When to shift? How to produce maximum area under the curve? 3.2 Carrera.
11-21-2006, 03:58 PM
#31
Originally Posted by mark kibort
also a little misleding as it leads you to believe that a lower gear box creates more thrust over every gear. there are no intercections, nor would you expect there to be, but there are trade offs. you shift at 15% lower rpm gain 15% more thrust, and the comparitive gear box would still be in a 30% higher for that period of time. torque in the old gear after that shift is the trade off, and continues until you run out of gears. (gearing doesnt make hp, it makes more effective the hp over a desired speed range of operation) now, if you plotted the HP utilized vs speed, this would be become more clear. (or acceleration vs speed)
, you are not making yourself particularly clear. My post was in responce to Adam's speculation that a close ratio 6 speed might have thrust curves that crossThe graphs I posted are thrust vs speed which is directly proportional to acceleration vs speed, if you see one the other is the same, different units but the same shape.
and I do understand clearly that gearing does not make hp.
11-21-2006, 04:37 PM
#32
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Originally Posted by mark kibort
again, shifting at a point that maximizes hp is key. not shifting at max hp, but shifting at near redline (depending on gear spacing and hp curve shape)
in a cup car where many times peak hp is redline, that is true, but most cars have an arc around max hp. so, it pays to shift above max hp , to max RPMs allowed or desired.
to your first statement, we really should focus on "at any speed" . then, the acceleration that is "hardest" will be at a point closest to max hp. you find me peak torque acceleration at "any point in time" and ill show you faster rate of acceleration at that same speed in a lower gear, closer to max HP!
MK
in a cup car where many times peak hp is redline, that is true, but most cars have an arc around max hp. so, it pays to shift above max hp , to max RPMs allowed or desired.
to your first statement, we really should focus on "at any speed" . then, the acceleration that is "hardest" will be at a point closest to max hp. you find me peak torque acceleration at "any point in time" and ill show you faster rate of acceleration at that same speed in a lower gear, closer to max HP!
MK
11-22-2006, 01:46 AM
#33
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That is absolutely right!
your example is not that far off of reality either. The R10 Audi diesel, vs the R8 turbo. both 650hp vs 650hp, but one has 800ft-lbs vs something half of that. the curves are different shape, so the close ratio gear box of the R8 makes up the difference. the R10 was faster, but in the end, it was because it had more hp! something like 650 vs 550 of the R8. (lots of other factors too)
I do like the fact that the same hp can be made at half the rpms. for us grass roots racers, it could mean engines that never wear out!
Mk
your example is not that far off of reality either. The R10 Audi diesel, vs the R8 turbo. both 650hp vs 650hp, but one has 800ft-lbs vs something half of that. the curves are different shape, so the close ratio gear box of the R8 makes up the difference. the R10 was faster, but in the end, it was because it had more hp! something like 650 vs 550 of the R8. (lots of other factors too)
I do like the fact that the same hp can be made at half the rpms. for us grass roots racers, it could mean engines that never wear out!
Mk
Originally Posted by murphyslaw1978
OK, I agree and just so I understand this, let's take this further: Assuming all else being equal, a Diesel Cummins Truck Engine @ 1900 RPM produces 400HP. Another high-revving Honda engine produces the same 400HP power, albeit @ 16,000 RPM. So, even though the torque of the truck is much higher (over 1600 ft-lbs) and the Honda torque is much lower, these engines produce the exact same power, although at different RPMs. So, again, everything else is equal (which is impossible), including weight, rotational weight, tires, and especially the area under the HP curve, it would seem to me that these 2 examples would be the same speed around the track, as long as the HP curves match and the gear respective gear changes result in the same HP drop.
11-22-2006, 01:51 AM
#34
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I understand. my only point was that the cuves dont tell the entire picture.
i think what needs to be seen, is connecting the thrust lines between each gear, that is where there would be intercection between the changing gears of the two different ratio gear boxes or tire sizes.
Here is a graph that gets the point across. notice the intersections of each gears resultant torque. (torque through the gear box at the wheels)
mk
i think what needs to be seen, is connecting the thrust lines between each gear, that is where there would be intercection between the changing gears of the two different ratio gear boxes or tire sizes.
Here is a graph that gets the point across. notice the intersections of each gears resultant torque. (torque through the gear box at the wheels)
mk
Originally Posted by Bill Verburg
I don't know if you understand or not , you are not making yourself particularly clear. My post was in responce to Adam's speculation that a close ratio 6 speed might have thrust curves that cross
The graphs I posted are thrust vs speed which is directly proportional to acceleration vs speed, if you see one the other is the same, different units but the same shape.
and I do understand clearly that gearing does not make hp.
, you are not making yourself particularly clear. My post was in responce to Adam's speculation that a close ratio 6 speed might have thrust curves that crossThe graphs I posted are thrust vs speed which is directly proportional to acceleration vs speed, if you see one the other is the same, different units but the same shape.
and I do understand clearly that gearing does not make hp.
Last edited by mark kibort; 07-15-2009 at 06:17 PM.
