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Author
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Topic: Shift points
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bunchmyfunky
CAFords Drag Racing Mod
Member # 360
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posted
 
 
When figuring out shift points do you base it on torque or HP?
Posts: 2433 | From: Vacaville | Registered: Jul 2001
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Pro50Eric
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Member # 2065
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posted
i've always just listened to the motor. you can pretty much tell when to shift. I don't even have a tach in my car. I just listen to the motor and watch the shiftlight. ![[burnout]](graemlins/burnout.gif)
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Recently Acquired!! 68 Camaro Outlaw 10.5
Posts: 107 | From: Va | Registered: Nov 2002
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Stimson
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Member # 51
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posted
Horspower of course. Torque doesn't matter... unless you're a clueless chevy redneck with a beer belly ![[Wink]](wink.gif)
Does your dyno graph show your HP curve at least 500 RPM past your peak HP spot?
Posts: 2373 | Registered: Jun 2000
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Elapid
GOROBGO
Member # 50
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posted
hey sawson, if torque doesn't matter, how come all the performance calculators (top speed, 1/4 mile times, and shift point) require you to input the torque curve and disregard horsepower??
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98 Cobra
83 Notch rolling chassis - fs
Posts: 1797 | From: Grass Valley, CA USA | Registered: Jul 2000
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mustang50
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Member # 2224
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posted
I shift at max hp that way I am always in the power band when racing. Right now its around 5100
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3.73 fms gears, 2 chamber flows, 9mm wires, mac shorty headers, x pipe, k and n, and 70 shot of N.O.S
Coming Soon: heads(ported), cam, and intake
"I only have one thing to say to you............. STRIKE THIS MOTHER FUKCER OUT!!!!"
Posts: 174 | From: san jo | Registered: Dec 2002
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Elapid
GOROBGO
Member # 50
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posted
thanks for calculator link, 93pony
i think i'll try for those 7400 rpm shiftpoints next time @ the track!
woohoo!
they calculate the optimum shift points by minimizing torque loss between shifts.
Calculated Optimum Shift Points
The table below shows your results based on the information you provided on the previous page. Your best shift point will be the RPM where there is the least change in torque between shifts.
Your best shift points are:
Best shift point for the 1-2 shift is 7400 with a LOSS of 342 Lb/Ft of torque.
Best shift point for the 2-3 shift is 7400 with a LOSS of 105 Lb/Ft of torque.
Best shift point for the 3-4 shift is 7200 with a LOSS of 29 Lb/Ft of torque.
Best shift point for the 4-5 shift is 7400 with a LOSS of 29 Lb/Ft of torque.
[ December 22, 2002, 09:41 PM: Message edited by: rob ]
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98 Cobra
83 Notch rolling chassis - fs
Posts: 1797 | From: Grass Valley, CA USA | Registered: Jul 2000
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93PONY
Mr. Valve Events
Member # 60
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posted
quote:
Originally posted by rob:
thanks for calculator link, 93pony
i think i'll try for those 7400 rpm shiftpoints next time @ the track!
woohoo!
they calculate the optimum shift points by minimizing torque loss between shifts.
It's all about the Torque!!! ![[Big Grin]](biggrin.gif)
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www.advancedenginedevelopment.com
SCT dealer
Dynotuning
(916)715-7569
Posts: 4265 | From: Fair Oaks, CA | Registered: Nov 2000
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bunchmyfunky
CAFords Drag Racing Mod
Member # 360
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posted
I ran my numbers thru the calculator and all my shift points are right at redline. For some reason that doesn't seem right to me. Drew is shifting my car by feel and is not seeing the shift light which is set at 5700 and he's running 2mph faster then me. I know I'm not that far off on my shifting speed to where I'm loosing 2mph. When I started short shifting my mph started to go up. Will Rearend gears make a difference in how these calculators figure out shift points?
Posts: 2433 | From: Vacaville | Registered: Jul 2001
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93PONY
Mr. Valve Events
Member # 60
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posted
Do you pre-load the shifter? I picked up a solid MPH from preloading in Heather's car. Dropped 1/2 second too!
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www.advancedenginedevelopment.com
SCT dealer
Dynotuning
(916)715-7569
Posts: 4265 | From: Fair Oaks, CA | Registered: Nov 2000
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2000BlackGT
Loyalty
Member # 283
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posted
quote:
Originally posted by 93PONY:
Do you pre-load the shifter? I picked up a solid MPH from preloading in Heather's car. Dropped 1/2 second too!
what is preloading the shifter?
Posts: 2833 | From: Chico, CA | Registered: Jun 2001
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93PONY
Mr. Valve Events
Member # 60
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posted
quote:
Originally posted by 2000BlackGT:
quote:
Originally posted by 93PONY:
Do you pre-load the shifter? I picked up a solid MPH from preloading in Heather's car. Dropped 1/2 second too!
what is preloading the shifter?
