looking for more opinions on what to base shift points on, torque or horsepower
#1
looking for more opinions on what to base shift points on, torque or horsepower
most people refer to torque when talking about shift points and shift extention and stall speed. this calculator http://www.prestage.com/carmath/dynochart.asp only asks for torque.
soo.. does horsepower have anything to do with it?
my problem is i am stalling right past my peak torque but i am stalling right into my peak horse power, am i missing out on some ET?
soo.. does horsepower have anything to do with it?
my problem is i am stalling right past my peak torque but i am stalling right into my peak horse power, am i missing out on some ET?
#2
TECH Senior Member
Parish, in a way it's the same thing. When asking for TQ at a given RPM, you're really asking for the HP. Same thing. Consider for a moment that a given TQ at a given RPM is ALWAYS a given HP...no matter what the engine.
If we based our converter choices on bringing us back to peak TQ, we'd go slower. When I ran 9.8s on motor with a 4400 converter, my SE was about 5900. My peak TQ was probably about 4700 RPM. If I had had a converter that would pull my RPMs back to that (or even close to that) I would have been running 10s...absolutely NO doubt about it. It would have taken like a 3300 stall to do that!
If we based our converter choices on bringing us back to peak TQ, we'd go slower. When I ran 9.8s on motor with a 4400 converter, my SE was about 5900. My peak TQ was probably about 4700 RPM. If I had had a converter that would pull my RPMs back to that (or even close to that) I would have been running 10s...absolutely NO doubt about it. It would have taken like a 3300 stall to do that!
#3
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Is the philosophy something like, you want to shift when
your rear wheel torque (next gear) is the same or better
than RWT (this gear)? That would imply that you want to
wait until torque-in-gear has fallen to 1/gear-ratio-step of
peak, or something like that?
your rear wheel torque (next gear) is the same or better
than RWT (this gear)? That would imply that you want to
wait until torque-in-gear has fallen to 1/gear-ratio-step of
peak, or something like that?
#4
Originally Posted by jimmyblue
Is the philosophy something like, you want to shift when
your rear wheel torque (next gear) is the same or better
than RWT (this gear)? That would imply that you want to
wait until torque-in-gear has fallen to 1/gear-ratio-step of
peak, or something like that?
your rear wheel torque (next gear) is the same or better
than RWT (this gear)? That would imply that you want to
wait until torque-in-gear has fallen to 1/gear-ratio-step of
peak, or something like that?
here is an article i found that agrees with Colonel but i can't say that i under stand it. http://www.allpar.com/eek/hp-vs-torque.html
i am starting to consider the posibility that Colonel knows what he is talking about though
#5
after reading on this subject it seems that most of the articles tell you that more torque at a higher rpm will make you go faster than more torque at a lower rpm.
that makes perfect sence to me, the more torque at a higher rpm the longer you can stay in that lower gear. but i can't really find any info(mathmatics) that can show me how skiping over the torque peek right up to the HP peak would make me faster. most everyone agrees that the force to your back will be the most at your TQ peak.
now if i had a choice of shifting up my tq peek rpm or shifting down my stall speed it looks like shifting up the tq peek rpm would make me the quickest.
that makes perfect sence to me, the more torque at a higher rpm the longer you can stay in that lower gear. but i can't really find any info(mathmatics) that can show me how skiping over the torque peek right up to the HP peak would make me faster. most everyone agrees that the force to your back will be the most at your TQ peak.
now if i had a choice of shifting up my tq peek rpm or shifting down my stall speed it looks like shifting up the tq peek rpm would make me the quickest.
#6
TECH Senior Member
You should read what I wrote before and ponder it's meaning. The formula that I gave in the other thread is all you need to understand the relation between TQ and HP. HP = TQ x RPM/5252 People tend to think of HP and TQ as two different forces when one is a force (force does NOT constitute work, action, or movement...three different words that say the same thing) and the other is a measure of work. It's simply a measure of what happends when TQ does what it's trying to do...move a resistance. It describes how much resistance the force is able to overcome (move) in a given amount of time or you could say it describes how much potential it has to accelerate a resistance (mass and weight.)
