Shift Points & Rear Gear - Ford Mustang Forum
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post #1 of 12 (permalink) Old 03-08-2018 Thread Starter
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Shift Points & Rear Gear

First off, when do y'all shift: right at max hp, a little before, after? The graph is a 3rd gear pull (95 GT T5) and it gets squiggly and funny at the end, but when would y'all be shifting if it were you?
My next question is: that that graph was with a 3.73 gear and I am switching to a 3.31, will the torque curve and shift points change? Or will they be the same but just a little slower getting there?
Thanks

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post #2 of 12 (permalink) Old 03-09-2018
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It really depends on how the car feels when you have it out on the road (or track). Ideally, when you shift, it drops the RPMS down somewhere closer to peak torque, and rises right through peak HP. If you shift the instant you hit your HP peak, your engine goes back to doing a little less work per second. Shifting so your car is slightly past its HP peak may let the next gear hit at a spot where it's making enough power to be worthwhile. Other cars drop off in power really fast past the peak, and those cars would be better off shifting a little earlier.

This is an awesome question, but the reality of the answer depends on too many variables to get it right. You've got to deal with things like redline, valve float, how fast power falls off past the peak, and how slowly torque falls off past peak torque. You can sort of see some of the answers on that paper, but remember, you're dealing with shiny smooth dyno drums under your tires there - not dirty pavement (or sticky track).

Maybe the best way to think about it is this: If you had an infinite number of gears and could shift instantly, you'd want to ALWAYS have your car at peak HP for maximum acceleration. Since you have a finite number of gears, your best bet is to 'bracket' that peak so it falls in between your shifts, giving you the maximum 'average' horsepower within that RPM band before the next gear. Each gear will be different, because there are different drops in RPM involved.

ANY car will accelerate harder in a lower gear, so it's worthwhile to multiply torque as long as you can get away with it. The rest just depends on your engine and traction quirks.

The only way you will ever know for sure is to try it consistently each way a few times, and time it. You could also use a datalogger, if you have one. Or, do what most of us do, and use the Butt-O-Meter to guess at it. =)

I should add - with your car's super flat torque curve, I'm betting it will give you best performance running it up near redline before your shifts, but then again, you're sort of splitting hairs. Your car won't be too fussy about shifting a tiny bit earlier than its absolute peak performance, and the extra stress on your engine probably would not be worth it.

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post #3 of 12 (permalink) Old 03-09-2018 Thread Starter
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Quote:
Originally Posted by Grimbrand View Post
It really depends on how the car feels when you have it out on the road (or track). Ideally, when you shift, it drops the RPMS down somewhere closer to peak torque, and rises right through peak HP. If you shift the instant you hit your HP peak, your engine goes back to doing a little less work per second. Shifting so your car is slightly past its HP peak may let the next gear hit at a spot where it's making enough power to be worthwhile. Other cars drop off in power really fast past the peak, and those cars would be better off shifting a little earlier.

This is an awesome question, but the reality of the answer depends on too many variables to get it right. You've got to deal with things like redline, valve float, how fast power falls off past the peak, and how slowly torque falls off past peak torque. You can sort of see some of the answers on that paper, but remember, you're dealing with shiny smooth dyno drums under your tires there - not dirty pavement (or sticky track).

Maybe the best way to think about it is this: If you had an infinite number of gears and could shift instantly, you'd want to ALWAYS have your car at peak HP for maximum acceleration. Since you have a finite number of gears, your best bet is to 'bracket' that peak so it falls in between your shifts, giving you the maximum 'average' horsepower within that RPM band before the next gear. Each gear will be different, because there are different drops in RPM involved.

ANY car will accelerate harder in a lower gear, so it's worthwhile to multiply torque as long as you can get away with it. The rest just depends on your engine and traction quirks.