Half-way to powershifting.
While at WOT in 1st pull back hard on the shifter. As soon as you hit the clutch it slams into 2nd. Same with 2nd, 3rd, etc.
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www.advancedenginedevelopment.com
SCT dealer
Dynotuning
(916)715-7569
Posts: 4265 | From: Fair Oaks, CA | Registered: Nov 2000
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JoeT
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Member # 298
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posted
pre-load shme-load.
Either you powershifted the gear or you didn't. ![[patriot]](graemlins/patriot.gif)
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1984 Ford Tempo AOD--- RIP
Posts: 6785 | From: San Jose | Registered: Jun 2001
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67stang
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Member # 549
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posted
quote:
Originally posted by bunchmyfunky:
I ran my numbers thru the calculator and all my shift points are right at redline. For some reason that doesn't seem right to me. Drew is shifting my car by feel and is not seeing the shift light which is set at 5700 and he's running 2mph faster then me. I know I'm not that far off on my shifting speed to where I'm loosing 2mph. When I started short shifting my mph started to go up. Will Rearend gears make a difference in how these calculators figure out shift points?
Buy a playback tach.... let Drew drive, and then replay the events and see what he's doing.
However, my personal experience has been that I have driven better Et's when my tach broke or failed, because i was listening to the car/feeling the car, rather than looking and reacting to a tach.
Victor Silva has always driven my car faster than I have, and never once has he asked me what my shift points are. Tells you something.... while theories and calculations are nice, only empircal results mean anything.
[ December 23, 2002, 12:31 AM: Message edited by: 67stang ]
Posts: 596 | Registered: Nov 2001
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Stimson
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Member # 51
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posted
rob- I've only seen one of those online shift point calculators that uses torque... if I remember right, it was a mostly chevy related site
mark- if your dyno graphs went well past your peak HP number, I/we can make an excell spread sheet for people to use to accurately calculate their shift points. Much more accurate than any online calculator I've seen... but it'll need HP data past the peak HP RPM.
Posts: 2373 | Registered: Jun 2000
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HaulinAss Motorsports
Its a STREETRaceCar!
Member # 541
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posted
quote:
Originally posted by Pro50Eric:
i've always just listened to the motor. you can pretty much tell when to shift. I don't even have a tach in my car. I just listen to the motor and watch the shiftlight.
Ditto!
Posts: 22469 | From: Sacramento | Registered: Nov 2001
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chosen1
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Member # 1906
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posted
[QUOTE]Originally posted by st5150:
[QB]Horspower of course. Torque doesn't matter...
since when does torque not matter? hp is a by-product of torque. for starters, you build the right motor with 'correct' amount of torque, the hp numbers take care of themselves.
shaun...that was a helpful link, thanks.
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1967 Fastback. Should go 10's -but doesn't
1993 Cobra
2003 Suzuki SVS
1966 Coupe -For Sale
Posts: 2205 | Registered: Sep 2002
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Stimson
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Member # 51
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posted
Hey guys, I'm using bunchmyfunky's dyno numbers to calculate his optimum shift points with a high degree of accuracy. If the demand exists (and my results greatly differ than the cheesy online calculators), I'll consider putting in the effort of making my own online calculator or writting a program that you can download and use to derive your own optimal shift points based on your dyno graph.
So far I've derived a third degree polynomial from his dyno numbers that represents his HP curve. Next I'll have to calculate the RPM drop for each gear of a T45 tranny. I'm pretty sure they're the same as a T5 right? I'll try to calculate and post a shift point for one of his gears before I go to sleep tonight.
Posts: 2373 | Registered: Jun 2000
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Stimson
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Member # 51
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posted
Okay.... done. I have a rough program on my graphing calculator that determines optimum shift points now. Here is what it does...
-took RPM vs HP data from bunchmyfunky's dyno graph and used a curve-fit program I found online to represent his HP curve as a third degree polynomial (HP=A*RPM^3+B*RPM^2+C*RPM+D). The coefficients (A, B, C & D) are really ugly, but the the polynomial proved to always be with in 2 HP at almost all points of bunchmyfunky's dyno graph. Accurate enough for our purposes ![[Smile]](smile.gif)
-now that we have this equation, we have to derive the intergral of it between two RPM's. The upper limit of this intergral is easy... it is our shift point. The lower limit however is the RPM his motor drops to after a shift is completed. It is a function of the shift point, and the transmissions gear ratios. I calculated the the optimal shift point on the 3-4 shift.. so the lower limit is: shift_point-(shift_point-shiftpoint*4th_gear_ratio/3rd_gear_ratio)
-yes, we have one ugly intergral on our hands. I don't feel like typing it out, but trust me, its ugly... but not difficult.
-now I just entered in the gear ratios (1.33 for 3rd and 1.00 for 4th) and the shift point and have the calculator perform the intergral for me.
