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Old 06-20-2006, 05:58 PM   #41
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Originally Posted by 986Jim
You guys can do all the math and internet jibba jabba you want, but the fact of the matter is you always shift at the highest RPM you possibly can, no matter what your torque curve looks like.

The engine accelerates faster at it's highest RPM regardless of HP. Your car will accelerate faster if you shift at redline even if your power is down lower. Talk about physics and engineering all you want.

When the lights drop the BS stops, and if you don't shift at redline your in second place. PERIOD.

Here is the dyno plot from my Dad's Maxima that he drag races. It has a VQ35DE in it (350Z motor) and makes a maximum of 259whp and 239ft/lbs of torque normally aspirated at the wheels (this isn't the max dyno plot just one of them I snapped. The car has cams and torque convert and headers etc few trick and stuff.

Look at the HP and torque curve. That says you should shift at 6200rpm. When he does that the car runs 13.3 @ 100mph or worse. When he shifts at 7200rpm as indicated on the dyno, the car is faster, best now 12.8 @ 106mph. Almost a half a second and in terms of racing thats a long time.

Acctually this dyno before I tuned the car (emanage ultimate) made 236whp and 219ft/lbs of torque. We picked up 21hp peak with my tuning. Between 6000-7000 power was dropping below 180whp and with timing and air fuel tuning I bumped it to what you see there. I made 60whp extra between 6000-7000rpm over stock with my tuning tricks on his car. It should run a 12.4-12.5 now I would think with 60whp extra in the top rpm range.

I really hate to argue with this statement because it's been covered already, but it's not correct. You could have an engine who's torque curve drops off dramatically after peak due to breathing issues or two gear ratios that are very close to each other and it would be beneficial to shift before redline.

Just looking at a horsepower/torque curve DOES NOT tell you when to shift. IT DOES NOT TELL YOU WHEN TO SHIFT! You have to look at gear ratios and speeds in gears, just as I've done for you guys.

Typically, however, you happen to be right, but without understanding why this is true, you won't always be right.


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Old 06-20-2006, 06:07 PM   #42
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I'm not sure that this should have turned into a horsepower vs torque arguement. An conversation of energy vs force is really pretty academic. Interesting, but ultimately you get the same answer either way you approach it. The calculation is just slightly different.

What I reallly wanted to show was a way to calculate the best shift points for acceleration. The spreadsheet that I've provided will do that and it's kinda fun to play with. I'm hoping that's what everyone takes away from it.
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Old 06-20-2006, 06:19 PM   #43
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...What I reallly wanted to show was a way to calculate the best shift points for acceleration. The spreadsheet that I've provided will do that and it's kinda fun to play with. I'm hoping that's what everyone takes away from it....
All I know is that I'm NEVER posting a thread about acceleration, I can tell you that.....
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Old 06-20-2006, 06:23 PM   #44
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All I know is that I'm NEVER posting a thread about acceleration, I can tell you that.....
LOL, I'm a glutton for punishment.
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Old 06-21-2006, 08:54 AM   #45
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the bottom line is that for a given acceleration run, you have a static amount of work to do. for instance, if your car weighs 2800 lb and you are running a quarter mile, you must move 2800 lb a distance of 1320 ft. you will be performing 3,696,000 ft-lb of work.

since the object is to minimize the time in which this work is accomplished, we must maximize power. work / time is the very definition of power. shift points should be chosen in such a way as to maximize average power AT THE WHEELS. this is why blue2K is correct in stating that the curves alone will not tell us the best shift points; gearing must be considered. the car with the highest average horsepower AT THE WHEELS over a given distance wins the race.
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Old 06-21-2006, 09:16 AM   #46
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Originally Posted by insite
the bottom line is that for a given acceleration run, you have a static amount of work to do. for instance, if your car weighs 2800 lb and you are running a quarter mile, you must move 2800 lb a distance of 1320 ft. you will be performing 3,696,000 ft-lb of work.

since the object is to minimize the time in which this work is accomplished, we must maximize power. work / time is the very definition of power. shift points should be chosen in such a way as to maximize average power AT THE WHEELS. this is why blue2K is correct in stating that the curves alone will not tell us the best shift points; gearing must be considered. the car with the highest average horsepower AT THE WHEELS over a given distance wins the race.
100% in agreement. From the time it takes to move that distance, you'll get an average acceleration and know what the speed is at the end.

Just to add, not just gearing and torque must be considered, but also the vehicle speed in gear.

Last edited by blue2000s; 06-21-2006 at 12:48 PM.
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Old 06-22-2006, 01:05 PM   #47
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100% in agreement. From the time it takes to move that distance, you'll get an average acceleration and know what the speed is at the end.
\

ah! concensus! i love it when we all just get along. :-)
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Old 06-23-2006, 04:38 AM   #48
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Originally Posted by insite
the car with the highest average horsepower AT THE WHEELS over a given distance wins the race.
This is simply NOT TRUE!!!! Spend some time at the rack track. Your Porsche can make 250whp between 4500rpm and 6500rpm range steady but a car that makes 200whp starting at 4500rpm and makes 300whp at 6500rpm will be faster.

