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Best RPM and shift point?

This is a discussion on Best RPM and shift point? within the Computer & Tuning forums, part of the LSx Technical Help Section category; I shift at 5400 and ran 13.10 at 108.54 in a stock 01 Z28 M6 I had the car dynoed ...

  1. #21
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    I shift at 5400 and ran 13.10 at 108.54 in a stock 01 Z28 M6 I had the car dynoed and it made 310 hp at 5300rph. I was shifting it at 6000 and the car ran 13.40's at 106 107mph.

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    1. you know the factory tach doesnt read as fast as the motor spins, so when you see 5500 rpms or whatever the case may be, your wrong. you could very well be at about 6300 or so. Bill (foff667) is very and i mean very knowlegeable when it comes to these things. Hence, the fact that he's a mod There are a few spreadsheet going around that could aid in you finding your shiftpoints based on your tire size, gears and power at each rpm( you need a dynograph for this) and with that you can find your best points.

    Nino

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    I believe there is a flaw in how you guys are coming up with these shift points...zfinke01 are you using a shiftlight to go by when you shift? Have you datalogged any of your runs to see what your rpm is when your actually shifting? Your saying you shift at 5400...if your not using a shift light and your using the stock tach do you know the stock tach can be off as much as 300 rpms even at idle? If you are using a shiftlight did you ever factor in the time your body takes to react to it? That 5400 setting your body might not react till 5500,5600 or even later...but hey you had it set at 5400 so thats what your considering your shift point. If you guys are going to throw out your #'s at least have something to back them up...a datalog would be great or anything concrete. I've done it on several ls1's as well as several gtp's & 3800 v6 fbodies that make peak hp at 5300 & shifting at 6500(actually shifting at this rpm...shift light at 6200) has gotten those cars new bests in mph/et.

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    heres the calc nino mentioned http://www.bgsoflex.com/shifter.html if you'd like to play around...but again I've been racing for 10 years and I've just about seen it all and what I havent yet I learn from.

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    I had the car dynoed and it made 310hp. 5350 and 333.8 ft. at 4200rpm. I do use a shift light and it is set at 5400. I do understand the time lag from when the light comes on to when I shift. I also have been racing professionally since 1990. I made my living working on top fuel cars, so I do know the ins and outs of racings, tuning, and driving.

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    then pls post up graphs to show us.

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    Quote Originally Posted by zfinke01
    I do use a shift light and it is set at 5400. I do understand the time lag from when the light comes on to when I shift.
    If you've been in the top fuel scene for 16+ years why not explain to everyone that because of the 1-2 shift coming on within about 2 seconds of launching sometimes your body cant react as fast as a shiftlight and 300-500 rpm overrevs are not uncommon? Instead you make a plain statement that reitterates what you've already said in an earlier post? Ok so far weve got this...you shift at 5400, you do use a shift light and its set at 5400, you had the car dynoed at 310hp@5300 rpms, and you had the car dynoed and it made 310hp.@5350...ok we get that part of it. Again we're here to help each other but throwing out statements rather then explaining to others that maybe havent driven top fuel dragsters for 16 years isnt really helping anyone and in fact is only confusing people more.

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    you can norally react to a shift light in about .100 to .200 of a second. In this amount of time the motor is only going to see mybe 50 rpm. You have to remember there is a load on the motor and it's a production piece it is not going to rev like a race motor. If you shift these motors at 6000 rpm you are out of the power band and wasting time. You may not feel it losing power but it is. The big thing is time. I don't know the exact time but from 5500 to 6000 is a long time when your talking tens or hundredth of a second. This is what this is all about.

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    1st gear will go about 180rpms in .100 seconds, 2nd gear on about 100rpms per .100 sec & 3rd gear about 60rpm.

    http://home.comcast.net/~whenn1/shiftpoints.xls
    http://home.comcast.net/~whenn1/4.14d.csv

    the first one is in excel format but already edited so you can see the difference...this was an exhaust ONLY Z28 with stock 3.42 gears and an m6 I did several single gear pulls including 1st second and 3rd gear and these are my results...so if your reaction time to your shift light in first gear was .200 your talkinga bout a 350 rpm over rev so in reality your 1-2 shift was at 5800 rpms...your 2-3 probably closer to 5600 & your 3-4 closer to 5600 more then likely.

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    I do not understand how in .200 of a second this motor rev 350 rpm. Rpm is revolutions per minute. Do you realize the motor would be spinning at 1750 revolutions per second. Not possible.

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    Also if you think about it the car is running for 13.?? seconds. So if you take an average rpm of your motor during your run divide it by your time you will get how many revolution the motor made during that run.