The only way you will ever know for sure is to try it consistently each way a few times, and time it. You could also use a datalogger, if you have one. Or, do what most of us do, and use the Butt-O-Meter to guess at it. =)

I should add - with your car's super flat torque curve, I'm betting it will give you best performance running it up near redline before your shifts, but then again, you're sort of splitting hairs. Your car won't be too fussy about shifting a tiny bit earlier than its absolute peak performance, and the extra stress on your engine probably would not be worth it.
Thanks man. I've generally been shifting around 6k which is about redline. I'm anxious to see how the 3.31's do. The 3.73's were tiresome.
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post #4 of 12 (permalink) Old 03-09-2018
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it should always be in the powerband of the engine (which of course is different than redline).............. and as I laughingly say, if your in the "midrange" of RPM, then you need to call AAA....because you are lost on the track

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post #5 of 12 (permalink) Old 03-09-2018
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I think the T5 is considered a close ratio tranny.
That means that the rpm drop between shifts should be minimal keeping the
engine in the power band when shifting gears at full throttle.
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post #6 of 12 (permalink) Old 03-12-2018 Thread Starter
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I was curious as to when I was shifting into 2nd to I watch a video and listened. It always felt like I was shifting within the first 60', but I'm shifting a little after. I think it's only going 30-40 mph or so.
https://m.youtube.com/watch?v=0Jp3S-nALIQ
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post #7 of 12 (permalink) Old 03-14-2018
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if you have a shift light.......set the rpm 500 lower than when you want to shift.

why.....because you have to allow for driver reaction time and car reaction time.

by the time everthing actually shifts you should be where you were suppose to be.

93' LX hatch, 460 w/150 plate, TH400, 9" w/ 3.60 spool. Best (so far!) of [email protected] 146 mph with 1.40 spinning 60' on steel heads
Reese,
Been saying single digit coming for 3 years.....guess I finally made it!
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post #8 of 12 (permalink) Old 03-17-2018 Thread Starter
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Quote:
Originally Posted by stang93mustang View Post
if you have a shift light.......set the rpm 500 lower than when you want to shift.

why.....because you have to allow for driver reaction time and car reaction time.

by the time everthing actually shifts you should be where you were suppose to be.
Sweet, thanks man. I have one, I just need to get 'er in.
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post #9 of 12 (permalink) Old 03-20-2018
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I forgot I have this video showing an example of time for car to react.

Btw......checked my phone if it was recording because I use it to control my GoPro

https://youtu.be/-Bl22FgrJpU

93' LX hatch, 460 w/150 plate, TH400, 9" w/ 3.60 spool. Best (so far!) of [email protected] 146 mph with 1.40 spinning 60' on steel heads
Reese,
Been saying single digit coming for 3 years.....guess I finally made it!
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post #10 of 12 (permalink) Old 03-25-2018 Thread Starter
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Quote:
Originally Posted by stang93mustang View Post
I forgot I have this video showing an example of time for car to react.

Btw......checked my phone if it was recording because I use it to control my GoPro

https://youtu.be/-Bl22FgrJpU
An automatic... Just kidding, if I built a dragster that's the way id go too.
What rpm was the light coming on and what rpm is the target?
What were all those switches that you were messin with at the end and how fast is that badboy?
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post #11 of 12 (permalink) Old 03-25-2018 Thread Starter
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Quote:
Originally Posted by stang93mustang View Post
I forgot I have this video showing an example of time for car to react.

Btw......checked my phone if it was recording because I use it to control my GoPro

https://youtu.be/-Bl22FgrJpU
Man, I gotta get a new video.. I think race season is coming soon so I'll get one w the new setup and I'll try to get one of the one good run of the night. I'll usually have one decent pass out of 3-4 and it's always the one that didn't get filmed.
You'll have to use your ears on this one but it's a t5 w a stock clutch and a house brand short throw shifter. I wasn't power shifting and I was trying to shift around 5,800 rpm. The stock tach needle was getting pretty close to hitting 6k and thats where the rev limit is set via msd box and I never hit it.
Im the blue. I red-lighted because it went green before I got staged, so I just backed up and tried to make a pass w/out either bogging or blowing the tires off.
Anyone wanna sell me a set of wheels and slicks that'll fit a '95 at a fair price?

https://m.youtube.com/watch?list=LLUvktzOuj7hWoCIUrjIItJw&v=0Jp3S-nALIQ
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drag racing is a little more than just driving straight. There is always something to improve.

93' LX hatch, 460 w/150 plate, TH400, 9" w/ 3.60 spool. Best (so far!) of [email protected] 146 mph with 1.40 spinning 60' on steel heads
Reese,
Been saying single digit coming for 3 years.....guess I finally made it!
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