Why, if the power tappers off, does it still pull hard past its peak power? I dont hit a wall or a taper off, or is it too small to notice?

 

I have to correct this - this statement is not correct - the 'always' part. Do some googling and you'll find lots of engines rated for more torque than horsepower. For example, check out the chart here: Motorcycle Performance Data and Specifications - Motorcyclist Magazine

Look at the Harley resultsThe exception being the V-Rod)
motorcycle measured hp (@ rpm) measured torque (lb. - ft. @ rpm)
FLHCRI Road King Classic ('99) 62.4 @ 5250 77.2 @ 3000
FXDSE Screamin' Eagle Dyna ('07) 89.4 @ 5500 105.2 @ 3000
FXDX Dyna Super Glide Sport ('99) 62.5 @ 5500 76.3 @ 3250
S.E. Road Glide ('00) 70.8 @ 5250 86.4 @ 2750
Sportster 1200 Roadster ('04) 67.4 @ 6000 72.2 @ 3750
Sportster XL1200S Sport ('98) 57.0 @ 5250 66.3 @ 3250
V-Rod ('02) 109.3 @ 8250 74.3 @ 7000


Read more: Motorcycle Performance Data and Specifications - Motorcyclist Magazine

 

If you've 'chipped' or otherwise modified/piggybacked the ECU, I'll pretty much guarantee that you're making more power, particularly if you can feel it - although you might not make any more peak HP, and therefore not get a higher number on a dyno, although most people won't spend the money on a quality ECU mod without getting more power out of the engine as a result. I do agree, however, that sometimes a modification may not make any more 'peak' HP (or Torque), but it will 'feel' faster and it probably is - in particular RPM/load ranges and situations, but may not make any more peak HP. A lot of people concern themselves with the peak HP and Torque figures, but a good dyno curve (HP and TQ) will perform better in almost all situations than a dyno curve that looks like a massing spike hitting a high(er) peak HP/Tq but having no substance throughout the rev/load range. A dyno will also, as mentioned, measure at WOT, not really measuring the responsiveness of an engine etc.

 

Dump trucks have more torque than hp, so do big block v8's (stock). And I agree that peak hp and torque figures are just baseline, a bike with 50hp and 50 ftlbs of torque with a sluggish musshy throttle response won't feel as good as a bike with 30 hp and 30 ftlbs of torque with amazing pumper carb or EFI throttle response

 

Ahh.. HP is a calculation. Torque is what's measured. Everything you feel is based on the torque curve, its' shape, over the given RPM range the engine is capable of. The peak torque figure and the RPM it's at is used to calculate HP. Big peak torque down low can be a lower HP engine than less torque peak numbers at higher RPM. Study the formula. HP = (RPM x TQ) / 5252
What you have to eventually realize is that a broad bell curve of torque is what makes a great engine and that peak HP isn't anything but a talking point.

 

This is because HP is a function of engine speed(rpm) and torque output. The torque figure will always be greater than HP at engine speeds below 5252 and HP will always be greater than torque above that rpm. That's how F1 engines makes huge HP numbers from small displacements because they spin up to almost 20K rpm. Formula for HP is torque(in lb/ft) X rpm / 5252 So an engine that produces 100 lb/ft of torque@ 5252 rpm makes 100 HP. If it still makes that same 100 lb/ft of torque @ 10504 rpm it now produces 200 HP. So what is more important? Simple analogy-torque is what accelerates you and HP determines how fast you go(top speed).

 

Damn-a little to slow on the response...

 

I like torque better

 

I'm talking rpm, not peak numbers, since that is what was being questioned - why the engine can rev beyond the power peak (torque). Horsepower will always peak at a higher rpm than torque due to the way that it is calculated. They will always have the same value at 5252 rpm because of the formula that calculates horsepower: hp = torque x rpm / 5252. Torque is the measure of power, horsepower is a measurement of ability to perform work using said power. There is usually enough torque at rpm above the peak to continue to work, especially in a high performance engine.

That is why the bike will continue to rev beyond its torque peak. The engine will actually pull until something holds it back; either the torque falls so low that it can't push the wind aerodynamically, hits the rev limiter, hits a flow limit for the engine, or flat out breaks something - aka float the valves. Fact is most bikes redline above peak horsepower, why I do not know. My old 400 triple, my Nighthawk S, Gold Wing, KLX650, and Zephyr all had the tach redline above the actual peak horsepower rating.

Many off roaders are designed to allow minor over-reving without hitting the limiter to enable the rider to run a bit further on a straight when the corner is just a shade further and a shift would actually cost quickness on the track. They run it in over-reving a bit rather than shift.

With two strokes it is near impossible to mechanically damage them by over reving them since there are no valves and the bottom end is all ball or roller bearings. The only way they blow is if there is some overstressed part or if the engine runs lean. They just run out and go flat on pull power.

 

You mean you don't like that surge you feel above the torque peak?

That is the engine's ability to perform work beyond the power peak. Realize that 25 ft-lb torque below the torque peak is as good as 25 ft-lb torque above your peak of 30 ft-lb. It is as strong at either side. That is why it pulls so strong up above the peak torque. There is adequate torque remaining to have it pull strongly - as strong as it would on the way up, but tapering off instead of growing.