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    Quote Originally Posted by zfinke01
    I do not understand how in .200 of a second this motor rev 350 rpm. Rpm is revolutions per minute. Do you realize the motor would be spinning at 1750 revolutions per second. Not possible.
    in your 1:1 4th gear maybe there would be a difference of only 50rpms I didnt take any 4th gear pulls in his car since it wouldve been well over 100mph on a public highway. But these are actual scans of an actual car that uses the same information to flash that shift light in your eyes. 1st & 2nd gear are very hard to shift at the same rpm because of the tq multiplication factor of the gears. My blown s-10 had a 3.49 1st gear & 3.73's out back meaning i made the 1-2 shift before the 60'...thats about 1.6 seconds from me launching to shifting into the next gear. Its just hard to react that quickly no matter who you are.

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    IMHO-with the stick shift there is no point to revving past the power curve.With 6 gears spaced close together you need to stay in the power curve ,not above or below.The mans got time slips to prove it-thats gonna show you what works and what doesn't more than any theoretical computer nonsense ever would. Drive the six-speed and find out for yourself.

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    you guys are right I give up shift at 5300 you'll go faster. I've never driven an m6 in my life at the track or otherwise. Man I have so much to learn.

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    Quote Originally Posted by foff667
    you guys are right I give up shift at 5300 you'll go faster. I've never driven an m6 in my life at the track or otherwise. Man I have so much to learn.
    Hey, I'm not here trying to be a jerk and say you don't know anything. I'm just saying I've owned an m6 for about 5 years (177,000 and still rolling strong) and my best friend has owned one right beside me for most of that time also. We both find that shifting at 5400 gets US the best times. I am confident that I shift when I believe I am shifting, after 5 years you just know your car that well. I understand that typical 98 up f-body "tach lag" could represent a large part of all of this, I would give up that it's turning a little more than that, but not 6,000. My shift points factor in driver error and everything do they not? Your shift points are set in a perfect environment, lets say, automatic with a shift kit. It bangs into the next gear at the set shift point and it's there, the m6 doesn't work that way and you must factor in other things when calculating shift points, tach lag clutch time etc. Do you see my point? 5400 in an m6 = 5800 auto with a shift kit. There is a difference in "driver shift points" and "actual shift points"

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    Quote Originally Posted by z_driver1
    Hey, I'm not here trying to be a jerk and say you don't know anything. I'm just saying I've owned an m6 for about 5 years (177,000 and still rolling strong) and my best friend has owned one right beside me for most of that time also. We both find that shifting at 5400 gets US the best times. I am confident that I shift when I believe I am shifting, after 5 years you just know your car that well. I understand that typical 98 up f-body "tach lag" could represent a large part of all of this, I would give up that it's turning a little more than that, but not 6,000. My shift points factor in driver error and everything do they not? Your shift points are set in a perfect environment, lets say, automatic with a shift kit. It bangs into the next gear at the set shift point and it's there, the m6 doesn't work that way and you must factor in other things when calculating shift points, tach lag clutch time etc. Do you see my point? 5400 in an m6 = 5800 auto with a shift kit. There is a difference in "driver shift points" and "actual shift points"
    and your still talking about your 2.73 geared lt1 car like its an ls1. You started off saying stay with the stock shift points of 55-5600 which ls1 stock shift points are at 6000+ rpms. Now you admit tach lag could represent a large part of all of this but even with me posting information on how fast rpms rise through 1st, 2nd, & 3rd gear your telling me its turning a little more then what you said & not 6000rpms which i already conceded in my other post that for 1/10th of a second the tach will move steadily upward at the rate of about 150rpms...if it takes you 2/10th of a second to react which is reasonable that would be and added 300 rpms over your initial quote of you saying you shift at 5400 making your final shift point actually ~5700 on the 1-2 and so on and so forth. I've already stated my case, your obviously not getting my point nor should you since your still talking about your lt1 and im talking about ls1's and THEIR respective powerband which again is different than an lt1's meaning I wont comment on what I dont know. Also you go into saying with an auto it bangs into the next gear & its there is a stretch...there are many factors in even with an automatic's shift...between tq mngt, the desired shift time calcs in the computer, tranny fluid temps, etc...i could setup a shift point of 6300 & with a 3500 stall & no tranny cooler it might not actually shift till 7000rpms. Beleive what you would like to believe about shift points...the information I provided is more then ample to help people understand when a car should shift. Its not about peak hp its about avg. hp and shifting at your peak hp will rarely give you the best avg. hp throughout a run.

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    I have an LS1 also. . .

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    i'm very proud of ya, thats very nice.

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    I'm gonna back off of this, I don't want an enemy nor to argue, especially someone I would consider knowledgable. We disagree on this one thing, but it would not be wise to allow ourselves to become biased against each other. If I'm wrong I'm wrong, I can handle it. I live with a woman. . .I'm ALWAYS wrong at home. . .lol. I'm calling a truce from my side

  20. #40
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    Hi
    Thank u guys 4 ur replays ,but I think u got a little bit out of the subject ,I wanted in my question to know which is better, to keep the rev limit stock @6000 or to extend it to 6100,6200,6300...6600?
    Thank you
    Regards

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