To expound a little more, which scenario has the potential for accelerating a given object faster? 1000 ft lbs of TQ at 2000 RPM or 250 ft lbs at 8000? Answer? They have THE SAME potential. Why? Because each scenario describes 380.8 HP. They have THE SAME potential for accelerating a given object. It is the HP number you need to be concerned with. THAT is your measure of work performed and potential for work (acceleration.)
To expound a little more, which scenario has the potential for accelerating a given object faster? 1000 ft lbs of TQ at 2000 RPM or 250 ft lbs at 8000? Answer? They have THE SAME potential. Why? Because each scenario describes 380.8 HP. They have THE SAME potential for accelerating a given object. It is the HP number you need to be concerned with. THAT is your measure of work performed and potential for work (acceleration.)
#7
TECH Senior Member
You want the most HP laid to the ground over the course of the 1/4. That's the true but short answer. How to determine what shift points and converter this relates to is alot more complicated. The peak HP and TQ figures have very little to do with this. The power curve (from well before and well after the HP peak), the gearing of the tranny, the converter characteristics, and the inertial properties of everything that rotates or reciprocates in the drivetrain and engine all play together to determine this. This last part dealing with inertia could be far out of my ability to teach (though I have a good feel for it) but it is a very important factor when RPMs start coming up quickly due to power and or gearing.
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Torque is force applied is the acceleration you get. You
would always want the highest available to you, right?
If the rear wheel torque is higher in the current gear than it
would be in the next higher, don't shift yet, I figure.
I took a dyno curve, and entered it into Excel, and scaled it
for the four gears and plotted it out. Did the same for M6 gears.
The auto with its wide gear ratio makes it so that your RWT
is always better in the current gear than the next; upshift
costs you RWT and acceleration so hang on as long as possible.
Until torque has dropped by about 40% you're still ahead. This
hasn't happened by 6200RPM (but you must shift anyway).
A closer-ratio transmission (like the current M6) will give you
better torque in the next gear, in some cases, prior to 6200
RPM - by just a little.
would always want the highest available to you, right?
If the rear wheel torque is higher in the current gear than it
would be in the next higher, don't shift yet, I figure.
I took a dyno curve, and entered it into Excel, and scaled it
for the four gears and plotted it out. Did the same for M6 gears.
The auto with its wide gear ratio makes it so that your RWT
is always better in the current gear than the next; upshift
costs you RWT and acceleration so hang on as long as possible.
Until torque has dropped by about 40% you're still ahead. This
hasn't happened by 6200RPM (but you must shift anyway).
A closer-ratio transmission (like the current M6) will give you
better torque in the next gear, in some cases, prior to 6200
RPM - by just a little.
#9
TECH Senior Member
"Torque is force applied is the acceleration you get. You
would always want the highest available to you, right?"
No. If this were the case then racers would shoot to keep their engine in the heart of the TQ range...and this is in no way what they do. If this were the case, with my '02 I would run a 3200 stall, shift at 5500, and have a shift extension of 4600 RPM. The reality is that if I did that, I wouldn't run 11.2s, I'd likely run low 12s.
FORGET maximizing the TQ range in regards to shift points. It has NOTHING to do with anything. Looking at TQ would suggest that in a perfect world, we'd want the RPMs to come up to the peak TQ RPM and then stay there all the way down the track. Well, I can tell you, that would make for one dogass slow run.
would always want the highest available to you, right?"
No. If this were the case then racers would shoot to keep their engine in the heart of the TQ range...and this is in no way what they do. If this were the case, with my '02 I would run a 3200 stall, shift at 5500, and have a shift extension of 4600 RPM. The reality is that if I did that, I wouldn't run 11.2s, I'd likely run low 12s.
FORGET maximizing the TQ range in regards to shift points. It has NOTHING to do with anything. Looking at TQ would suggest that in a perfect world, we'd want the RPMs to come up to the peak TQ RPM and then stay there all the way down the track. Well, I can tell you, that would make for one dogass slow run.
