Peak HP, Avg HP, or Area under the curve; which is the better measure of HP?
10-21-2010, 04:56 PM
#46
Rennlist Member
yeah, I dont fully understand the graph comparison. the shift points are not the same as far as rpm, gearing looks to be different, so maybe someone can clarify the comparison so we can take away something meaningfull from it.
what are we looking at here?
what are we looking at here?
Side questions to the shift points "Z" posted:
1) Murph's 1st gear shows ~6350 rpm - how did he get it to shift that high in 1st, when it seems most auto's shift much earlier than that ? Search of past posts suggests 1-2 shift somewhere around 5600rpm +/- 200rpm ??
2) 3rd to 4th is only ~6k rpm - mis-shift? or already in "D"?
3) Conversely, it looks like Andrew short-shifted to 2nd (wheel spin?), hit the rev limiter in 3rd, but overall maintained a lower rpm floor of ~4800rpm vs- Murph's 4250rpm ==> doesn't this suggest that Andrew's GT would be better suited for a CS setup? and an AT to a TS?
[not touching CS vs- TS variables like cost, install complexity, aesthetics, etc, just the data shown here]
1) Murph's 1st gear shows ~6350 rpm - how did he get it to shift that high in 1st, when it seems most auto's shift much earlier than that ? Search of past posts suggests 1-2 shift somewhere around 5600rpm +/- 200rpm ??
2) 3rd to 4th is only ~6k rpm - mis-shift? or already in "D"?
3) Conversely, it looks like Andrew short-shifted to 2nd (wheel spin?), hit the rev limiter in 3rd, but overall maintained a lower rpm floor of ~4800rpm vs- Murph's 4250rpm ==> doesn't this suggest that Andrew's GT would be better suited for a CS setup? and an AT to a TS?
[not touching CS vs- TS variables like cost, install complexity, aesthetics, etc, just the data shown here]
10-21-2010, 05:09 PM
#47
Rennlist Member
yes, it will yeild P, but how do we account for the extra time spent in the upper range of each shift point? it has to be a weighted factor.
For example, you could have the same area under the curve but the curves can be different even over the same RPM range. (e.g. 4000rpm to 6500rpm for example) ignoring aero drag, one curve shifted to the right might be faster with respect to distance (s) covered over a given time (t). but with aero drag going up with the square of speed, it might be better to not waist the power at the faster speed of each shift, and apply it were it can effect acceeleration to a greater degree.
There is nothing useless about a Hp-second. it is unit measure of work or energy. just like a watt-second, which is a joule. he who has and uses the most joules wins, right?
p(ave)=delta W/delta t
For example, you could have the same area under the curve but the curves can be different even over the same RPM range. (e.g. 4000rpm to 6500rpm for example) ignoring aero drag, one curve shifted to the right might be faster with respect to distance (s) covered over a given time (t). but with aero drag going up with the square of speed, it might be better to not waist the power at the faster speed of each shift, and apply it were it can effect acceeleration to a greater degree.
There is nothing useless about a Hp-second. it is unit measure of work or energy. just like a watt-second, which is a joule. he who has and uses the most joules wins, right?
p(ave)=delta W/delta t
the only way to anaylze this is the convert rev/min to rev/sec and integrate torque over a given range...
this will yeild W/t or P
HP-sec, etc., are useless
but as someone said, run them side by side and all doubt is removed...
btw: you don't need a calculator to integrate an exponential
int(x^n) = 1(n+1) x^(n+1)
example:
int(3 x^3) = 3/(3+1) x^(3+1) = 3/4 x^4
check: deriv(3/4 x^4) = 4 3/4 x^(4-1) = 3 x^3
this will yeild W/t or P
HP-sec, etc., are useless
but as someone said, run them side by side and all doubt is removed...
btw: you don't need a calculator to integrate an exponential
int(x^n) = 1(n+1) x^(n+1)
example:
int(3 x^3) = 3/(3+1) x^(3+1) = 3/4 x^4
check: deriv(3/4 x^4) = 4 3/4 x^(4-1) = 3 x^3
10-22-2010, 03:45 AM
#48
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Side questions to the shift points "Z" posted:
1) Murph's 1st gear shows ~6350 rpm - how did he get it to shift that high in 1st, when it seems most auto's shift much earlier than that ? Search of past posts suggests 1-2 shift somewhere around 5600rpm +/- 200rpm ??
