View Poll Results: Where do you shift your 996 3.6L street engine'd racer
shift at redline to maximize HP and acceleration on any straight
13
36.11%
shift at 300rpm below redline to save then engine and its "noise" anyway.
11
30.56%
I dont know, but want to learn how to maximize acceleration on any straight on the track.
1
2.78%
I dont know and dont care. Ill just do whatever VR says I should do.
11
30.56%
Multiple Choice Poll. Voters: 36. You may not vote on this poll
996 3.6L street engine race car owners. Where do you shift?
02-09-2011, 01:41 PM
#16
Nordschleife Master
The way to find the answer, which I think Greg is offering to do, is to calculate wheel torque in each gear across the powerband. Then you look at where the lines cross for each successive gear. If the thrust force of the next higher gear is lower than the thrust force in the preceeding gear, you keep accelerating all the way up to redline. I've never run the numbers on the 996, but given that the gearbox is geared for the street and has what we would consider relatively high gaps, I am going to guess that fastest acceleration in 3rd and 4th gear will always be achieved by running the engine up to the limiter before shifting.
02-09-2011, 01:42 PM
#17
Rennlist Member
Thread Starter
the way I present?? Really?
hmm, why dont you do both of us a favor. read the last thread and my post regarding the comments made about the topic. see what I said, and then see what the reponse back from who ever. I re read it and I think it was very informative, especailly if I am right. you often hear of folks short shifting intuitively, as VR has suggested, even if it is by 300rpm. Most of us *(are racers) and want the most out of our cars, so why would this be a good idea, even though their data (which we have never seen ) supports their point?
What I presented is hard core fact and it can barely be argued to the contrary if we are talking straight line acceleration. thats like saying, if you take a longer time to shift, your drag times will be better. Its just not true!
Their data is swayed by many other factors, as we all know, existing during a lap.
if you can handle the power, shift at a point that maximizes HP for your engine.
hmm, why dont you do both of us a favor. read the last thread and my post regarding the comments made about the topic. see what I said, and then see what the reponse back from who ever. I re read it and I think it was very informative, especailly if I am right. you often hear of folks short shifting intuitively, as VR has suggested, even if it is by 300rpm. Most of us *(are racers) and want the most out of our cars, so why would this be a good idea, even though their data (which we have never seen ) supports their point?
What I presented is hard core fact and it can barely be argued to the contrary if we are talking straight line acceleration. thats like saying, if you take a longer time to shift, your drag times will be better. Its just not true!
Their data is swayed by many other factors, as we all know, existing during a lap.
if you can handle the power, shift at a point that maximizes HP for your engine.
02-09-2011, 01:46 PM
#18
Rennlist Member
Thread Starter
Yes, and this is the point of all this. But, what greg is offering is totally unessesary, unless you dont understand the concepts of power.
in the end, the power curve dictates your ability to accelerate, (as does the curves or plots Greg is offering) they will be identical. shift at a point where equal power is found after the shift and you maximize area under the HP curve.
shift earlier, and you are leaving sometimes BIG HP on the table (for racers, 20-40hp is big, even if it is only for a second or so depending on the gears)
again, the gear spacing is .85 and .8 for 4-5th and 3-4th shifts. take the RPM at redline, and see what the RPM drop is. see if lower shift points gives you more or less HP after a shift and compare. its really simple.
Mk
in the end, the power curve dictates your ability to accelerate, (as does the curves or plots Greg is offering) they will be identical. shift at a point where equal power is found after the shift and you maximize area under the HP curve.
shift earlier, and you are leaving sometimes BIG HP on the table (for racers, 20-40hp is big, even if it is only for a second or so depending on the gears)
again, the gear spacing is .85 and .8 for 4-5th and 3-4th shifts. take the RPM at redline, and see what the RPM drop is. see if lower shift points gives you more or less HP after a shift and compare. its really simple.
Mk
The way to find the answer, which I think Greg is offering to do, is to calculate wheel torque in each gear across the powerband. Then you look at where the lines cross for each successive gear. If the thrust force of the next higher gear is lower than the thrust force in the preceeding gear, you keep accelerating all the way up to redline. I've never run the numbers on the 996, but given that the gearbox is geared for the street and has what we would consider relatively high gaps, I am going to guess that fastest acceleration in 3rd and 4th gear will always be achieved by running the engine up to the limiter before shifting.
02-09-2011, 01:48 PM
#19
Rennlist Member
Thread Starter
with your curves, it definitly pays a little to shift earlier, but only from 4-5th gear shift. (3-4th pays to redline or 7200rpm anyway ) that HP curve falls off pretty steep. so, shifting at 7k is not that bad an idea for you .
In this case, with the curve as it is, increasing redline doesnt buy you much, unless you had a 928 long gear box.
