dragbikercr
Expert Class
Posts: 197
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posted June 17, 2011 07:22 AM
Shift points rpm and torque question...
Ive been searching all over this website on shift points for drag racing. I see alot of guys are shifting at approximately 10,500 - 11,200 rpm. Now at this rpm is this for mph only, or is it for e.t. and mph?
Reason I ask is a guy at the track dyno'd a 14 and said the shift point should be at 9,750., any higher rpm and your running out of the power curve. Is this the torque curve for e.t or what is this about?
Kinda confused and looking for a little knoweldge on these shift points...
  
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smokinZX14
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posted June 17, 2011 07:45 AM
The closest to the limiter you can get without hitting it will yeld the best MPH and ET .. Tach will show 11200 but the real RPM is right around 10600 ..
____________
Smokin Performance Cycles..
Tampa Bay , FL .. Brocks Performance Dealer ..
Gen 2 ZX14R Best ET 8.43 , Best MPH 164.95
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Shane661
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posted June 17, 2011 07:57 AM
 Edited By: Shane661 on 17 Jun 2011 15:58
On the two 14's we have the limiters were at 10980 and 10960 as tested on the dyno. They can spin close to 11500 on the tach, but as Lee says, you will want to shift a bit earlier than that. 
I always test the limiter and see what it says on the tach; just the angle you view it from can make a difference as to the "number" you see.
Shane
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dragbikercr
Expert Class
Posts: 197
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posted June 17, 2011 08:01 AM
So setting the shift point for about 10, 800 - 11,000 rpm would yield the best e.t. and mph and still be safe for the engine?
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Shane661
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posted June 17, 2011 08:02 AM
Edited By: Shane661 on 17 Jun 2011 16:06
quote:
So setting the shift point for about 10, 800 - 11,000 rpm would yield the best e.t. and mph and still be safe for the engine?
Are you using an autoshift? 10800 would be a safe # to try, imo. You aren't going to hurt the engine anywhere below the limiter, unless there are other issues.
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Shane661
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posted June 17, 2011 08:04 AM
Edited By: Shane661 on 17 Jun 2011 16:07
What the dyno guy is missing is the "shift recovery rpm". You want the bike to be making a lot of power when it grabs the next gear....and shifting at 9750 is not the ticket for that. The rpm will drop out of peak power when it goes into the next higher gear.
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dragbikercr
Expert Class
Posts: 197
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posted June 17, 2011 08:30 AM
Yup I am using the Raptor Performance shift light with autoshift.
The shift recovery makes sense. It would then drop rpm to far to recover quickly without the bike working harder, losing e.t. and mph.
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Shane661
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posted June 17, 2011 08:33 AM
If you want to get an idea of where the rpm will drop on your shifts, use this tool:
http://www.gearingcommander.com
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dragbikercr
Expert Class
Posts: 197
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posted June 17, 2011 08:56 AM
Thanks Shane. Awesome website to mess around with, "what if" scenarios.
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GREYHOUNDMOSES
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Posts: 324
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posted June 17, 2011 09:13 AM
Edited By: GREYHOUNDMOSES on 17 Jun 2011 18:48
Can anyone explain why the shift point is done on the power curve and not the torque curve.
I always believed acceleration came from torque?
The dyno guys figure for revs corresponds well with using the "hump" of the torque curve.
BTW I've tried shifting to use the torque peak and it DOESN'T work but I can't grasp why. 
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smokinZX14
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posted June 17, 2011 02:29 PM
quote:
So setting the shift point for about 10, 800 - 11,000 rpm would yield the best e.t. and mph and still be safe for the engine?
You will have to test it and find out what is best RPM for your set up .. Keep in mind a dyno acts different than the track .. On a dyno you might see the rev limiter at 10800 but on the track you may see it come in at 10600 .. Here is why , on a dyno you have the drum spinning .. The drum over rides the soft limiter and bangs into the hard limiter .. The drums weight causes this problem ..
You really can't feel but you can see it on a dyno , the power will start to tail off and then you will smack the hard limiter ( that you can hear and feel ) My best guess it the soft limiter is 200 or so RPM below the hard limiter .. Again you will have to test a few different RPMs to find the best RPM for your set up ..
____________
Smokin Performance Cycles..
Tampa Bay , FL .. Brocks Performance Dealer ..
Gen 2 ZX14R Best ET 8.43 , Best MPH 164.95
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entropy
Moderator
Posts: 8671
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posted June 17, 2011 02:47 PM
Edited By: entropy on 17 Jun 2011 22:52
quote:
Can anyone explain why the shift point is done on the power curve and not the torque curve.
I always believed acceleration came from torque?
The dyno guys figure for revs corresponds well with using the "hump" of the torque curve.
BTW I've tried shifting to use the torque peak and it DOESN'T work but I can't grasp why.
This is an excellent question, one I wrestled with when i was drag racing.
torque is force at a given rpm
max torque is where yr motor is running at max efficiency, air/fuel in, burnt air out.
tq falls off at hi rpm as yr motor is gasping for air and efficiency drops, but even tho each rpm is producing less force, you have more rpm.
whereas
horsepower is energy, basically tq x rpm (a simplification)
hp is what gets you down the track.
hp peak is almost always at a higher rpm than tq peak.
as stated above look at yr hp curve to determine shift points.
Almost always optimum shift points are as close to the limiter as you can get.
ALMOST ALWAYS. 
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rotts4u
Novice Class
Posts: 95
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posted June 17, 2011 08:00 PM
Here is an article I wrote on this topic a few years ago for Sport Rider Magazine. This should tell you the answers you seek
http://www.sportrider.com/tech/146_0402_art/index.html
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entropy
Moderator
Posts: 8671
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posted June 17, 2011 09:42 PM
quote:
Here is an article I wrote on this topic a few years ago for Sport Rider Magazine. This should tell you the answers you seek
http://www.sportrider.com/tech/146_0402_art/index.html
Don,
great article (as usual) 
Karl
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GREYHOUNDMOSES
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posted June 17, 2011 11:14 PM
Assist: http://www.sportrider.com/tech/146_0402_art/index.html
Great info. Thanks.
It clarifies what I knew to be true but couldn't explain!
I haven't run the numbers yet but I suspect with the ZX14 power curve for most people (without a built motor) the "driving force" curves won't cross in any gear giving the theoretical shift point in all gears as close to the limiter as possible without hitting it. Just as we thought 
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BobC
Pro
Posts: 1736
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posted June 18, 2011 02:18 AM
If you look at the shape of the power curve you will see that it drops very little between peak power and the engine rev-limiter. Which is why you hang on to a gear for as long as possible for maximum acceleration.
____________
Candy Thunder Blue 2006 ZZR1400
Stock wheelbase
Max: 205.4 mph in 1.25 miles
2012 ZZR1400 in Golden Blazed Green
Brock CT Full System. etc
Max: 203.1 in 1 mile (so far)
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