2) 3rd to 4th is only ~6k rpm - mis-shift? or already in "D"?
3) Conversely, it looks like Andrew short-shifted to 2nd (wheel spin?), hit the rev limiter in 3rd, but overall maintained a lower rpm floor of ~4800rpm vs- Murph's 4250rpm ==> doesn't this suggest that Andrew's GT would be better suited for a CS setup? and an AT to a TS?
[not touching CS vs- TS variables like cost, install complexity, aesthetics, etc, just the data shown here]
1) Murph's 1st gear shows ~6350 rpm - how did he get it to shift that high in 1st, when it seems most auto's shift much earlier than that ? Search of past posts suggests 1-2 shift somewhere around 5600rpm +/- 200rpm ??
2) 3rd to 4th is only ~6k rpm - mis-shift? or already in "D"?
3) Conversely, it looks like Andrew short-shifted to 2nd (wheel spin?), hit the rev limiter in 3rd, but overall maintained a lower rpm floor of ~4800rpm vs- Murph's 4250rpm ==> doesn't this suggest that Andrew's GT would be better suited for a CS setup? and an AT to a TS?
[not touching CS vs- TS variables like cost, install complexity, aesthetics, etc, just the data shown here]
The shift from 3rd to 4th would be going into "D", and is right after he completed the 1/4 mile already.
Without knowing for sure, I'd have to guess he just short shifted a little bit. He has lower gearing, and you can see that the slope of the RPM increase is greater than Tim's car there, so he's got even more of the problem of the tach and engine shooting up fast there in 1st gear. It's not that easy to hit it at exactly the right time every time when things are happening as fast as they are, especially since he has to react and shift manually. With the automatic, you start with the shifter in "2", and the transmission shifts from 1st to 2nd by itself.
You can see from the RPM chart that even the RPMs of the A/T S4 car never drop down far enough after the first part of 1st gear to take advantage of any greater power that a twin screw might possibly provide there. The black stripes on some of the roads near Tim's house are a pretty good indication that any extra power down low in 1st gear really isn't going to help with making the car quicker down there, but rather only in wearing out the rear tires even faster and making it harder to launch consistently.
Andrew's car is a GT with a 5-speed manual, and Tim's an S4 with a 4speed automatic. Both the transmission and differential gearing are different between the two cars. The main point of the RPM graph was to illustrate that neither car ever drops below about 4,250 RPM after it gets beyond the first half of 1st gear, so whatever power it makes below that point is irrelevant once you get past it. Below that point in 1st gear, traction is already a factor, so more power there won't make it go any faster there either, unless traction is increased there too.
Last edited by Z; 10-22-2010 at 05:16 AM.
10-22-2010, 09:04 AM
#49
Nordschleife Master
https://rennlist.com/forums/7681660-post13.html
By my [x, 1.5x] measure, I am counting 575 whp average.
That engine is really my bogey. I am trying to beat that dyno graph but with stock long block, factory computers, 93 octane pump gas, and with single digit knock cont per 10 second dyno pull. So far, I am close on peak hp because I have complete freedom to tune the boost profile, but I am still significantly short on the average hp because I am hitting the knock constraint.
I have a couple of ideas and will head back to the dyno when JDS delivers the EZ-K map with more range.
10-22-2010, 01:33 PM
#50
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I guess if you are going to compare these two S/C they should be on the same car same Transmission same tire size and same tire compound same psi. To get an apples to apples comparison .
10-22-2010, 01:36 PM
#51
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Actually, mostly right. you want to shift at a point, usually well past max HP and it is starting to go down, in our cases, usually like an arc. Then, you shift at the part of the dowward HP side of the arc, past max HP, at a point where the resultant shift, is equal. maybe a 100rpm past, due to the time it takes to shift, (where you would have a negative acceleration between shifts, which is near .3 of a second). absolutely right about ignoring the torque curve. you cant easily look at it to determine what the shift point will be. its almost impossible to eye ball it, and it is counter intuitive.
