Shift points and hp peak...
09-12-2011, 08:23 PM
#1
TECH Addict
Thread Starter
iTrader: (1)
Join Date: Mar 2008
Posts: 2,351
Likes: 0
Received 0 Likes
on
0 Posts
Shift points and hp peak... Now keep in mind this is subject to different cams, but their can't be THAT big of a difference in a4 cam dyno profiles.
...So I did a little research today. Assuming your peak power is at 6000 rpm. It slowly ramps up and trails off from this. In a 3.42 geared/moderate stall car your 1-2 shift drops you about 2600 rpm. So going by the "ideal" of shifting about 4-500 past your peak, your rpms would drop to the 3800rpm range. But this is a considerable amount before your peak power is hit again. Not only that, but the "area under the curve" is much lower. The hp curve in order to be at it's highest for the longest rpm range should be shifted at nearly 7000rpm.
What shifting that "low" does give you is more time at closer to peak TORQUE.
So this begs the question, which is better? Why is 4-500rpm the general consensus if hp is what truly moves you?
Has anybody done any real world research on this?
...So I did a little research today. Assuming your peak power is at 6000 rpm. It slowly ramps up and trails off from this. In a 3.42 geared/moderate stall car your 1-2 shift drops you about 2600 rpm. So going by the "ideal" of shifting about 4-500 past your peak, your rpms would drop to the 3800rpm range. But this is a considerable amount before your peak power is hit again. Not only that, but the "area under the curve" is much lower. The hp curve in order to be at it's highest for the longest rpm range should be shifted at nearly 7000rpm.
What shifting that "low" does give you is more time at closer to peak TORQUE.
So this begs the question, which is better? Why is 4-500rpm the general consensus if hp is what truly moves you?
Has anybody done any real world research on this?
09-12-2011, 10:33 PM
#3
Not only is this completely dependent on the stall, engine size, and cam, but it is not HP that moves you...it is tq. To over simplify, HP is speed (how fast you hit the wall) - TQ is how quickly you get there(and how far you take the wall with you). For drag racing, you want to take advantage of your platforms strongest abilities, which in our case means harnessing the car's TQ most effectively.
If you were a high strung tiny engine like a 4cyl that makes garbage tq, then you would be relying on HP, since the gain of running in your tq curve is overshadowed by how little power you are making down there. On my bike, my best ETs are when I keep things wwwaaaaaayy above peak tq, and even quite a bit past peak power. The RPMs are worth more to me then the tiny bit more tq or the fact that it stopped pulling.
Different engines like different things, in the case of SBCs and their inherent power curves that happens to be a stall around ~500rpm below peak tq, with the proper shift extension to keep you in your meaty power range.
Besides all of that, if your 1-2 shift drops you almost 3krpms then you don't have nearly enough stall/gear...period.
If you were a high strung tiny engine like a 4cyl that makes garbage tq, then you would be relying on HP, since the gain of running in your tq curve is overshadowed by how little power you are making down there. On my bike, my best ETs are when I keep things wwwaaaaaayy above peak tq, and even quite a bit past peak power. The RPMs are worth more to me then the tiny bit more tq or the fact that it stopped pulling.
Different engines like different things, in the case of SBCs and their inherent power curves that happens to be a stall around ~500rpm below peak tq, with the proper shift extension to keep you in your meaty power range.
Besides all of that, if your 1-2 shift drops you almost 3krpms then you don't have nearly enough stall/gear...period.
09-12-2011, 11:35 PM
#5
It is a totally different story on a small engine...to use my bike as an example again, peak TQ is happens 6,000 rpms lower then peak HP and is only 1/3 of the peak power. In a V8 that makes almost as much TQ as HP you obviously want to set it up differently.
There are very few blanket statements and 100% truths in racing, and this is not one of them, so there really isn't any argument - it depends on the vehicle.
09-13-2011, 12:38 AM
#7
A stock one does 
. Bone stock from the factory you should be shifting between 5K and 5.2K. A quick rule of thumb for autos, and a good place to start, is to have your stall rating 500-300rpm before peak TQ and your shift points 300-500rpm after peak hp (depending on how fast it falls off - is it a quick drop, or a steady plateau?).
This is why you cant say a blanket RPM for all LT1s. It depends on engine size, cam, stall, gear, and powerband.
If I told you to shift your car at 7800rpms, you would laugh at me. Even if your motor was capable of that rpm, with your power range and gearing you would run a horrible time. On the other side of the spectrum, if I shifted my last build at 5,200 rpm like a stock LT1 instead of 6300 I probably would have ran a full second slower.