#10
TECH Senior Member
"The auto with its wide gear ratio makes it so that your RWT
is always better in the current gear than the next"
Jimmy, you forgot that with an auto you have a TQ converter giving you excellent shift extension. It is actually MUCH easier to maintain your RPMs after a shift with an auto (and a high stalling converter) than it is with an M6.
is always better in the current gear than the next"
Jimmy, you forgot that with an auto you have a TQ converter giving you excellent shift extension. It is actually MUCH easier to maintain your RPMs after a shift with an auto (and a high stalling converter) than it is with an M6.
#11
Colonel, it's not that i don't believe you, you have way more experience with this kind of thing than me. it is just that 80% of the info i can find suports the torque is king theory. not saying that you try and center around the torque peek but rather shoot for the highest torque at the tranny output shaft.
i understand that torque is not work, that is an easy concept.
how about this simple test that i saw mentioned in some of my reading. put the tranny in 1st, cruze along at your max tq rpm, then punch it, you get set back hard. now take it up to the max hp rpm and do the same thing, not as big of a hit is it, not in my truck anyways.
how about this test, wich i haven't tried yet but probably will be able to tomorrow. lock the converter up in 2nd. on a nitrous pull my rpm will be 4800 after the shift, if i lock it up the rpm will drop to 3900-4000. i dont care about the mph, acording to your theory i should run a slower ET?
i understand that torque is not work, that is an easy concept.
how about this simple test that i saw mentioned in some of my reading. put the tranny in 1st, cruze along at your max tq rpm, then punch it, you get set back hard. now take it up to the max hp rpm and do the same thing, not as big of a hit is it, not in my truck anyways.
how about this test, wich i haven't tried yet but probably will be able to tomorrow. lock the converter up in 2nd. on a nitrous pull my rpm will be 4800 after the shift, if i lock it up the rpm will drop to 3900-4000. i dont care about the mph, acording to your theory i should run a slower ET?
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I guess I can see it both ways: Yes, peak torque feels much stronger than peak HP. But, since HP is derived from torque and time, more power could be had by shifting after peak torque.
For Jim's specific example here, he doesn't want to move shifts way up in rpms. He's stalling to 4800 now, and shifting at 5600, then going back to 4800 for the extension. Is this short extension hurting his ET? When he moves to a stroker and Turbo, both big torque producers, what will the effects be if he's stalling past peak torque?
Now, if the answer is "stall it past peak torque" for best ET, then could it be safe think this: A BIG heads cam car would ET the same as a big cube stroker if both engines made the same hp numbers and stalled to that point. Why go with a big CI motor, when you could just lighten the valvetrain, shorten the stroke, stall to 6000 and shift at 7500 with a big *** cam?
For Jim's specific example here, he doesn't want to move shifts way up in rpms. He's stalling to 4800 now, and shifting at 5600, then going back to 4800 for the extension. Is this short extension hurting his ET? When he moves to a stroker and Turbo, both big torque producers, what will the effects be if he's stalling past peak torque?
Now, if the answer is "stall it past peak torque" for best ET, then could it be safe think this: A BIG heads cam car would ET the same as a big cube stroker if both engines made the same hp numbers and stalled to that point. Why go with a big CI motor, when you could just lighten the valvetrain, shorten the stroke, stall to 6000 and shift at 7500 with a big *** cam?
#13
TECH Senior Member
"80% of the info i can find suports the torque is king theory."
Ok, please read carefully (in fact, go back and re-read what I've been saying in this thread again CAREFULLY. Give it some thought.)
What I've been trying to get across is that TQ and HP are not an either/or thing. It's not a one or the other is a better thing. It's realizing that they are, in a sense, THE SAME THING! I don't seem to be able to get this point across to most people. Yes, TQ is completely and 100% important IF, and let me say again IF, we include the RPM that is associated with whatever figure we're talking about. If I say 500 ft/lbs of TQ and nothing else...what does that mean in terms of acceleration potential? It means NOTHING! Now, if I say 500 ft/lbs of TQ at 5000 RPM, what does that mean? It means 476 HP and THAT tells you of the potential for moving an object (which is to say, the potential for performing WORK...which is what HP is...an expression of work.)