Now the red curve on the graph, pays for redline each shift, no matter the gear.
what was the mod that gave the HP gains, but hurt the shape of the curve, which obiously is a fantastic trade off?
In this case, with the curve as it is, increasing redline doesnt buy you much, unless you had a 928 long gear box.
Now the red curve on the graph, pays for redline each shift, no matter the gear.
what was the mod that gave the HP gains, but hurt the shape of the curve, which obiously is a fantastic trade off?
02-09-2011, 02:15 PM
#20
Rennlist Member
with your curves, it definitly pays a little to shift earlier, but only from 4-5th gear shift. (3-4th pays to redline or 7200rpm anyway ) that HP curve falls off pretty steep. so, shifting at 7k is not that bad an idea for you .
In this case, with the curve as it is, increasing redline doesnt buy you much, unless you had a 928 long gear box.
Now the red curve on the graph, pays for redline each shift, no matter the gear.
what was the mod that gave the HP gains, but hurt the shape of the curve, which obiously is a fantastic trade off?
In this case, with the curve as it is, increasing redline doesnt buy you much, unless you had a 928 long gear box.
Now the red curve on the graph, pays for redline each shift, no matter the gear.
what was the mod that gave the HP gains, but hurt the shape of the curve, which obiously is a fantastic trade off?
most likely it is a combination of fabspeed xpipe 200cell cats and softronic flash. torque bump at 4500rpm is definitely softronic and it is pretty ****ty on a track as it happens quite sudden and if not careful car may spin but after 5K it became awesome - it really pulls very equally until redline. it was very different before those changes despite what graph shows - car did not pull in proper uniform fashion before, it was a definite 'drop' and tone changes - you can also see that on timing graph there - after mods it became much more stable.
again, on the other side - it may be specific to my car only as i got it in pretty virgin state with MAF sensor never cleaned so i cleaned it up from inside out literally then started adding stuff.
dirty maf and dirty stock air filter could be causing a lot of issues on that first curve, so, who knows.
02-09-2011, 02:19 PM
#21
Nordschleife Master
Yes, and this is the point of all this. But, what greg is offering is totally unessesary, unless you dont understand the concepts of power.
in the end, the power curve dictates your ability to accelerate, (as does the curves or plots Greg is offering) they will be identical. shift at a point where equal power is found after the shift and you maximize area under the HP curve.
shift earlier, and you are leaving sometimes BIG HP on the table (for racers, 20-40hp is big, even if it is only for a second or so depending on the gears)
again, the gear spacing is .85 and .8 for 4-5th and 3-4th shifts. take the RPM at redline, and see what the RPM drop is. see if lower shift points gives you more or less HP after a shift and compare. its really simple.
Mk
in the end, the power curve dictates your ability to accelerate, (as does the curves or plots Greg is offering) they will be identical. shift at a point where equal power is found after the shift and you maximize area under the HP curve.
shift earlier, and you are leaving sometimes BIG HP on the table (for racers, 20-40hp is big, even if it is only for a second or so depending on the gears)
again, the gear spacing is .85 and .8 for 4-5th and 3-4th shifts. take the RPM at redline, and see what the RPM drop is. see if lower shift points gives you more or less HP after a shift and compare. its really simple.
Mk
02-09-2011, 04:25 PM
#23
Drifting
The way to find the answer, which I think Greg is offering to do, is to calculate wheel torque in each gear across the powerband. Then you look at where the lines cross for each successive gear. If the thrust force of the next higher gear is lower than the thrust force in the preceeding gear, you keep accelerating all the way up to redline. I've never run the numbers on the 996, but given that the gearbox is geared for the street and has what we would consider relatively high gaps, I am going to guess that fastest acceleration in 3rd and 4th gear will always be achieved by running the engine up to the limiter before shifting.
Edit- I did whip this up quick, so the units are meaningless without final drive etc. Also, the precision of the dyno numbers leaves something to be desired
An alternative way of doing it is to calculate Work with W=Pt and ignore the wheel torques but you still need to know the shift points.
02-09-2011, 05:05 PM
#25
Super Moderator
Needs More Cowbell
Lifetime Rennlist
Member
Needs More Cowbell
Lifetime Rennlist
Member
Just a comment from the cheap seats....
Please stay on topic and avoid personal comments/attacks.
We won't be having a sequel to the events that led up to the last time I had to "take out the trash" in the Racing/DE forum.
Thank you.
Please stay on topic and avoid personal comments/attacks.
We won't be having a sequel to the events that led up to the last time I had to "take out the trash" in the Racing/DE forum.
Thank you.
02-09-2011, 05:22 PM
#27
Rennlist Member
Thread Starter
good graph. Its much easier to discuss with actual data. (even if it just proportional). I wouldnt go so far as to say its "meaningless", as that will not change the shift points of the respective RPM, but certainly would change the vehicle speeds.
wow, look at the power difference for short shifting. Now, could any motec data be found to dispute the advantage of taking the 3.6 to redline for max acceleration down a straight? looks like, even a 200rpm short shift costs between 20-40hp as was mentioned!