Highest peak HP wins. It doesn't matter if it makes it over a wider range or not. Accelerations is one thing, you can math that to death, but the motors ability to accelerate or rev in a gear is a whole other story. The second car has higher peak power but less power overall will be faster. You simply can NOT argue this, it's a proven fact, goto a drag racing forum and ask, they will math you to death.

Even in the car with 250whp over a steady range will still want to shift at the highest absolute RPM point even if power is dropping off at that point, it will still be faster.

It's not about the most power across a band, is ONLY about the most power. Stop using math, and goto the race track and see what happens. Cars with big long flat power bands can get beaten by cars with lots of peak HP, because thats what wins races.

You guys are argueing with text books in a argument that takes races in real cars. You can't justify it with math, goto the track you'll figure it all out there.

This is as bad as the bench racing at clubsi for god sakes.
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Old 06-23-2006, 05:55 AM   #49
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Originally Posted by 986Jim
This is simply NOT TRUE!!!! Spend some time at the rack track. Your Porsche can make 250whp between 4500rpm and 6500rpm range steady but a car that makes 200whp starting at 4500rpm and makes 300whp at 6500rpm will be faster.

Highest peak HP wins. It doesn't matter if it makes it over a wider range or not. Accelerations is one thing, you can math that to death, but the motors ability to accelerate or rev in a gear is a whole other story. The second car has higher peak power but less power overall will be faster. You simply can NOT argue this, it's a proven fact, goto a drag racing forum and ask, they will math you to death.

Even in the car with 250whp over a steady range will still want to shift at the highest absolute RPM point even if power is dropping off at that point, it will still be faster.

It's not about the most power across a band, is ONLY about the most power. Stop using math, and goto the race track and see what happens. Cars with big long flat power bands can get beaten by cars with lots of peak HP, because thats what wins races.

You guys are argueing with text books in a argument that takes races in real cars. You can't justify it with math, goto the track you'll figure it all out there.

This is as bad as the bench racing at clubsi for god sakes.
If you refuse to understand what's being said here, there's not much point to countering your arguements. Hopefully anyone else reading this thread doesn't pick up any of your misunderstanding.
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Old 06-23-2006, 07:26 PM   #50
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I understand perfectly well what your saying. The title of this thread is Shift Points for Maximum Acceleration. That is absolute Redline no matter what. Period end of story. There simply is noting else to say.

I race and can tell you that to go fast in a straight line or around corners you rev right to redline no matter what the curve looks like. I have raced for a lot of years in a lot of different cars in many forms of motorsport. What I say is from my personal racing and being part of race teams. Everything from Drag in 6 second cars to import drag, to motorcycle, to road course with VW's and Acura's to Porsche.

If you blab on about this type of stuff around people who race a lot like I do you get laughed at like a bench racer, which is what this all is. It's just that simple.

Listen, I'm not trying to be rude or anything so please don't take it that way. Simply this thread is about where you shift to go the fastest. Thats redline every time in almost every circumstance. 99% of the time thats the fastest way, the other 1% is well whatever it is. If your only out 1% of the time your going a lot faster than you would if you tried to make up different points to shift at in your car.

Hope that helps. If you want to counter my points feel free, I'm really not going to respond to this anymore were beating a dead horse here really.
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Old 06-23-2006, 07:43 PM   #51
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Originally Posted by 986Jim
I understand perfectly well what your saying. The title of this thread is Shift Points for Maximum Acceleration. That is absolute Redline no matter what. Period end of story. There simply is noting else to say.

I race and can tell you that to go fast in a straight line or around corners you rev right to redline no matter what the curve looks like. I have raced for a lot of years in a lot of different cars in many forms of motorsport. What I say is from my personal racing and being part of race teams. Everything from Drag in 6 second cars to import drag, to motorcycle, to road course with VW's and Acura's to Porsche.

If you blab on about this type of stuff around people who race a lot like I do you get laughed at like a bench racer, which is what this all is. It's just that simple.

Listen, I'm not trying to be rude or anything so please don't take it that way. Simply this thread is about where you shift to go the fastest. Thats redline every time in almost every circumstance. 99% of the time thats the fastest way, the other 1% is well whatever it is. If your only out 1% of the time your going a lot faster than you would if you tried to make up different points to shift at in your car.

Hope that helps. If you want to counter my points feel free, I'm really not going to respond to this anymore were beating a dead horse here really.

