Engine Swap 720, Hayabusa

[Gangulous]

Ive been looking around for awhile for an engine swap that wont be super difficult for space and i think a hayabusa engine would be easy enough to get runnnig give me the power i want and also give me room to upgrade and get more power. Just want to know if anyone has done this or thought about it with maybe a different bike engine but these are fairly inexpensive and make good power. Does anyone think it couldnt be done or shouldnt?

[Gangulous]

This video gives me hope it can be done because thus is by no means my daily and is going to be the project.

V

 

[datzenmike]

What it has in power it lacks in take off torque. Your truck weighs what? 6 times what a bike weighs? That UTE is lightened!!!! for a reason.

 

I suppose you will keep the Hayabusa transmission?  Probably run the Hayabusa transmission into the 720 transmission left in first gear? or second? The Hayabusa likes to rev. If you use the 720 transmission highway revs at 60MPH would only be around 3,000 in 4th. First would be like 3x that. Maybe second gear? Got to get the revs up.

 

 

[Stoffregen Motorsports]

Mike is right. Gearing and torque are going to be a problem. You'd smoke the clutch every time you took off from a stop.

 

Our race car has a 2.38 first gear and a single disc quarter master clutch. The motor makes no power until 5500 RPMs. All these factors combine to make starts a real problem. Typically the clutch lasts only about five races.

Edited June 11 by Stoffregen Motorsports

[datzenmike]

If you run the Hayabusa transmission and leave it in first gear, (2.615) at 60 MPH you will be revving close to 7,800 RPMs. I don't know your differential ratio but this will be in the ball park. The other gears won't even get used.

 

If you keep the 720 transmission and leave in first gear this multiplies by 3.321 so in 6th gear (about one to one) 60 MPH would be revving close to 10,000. Now that sounds way better and you get to use all the gears and first 2.615 X 3.321 is 8.68 so take offs will be a snap.

[Gangulous]

5 minutes ago, datzenmike said:

If you run the Hayabusa transmission and leave it in first gear, (2.615) at 60 MPH you will be revving close to 7,800 RPMs. I don't know your differential ratio but this will be in the ball park. The other gears won't even get used.

 

If you keep the 720 transmission and leave in first gear this multiplies by 3.321 so in 6th gear (about one to one) 60 MPH would be revving close to 10,000. Now that sounds way better and you get to use all the gears and first 2.615 X 3.321 is 8.68 so take offs will be a snap.

So if i were to keep rhe transmission in first it could be a viablee option or no? Cause i may be a dumb dumb but what it sounds like is the issue is the rpm the engine has to be at to make decent power id be toasting the clutch to get the truck rolling? 

[datzenmike]

Sounds about right. With an 8.6 to 1 first gear and (assuming a 3.889 differential) 14,000 RPMs (is this close to Hayabusa red line?) would be 32 MPH. 

[Gangulous]

4 hours ago, datzenmike said:

Sounds about right. With an 8.6 to 1 first gear and (assuming a 3.889 differential) 14,000 RPMs (is this close to Hayabusa red line?) would be 32 MPH. 

Thank you for being so helpful. Would leaving the transmission for the Busa engine and somehow mating it up to the 720 transmission help overcome the clutch issue or would it just cause the Busa’s transmission to slip and or would the clutch on the 720 still slip? Would i be better off making a gear reduction off the busa driveshaft and mating it to the transmission that way say with double roller chain or maybe a gearbox? I feel like that would help keep it transversely mounted. If anyone has any suggestions lmk thank you!

[datzenmike]

Can't use the 720 clutch, way too complicated and no need really, use the Hayabusa clutch.

 

These are approximate RPMs/MPH as I don't know your rear differential and your exact transmission.

 

Engine tag...

 

 

Lower line is transmission and axle. Axle is HF38 for a 3.889, yours might be different. Also what year 720, king cab? regular cab? 

[Gangulous]

It’s an 84 720 2wd it’s an HF37, FS5W71B. Single cab short bed

[Gangulous]

Would the rpm’s not be an issue when trying to engage the clutch on the busa? Or would a heavy enough clutch fix that? 

[datzenmike]

If the gearing is low enough it will pull away without excessive clutch slipping. One advantage is the removal of the Z24 engine, alternator, starter, radiator, clutch and flywheel. The engine is 280 pounds so probably well over 300 pounds minus the weight of the Hayabusa and transmission. Any Idea what it weighs?

 

The nose of the input shaft into the transmission needs to be supported. Normally it rides in the end of the crankshaft. It is splined. Maybe you could make up something

 

I know basically nothing about the Hayabusa and where the power starts to come on. 14K At 32 MPH is 7K at 16 MPH.

[Gangulous]

http://zx14ninjaforum.com/messages.cfm?threadid=530E75E5-F87C-D237-103A865EB9D56D06

I found this graph for a zx14R which i could potentially get for cheaper. Ik it’s not the same as the Busa but after some looking i saw the ZX makes more hp and torque stock.

[datzenmike]

Doesn't show off idle. Too bad as this is the critical point for getting 1.5 tons of truck off the line and moving. I see the lowest reading is about 80- ft lbs at 3K??? The 3.321 first gear in the 720 transmission and the 3.7 differential multiplies this. 3.321 + 3.7 = 12.3 X 80 ft lbs = 980 ft lbs.

 

I wonder if the tires might break loose?

[Gangulous]

Could this be remedied by maybe a rear end swap with a different gear ratio? Cboys put a Busa motor into a kei truck with a ford rear end and ik that is a much lighter truck but that thing ripped. There’s was bed mounted and i could potentially push the motor into the back and make a custom driveshaft. Could also eliminate power loss.

[datzenmike]

You would loose the torque multiplication of the transmission. To compensate you would need an 8.0 to one differential.

[Gangulous]

Rich rebuilds put a busa engine in a rabbit and i believe they used a ford 8.8 rear end. Maybe that could be used? then just mount a short drive shaft from the busa and or whatever engine i choose transmission and just make some linkage to shift it up front? 

[datzenmike]

Rabbits don't weigh much.

[Odisomus]

I was shown once what was referred as a smartcar with a hayabusa motor which was what the person called electric cars at that time it must have been before the year 2005. I was young and the Internet was still fairly new so I didn't follow up on it like I would have if I was shown the same video today. 

Anyways the video was probably on the most dominant free video streaming website since it was on a home computer. The video wasn't much more than a front wheel drive tiny two seater roast the front tires through all gears while spinning donuts in forward and reverse.  I have no further info about it but wanted to have input that showed someone's done it a while ago so you might even find adaption kits out there or be able to piece over together. I didn't read this thread beyond the original post so I'm sorry if this is redundant but I appreciate all the input on all the topics here they have helped me so much be success at increasing the amount of repairs I can personally now compete on my 1985 Nissan 720 Kingcab.

[datzenmike]

The Smart car and Hayabusa probably weighed 1,000 pounds. The 720 is close to 3 times that.