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Post by iiirii on Oct 16, 2014 1:04:14 GMT -5
Hi Apologies if this has been asked a million times, I'm building a bike engined rally car, Thinking of using a Justy rear diff and axles etc: as they are small / was considering a R160 but they are very long. Is there a general rule of thumb for hp reliability ?
Will a justy rear end tolerate 220hp on gravel ?
Appreciate constructive comments
Cheers
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Post by indkid87 on Oct 16, 2014 7:21:14 GMT -5
I haven't heard anything regarding the strength of the diff or anyone having problems with it. Supposedly the transmission will support 200 hp so I would assume it'd be a bit more than that.
However, if you're going through the trouble of a motor swap I'd change the diff as well. Simply because there are zero tuning options for it. I'd swap for something more common that you can get an lsd for.
-Dave
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Post by sp0ngebob on Oct 16, 2014 10:43:45 GMT -5
its an open differential. unless you plan on replacing the diff with an LSD theres 0 value to this on dirt. or if you intend to weld the spider gears i guess that could work.
diffs break because you stick a launch. on slippery surfaces you should be fine.
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Post by madmatt on Oct 16, 2014 15:55:31 GMT -5
Force (torque)breaks things... not horsepower...
What sort of torque you talking? I can't see a bike engine and transmission output making the sort of torque it would take to break the Justy rear diff. Are you using the bike transmission? and what sort of final drive out of the bike motor? anything?
Oh, and not just launches break diffs... rally breaks them on landings, bumps, hooking up in turns. Depends on the surface. Good gravel tires give an amazing amount of grip.
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Post by madmatt on Oct 16, 2014 15:56:13 GMT -5
oh yeah, and where are you gonna rally this beast?
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Post by iiirii on Oct 16, 2014 16:55:40 GMT -5
Hi Its a GA2 Honda City Hayabusa gen 1 engine They are about 180 hp standard, mine should be a bit over 200 Torques about 120 foot lb I took the rear cover off both the R160 & the justy and put them side by side. I know the R160 would easily handle the abuse ( but they are too long) I was hoping the internals of the 160 would go in the case of the Justy, but they wont. Ideally a short nose R160 would be great, which is how I spotted the justy diff. Its just a fraction smaller so Im hopefull it will be fine. Probably run a spool Cheers
oh , In NZ
Thanks
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Post by sp0ngebob on Oct 16, 2014 17:28:29 GMT -5
Force (torque)breaks things... not horsepower... What sort of torque you talking? I can't see a bike engine and transmission output making the sort of torque it would take to break the Justy rear diff. Are you using the bike transmission? and what sort of final drive out of the bike motor? anything? Oh, and not just launches break diffs... rally breaks them on landings, bumps, hooking up in turns. Depends on the surface. Good gravel tires give an amazing amount of grip. so....hp is a derived number from tq. its (tq x revvs)/5252. so yes HP does break diffs in a roundabout way. and if you break a diff on landing that means you likely smashed the case as opposed to broke the ring/pinion gear which mostly will come from sticking a launch. this all presumes the open diff doesnt just light one tire. and i sincerely doubt he will break a diff due to power or any of the cases you listed. this isnt some group B rally car its a motorcycle engine.
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Post by indkid87 on Oct 16, 2014 18:35:35 GMT -5
Ahhh, so it's not going in a justy?
Still I'd look for a more common diff with readily available rebuild and hop up parts.
It's definitely possible to break a ring and pinion upon landing. You're suddenly going from zero traction to lots of traction. Especially if you don't take your foot out of the throttle.
-Dave
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Post by madmatt on Oct 16, 2014 22:40:41 GMT -5
Force (torque)breaks things... not horsepower... What sort of torque you talking? I can't see a bike engine and transmission output making the sort of torque it would take to break the Justy rear diff. Are you using the bike transmission? and what sort of final drive out of the bike motor? anything? Oh, and not just launches break diffs... rally breaks them on landings, bumps, hooking up in turns. Depends on the surface. Good gravel tires give an amazing amount of grip. so....hp is a derived number from tq. its (tq x revvs)/5252. so yes HP does break diffs in a roundabout way. and if you break a diff on landing that means you likely smashed the case as opposed to broke the ring/pinion gear which mostly will come from sticking a launch. this all presumes the open diff doesnt just light one tire. and i sincerely doubt he will break a diff due to power or any of the cases you listed. this isnt some group B rally car its a motorcycle engine. Yep, torque over time... and his hyabusa makes a "big hp" number cause it does it by spinning like mad... and without really low gearing that torque that would be the force to break the ring and pinion won't be there... so yeah, both right. Landings and bumps and break diffs by shock loading the diff, most folks get on the gas in the air to rotate the nose up (like a motocross bike) then you have wheels spinning xx faster then you are going when you land, so sorta like a launch I guess... You NZ (and aussies...) get all the fun. No way we can rally bike engined car here... The infamous Crow Justy wouldn't fly either (maybe in the US) Here, motor has to be product line derived, and drive config can't change... No bike motors, no Duratec's in Volvo's...
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