[som]

I was just curious as to why Harley puts such large engine in their motorcyles. It's not like a truck where you get pulling power. Super Bikes have quite a bit smaller engines and they can obtain fast speeds and as far as I know harleys are not the 'fastest' bikes in the world..

I am not trying to flame harley in any way, I am trying to come up with an answer in why Harley uses such large engines when in my mind they are not being used to their full capabilities.

 

[JMS]

Long stroke (undersquare bore) = Low rpm torque = pulling power.

JMS

 

[som]

But why, It's not like you pull anything on a motorcyle. There has to be other reasons why they make them with such large engines. Is it for the unique Harley sound?

 

[dave51]

The larger the engine, the shorter the penis. Which is why I ride a Honda Trail 70.

Just kidding guys.

 

[Kags]

Its all about torque. Thats the name of the game . All TC's will out pull (in torque) alot of supersports. Only the liter class has more & keep in mind the rev nearly twic as high. If you want to move a 700lbs bike down the road quickly you need a big motor. The newest liter bike barely weigh 400 lbs.
Looks: the American V-twin is one of the most eye pleasing motors in all of motorcycling.
Air cooled: the fins add bulk/ over all size in looks.
Easy to work on: let me see you (or anyone) replace the pistons on a ZX6R without removing the motor. ever try to work on the carb on one of them bikes? How about chainging a fouled plug, better hope its the # 1 on a Honda and you still need take the plastic off.

 

[JMS]

som, who is "they", what is "them" and what is your definition of large ?

JMS

 

[som]

Its all about torque. Thats the name of the game . All TC's will out pull (in torque) alot of supersports. Only the liter class has more & keep in mind the rev nearly twic as high. If you want to move a 700lbs bike down the road quickly you need a big motor. The newest liter bike barely weigh 400 lbs.
Looks: the American V-twin is one of the most eye pleasing motors in all of motorcycling.
Air cooled: the fins add bulk/ over all size in looks.
Easy to work on: let me see you (or anyone) replace the pistons on a ZX6R without removing the motor. ever try to work on the carb on one of them bikes? How about chainging a fouled plug, better hope its the # 1 on a Honda and you still need take the plastic off.

Thanks alot, You clarified alot for me. I never really thought about how much less a super bike weights in comparison to a Harley!

 

[Kags]

I forgot to say the baggers come in over 800lbs...

 

[som]

My basis for starting this thread is that I have a Yamaha YZF-R6, And I raced a 2002 Honda shadow that was 1300cc. ( I know Hondas are not Harley's but for comparison sake)

There was no comparison. Off the line I was in the lead and finished even stronger and farther ahead of the Shadow. even though the shadow has
double the engine size.

This sparked my intrest in why would bike manufactures make a bike with such a large engine, It seems to me that they are not useing the engines to the full capabilities.

I know someone earlier stated that it was torque. Now I ask why do you need toruqe, You don't nessicarily pull things one a motorcyle.

Can someone help me clarify this please.


In a side note, This thread is not degrating Harley or Street bikes in any way.

 

[JMS]

som, carrying something on a scooter = pulling something. An engine with a lot of torque at low rpm that redlines at 3000 rpm (like my tractor) can pull a house (push, pull, carry). Try this, load your bike to the GVWR and ride around, borrow a Shadow loaded to the GVWR and ride around. I think that you will then understand.

JMS

 

[som]

Thanks JMS, I understand now.

 

[ChopperDude]

Also...

Could there be something to "less RPM's (Harley) relating to longer engine life"?

Think about it... with superbikes, it takes LOTS more revs to make them go. But that's also what makes them more disposable. A Harley engine has a much longer life just because it goes through so many less RPM's.

Most objects have a certain lifespan... once you've used up that lifespan, you gotta throw it away. Superbikes use up their lifespan due to the many RPM's they use in doing work, whereas Harley engines use much less RPM's in doing their job.

Realize, I'm compressing a lot of argument into a little space here... but I think this is a MAJOR difference between the long life of a Harley engine, compared to the shorter life of a superbike engine.

A piston can only go through it's cylinder so many times. A superbike exhausts that number faster than the harley.

