50cc road race 2 stroke versus 50 cc saw.

[jonseredhusky]

Guess how much power a 50 cc road race bike makes? Nearly 30 BHP!!!!!! The de-tuned road version even makes 18 BHP. So.... when people tell you that chainsaws are overstressed powerful beasts tell them to get on a race bike. LOL!! The average 50cc saw makes 3-4 BHP and pulls torque right from the bottom. The race bike needs 11,000 rpm BEFORE it makes virtually any torque at all and revs to 20,000 rpm.

This is why saws last so long. Think of them as super low tuned versions of the 50 cc race bike. Most saw failures or early life failures are related to poor tuning (lean mixtures), poor cooling, incorrect oil/fuel pre mix etc etc.... I have a saw here that is 33 years old. Runs like a watch. Bore is perfect and compression is 10% down on new spec. And it's done over a thousand hours of use!

Cheers from downunder.

 

[TimberMcPherson]

Which 50cc bike makes nearly 30hp? Thats a heap considering the RS125's are about 50hp.

Motorcycle engines have a few key advantages over chainsaws, the main one being liquid cooling, the other being that the engines dont have to be run sideways and upside down and weight isnt as much of an issue providing you can get the hp so they are able to have a wet bottom end, and they can have narrow power bands as this can be spread with the gearbox. Cost isnt such a problem with racebike engines so the very best materials, production standards and machining is often used.

Is easy to make a high HP motor if you have the money, the hard bit is to lengthen the time before they go pop.

 

[jonseredhusky]

The 2008 Gilera and Derbi 50 cc factory race bikes make 27 BHP at the crank. The RS 125 makes 37 BHP at the crank by the way. Cheers!

 

[romeo]

No contest between the 2 motors. My sons cobra 50 has huge transfers (7 of them) as compared to any saw I have ever seen. Bikes also have a huge intake and exh as compaired to a saw. Longer stroke, reeds, and well matched pipes on the bike motor also.

 

[Lakeside53]

Between top end overhauls

Saws: 2000-3000 hours
Racing Bikes: I can't remember... maybe 50? less?

 

[romeo]

Between top end overhauls

Saws: 2000-3000 hours
Racing Bikes: I can't remember... maybe 50? less?

Thats about right, even less for my sons since I am a fanatic. 10 to 40 hours seems to be the "sweet spot".

 

[timberwolf]

Saws are pretty limited too by size and weight, as well as cost. Also saws are pretty limited by cooling. I think race type saws can be built to get same ball park HP numbers, but they can't do it very long without heating up and failing.

The short stroke configuration in saws keeping size and weight down hurt how much torque they can put into the cank and just how much HP is to be had.

Plain and simple they are built to serve different masters. If saws were built as performance minded as modern bikes the HP numbers would be a lot higher... so would the price tag.

 

[Jim Mesthene]

The de-tuned road version even makes 18 BHP.

Tell me more about that one.

 

[mattinky]

Between top end overhauls

Saws: 2000-3000 hours
Racing Bikes: I can't remember... maybe 50? less?

I'd say those 50cc roadrace bikes get the top ends rebuilt long before 50 hours, probably after each race

 

[thomas72]

On the dirt bikes they get rebuilt about every race just so the bikes are at their best. My 500 last about 200 hours before it is time for rings, and I have about 65 hours on it and it is around 162 psi, and the factory spec is 164 psi. With the big transfer ports, power valve,reeds,slide carb, and turned exhaust my bike produces around 100 hp at the engine and around 65 to 70hp at the tire at 7000 rpm. The CRF 450 does not like the KX500 too much.

 

[mattinky]

On the dirt bikes they get rebuilt about every race just so the bikes are at their best. My 500 last about 200 hours before it is time for rings, and I have about 65 hours on it and it is around 162 psi, and the factory spec is 164 psi. With the big transfer ports, power valve,reeds,slide carb, and turned exhaust my bike produces around 100 hp at the engine and around 65 to 70hp at the tire at 7000 rpm. The CRF 450 does not like the KX500 too much.

100 hp out of a KX500? I think you're dreaming

 

[Tzed250]

On the dirt bikes they get rebuilt about every race just so the bikes are at their best. My 500 last about 200 hours before it is time for rings, and I have about 65 hours on it and it is around 162 psi, and the factory spec is 164 psi. With the big transfer ports, power valve,reeds,slide carb, and turned exhaust my bike produces around 100 hp at the engine and around 65 to 70hp at the tire at 7000 rpm. The CRF 450 does not like the KX500 too much.