Things like stall rating and shift points depend on where the car is making power, its not exactly complicated and I don't see what you're trying to get at...
. Bone stock from the factory you should be shifting between 5K and 5.2K. A quick rule of thumb for autos, and a good place to start, is to have your stall rating 500-300rpm before peak TQ and your shift points 300-500rpm after peak hp (depending on how fast it falls off - is it a quick drop, or a steady plateau?).This is why you cant say a blanket RPM for all LT1s. It depends on engine size, cam, stall, gear, and powerband.
If I told you to shift your car at 7800rpms, you would laugh at me. Even if your motor was capable of that rpm, with your power range and gearing you would run a horrible time. On the other side of the spectrum, if I shifted my last build at 5,200 rpm like a stock LT1 instead of 6300 I probably would have ran a full second slower.
Things like stall rating and shift points depend on where the car is making power, its not exactly complicated and I don't see what you're trying to get at...
Trending Topics
09-13-2011, 12:40 AM
#8
Here is an "Oldie but Goody" that I had buried in my bookmarks that I suggest you read: http://www.vettenet.org/torquehp.html.
This part in particular.
This page also explains why RPM's are so important, especially to small engines. They aren't making much TQ, but since all the forces that move a car are calculated by ratios of work over a set amount of time, if it makes the same TQ at a higher RPM then you will be making more power, and run a better number.
This part in particular.
The Case For Torque
Now, what does all this mean in carland?
First of all, from a driver's perspective, torque, to use the vernacular, RULES :-). Any given car, in any given gear, will accelerate at a rate that *exactly* matches its torque curve (allowing for increased air and rolling resistance as speeds climb). Another way of saying this is that a car will accelerate hardest at its torque peak in any given gear, and will not accelerate as hard below that peak, or above it. Torque is the only thing that a driver feels, and horsepower is just sort of an esoteric measurement in that context. 300 foot pounds of torque will accelerate you just as hard at 2000 rpm as it would if you were making that torque at 4000 rpm in the same gear, yet, per the formula, the horsepower would be *double* at 4000 rpm. Therefore, horsepower isn't particularly meaningful from a driver's perspective, and the two numbers only get friendly at 5252 rpm, where horsepower and torque always come out the same.
In contrast to a torque curve (and the matching pushback into your seat), horsepower rises rapidly with rpm, especially when torque values are also climbing. Horsepower will continue to climb, however, until well past the torque peak, and will continue to rise as engine speed climbs, until the torque curve really begins to plummet, faster than engine rpm is rising. However, as I said, horsepower has nothing to do with what a driver *feels*.
You don't believe all this?
Fine. Take your non turbo car (turbo lag muddles the results) to its torque peak in first gear, and punch it. Notice the belt in the back? Now take it to the power peak, and punch it. Notice that the belt in the back is a bit weaker? Fine. Can we go on, now? :-)
Now, what does all this mean in carland?
First of all, from a driver's perspective, torque, to use the vernacular, RULES :-). Any given car, in any given gear, will accelerate at a rate that *exactly* matches its torque curve (allowing for increased air and rolling resistance as speeds climb). Another way of saying this is that a car will accelerate hardest at its torque peak in any given gear, and will not accelerate as hard below that peak, or above it. Torque is the only thing that a driver feels, and horsepower is just sort of an esoteric measurement in that context. 300 foot pounds of torque will accelerate you just as hard at 2000 rpm as it would if you were making that torque at 4000 rpm in the same gear, yet, per the formula, the horsepower would be *double* at 4000 rpm. Therefore, horsepower isn't particularly meaningful from a driver's perspective, and the two numbers only get friendly at 5252 rpm, where horsepower and torque always come out the same.
In contrast to a torque curve (and the matching pushback into your seat), horsepower rises rapidly with rpm, especially when torque values are also climbing. Horsepower will continue to climb, however, until well past the torque peak, and will continue to rise as engine speed climbs, until the torque curve really begins to plummet, faster than engine rpm is rising. However, as I said, horsepower has nothing to do with what a driver *feels*.
You don't believe all this?
Fine. Take your non turbo car (turbo lag muddles the results) to its torque peak in first gear, and punch it. Notice the belt in the back? Now take it to the power peak, and punch it. Notice that the belt in the back is a bit weaker? Fine. Can we go on, now? :-)
Last edited by Puck; 09-13-2011 at 12:46 AM.
09-13-2011, 08:07 AM
#9
Here is an "Oldie but Goody" that I had buried in my bookmarks that I suggest you read: http://www.vettenet.org/torquehp.html.
This part in particular.
This page also explains why RPM's are so important, especially to small engines. They aren't making much TQ, but since all the forces that move a car are calculated by ratios of work over a set amount of time, if it makes the same TQ at a higher RPM then you will be making more power, and run a better number.