And right again with your response to me. when racing, ill rarely ever touch the sub 4300rpm range, ever. (even though max engine torque, is far greater in the sub 4000range)
mk
And right again with your response to me. when racing, ill rarely ever touch the sub 4300rpm range, ever. (even though max engine torque, is far greater in the sub 4000range)
mk
Why would you do that if you were trying to achieve maximum acceleration? The whole topic really shouldn't be that complicated, especially for you 5-speed guys. Go out and do a run through the gears shifting at the RPM where you're horsepower starts to fall off, so that you're maximizing engine horsepower produced over the length of the run. Then do another run, only this time shifting at the RPM where your torque starts to fall off, so that you're maximizing engine torque produced over the run. Which was faster?
The majority of A/T equipped 928s that I've taken a look at didn't have something related to the transmission adjusted properly, or at least to the way I'd say was proper for maximum performance. That's part of it. The other part is that with the supercharger on it, the engine goes through the RPM range a lot faster than it did stock, and is higher by the time the shift is executed. Tim raised the rev limiter a little bit because the engine would bounce off of it once or twice before the shift would be completed. It's not the shift slipping, but rather that by the time the system tells it to shift, the engine's already at a higher RPM. 5-speed guys tend to have the same problem after a stage-3 supercharger install. They're not used to seeing the tach go up that fast, and by the time they shift, the rev limiter's been hit. It takes them some practice to get used to it, and learn to shift either faster or a little earlier to complete the shift before the rev limiter is hit.
The shift from 3rd to 4th would be going into "D", and is right after he completed the 1/4 mile already.
Without knowing for sure, I'd have to guess he just short shifted a little bit. He has lower gearing, and you can see that the slope of the RPM increase is greater than Tim's car there, so he's got even more of the problem of the tach and engine shooting up fast there in 1st gear. It's not that easy to hit it at exactly the right time every time when things are happening as fast as they are, especially since he has to react and shift manually. With the automatic, you start with the shifter in "2", and the transmission shifts from 1st to 2nd by itself.
You can see from the RPM chart that even the RPMs of the A/T S4 car never drop down far enough after the first part of 1st gear to take advantage of any greater power that a twin screw might possibly provide there. The black stripes on some of the roads near Tim's house are a pretty good indication that any extra power down low in 1st gear really isn't going to help with making the car quicker down there, but rather only in wearing out the rear tires even faster and making it harder to launch consistently.
Andrew's car is a GT with a 5-speed manual, and Tim's an S4 with a 4speed automatic. Both the transmission and differential gearing are different between the two cars. The main point of the RPM graph was to illustrate that neither car ever drops below about 4,250 RPM after it gets beyond the first half of 1st gear, so whatever power it makes below that point is irrelevant once you get past it. Below that point in 1st gear, traction is already a factor, so more power there won't make it go any faster there either, unless traction is increased there too.
The majority of A/T equipped 928s that I've taken a look at didn't have something related to the transmission adjusted properly, or at least to the way I'd say was proper for maximum performance. That's part of it. The other part is that with the supercharger on it, the engine goes through the RPM range a lot faster than it did stock, and is higher by the time the shift is executed. Tim raised the rev limiter a little bit because the engine would bounce off of it once or twice before the shift would be completed. It's not the shift slipping, but rather that by the time the system tells it to shift, the engine's already at a higher RPM. 5-speed guys tend to have the same problem after a stage-3 supercharger install. They're not used to seeing the tach go up that fast, and by the time they shift, the rev limiter's been hit. It takes them some practice to get used to it, and learn to shift either faster or a little earlier to complete the shift before the rev limiter is hit.
The shift from 3rd to 4th would be going into "D", and is right after he completed the 1/4 mile already.
