Anyone know why a Harley Motor puts out less power

[No_6]

In last month's Motorcyclist, they review the new $30,000 Buell racebike. It has a 1.4l Harley Pushrod 45 degree twin putting out about 150HP (crank) and 100 ft/lbs of torque. By comparison, the $17,000 Ducati 999R turns out 150HP and 98 ft/lbs of torque and is a 0.998 l, 90 degree V-twin. Of course the Duc revs 3,000 RPMs higher, and you hit the meat of the torque about 1,200 rpms later than the Buell; but still, same HP/torque with 40% less displacement. What's up with that?

 

 

 

Is 45 degrees a less efficent V angle than 90? Does the pushrod design create greater inefficiency? Is it the fact that the Buell is air-cooled?

 

 

 

Inquiring minds must know.

[Boxologist]

probably cam duration and compression ratio differnces. i'm not solid on motorcycle tuning.

[slngsht]

In last month's Motorcyclist, they review the new $30,000 Buell racebike. It has a 1.4l Harley Pushrod 45 degree twin putting out about 150HP (crank) and 100 ft/lbs of torque. By comparison, the $17,000 Ducati 999R turns out 150HP and 98 ft/lbs of torque and is a 0.998 l, 90 degree V-twin. Of course the Duc revs 3,000 RPMs higher, and you hit the meat of the torque about 1,200 rpms later than the Buell; but still, same HP/torque with 40% less displacement. What's up with that?

 

 

 

Is 45 degrees a less efficent V angle than 90? Does the pushrod design create greater inefficiency? Is it the fact that the Buell is air-cooled?

 

 

 

Inquiring minds must know.

 

 

 

Probably none of those...

 

 

 

First suspect is cam design - perhaps harley goes for more torque at the low end and sacrifice top end power.

 

 

 

Second is combustion chamber design - maybe they're just not as good.

 

 

 

Less absolute power is not necessarily a bad thing. In my opinion, hp/liter is the most over-rated way of determining how "good" an engine is.

 

 

 

The things that really matter are packaging and weight considerations - like power / weight of engine; and brake specific fuel consumption - how efficiently the engine produces power.

 

 

 

Also, unless it's hooked up to a zillion speed tranny, and you want to shift all the time, the dynamic range of the engine is very important. Another way to look at that is the area under the torque curve.

 

 

 

You may have an engine that makes great power numbers between 8K and 10K, and everybody goes wow, but the engine that makes more conservative absolute numbers between 2K and 7K is a better engine IMO.slngsht2006-12-18 07:00:03

[Birkin42]

There are so many things that affect torque/power curve & efficiency of an engine. Displacement is just one factor. The higher technology engines tend to use more rpm's to get the air flow so they can keep the size and weight down. Look at an F1 engine with about 800 hp from 3 litres and 8 cyliners run at 19,000 rpm. A MotoGP bike engine is about 245 hp from 990 cc's, but they need a bit more smoothness in the power curve since the bike isn't much over 350 lbs.

 

 

 

In the case of an air cooled Harley, it's biggest problems are the rotating interia (very long rods and very heavy crank), poor cylinder head geometry caused by the layout & push rods, and getting rid of heat (particularly from the rear cylinder). Most air cooled engines can be tuned to make a lot of hp, but not for very long. There are some pretty fast HD drag bikes for example.

 

 

 

I last road a Buel back in 98 and I was pretty disappointed. I hit the rev limited before I thought I was even in the power band. A current at that time Japanese 600 would eat it for breakfast, and it was the top of line, fastest Buel they had on offer.

 

 

 

I would think that some of the newer liquid cooled models have a bit more potential, but you have to keep in mind who HD is selling bikes to and what they want. They want a cruser bike with a wide torque curve. Big hp, other then for braggin rights, isn't really important.

 

 

 

Japanese and Italian sport bikes on the other hand are looking for big power from the smallest, lightest package. They live or die by the results on the track. Hense next year there is always lighter or more powerful bikes coming out. These are great fun to ride in a sporting manner, but aren't always as flexible and as easly to ride as a torquey motor when just crusing.

 

 

 

In comparing them to car engines, most car engines are like the HD. If you want a screamer like a sport bike engine, look at a VETC Honda with a 8 or 9000 rpm red line and not much torque.

 

 

 

I guess it depends on what you like and want. For me, for a daily driver, torque is nice, but to have fun, give me rpm's with a reasonable, but not too wide power band. Maybe not the fastest or most forgiving, but very rewarding when you get it right.

[No_6]

Good answers, thanks.

 

 

 

The Ducati has just as much torque as the Harley motor, it's just spread out a little more.

 

 

 

According to the article, the Buell has no power curve. You're getting nearly 100% of the power from the second you crack the throttle. The reviewer said that the back tire would spin up no matter how little throttle you gave it. To me, that sounds like a bike that would be nearly impossible to ride anywhere but the racetrack, and even then it sounds, frankly, deadly--and I don't mean that in the tough-guy competitive sense, but in the hair-trigger, send your rider off the bike in a high-side sense.

 

 

 

I definitely appreciate good torque... no matter what kind of vehicle I am in or on, but it has to be usable.

[slngsht]

Good answers, thanks.

 

 

 

The Ducati has just as much torque as the Harley motor, it's just spread out a little more.

 

 

 

According to the article, the Buell has no power curve. You're getting nearly 100% of the power from the second you crack the throttle. The reviewer said that the back tire would spin up no matter how little throttle you gave it. To me, that sounds like a bike that would be nearly impossible to ride anywhere but the racetrack, and even then it sounds, frankly, deadly--and I don't mean that in the tough-guy competitive sense, but in the hair-trigger, send your rider off the bike in a high-side sense.

 

 

 

I definitely appreciate good torque... no matter what kind of vehicle I am in or on, but it has to be usable.

 

 

 

If it's truely that overpowering, then it's a good engine... they just need to have a smaller version of it on the bike.

[No_6]

If it's truely that overpowering, then it's a good engine... they just need to have a smaller version of it on the bike.

 

 

 

If it were smaller, it wouldn't be anywhere close to competitive to the bikes it is racing against... 600cc I4s. As it is, their best finish (when they've managed to finish at all) is 8th...

 

 

 

Oh yes, I forgot to mention that the motor breaks. A LOT. At the Daytona 200 this year, all 4 of their bikes broke and DNF.

 

 

 

I wouldn't go so far as to say the motor is overpowering. It's just an all or nothing motor. There are plenty of bikes out there with way more horsepower/torque but are much, much easier to manage. That Harley would be left for dead by any I4 750 or 1000, or the liquid-cooled 999 V2.