Top speed and horse power curves

[ROCKAFELLA]

Would a bike with a linear power curve be able to produce a higher top speed than a bike that hits max power at a lower rpm and holds it to redline? Meaning a bike with a power line that increases all the way through the rpm range instead of one that hit max power at say 8,000 rpm and held that power clear to max rpm?

Comparing 2 bike that made the same hp and had the same gearing.  

[Steve A]

Both same top end.

2nd example - drag racing.

[BusaGeek]

It sounds like you are describing a torque curve rather than a power curve.  A flat torque curve is the same as linear power curve.  I've never seen an engine that holds constant power for 3000rpm.  

I think you meant to compare a bike with a peaky torque curve (non-linear power curve) to a bike with a flat torque curve (linear power curve).  In that case, both bikes would pull the same ultimate top speed unless the peaky bike fell out so bad that it couldn't get into the peak in sixth at all, or if it were geared badly.  The linear bike wouldn't have either of those problems.

Flip side of the coin -- if the two engines are similar in size and configuration, the peaky one will almost always have higher HP numbers.  That's why it is peaky, the owner tried to squeeze a few more ponies out of it at the cost of driveability.

[StreetnTrack]

Rock, shoot me a email or give me a call.

[ROCKAFELLA]

I'll call you today Chuck.

Hey busageek - my bike hits 300hp at 7500rpm, peaks at 315hp, and still has 300 at 10000rpm - so ok it holds 300hp for only 2500rpm.

I am trying to get some opinions to compare with someone who is close with Velosity that said a bike that makes power all through the rpm range would run a higher top speed than one such as mine{one that peaks early, but still holds}.

Once again I am talking same hp numbers with same gearing.

[THEMOTORHEAD]

the bike with the longer curve will accellerate faster and go the smae speed as long as the hp numbers are the same where rpms and top speeds meet.
a non intercooled bike will loose about 20% of its hp on the road over 1 on the dyno(inake temps on the dyno reach only about 120 degrees vs road of temps of 275-300 and water injection my drop the temps but it will never restore the lost hp the orig temps created)

the only thing the non intercooled bike will have is less air drag due to air passing through the radiator only and not also through a cooler
vs an intercooled ones
due to the charge temp climb(long pull)
if you want even more hp on top just mod your wastegates exit hole
how much is up to you  

[Lofty]

It depends on how radically the bike with the broader power band made its power. If you have a power curve that skyrockets from 2000 RPM straight up to 8000 RPM before it starts to level off, thats going to be a very difficult bike to ride, especially from a dead stop launch. It might make more power but controling the power is the key.

As far as where the bike makes power, for straight line racing, Ill take a bike making more power near the rev limiter, than one that made its peak at 8 or 9 thousand RPM and started dropping after that. Even if it made more peak HP.

Its a common misconception that you want to sacrifice peak HP at redline for more power at the mid range. That mentality comes from road racers that are always on and off the throttle going in and out of turns and theyre constantly accelerating from the mid range of the rpm band.

For straight line racing, I dont care what my mid range power is like. Im only gonna be in the mid range power band for one gear, after that, its all shifting near the rev limiter.

The picture below is a crude example of a dyno sheet with different power curves. For straight line racing, Id rather have the red bike. Sure the blue bike makes 25 more peak hp than the red bike, but it does it all the way back at 7500 RPM. At the rev limiter, its making 25 less HP.

Heres the scenario. Both bikes line up to race from a dead stop for one straight mile, all 6 gears.

When they launch from first gear, the blue bike pulls hard but has to bobble the throttle to keep from either spinning the tire or flipping over. The power curve is sharp and aggresive, hard to control. The red bike is pulling smooth and predictably all the way to the rev limiter, easy to control. For the sake of the discussion, lets assume the blue bike pulled ahead by 3 bikes though. Now when they hit second gear, thats the last they'll ever see of the mid range power of either bike. Assuming they shift at 11,000 RPM, the revs are gonna drop back during the shift to lets say 9500 or 10,000 rpm on a quick shift, then they climb back to 11,000, shift to 3rd, back from 9500 to 11,000, shift to fourth and so on till the race is over.

So, after 1st gear, the blue bike never got to take advantage of its higher HP because it was all the way back at 7500 RPM, not where he was shifting at. From 10,000 to 11,000, the blue bike was actually dropping in HP whil the red bike was making more and subsequently pulling away from the blue bike.

 

class over  

[BusaGeek]

The blue bike will beat the red bike as long as he is smart enough to shift at 8000rpm.  He'll need a little taller gearing to beat the red bike at the top end.