This part in particular.
This page also explains why RPM's are so important, especially to small engines. They aren't making much TQ, but since all the forces that move a car are calculated by ratios of work over a set amount of time, if it makes the same TQ at a higher RPM then you will be making more power, and run a better number.
Learned something new today
09-13-2011, 08:48 AM
#10
Village Troll 
iTrader: (2)
I've also read of those preaching shift points where RPM starts off at torque peak. It's all crap. Shift points should be concentrated around power peak. If the car is making power at 8500rpm and the engine can take the RPM then that's where shift points should be honed in...
09-13-2011, 09:40 AM
#12
Wow..........a thread of complete of bullsh!t !
And congratulations Puck, you are leading the charge big time. This is how "popular wisdom" crap gets started, the very crap that has lulled you into thinking you understand this topic!
Finally, two posts up, SS RRR states a fact.
Torque at the rear wheels is what pushes the car, NOT torque at the crankshaft! And....guess what.....max hp at the crank takes advantage of gear reduction through the tranny and rearend to make MAXIMUM torque at the wheels. Your observation with high revving bike engines should drive that point home to you if you think about it.
And congratulations Puck, you are leading the charge big time. This is how "popular wisdom" crap gets started, the very crap that has lulled you into thinking you understand this topic!
Finally, two posts up, SS RRR states a fact.
Torque at the rear wheels is what pushes the car, NOT torque at the crankshaft! And....guess what.....max hp at the crank takes advantage of gear reduction through the tranny and rearend to make MAXIMUM torque at the wheels. Your observation with high revving bike engines should drive that point home to you if you think about it.
09-13-2011, 09:52 AM
#13
LSWHO, to help answer your original question, here's my case for example:
hp curve centered around a 6400 peak (torque peak at 4600 rpm, not that it matters very much except for choosing the correct torque converter) , I shift at 7100 rpm (my PCM limit), rpm falls to 5400 in the next gear, which indicates a shift extension of 1700 rpm. I'm operating from 1000 rpm below to 700 rpm above my hp peak. The hp curve slope before and after the peak is close to a mirror image, therefore if my PCM allowed I might even drop ET another few hundredths by shifting higher. A lot of cam valvetrain setups drop off more quickly after hp peak; for those you would not want to rev as far past the peak.
But always always always, you have to rev beyond hp peak for best ET.
hp curve centered around a 6400 peak (torque peak at 4600 rpm, not that it matters very much except for choosing the correct torque converter) , I shift at 7100 rpm (my PCM limit), rpm falls to 5400 in the next gear, which indicates a shift extension of 1700 rpm. I'm operating from 1000 rpm below to 700 rpm above my hp peak. The hp curve slope before and after the peak is close to a mirror image, therefore if my PCM allowed I might even drop ET another few hundredths by shifting higher. A lot of cam valvetrain setups drop off more quickly after hp peak; for those you would not want to rev as far past the peak.
But always always always, you have to rev beyond hp peak for best ET.
09-13-2011, 10:08 AM
#14
First off, Never did I say to EVER shift at peak TQ, and clearly suggested to start with your shift points ~300rpm behind peak HP. Please read what I am saying before you assume I'm spewing bullshit.
Allow my to quote myself:
Also he said a STOCK car - not a bolt-on car, not a geared car, not a stalled car, a factory stock car. With just a drop-in filter my best times in my stock car were shifting at 5200. After full bolt-ons+stall my best times were shifting at 5700.
TQ at the wheels is COMPLETELY dependent on drivetrain and gearing, which should complement the engines power curve - not the other way around.
Allow my to quote myself:
TQ at the wheels is COMPLETELY dependent on drivetrain and gearing, which should complement the engines power curve - not the other way around.
09-13-2011, 10:11 AM
#15
Village Troll
iTrader: (2)
Drag racing is all about horse power. Not torque. You want to praise torque, go to a tractor pull.
That's still crap. What part of a bolt-on car or any of the other things you mention actually influences power peak in the RPM band?
That's still crap. What part of a bolt-on car or any of the other things you mention actually influences power peak in the RPM band?
09-13-2011, 02:41 PM
#17
You guys argue about the dumbest stuff.
LSWHO....
Take your car to the track.
Shift it at 6k, get your timeslip.
Make another pass but shift at 6100, get your timeslip, and compare.
Noone is going to be able to tell you the exact shift rpm you'll need. Every car is different.
LSWHO....
Take your car to the track.
Shift it at 6k, get your timeslip.
Make another pass but shift at 6100, get your timeslip, and compare.