The reason that you feel more in the seat of your pants when stomping it from the TQ peak than when stomping it from the HP peak is simply because your are going slower in a given gear (because you are at a lower RPM) when you do it. Inertia, read up on it. The faster you go, the harder it is to fight it. Wind resistance is also an exponentially increasing factor as speed rises. You may also be feeling the effects of TQ multiplication if there is a TQ converter involved. Now, make it a manual tranny, give the scenario the SAME overall gearing (tranny, rearend, and tire rollout) and make it the SAME MPH...you'll register a higher G-force when stomping it from the HP peak than the TQ peak. I guarantee you that's a fact. It's not a philosophy, it's physics.
Ok, please read carefully (in fact, go back and re-read what I've been saying in this thread again CAREFULLY. Give it some thought.)
What I've been trying to get across is that TQ and HP are not an either/or thing. It's not a one or the other is a better thing. It's realizing that they are, in a sense, THE SAME THING! I don't seem to be able to get this point across to most people. Yes, TQ is completely and 100% important IF, and let me say again IF, we include the RPM that is associated with whatever figure we're talking about. If I say 500 ft/lbs of TQ and nothing else...what does that mean in terms of acceleration potential? It means NOTHING! Now, if I say 500 ft/lbs of TQ at 5000 RPM, what does that mean? It means 476 HP and THAT tells you of the potential for moving an object (which is to say, the potential for performing WORK...which is what HP is...an expression of work.)
The reason that you feel more in the seat of your pants when stomping it from the TQ peak than when stomping it from the HP peak is simply because your are going slower in a given gear (because you are at a lower RPM) when you do it. Inertia, read up on it. The faster you go, the harder it is to fight it. Wind resistance is also an exponentially increasing factor as speed rises. You may also be feeling the effects of TQ multiplication if there is a TQ converter involved. Now, make it a manual tranny, give the scenario the SAME overall gearing (tranny, rearend, and tire rollout) and make it the SAME MPH...you'll register a higher G-force when stomping it from the HP peak than the TQ peak. I guarantee you that's a fact. It's not a philosophy, it's physics.
#14
TECH Senior Member
"Yes, peak torque feels much stronger than peak HP."
Not when inertial resistance is the same.
"He's stalling to 4800 now"
He doesn't know what he's stalling to but it's certainly NOT 4800.
"Is this short extension hurting his ET?"
Yes, absolutely, yes.
"When he moves to a stroker and Turbo, both big torque producers, what will the effects be if he's stalling past peak torque?"
He's already stalling past peak TQ. If he starts stalling close to peak HP, start worrying.
"A BIG heads cam car would ET the same as a big cube stroker if both engines made the same hp numbers and stalled to that point. Why go with a big CI motor, when you could just lighten the valvetrain, shorten the stroke, stall to 6000 and shift at 7500 with a big *** cam?"
They would both accelerate at the same rate IF THE ENTIRE RPM RANGE that was used overlapped on the HP side and IF that RPM range was THE SAME. Why does it matter if one makes the same shape power curve but at a higher RPM so long as the gearing and converter are matched to it? The reasons are losses to friction and inertia (the difference in inertia being the largest of the two.) The faster you have to accelerate the parts (engine and drivetrain), the more power is wasted to inertia. Friction increases with RPM too. IN OTHER WORDS, you won't see as much HP to the ground the faster you are accelerating the parts (and to point out again, you accelerate the parts faster with numerically higher overall gearing.)
Not when inertial resistance is the same.
"He's stalling to 4800 now"
He doesn't know what he's stalling to but it's certainly NOT 4800.
"Is this short extension hurting his ET?"
Yes, absolutely, yes.
"When he moves to a stroker and Turbo, both big torque producers, what will the effects be if he's stalling past peak torque?"
He's already stalling past peak TQ. If he starts stalling close to peak HP, start worrying.
"A BIG heads cam car would ET the same as a big cube stroker if both engines made the same hp numbers and stalled to that point. Why go with a big CI motor, when you could just lighten the valvetrain, shorten the stroke, stall to 6000 and shift at 7500 with a big *** cam?"
