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100 HP and under 300 lbs. possible?

70K views 344 replies 86 participants last post by  XxGRYMMxX 
#1 ·
If you were to build a street legal bike for the purpose of canyon carving that made at least 100 HP and weighed no more than 300 lbs. wet, how would you do it? Try to keep it as fairly bolt together as possible. ie- no custom frames, carbon swing arms, shit like that... is it even possible?
 
#3 ·
That's <140kg in metric, which is less than a Moto GP bike (153kg last year, 157kg this year).

I think you'd have to build more on a lightweight Moto 3 philiosophy. Those bikes weigh next to nothing, and hit ballpark 65hp with a 250 single. So start from lightweight eg. RS250 which is 140kg with original pipes and all the plastics, and makes 72 claimed hp, then see what power you can get from that engine, maybe a big bore kit. Someone has done an RD350LC conversion into that chassis, these can apparently big bore to 485cc. At that point if you don't mind a strong grenade tendency they apprently can get to 120hp, so 100hp should be achievable without any more than the usual stinkwheel reliability issues, fuel thirst and expensive oil cravings.

In short, I really don't see you managing the weight requirement with a 4T.
 
#7 ·
The RS250R weighed under 130kg wet and they made md 90's in rwhp
So, 300 or 350cc kit in it, lots of clever Honda GP advice and there's the bike!

There was some ridiculously like all carbon and magnesium 4 cylinder 2t floating around the net a week or two ago
 
#9 ·
Because this bike weighed 400lb, which is 100lb more than he wants. Thus you can't realistically start from an RG500 to get the target bike.

Don't start by a suitably powerful bike and taking away 100lb, Start instead from a sub or near to 300lb bike and try to get above 100hp. Like a 250 two-stroke, with a bigger engine wedged into it - but the engine has to be a twin, or it's going to be too heavy. Like a 250 twin, or a 350 twin bored out to whatever you can get away with.
 
#10 ·
On a more conventional street bike like the '93 CBR900RR, which started at a svelte (rated) 400 or so pounds dry. Also rated at making over 120hp.


Stripped to the bare bones, minimal tail, barely any wiring, tiny battery, detabbed everywhere, even fitting a 160 rear tire and 120 front in place of the 180/130 trying so desperately to hit the 340lb mark. Still yet to get it weighed, but I'm sure my end resulting power to weight ratio will hit damn close to the mark your asking for.

Modern 600's gutted of all the unnecessary bits could get down around the 335lb mark with some readily available titanium and fiberglass parts.





It's more than possible. But it's gonna take some compromises and some real attention to every part your going to use. Honestly getting into the territory of Ferrari where your drilling and milling parts to drop ounces. A build like that could get out of control really quick. :D
 
#11 ·
Even my bike dry is 380 lbs
I do think the RS250 chasss with more motor, reason...don't nee one. Th RS chassis is God. There are 350cc ones makeing over 100hp to kny knowledge

Otherwise, just buy a new 600 and enjoy a better set of suspenders and better chassis?
 
#15 ·
Dave the guy who does all of my paintwork, has an Aprilia RS250, which has been fitted with a motor based on the 350 powervalve motor, but with new crank, cylinders, heads, pistons, FCR39 etc, 500cc and 120bhp. He's been building this bike for the last few years, with radial braked front end, lighter wheels, race plastics etc. This bike should weigh in at around 140kgs wet.
The motor has been built by an Aussie mob called the twostroke tuning shop or something very similar. They designed their own cranks, cylinders, pistons, heads, powervalves, ignition system etc etc. If you look on youtube there are some vids of the 500cc motor in the RS250 chassis.

Personally I'd be looking at grafting two RM250 cylinders onto an RGV 250 bottom end to make a V twin 500cc stroker, and slotting that into something like a 125cc or a lightweight trellis frame.
Of course if money was no object I would be building a V twin twostroke 1000cc motor from scratch based on something like a pair of CR500 cylinders or similar, I would make it a modular construction, to enable two of them to be grafted together into a 2 litre V4 stinkwheel.
Failing that using a 275bhp V4 stroker motor from a snowmobile with a dry clutch and bike gearbox would suffice.
I only weigh 50kgs, so I can happily sacrifice a few kgs of extra weight on the bike as the total package weight will still be less than 200kgs wet with rider. (My current bike is 220kgs wet with rider and 144bhp 70lb/ft of torque) I can get the weight lower if I go for a good shit before putting my leathers on!!!
 
#17 ·
Real interesting posts you guys are making... thank you all very much. I see everyone leaning towards the 2T for obvious reasons, but if one were to go the 4T route, what would be a lighter config- twin or four, and given whichever is lighter, how close to 300 do you think it could be reasonable brought to without getting out of hand?
 
#18 ·
Look at the weights of the current crop of Moto2 bikes and you'll see that using a 4 cylinder 4 stroke motor is going to be pushing it with regards to hitting the 140kg target weight. Using a 2 stroke makes it much more likely to achieve it. As a rough g idea Mick Doohans NSR500 GP bike was making around 170bhp, and weighed at less than the road going NSR125 at the time.
You can get them light, but it gets very expensive to achieve.
 