Without knowing for sure, I'd have to guess he just short shifted a little bit. He has lower gearing, and you can see that the slope of the RPM increase is greater than Tim's car there, so he's got even more of the problem of the tach and engine shooting up fast there in 1st gear. It's not that easy to hit it at exactly the right time every time when things are happening as fast as they are, especially since he has to react and shift manually. With the automatic, you start with the shifter in "2", and the transmission shifts from 1st to 2nd by itself.
You can see from the RPM chart that even the RPMs of the A/T S4 car never drop down far enough after the first part of 1st gear to take advantage of any greater power that a twin screw might possibly provide there. The black stripes on some of the roads near Tim's house are a pretty good indication that any extra power down low in 1st gear really isn't going to help with making the car quicker down there, but rather only in wearing out the rear tires even faster and making it harder to launch consistently.
Andrew's car is a GT with a 5-speed manual, and Tim's an S4 with a 4speed automatic. Both the transmission and differential gearing are different between the two cars. The main point of the RPM graph was to illustrate that neither car ever drops below about 4,250 RPM after it gets beyond the first half of 1st gear, so whatever power it makes below that point is irrelevant once you get past it. Below that point in 1st gear, traction is already a factor, so more power there won't make it go any faster there either, unless traction is increased there too.
10-22-2010, 01:44 PM
#52
Rennlist Member
10-22-2010, 02:52 PM
#53
Rennlist Member
thanks for the additional insight Z. Seems true that high hp cars really do come down to driver capability to feed the appropriate level of power...in this example it seems Andrew and Murph both delivered well for their specific setups.
For me, this discussion is helpful to navigate lower hp situations (<500whp) and related acceleration to drivability for street use only. Especially when considering low boost applications within a persons "typical" driving style. Someday I hope to get into higher hp as I think most do, but for now 400whp is my target and with so many stock cars in the 400hp range, it's helpful to to actually see results like these with supporting data/graphs to tie it all together.
Clearly with such high hp in both cars, 1st gear is kinda useless as you say, since traction is exceeded far before reaching any max hp curve consideration. Funny enough, it again seems the CS setup is better suited with launch effectiveness to kinda feed a smoother power increase, even though it takes longer to get to the same hp level as the TS. If splitting hairs, it looks like the TS should clearly be faster at high-gear passing at freeway speed, where the lower rpms are relevant.
...seems the hp-second concept is appropriate, matched to each driver's style.
Good stuff.
For me, this discussion is helpful to navigate lower hp situations (<500whp) and related acceleration to drivability for street use only. Especially when considering low boost applications within a persons "typical" driving style. Someday I hope to get into higher hp as I think most do, but for now 400whp is my target and with so many stock cars in the 400hp range, it's helpful to to actually see results like these with supporting data/graphs to tie it all together.
Clearly with such high hp in both cars, 1st gear is kinda useless as you say, since traction is exceeded far before reaching any max hp curve consideration. Funny enough, it again seems the CS setup is better suited with launch effectiveness to kinda feed a smoother power increase, even though it takes longer to get to the same hp level as the TS. If splitting hairs, it looks like the TS should clearly be faster at high-gear passing at freeway speed, where the lower rpms are relevant.
...seems the hp-second concept is appropriate, matched to each driver's style.
Good stuff.
10-22-2010, 03:36 PM
#54
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10-22-2010, 04:16 PM
#56
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I love those kind of graphs! thanks for posting. look at that acceleration. now, lets find the torque curves, or the HP curve. oh yeah, acceleration is inversely proportioal to speed (and proportion to power)
10-22-2010, 04:38 PM
#57
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10-22-2010, 06:57 PM
#58
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10-22-2010, 07:44 PM
#59
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for overall acceleration for a wide range, its very fair. after alll, gearing doesnt provide HP, ONLY optimization for that hp over a vehicle speed range. If the final speed expected in the quarter mile is 115mph, then the 2.2 might workbest, if it is 100mph, the 2.54 might work best. lots of factors, so little time.
10-22-2010, 08:17 PM
#60
Nordschleife Master
Driver -> shift points
Passenger -> **** points