11-22-2006, 08:46 AM
#35
Originally Posted by mark kibort
I understand. my only point was that the cuves dont tell the entire picture.
i think what needs to be seen, is connecting the thrust lines between each gear, that is where there would be intercection between the changing gears of the two different ratio gear boxes or tire sizes.
Here is a graph that gets the point across. notice the intersections of each gears resultant torque. (torque through the gear box at the wheels)
mk
i think what needs to be seen, is connecting the thrust lines between each gear, that is where there would be intercection between the changing gears of the two different ratio gear boxes or tire sizes.
Here is a graph that gets the point across. notice the intersections of each gears resultant torque. (torque through the gear box at the wheels)
mk
11-22-2006, 10:20 AM
#36
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A GT3 Cup car has peak HP at 7600 rpm, but can easily rev to 8300. Depending on your gearing, it is likely that 5th and 6th will cross and possible that even 4th will cross with 5th.
A 2 valve engine will probably never cross (as far as I can tell, all your examples are 993's), but the 4 valve engines have the capability to keep turning past optimum HP, similar to Mark's example.
A 2 valve engine will probably never cross (as far as I can tell, all your examples are 993's), but the 4 valve engines have the capability to keep turning past optimum HP, similar to Mark's example.
11-22-2006, 11:18 AM
#37
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Interesting subject
I think I agree with both Kibort and Bill Verdug, although not sure I understood everything. Basically you need to shift at the point where your thrust becomes less than the thrust you would get in the next gear after you shift (based on RPM drops).
In our cars ( I know more turbo engines than NA) that means almost always that you need to shift at redline.
I have tried several gearbox configurations, and more than 90% of the times, redline achieves the best result.
My car does better times (on datalogger) the closer to the RPM limiter I shift in-gear.
The only thing that puzzles me a bit is the lines drawn by Bill, they seem to be very far apart. Close and short ratios alll gave me a very similar pattern to the one posted below. My sequential gearbox has very tall 1-2 nd gears and short 4-5-6th, and it looks quite similar.
Here is an example of what the thrust, extrapolated from an actual engine dyno curve on a modded 993TT, with a 993TT gearbox, real weight, tire sizes etc.. looks like.
The actual recorded long G data from my datalogger matched almost perfectly the graphs shown here when overlayed on top of each other during a 60-130mph run, which tells me this is what is really happening in real life.
I think I agree with both Kibort and Bill Verdug, although not sure I understood everything. Basically you need to shift at the point where your thrust becomes less than the thrust you would get in the next gear after you shift (based on RPM drops).
In our cars ( I know more turbo engines than NA) that means almost always that you need to shift at redline.
I have tried several gearbox configurations, and more than 90% of the times, redline achieves the best result.
My car does better times (on datalogger) the closer to the RPM limiter I shift in-gear.
The only thing that puzzles me a bit is the lines drawn by Bill, they seem to be very far apart. Close and short ratios alll gave me a very similar pattern to the one posted below. My sequential gearbox has very tall 1-2 nd gears and short 4-5-6th, and it looks quite similar.
Here is an example of what the thrust, extrapolated from an actual engine dyno curve on a modded 993TT, with a 993TT gearbox, real weight, tire sizes etc.. looks like.
The actual recorded long G data from my datalogger matched almost perfectly the graphs shown here when overlayed on top of each other during a 60-130mph run, which tells me this is what is really happening in real life.
11-22-2006, 12:07 PM
#39
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An easier way to look at this would be to look at the gear ratio for the spacing and see how it strattles the HP curve from the dyno. then, when you do this kind of analysis, you will see that you never have a point where the next gear takes over with higher rear wheel torque.
as it shows in this graph, you cant really short shift, without loosing some rear wheel torque at any vehicle speed. however, there are points where it gets very close. Nice to see this,so if you dont need every ounce of acceleration , you can save the engine when you have a big lead!
mk
as it shows in this graph, you cant really short shift, without loosing some rear wheel torque at any vehicle speed. however, there are points where it gets very close. Nice to see this,so if you dont need every ounce of acceleration , you can save the engine when you have a big lead!
mk
Originally Posted by Jean
Interesting subject
I think I agree with both Kibort and Bill Verdug, although not sure I understood everything. Basically you need to shift at the point where your thrust becomes less than the thrust you would get in the next gear after you shift (based on RPM drops).
In our cars ( I know more turbo engines than NA) that means almost always that you need to shift at redline.
I have tried several gearbox configurations, and more than 90% of the times, redline achieves the best result.
My car does better times (on datalogger) the closer to the RPM limiter I shift in-gear.
The only thing that puzzles me a bit is the lines drawn by Bill, they seem to be very far apart. Close and short ratios alll gave me a very similar pattern to the one posted below. My sequential gearbox has very tall 1-2 nd gears and short 4-5-6th, and it looks quite similar.
Here is an example of what the thrust, extrapolated from an actual engine dyno curve on a modded 993TT, with a 993TT gearbox, real weight, tire sizes etc.. looks like.