#19 ·
By the end of this thread, the guy was able to get a Daytona 675 down to a bit over 300 lbs
stripped of anything unneeded, aftermarket exhaust, Carbon wheels, titanium this and that.
Pics don't work anymore :(
Think i have a pic saved on my PC
www.triumph675.net/forum/showthread.php?t=28936

Thanks guys. I have my standard 675 (fully faired, etc), and the fighter with the carbon brakes (1.4kgs/3lbs lighter) and the carbon front wheel makes the standard 675 feel like a bus for agility. The stock 675 steers sweetly, true, but with the focus on the centralised mass, especially on removing mass from up high, then the fighter may as well be a different bike. It's in a whole other league. Sitting on it, and waggling it side to side, it makes a Ninja 250R feel positively porky, much to the surprise of a rider (of said 250R) on one of my rides.

The bike now weighs in at a paltry 145kgs (319lbs) with an empty tank of fuel, compared to 179kgs for the stock bike. That's a whopping 34kgs (75lbs) lighter than stock. In track mode, it'd be about 2.3kgs (5lbs) lighter again.

Edit: found the pic


 
#49 ·
By the end of this thread, the guy was able to get a Daytona 675 down to a bit over 300 lbs
stripped of anything unneeded, aftermarket exhaust, Carbon wheels, titanium this and that.
Pics don't work anymore :(
Think i have a pic saved on my PC
www.triumph675.net/forum/showthread.php?t=28936




Edit: found the pic


I see at least 10lbs that could be lost from this bike. Gauges, mirrors, turn signals, smaller/lighter headlight and associated bracket, bob the tail, aftermarket rear sets, lose the seat and go with a foam pad.

Shit that's prob closer to 20lbs.
 
#21 ·
Hawk gt can be lightened to around 300, an all out motor will make 75 plus. Its a doable plan, just takes some well thought out decisions and lots of green. If money were no object my hawk would have carbon body work and wheels , ti sub frame, I think you get the picture.
 
#26 ·
My question is - can you handle this kind of HP to weight ratio on a 2-stroke? :D
My honest answer is- I don't know. The most hairy- chested two stroke I've ever been on was a rather pedestrian CR250. I would like to get my hands on a CR500 to see what they're about. The only drawback I see to a two stroke on the street is the premix dilemma. That's a non- issue on a race bike, but having to carry around a bottle of oil and always guessing at the amount needed for proper ratio, or not venturing more than about 30 miles from home doesn't make it at all practical for what I want to do.

I guess since those knowledgeable on the subject have made it quite clear that the only way to meet the numbers specified is by way of some pretty rare and expensive two stroke technology, I should ask what is the lightest 4T engine out there that can make 100 HP? After that, I guess the next question is, how light can I expect it to be given the use of mass produced swinger, forks and wheels? I weighed a friends '05 GSXR600 the other day and with a half tank, we came up with 375 lbs. I guess I have no concept of how much all the stuff weighs, but I'd like to think that between the fairings and bracketry, lights (OEM vs. smaller aftermarket), back half of the subframe, battery (OEM vs. lipo), and exhaust (again OEM vs. carbon shorty), there's at least 50 lbs?

And finally, am I thinking in the wrong direction? My goal is something that is extremely nimble with good handling characteristics and a decent power to weight ratio. Something that has about a 75 mile range and won't break the bank (under 5K). I guess a KTM SM690 pretty much fits that bill, but this site isn't about what works out of the box. :)
 
#24 ·
#27 ·
I still think, even with the lightest stock frame you can find, you're still not going to hit the mark for weight. For example, a CBR1KRR engine weighs 140 lbs. You're halfway there and still need pretty much everything.
 
#30 ·


ARILIA RS125 with a GSXR600 motor FTW!!!

(With race body work, and maybe some mag wheels.)

:D Luis


EDIT: Realistically, a I4 may just be too much motor for that frame...

I know an SV650 engine may only make 85 HP somewhat reliable...

Maybe, a Ducati 848 motor will hit the power range, and be narrower than any I4 engine...

You will need more brakes than a single front rotor... And, a bigger rear wheel and tire...

What is your dream budget like??????????????????????????? ....I think with $16,000.00 well spent you can do it!!!
 
#52 ·
A friend of one of my old teaching colleagues slotted a Ducati 600SS motor into a Cagiva Mito chassis.
My ZRX1000R weighs in at 169kgs with fuel or 371.8lbs in old money. Power is currently 144bhp and 70lb/ft of torque, power to weight ratio is 1.17kgs per bhp, or 2.57lbs per bhp.
The cost so far is in the region of £16000 or about $25000. I built it because I wanted to build a bike that looked OldSkool, but had modern handling and performance, and importantly fitted me like a glove. I used a ZRX400 chassis, and slotted an 05/06 Z1000/ZX9R hybrid motor into it. Over winter there'll be a few changes, like knife edged polished and balanced crank and rods, custom made drop in high comp JE pistons, and some reprofiled cams, which should see in excess of 160bhp. A little more weight will be coming off which should get it to my target of 165kgs.
Attaining a weight of 140kgs wet starts to get rather expensive, but it is achievable, with the use of Carbon Fibre, and a lightweight tubular frame, either a lattice construction using something like Reynolds 531 equivalent tubing, or a carbon fibre monocoque construction ( although somewhat better than Ducatis recent foray into carbon fibre frames.
 
#31 · (Edited)
Britten V1000??? What was the power to weight ratio on that hellion???

nevermind...


166 HP @ 11,800 rpm

138 kg (303.6 lb) weight


Go fuck yourself san diego.
 
#32 ·
Then you have Burt Munro's stable of modified bikes, some under 200lbs..
 
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