft.

I just like the power curve of the 1250, The busa can be made to deliver some crazy power with a lot of aftermarket support and probably a lot more of them around. The last engine "kit" I sold was from my personal Busa. I got $850 for it with the computer and wiring harness. I sold it cheap since it had 165K miles. If you do get a Busa the best years are 2003 and above. The 1999-2000 had a much slower computer, a weaker stator/pickup but they did have an external fuel pump bolted to the engine. The 2001-early2002 was a one year electrical system. Its not a big deal but hard to find a power commander for. 2003 and above is pretty much sorted, There was a couple Cam Chain Tensioner recalls, any Suzuki dealer can punch in the VIN and tell you if they have been done,

They can take a good amount of abuse, Its shenanigans like this that made me find the weak spots, With the stock tires I could hammer it on dry pavement with no trouble, once I started putting the sticky tires on it I would have to light it up on the stripe or risk putting the chain through the waterpump again.

Good to know!

In reply to MulletTruck:

What do you think of the R1 engine?

Anyway people choose to go the money needs to be spent on the transmission,

If you mount it straight above the diff - how will you tension the chain to handle the movement of suspension? You need some length to allow sag or room for an idler sprocket.

Its a good bike engine but not very sturdy, the cases on any of the "Race" bikes is the weak spot. There is a lot of pressure on the gear sets pushing apart, Undercutting helps but deft throttle control is needed. I know Leno has a R1 powered car but he is easy on the trans and it had a bunch of work done to it.

The valves are also in issue if it gets and stays hot. Having 5 holes per cylinder it needs to be watched. In stunt bikes where they just hammer them all day I have had to do a bunch of replacement heads from the valves getting so tight that there is no room for shims to put them back to spec.

The make some power above 7K RPM but not too much at the lower RPMs Really have to wind them up compared to others to make them fun to drive, Some people like that sort of thing.

D2W wrote: In reply to MulletTruck: What do you think of the R1 engine?

IRS is usually the fix for that if you dont want to run a driveshaft.

Huckleberry wrote: If you mount it straight above the diff - how will you tension the chain to handle the movement of suspension? You need some length to allow sag or room for an idler sprocket.

Since the bandit 1250 is good, what about a water cooler gsxr1100? They can be found real cheap here.

In reply to physician:

As long as you're not in a big hurry to get off the line.