 

[Ol Rob]

I have seen very few super bike type engines actually worn out. The bike is generally wadded up way before the engine expires. I have heard of many making it past the 100K mark though. I think it is all in the maintenance as with anything.
Try this on for size, a lawn mower turns at 3000-3500 rpms and cuts a 22" path, give or take. A weed eater turns at 9K-11K rpm and cuts a 10" path. Kinda how I compare a Harley to a crotch rocket. LOL Just kidding, no flame intended -Rob

 

[roycrown]

27 years ago I had a Yamaha RD 250, a very nice bike at the time. Sharp looking, very quick, great handling and brakes, plus the added benefit of "that smell" (2 stroke). A riding buddy traded his DT 250 on a brand new SuperGlide. He was one of the VERY few Harley riders at that time who would ride with us "regulars" on our Yammie's/Kawa's/Suzie's etc. Almost daily I would challenge him to some sort of accelleration contest. Every sinlge time I would get him easily out of the hole and be 2 or 3 bikes ahead of him up to about 30mph or so. From 30 to 75 he was "right there" with me, not ahead of me, not even beside me, but in my peripheral vision. After 80mph he would pass me, and be gone, long gone. I used to think it was cool that a 250cc. could "outrun" a 1200cc. up to 75mph. My 250 gave itself up for the Rising Sun just as the 70's came to a close. My freind still has and still rides that same SuperGlide.

 

[Kags]

I have to disagree there Chopper Dude. Ive seem 45,000 mile sport bikes that look and sound as good as many other low mile sport bikes. It is all about how well the bike are cared for & of course how hard there ridden. The majority of Harley owners would agree rev a BT to the red line all the time and you have a rebuilt on your hands quickly. Rev a sports bike to red line all the time and it will last just as long but more than likely longer than any Harley motor. Fact is not even sport bike rider go around hitting the rev limiter all the time. A GSXR-1000 is as fast as my 95" FXDXT when its only rev to 5000 prms & I got to go to 6000. 4 cyc dont always need to be reved high.

Compairing V-twin's to inline 4's is near pointless. The real reason for the HP difference should be simple to understand. 4 cyc. motors have power on every stroke, a V-twin every other stroke. The basic enginerring make all the differance. Add high CR water cooling ect and the motors are worlds apart.

The fact remains that the 4's tend to have less torque and more HP then the V-twins.

 

[SIN]

You could say a Harley and a "super bike" are like a NASCAR and a Formula one.

The NASCAR engine is limited to a lower RPM by design and has to power a much heaver vehicle "like a Harley it's the torque that gets the car up to speed. It has to rely on torque to get it up to speed.

The formula one is lighter and can turn about twice the RPM but it is horsepower not the torque that the vehicle uses to get up to speed.
Being much lighter and no need for as much torque it is able to use much lighter engine parts and reduce the recipacatiting weight by design
That is what gives it the ability to turn high RPM' and not come apart.

In racing you want the best of both worlds but have to settle for the highest power to weight ratio depending the limitations of your design.

The antiquated design of the Harley engine is limited in RPM due to its design but it makes up for that with its torque and simplicity.

 

[JMS]

Crankshaft torque : for a given displacement, the number of cylinders is irrelevant. The reason that some engines have more crankshaft torque than horsepower, for a given displacement,at a given rpm, is directly related to the stroke. Now, you get into piston speed and friction and G forces related to piston/rod weight.The reason that muticylinder engines can make more horsepower (simplified) is that the piston/rod/valvetrain weight is less, allowing higher rpm's.
Rear wheel torque : depends on gearing, if you could have an unlimited transmission size, you could have 100 ft-lbs of rear wheel torque from a 20 c.i. engine, though to go 70 mph you would probably need 20 gears. Torque is an objective, measured quantity and has nothing to do with the # of cylinders. HP is a calculated #, derived from measured torque. Note in this equation that torque = horsepower always, in any motor, at 5252 rpm : HP = torque x rpm / 5252 .

JMS

 

[supersport]

I wonder, for the sake of comparison. If you rev limited a V-Max and A full tilt boogie 95" Dyna(hi-comp, tweeked carb, hot cams and ign.) to 3000 RPM and dragged 'em out which would come out on top?

 

[JMS]

SIN, stroke, piston & valvetrain weight limits rpm. If I remember correctly, a pushrod mercedes benz engine won the 1994 Indy 500. Don't quote me on the year.

JMS

 

[SIN]

Yea your right JMS little AL