-I kept entering a new shift point and had the calculator tell me the "area under the curve" for that shift point from 3rd to 4th gear. The larger the number, the larger chunk of his motors powerband was used.
-Results? 6550 RPM provided the largest area under the curve for the 3-4 shift!
-Analysis? Like I said before I spent over two hours working this out by hand(and calculator)... you really need data at least 500-700 RPM past your peak HP RPM to determine your optimal shift point. In this case, the polynomial projection isn't accurate (doesn't drop off fast enough to accurately represent bunchmyfunky's powerband) after 5800 RPM. However, it implies that bunchmyfunky's 3rd to 4th gear shift should be a fair amount past 5800 RPM.
-Conclusion: EXCEL and any other microsoft product is a freak'n joke. I initially used it to derive the polynomial and after an hour of wondering why my model to solve this problem wasn't working... I realized bill gates' POS program gave me a BS polynomial! Foolish of me to think I could use any microsoft product to get a dependible and accurate result! ![[Mad]](mad.gif)
-Final thoughts: You really need the "big picture" on the dyno if you want to determine your shift points from it.
-Translation? REV IT UNTIL THE HP REALLY STARTS TO DROP on the dyno so you can get the proper data to determine your shift points
[ December 24, 2002, 11:48 AM: Message edited by: st5150 ]
Posts: 2373 | Registered: Jun 2000
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nickn
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Member # 193
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posted
quote:
Originally posted by chosen1:
[QUOTE]Originally posted by st5150:
[QB]Horspower of course. Torque doesn't matter...
since when does torque not matter? hp is a by-product of torque. for starters, you build the right motor with 'correct' amount of torque, the hp numbers take care of themselves.
shaun...that was a helpful link, thanks.
I think he means to say peak TQ does not matter, HP and TQ are together as one in a way, HP = TQ x RPM / 5252 this equation can be changed around, to calculate the TQ.
Unless your motor only spins say 5500-6k rpm I guess you could say TQ is important, but in reality you are just saying low rpm HP aren't you?
high rpm HP or TQ if you will is better, thats where you race.
http://www.vettenet.org/torquehp.html
Posts: 656 | From: Ca | Registered: Mar 2001
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Elapid
GOROBGO
Member # 50
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posted
hey sawson,
how much different is your calculation from the one acheived by plugging the torque curve into the online calculator>?
was it worth it?
I just realized that you are most likely deriving the torque curve from the HP data, basically reversing the process in an awkward fashion...
http://www.revsearch.com/dynamometer/torque_vs_horsepower.html
we MEASURE torque on the dyno, HP is CALCULATED from torque measurements. since the HP curve is a calculated value, you will be introducing error by starting with this calculated value compared to using the measured value, torque.
hope this helps!
rob
torque is how hard the tires try to spin, HP is a measure of that force over time.
[ December 24, 2002, 10:25 AM: Message edited by: rob ]
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98 Cobra
83 Notch rolling chassis - fs
Posts: 1797 | From: Grass Valley, CA USA | Registered: Jul 2000
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nickn
¯
Member # 193
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posted
quote:
Originally posted by Tri-Bar:
Torque = How fast the car will get there.
HP = How fast the car will go.
You shift by the torque curve,
when the torque starts to fall of you shift, remeber when you shift TQ mulitiplication through the gears reduces...
so where should this car be shifted?
[ December 24, 2002, 01:58 PM: Message edited by: nickn ]
Posts: 656 | From: Ca | Registered: Mar 2001
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Stimson
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Member # 51
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posted
rob- I used http://www.prestage.com/carmath/dynochart.asp along with bunchmyfunky's data:
RPM TQ
3000 266.2
3100 267.7
3200 269.7
3300 274.3
3400 278
3500 279.5
3600 281
3700 281.7
3800 283.2
3900 285.4
4000 286.3
4100 286.4
4200 285.8
4300 283.8
4400 281.9
4500 278.3
4600 275.1
4700 270.9
4800 267
4900 262.1
5000 255.7
5100 249.1
5200 242.5
5300 238
5400 231.7
5500 226.1
5600 220.2
5700 215.1
I find it kind of silly that this online calculator requests TQ at a given RPM...... TQ at a given RPM IS HORSEPOWER. I don't know why they're beating around the bush here
Anyways, here are the results it gave me:
quote:
Best shift point for the 1-2 shift is 5700 with a LOSS of 178 Lb/Ft of torque.
Best shift point for the 2-3 shift is 5700 with a LOSS of 43 Lb/Ft of torque.
Best shift point for the 3-4 shift is 5700 with a LOSS of 0 Lb/Ft of torque.
Rather inconslusive and a bit misleading since it doesn't give you the whole picture. Then again, I'm skeptical that the author of that calculator comprehends the whole picture as well judging by all the useless and impractical data it gives you
Posts: 2373 | Registered: Jun 2000
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