Noone is going to be able to tell you the exact shift rpm you'll need. Every car is different.
09-13-2011, 05:07 PM
#19
TECH Fanatic
iTrader: (2)
Join Date: Dec 2010
Location: Oklahoma
Posts: 1,084
Likes: 0
Received 0 Likes
on
0 Posts
Horsepower is a direct relationship to an engine's ability to do work.
Torque is an engine's advantage to do that work.
They are both equally important.
You can't have one and not another; unless you are freeze frame racing.
Think of it like this: Horsepower is an engines torque in a time related format.
What moves you down the track isn't torque or horsepower by itself, but as a combination of leverage to do work in a certain amount of time.
You want to have more of BOTH...
To add to a little more Food for thought.... work is what is required to move the car down the track. Now lets say that your torque curve drops 50 lb/ft at peak Hp. but you're up 50 hp from peak tq. Now does that mean that the car is doing less work??? NO. It could still be making more work.
When a piston is coming down in the combustion stroke makes power it makes only so much torque for that one cycle. so if you make 30lb/ft of torque on that stroke and you only get 3 strokes per second you only made 90lb/ft/sec. Now say that any more strokes/sec will make less lb/ft per stroke. Now you only make 25lb/ft per stroke. But now you get 4 strokes per second. So you now make 100lb/ft/sec. So which is better? these are just an example and don't reflect actual numbers for a vehicle, but this illustrates the HP/torque/work relationship.
like joelster said, take it to the track and test it. That is the only way to get the best shift point.
Torque is an engine's advantage to do that work.
They are both equally important.
You can't have one and not another; unless you are freeze frame racing.
Think of it like this: Horsepower is an engines torque in a time related format.
What moves you down the track isn't torque or horsepower by itself, but as a combination of leverage to do work in a certain amount of time.
You want to have more of BOTH...
To add to a little more Food for thought.... work is what is required to move the car down the track. Now lets say that your torque curve drops 50 lb/ft at peak Hp. but you're up 50 hp from peak tq. Now does that mean that the car is doing less work??? NO. It could still be making more work.
When a piston is coming down in the combustion stroke makes power it makes only so much torque for that one cycle. so if you make 30lb/ft of torque on that stroke and you only get 3 strokes per second you only made 90lb/ft/sec. Now say that any more strokes/sec will make less lb/ft per stroke. Now you only make 25lb/ft per stroke. But now you get 4 strokes per second. So you now make 100lb/ft/sec. So which is better? these are just an example and don't reflect actual numbers for a vehicle, but this illustrates the HP/torque/work relationship.
like joelster said, take it to the track and test it. That is the only way to get the best shift point.
09-13-2011, 05:10 PM
#20
TECH Addict
Thread Starter
iTrader: (1)
Join Date: Mar 2008
Posts: 2,351
Likes: 0
Received 0 Likes
on
0 Posts
A stock one does . Bone stock from the factory you should be shifting between 5K and 5.2K. A quick rule of thumb for autos, and a good place to start, is to have your stall rating 500-300rpm before peak TQ and your shift points 300-500rpm after peak hp (depending on how fast it falls off - is it a quick drop, or a steady plateau?).
This is why you cant say a blanket RPM for all LT1s. It depends on engine size, cam, stall, gear, and powerband.
If I told you to shift your car at 7800rpms, you would laugh at me. Even if your motor was capable of that rpm, with your power range and gearing you would run a horrible time. On the other side of the spectrum, if I shifted my last build at 5,200 rpm like a stock LT1 instead of 6300 I probably would have ran a full second slower.
Things like stall rating and shift points depend on where the car is making power, its not exactly complicated and I don't see what you're trying to get at...
. Bone stock from the factory you should be shifting between 5K and 5.2K. A quick rule of thumb for autos, and a good place to start, is to have your stall rating 500-300rpm before peak TQ and your shift points 300-500rpm after peak hp (depending on how fast it falls off - is it a quick drop, or a steady plateau?).This is why you cant say a blanket RPM for all LT1s. It depends on engine size, cam, stall, gear, and powerband.
If I told you to shift your car at 7800rpms, you would laugh at me. Even if your motor was capable of that rpm, with your power range and gearing you would run a horrible time. On the other side of the spectrum, if I shifted my last build at 5,200 rpm like a stock LT1 instead of 6300 I probably would have ran a full second slower.
Things like stall rating and shift points depend on where the car is making power, its not exactly complicated and I don't see what you're trying to get at...
Sounds like that's a "no."
According to what I have seen, my car would benefit from a 7000rpm shift. Which isn't going to happen. I'll try 6800 and 6500 and go from there.