The actual recorded long G data from my datalogger matched almost perfectly the graphs shown here when overlayed on top of each other during a 60-130mph run, which tells me this is what is really happening in real life.
I think I agree with both Kibort and Bill Verdug, although not sure I understood everything. Basically you need to shift at the point where your thrust becomes less than the thrust you would get in the next gear after you shift (based on RPM drops).
In our cars ( I know more turbo engines than NA) that means almost always that you need to shift at redline.
I have tried several gearbox configurations, and more than 90% of the times, redline achieves the best result.
My car does better times (on datalogger) the closer to the RPM limiter I shift in-gear.
The only thing that puzzles me a bit is the lines drawn by Bill, they seem to be very far apart. Close and short ratios alll gave me a very similar pattern to the one posted below. My sequential gearbox has very tall 1-2 nd gears and short 4-5-6th, and it looks quite similar.
Here is an example of what the thrust, extrapolated from an actual engine dyno curve on a modded 993TT, with a 993TT gearbox, real weight, tire sizes etc.. looks like.
The actual recorded long G data from my datalogger matched almost perfectly the graphs shown here when overlayed on top of each other during a 60-130mph run, which tells me this is what is really happening in real life.
11-22-2006, 01:54 PM
#40
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Your chart suggests that your shift point be around 6300 rpm. That correlates well with what my race engine builders have told me. Generally, you carry a few hundred rpm past peak hp and upshift, so you can keep the hp rising in the next gear.
The point you make is relative to gearing, more than "area under curve", as wide spacing will drop you very far down the hp curve on the left side of the shift point.
Recall, torque relates to the power of each impulse, wheras hp relates to that multiplied by engine speed. HP and torque are identical at 5250rpm by virtue of the conversion formula. The attempt to generalize by location of the torque peak on the rpm graph is futile, and is more futile the higher your peak hp occurs.
For all of us amateurs, the bigger question is how much life do you want to take out of the engine by shifting at high rpm's? Personally, I have always selected the option of fewer rebuilds to fastest laps, with the exception of using everything you've got to get by when you catch the guy in front. AS
The point you make is relative to gearing, more than "area under curve", as wide spacing will drop you very far down the hp curve on the left side of the shift point.
Recall, torque relates to the power of each impulse, wheras hp relates to that multiplied by engine speed. HP and torque are identical at 5250rpm by virtue of the conversion formula. The attempt to generalize by location of the torque peak on the rpm graph is futile, and is more futile the higher your peak hp occurs.
For all of us amateurs, the bigger question is how much life do you want to take out of the engine by shifting at high rpm's? Personally, I have always selected the option of fewer rebuilds to fastest laps, with the exception of using everything you've got to get by when you catch the guy in front. AS
11-22-2006, 02:45 PM
#41
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Originally Posted by Alexander Stemer
Your chart suggests that your shift point be around 6300 rpm. That correlates well with what my race engine builders have told me. Generally, you carry a few hundred rpm past peak hp and upshift, so you can keep the hp rising in the next gear.
It has to do more with what RPMs you will be at, after shifting (per the thick redline on the second picture posted below), rather than your peak torque RPM.. The more you use the peak thrust available on your car the faster you will go.
In my particular example, the optimum shifting points are per the little attachment...At redline (7070RPM) in the first three gears, 6,770 in 4th and 6,530RPM in 5th. The engine dyno curve (the upper colour box on the left) does not really tell the story about when is best to shift based on thrust to the wheels (lower colour box on the left)
To be back on topic, if I can have the datapoints for engine (for accuracy) dyno chart of the 3.2Ltr, I can figure what are the best shifting points as far as going fastest in straightline is concerned and/or have the biggest area under the curve per the thrust chart.
Bill, 6500RPM is part of the reason I agree. Torque curves and gear staging might be the other..
11-22-2006, 03:25 PM
#43
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Bill , I have a couple of Race Technology AX22 GPS loggers and an AIM Pro that I never use. These graphs are not from the datalogger though,what I meant earlier is that I overlay the logged G curves (thrust curves) over the ones I calculate with my model (picture above) to do a reality check.. Also, this is maybe the best way to know what sort of real power an engine has, if datalogged Long G curves are too far off, means dyno is wrong most likely.
11-22-2006, 03:38 PM
#44
Originally Posted by Jean
. Also, this is maybe the best way to know what sort of real power an engine has, if datalogged Long G curves are too far off, means dyno is wrong most likely.
11-22-2006, 06:37 PM
#45
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Thats why using the dyno HP curves are so useful. you dont need to calculate or have data aqu. systems to maximize "thrust" or acceleration. alll you need is your gear spacing. visually, look at the 2000rpm or 1500rpm spread (whatever the spacing is for each gear change) and wrap it around your HP curve. this way, you are assured you are maximizing HP. by doing this, you are maximizing thrust and acceleration because, acceleration is proportional to power at any speed.
However, those graphs are pretty cool!
MK
However, those graphs are pretty cool!
MK
Originally Posted by Bill Verburg
I agree the only way to get truly valid data is an accurate data acquision setup. I will look into the Race technology stuff. Thanx.