They would both accelerate at the same rate IF THE ENTIRE RPM RANGE that was used overlapped on the HP side and IF that RPM range was THE SAME. Why does it matter if one makes the same shape power curve but at a higher RPM so long as the gearing and converter are matched to it? The reasons are losses to friction and inertia (the difference in inertia being the largest of the two.) The faster you have to accelerate the parts (engine and drivetrain), the more power is wasted to inertia. Friction increases with RPM too. IN OTHER WORDS, you won't see as much HP to the ground the faster you are accelerating the parts (and to point out again, you accelerate the parts faster with numerically higher overall gearing.)
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Originally Posted by Colonel
you won't see as much HP to the ground the faster you are accelerating the parts (and to point out again, you accelerate the parts faster with numerically higher overall gearing.)
#16
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Steve your knowledge in very interesting...
U explained this very well..
I was talking to Transmission specialties today about running a T350 in my car and we went over ALOT of info.I was always under the impression u would wanna leave the line at peak TQ and I got this reply----->NO NO NO from the tranny tech.
He said u wanna (DRAG RACE) in your higer HP peak when leaving the line which blew me away.He said after your 1st shift your gonna wanna stay there and beyond all the way down the 1/4.
We discussed what he thought would work for me and I told him I still wanna drive the car alittle bit.Well after giving him weight,**** points,dyno info,peak numbers,old ets and tranny combo I have now along with gearing and tire size he suggested 1st to send him the dyno sheet (I live by TS so I can show him it) and he thought something in the 4500 to 5000 range was what I should be running in my car.
He also told me a 2.75 1st gear in a 3500lb car would help ALOT.He said I might wanna consider a 3.90 gear instead of the 4.10 with the 26in Slick but to try it first and see how it works.He told me I WILL PICK UP ET for sure over the foot braked 4200 VIG/4L60E I have now.
Sound about right for my radical H/C setup? (6300 PEAK HP/4500 PEAK TQ)
(Shift at 6600)
Just gotta put the 2500 together and then its T-Brake time
Good reading guys..
U explained this very well..
I was talking to Transmission specialties today about running a T350 in my car and we went over ALOT of info.I was always under the impression u would wanna leave the line at peak TQ and I got this reply----->NO NO NO from the tranny tech.
He said u wanna (DRAG RACE) in your higer HP peak when leaving the line which blew me away.He said after your 1st shift your gonna wanna stay there and beyond all the way down the 1/4.
We discussed what he thought would work for me and I told him I still wanna drive the car alittle bit.Well after giving him weight,**** points,dyno info,peak numbers,old ets and tranny combo I have now along with gearing and tire size he suggested 1st to send him the dyno sheet (I live by TS so I can show him it) and he thought something in the 4500 to 5000 range was what I should be running in my car.
He also told me a 2.75 1st gear in a 3500lb car would help ALOT.He said I might wanna consider a 3.90 gear instead of the 4.10 with the 26in Slick but to try it first and see how it works.He told me I WILL PICK UP ET for sure over the foot braked 4200 VIG/4L60E I have now.
Sound about right for my radical H/C setup? (6300 PEAK HP/4500 PEAK TQ)
(Shift at 6600)
Just gotta put the 2500 together and then its T-Brake time
Good reading guys..
#17
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Jimmy blue: When doing your calculations with an A4, you need to take into account the torque multiplication of the torque converter. A 4000 stall is likely putting out 15% torque multiplication on the upshift and, as Colonel said, is being fed by higher HP due to the shift extension. Also (assuming good springs so you could shift at 6600 rpm with the stock cam) when you shoot way past your redline, your engine's acceleration slows down, even if the torque is the same as after shifting.
JS: I can see the theory your friend espouses, but I haven't seen anybody run consistently fast with a 4600 or higher stall in a typical LS1 set-up (i.e. bolt-on or H&C + LS6 intake). Maybe the newer intakes will change the powerband and require the use of a 5000 stall, but currently I see rapidly diminishing returns over 4000, and 4400 seems to be about the max.
JS: I can see the theory your friend espouses, but I haven't seen anybody run consistently fast with a 4600 or higher stall in a typical LS1 set-up (i.e. bolt-on or H&C + LS6 intake). Maybe the newer intakes will change the powerband and require the use of a 5000 stall, but currently I see rapidly diminishing returns over 4000, and 4400 seems to be about the max.
Last edited by Ragtop 99; 01-19-2004 at 03:59 PM.