Rockafella,
I didn't realize you had a turbo.  Non-turbo engines can't hold the HP peak, but a turbo can because the peak is essentially artificially set by the waste gate.  The bike doesn't really stop making power, you just decide that you don't want it to make power any higher.

[THEMOTORHEAD]

YUP THE BLUE BIKES THE BETTER STREET BIKE
IT SPOOLS FASTER AND IS MORE FUN TO RIDE
BUT IF NOT GEARED FOR ITS POWWERRBAND(WHICH DROPS TO MUCH)(WASTEGATES BLOWING OPEN OR SOMEONES GOT A LIGHT DYNO DRUM AND IS LOOSING LOAD THUS BOOST).
PERSOANNALY I LIKE THE BLUE CURVE(decent accept the drop)
JUST LIMIT THE WASTEGATES FLOW OR TRAVEL(ABOUT $5}
AND IT WILL CARRY RIGHT TO REDLINE LIKE THE SLOW SPOOLING BIKE WITH THE MORE EXPENSIVE WASTEGATE THATS NOT A SWING TYPE THUS NOT IN THE EXH PATH THUS LESS PROWN TO GET PUSHED OPEN BY GROWING STRENGTH OF THE EXH. PULSES IN THE UPPER RPMS

[NLR-power and control]

yep,
for a streetbike Ill take the blue...alot more fun and fun is what it is about. It will respond faster and pull harder. It will make more torque and thats what you want...gear it right and away you go.

[ROCKAFELLA]

Well this whole topic was to try and find out if this Velocity turbo owner was right about his 300hp bike going faster on the top end then one with a 300hp MCX kit. He said the linear power curve would allow it to go faster because it built power this way. I figure 300hp at 10,000rpm is 300hp at 10,000rpm. So both hitting the same numbers and using same gear would do about the same speed.

[Lofty]

Re-gearing the bike and short shifting it aint gonna work. If you shifted it at 7500 and Im shifting at 11,000, Ive got another 3500 RPM to play with. I can run a shorter gearing and go the same speed which means Im gonna pull harder through the gears and Ill be makin power while youre shifting.

If both bikes are making the same peak horsepower at the same rpm, then the bike thats been making it longer will get there first, considering the power is controlable.

Dennis, I understand what you mean when you talk about a torquey bike that makes its peak power real fast being fun, but thats all its good for. Insanely fast rising torque and HP curves are only good for smoking the tire at 100 MPH, not for acceleration contests.

We've done this over and over and over again down here, not just with turbo bikes but naturally aspirated as well.

[BusaGeek]

Lofty,
That logic only hold if the blue bike is stupid enough not to gear differently for his bike.  Since he makes peak power at 7500rpm, a 28T rear sprocket should do the trick.  Now each gear will carry him a long way and he won't be shifting all the time.

325HP at 7500rpm = 227.5 ft-lbs of torque, 300HP at 11000rpm = 143.2ft-lbs of torque.  That is 1.6 times the amount of crankshaft torque as 300HP at 11000rpm.  He can easily pull the gears.

[Lofty]

How do you figure your HP to torque numbers?

[BusaGeek]

HP = torque * rpm/5250

That won't give peak torque, but torque at the point in question.

[Lofty]

OK, I was gonna say, when I turn the boost down on my bike to make 300 and it does it near the limiter, it makes way more than 140 foot pounds of torque.

[Dwight-PA]

[Lofty]

Anyone who thinks a 300 HP bike at the limiter isnt gonna be fun to ride is either demented or just plain crazy.

Heres my bike at around 16 pounds of boost, more fun than most would know what to do with.

 

Turn it up to 21-22 pounds and you get this.....insane!!

 

[BusaGeek]

Dwight-PA, I just used that as the easy way out.  The best solution is overdrive gears and an 18/38 combo.

Lofty, I think my 200HP bike is fun and I would be thrilled to ride a 300HP turbo 'Busa.  But the blue bike would still win.  Also the blue line really looks like it has 450HP potential with a few minor adjustments.

[Kirk]

What about the purple bike?  

[Dwight-PA]

[Dwight-PA]

[Lofty]

quote:Originally posted by Kirk:
What about the purple bike?    

Shes not gonna be purple anymore.

Heres what she looks like right now.

 

[Spinn]

Personally I would rather have the red line rather than the blue. I care more about going fast than thinking that I am going fast. I am not saying that the blue is slow but I think that the red would be faster for top ends and drag racing. With the red line it is easier to go faster. I am not a drag race expert but I did not think any drag racers shift throug all of the gears 3000 RPM's below redline. Once again I could be wrong about the shift points for each gear. I could see short shifting first only.

[THEMOTORHEAD]

for 25 cents the blue line will carry its hp like the red only it will keep its 100 hp advantage in the midrange.
pretty simple and common mod.