No way on this green earth.

A KX500 is good for about 60HP.

At the Zenith of air-cooled 125cc MX bikes, about 1979-1980, the rings had to be replaced after each moto, and the piston after 2 motos

1 moto=30 minutes+2 laps.

 

[mattinky]

No way on this green earth.

A KX500 is good for about 60HP.

At the Zenith of air-cooled 125cc MX bikes, about 1979-1980, the rings had to be replaced after each moto, and the piston after 2 motos

1 moto=30 minutes+2 laps.

You are correct, I've raced and wrenched on dirt bikes most of my life and the KX500 is rated at 55-62 hp depending on the year, however, they are spooky fast - no doubt about that

 

[Mr.]

Derbi GPR 50

[More Pictures] [Compare Bike]
[Discuss this bike on the forum.]

Stroke: 2
Cilinders: 1
Displacement: 49.9 cc
Bore and stroke: 39.8 x 40.0 mm
Cooling: Liquid
Lubrication: Seperate, automatic
Horsepower: 9 HP
Kilowatts: 6.6 KW
Carburetor: Dell'Orto PHVA 17
Ignition: CDI
Gears: 6
Dry weight: 85 KG
Starter: Electric
Fueltank capacity: 7.25
Estimated price: 2700,- Euro's

Back to the Main page

 

[BloodOnTheIce]

Yes the major chainsaw manufacturers could make a 30hp chainsaw, but how much would it cost? how long would it last? and how much would it weigh and who would buy it? It's nice to daydream about a 30hp production saw but it's not realistic.

 

[wanab]

My 500 last about 200 hours before it is time for rings, and I have about 65 hours on it and it is around 162 psi, and the factory spec is 164 psi. With the big transfer ports, power valve,reeds,slide carb, and turned exhaust my bike produces around 100 hp at the engine and around 65 to 70hp at the tire at 7000 rpm. The CRF 450 does not like the KX500 too much.

i think some of the factory bikes (hon,yam,husky)where rumored to be a bit over 70HP. heres the thing about bikes. you body can only ride so much HP. they could have made more.


200 hours on rings? with 65 hours on rings you will be lucky to make 100, under the best of conditions. the bike may still run but...


you looking ay about 10% loss to the rearwheel on a dirtbike, not even close to the 30% you state.

with the 2 stroke MX'ers they found about 40 RWHP to be optimal. i think with the 4 strokes it may be a bit higher.

 

[drmiller100]

pretty easy to get a 1000 cc 2 cylinder snowmobile engine to make 180 horsepower.

cut one in half, and you have 90 ponies.

i'm told by very reputable folks the cr500 can make at least as much power as the sled motors.

sled motors only need to survive 500 or 600 hours of WOT.

 

[2000ssm6]

100hp out of a KX/CR 500? That would be crazy fast. I had a Kx265 that made about 50hp at the wheel, my arse spent more time in the dirt than on the seat. Loads of fun though.

I did get the chance to ride a CRF450 a few months back. One of the guys riding with us washed out and busted up his knee early in the day so I put him on my 400EX and I grabbed the CRF, big mistake, LOL. That bike was a beast, rode it for about 2 hours and was beat, dam what a workout.

 

[TimberMcPherson]

The RS125's put out more than 37hp, standard they were over 40 back in the 90's, and from what I read they are able to be made to push 50 now. I was racing RGV250's at the time and was looking at buying a rs125 new from japan. Even if we are talking different hp measurements its tough to see that theres only 10hp between a 50 and 125.

Heres a question. If the 500's were 180hp, the 250's were 80hp, the 125s were 40 something hp, if you look at the ratio of displacement VS hp, how can the 50cc be 27hp?

 

[jonseredhusky]

The RS125's put out more than 37hp, standard they were over 40 back in the 90's, and from what I read they are able to be made to push 50 now. I was racing RGV250's at the time and was looking at buying a rs125 new from japan. Even if we are talking different hp measurements its tough to see that theres only 10hp between a 50 and 125.

Heres a question. If the 500's were 180hp, the 250's were 80hp, the 125s were 40 something hp, if you look at the ratio of displacement VS hp, how can the 50cc be 27hp?

Sorry mate. I meant to say the 125 makes 37 BHP at the rear wheel not the crank. Oops!! But the latest 250's make over a 100 HP at the crank now. The 125's now make 60-70 BHP at the crank. The 50's now make 30 BHP at the crank. About 20 at the rear wheel. Thanks for the interest!!