Thanks for the post.
wow, look at the power difference for short shifting. Now, could any motec data be found to dispute the advantage of taking the 3.6 to redline for max acceleration down a straight? looks like, even a 200rpm short shift costs between 20-40hp as was mentioned!
Thanks for the post.
Here you go. At 7000RPM you have to make the decision as to rev up or shift. These options are highlighted in bold.
Edit- I did whip this up quick, so the units are meaningless without final drive etc. Also, the precision of the dyno numbers leaves something to be desired
An alternative way of doing it is to calculate Work with W=Pt and ignore the wheel torques but you still need to know the shift points.
Edit- I did whip this up quick, so the units are meaningless without final drive etc. Also, the precision of the dyno numbers leaves something to be desired
An alternative way of doing it is to calculate Work with W=Pt and ignore the wheel torques but you still need to know the shift points.
Last edited by mark kibort; 02-09-2011 at 05:41 PM.
02-09-2011, 05:24 PM
#28
Rennlist Member
Thread Starter
Sorry, didnt mean to come off that way. I was just trying to show that the HP curve in the end is all you really need to show shift points which is much easier to see. BUT, the spreadsheet does give values to see the level of differences.
yes, the discussion is good.
yes, the discussion is good.
02-09-2011, 05:32 PM
#29
Rennlist Member
Thread Starter
Definitely there are somethings going on. I think I understand the raised redline, as when getting to the real redline, you dont want to bump off it. (not good for the engine to have a "miss" at 7000rpm. )
as far as the red curve, stock curve goes, you see if you short shift, even as much as 200rpm, it would cost you near 40hp!! (for the time it would normally take to get from 6900 to 7200rpm! 3rd to 4th gear shift) that is a HUGE loss by shifting earlier. Also, its really actually longer, because at the lower HP leve, you accelerate slower and you spend even more time at that lower hp level!
This is why this is such a great topic of discussion. you cant make statements about when to shift, unless you really know the HP curve (or torque curves).
And, look at that plummeting torque curve. common thougth would be that your torque is falling, why not shift? this is because as we have been saying, if you shift, the acceleration would be reduced even further!!
) as far as the red curve, stock curve goes, you see if you short shift, even as much as 200rpm, it would cost you near 40hp!! (for the time it would normally take to get from 6900 to 7200rpm! 3rd to 4th gear shift) that is a HUGE loss by shifting earlier. Also, its really actually longer, because at the lower HP leve, you accelerate slower and you spend even more time at that lower hp level!
This is why this is such a great topic of discussion. you cant make statements about when to shift, unless you really know the HP curve (or torque curves).
And, look at that plummeting torque curve. common thougth would be that your torque is falling, why not shift? this is because as we have been saying, if you shift, the acceleration would be reduced even further!!
red curve was pure stock pre-mod, final curve was done on same dyno in same weather after all mods were done, so what did what is difficult to say, it is final cumulative effect. increase to 7500 just helps to avoid cut-off before upshift.
most likely it is a combination of fabspeed xpipe 200cell cats and softronic flash. torque bump at 4500rpm is definitely softronic and it is pretty ****ty on a track as it happens quite sudden and if not careful car may spin but after 5K it became awesome - it really pulls very equally until redline. it was very different before those changes despite what graph shows - car did not pull in proper uniform fashion before, it was a definite 'drop' and tone changes - you can also see that on timing graph there - after mods it became much more stable.
again, on the other side - it may be specific to my car only as i got it in pretty virgin state with MAF sensor never cleaned so i cleaned it up from inside out literally then started adding stuff.
dirty maf and dirty stock air filter could be causing a lot of issues on that first curve, so, who knows.
most likely it is a combination of fabspeed xpipe 200cell cats and softronic flash. torque bump at 4500rpm is definitely softronic and it is pretty ****ty on a track as it happens quite sudden and if not careful car may spin but after 5K it became awesome - it really pulls very equally until redline. it was very different before those changes despite what graph shows - car did not pull in proper uniform fashion before, it was a definite 'drop' and tone changes - you can also see that on timing graph there - after mods it became much more stable.
again, on the other side - it may be specific to my car only as i got it in pretty virgin state with MAF sensor never cleaned so i cleaned it up from inside out literally then started adding stuff.
dirty maf and dirty stock air filter could be causing a lot of issues on that first curve, so, who knows.
02-09-2011, 05:44 PM
#30
Rennlist Member
Apparently to some people.
Clearly slowpokes like you, PedroNole, Viking, mglobe, me, etc etc etc could not POSSIBLY know anything, despite our real-world data & experience, when confronted by the theoretical world of a classroom instructor.
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