You don't understand the curves if you even looked at them, and you don't understand the physics. I'm glad you've finally decided to stop repeating yourself because I'm getting tired of telling you that you're wrong.
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Old 06-24-2006, 06:53 PM   #52
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Originally Posted by blue2000s
You don't understand the curves if you even looked at them, and you don't understand the physics. I'm glad you've finally decided to stop repeating yourself because I'm getting tired of telling you that you're wrong.
Spend some time at the track there internet smart guy. I suggest a beginner DE course would help you a lot. Leave your calculator at home nobody there will want hear anything you have to say either.
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Old 06-24-2006, 08:12 PM   #53
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smart guy..
Finally, Thank you.
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Old 06-24-2006, 08:32 PM   #54
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[QUOTE=986Jim]

Highest peak HP wins. It doesn't matter if it makes it over a wider range or not. Accelerations is one thing, you can math that to death, but the motors ability to accelerate or rev in a gear is a whole other story. The second car has higher peak power but less power overall will be faster. You simply can NOT argue this, it's a proven fact, goto a drag racing forum and ask, they will math you to death.

Even in the car with 250whp over a steady range will still want to shift at the highest absolute RPM point even if power is dropping off at that point, it will still be faster.

It's not about the most power across a band, is ONLY about the most power. Stop using math, and goto the race track and see what happens. Cars with big long flat power bands can get beaten by cars with lots of peak HP, because thats what wins races.
QUOTE]






You seem to disregard the theoretical explanations, so I have a few real world experiences for you. My two previous cars were a LT-1 Z28 and a highly modified Acura RXS-s.

The Z-28 made gobs of tq but couldn't breath up high. I ran better times short shifting instead of holding to readline. Additionally, I frequently raced a local guy who had a NSX. His car made about 17 more whp than mine, but my tq numbers were much higher (about 75) and power curve much flatter. The race was a driver's race, he won some and I won some, but according to your experiences, his car should have beat mine each time, especially since his car was lighter.
His trap was higher and if we raced farther, he would eventually walk away, but you see how this situation counters your statement.

My Acura RSX-s made 174 hp and 140 ft-lbs at the wheels when stock. After modifications it made 213 whp but tq ony increased by 3 ft-lbs. I currently own a Cooper-S used for daily dutuies, which makes 183 hp and 176 ft-lbs at the wheels. The cars have identical 1/4 times. The trap speed of the Acura is higher and on the highway at higher speeds, the higher reving higher hp engine wins, but in auto-x and in the 1/8 and 1/4, the broader power band and responsiveness mades up for the lower peak power.

The power band is more important than peak power, and for someone who spends time at the track I'm surprised you don't see this. How many 700-800 hp Supras-MKIVs have you seen run slower than 500-600 hp ones. In order to make this much power, the twin turbo is swapped for a single larger one. It makes big power, but takes so long to spool up ( which means a peaky power curve ) that it's too late by the time is really kicks in. The lower hp cars use twin (actually sequential) turbos, which means power from low to high (flatter curve). I have two co-workers with Supras i described above, 550hp vs 920 hp and the lower hp usualy wins. This is also true for the Suby Sti. When modified to make more hp, they sacrifice a flat power band, which means they lose the hole shot and play catch up the rest of the race. This is a fairly common occurance to see at the tracks.
This should clearly illustrate that peak hp does not win races, in wins braggin rights.
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Old 06-24-2006, 09:48 PM   #55
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Hi,

I've stayed away from this thread after the theoreticians entered the fray, but I have to say that I side with both 986Jim and mtch. This may seem a contradiction, but each completes a part of the total picture.

You can run calculations and sims all day long, but real life offers another dimension that cannot always be accounted for in the lab.

People know what they know, but that doesn't mean they know everything. I think I am well founded in the fundamentals of engineering, enough to have a passing knowledge of what I'm talking about. Should my resume' be in question, I have a BS in Materials Science (minor in Physics) from Purdue University. I have a BS in Aeronautical Engineering from Massachusetts Institute of Technology, I have an MS in Aeronautical Engineering from University of Minnesota (Courtesy of the US Taxpayer - Thanks!). In addition, I am a graduate of the US Navy Test Flight School - United States Navy Flight Test Center at Patuxent River Naval Air Station, and a Certified Test Pilot with in excess of 3700 Flying hours.

All I can say is that we were continually surprised at Pax River when real-world test data conflicted with our preconcieved calculations. And, this wasn't Ivory Tower Academia, this was hanging it out beyond the envelope 9-5, M-F.

What's interesting to me in this impirical discussion, is that no one has yet mentioned Drag Coefficients and Frontal Areas - surely you're aware that the effect of these is not at all negligible in the context of the discussion here - remember your inverse square laws governing Drag?...

Happy Motoring!... Jim'99

Last edited by MNBoxster; 06-24-2006 at 10:00 PM.
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Old 06-25-2006, 04:17 AM   #56
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Quote:
Originally Posted by mtch
The Z-28 made gobs of tq but couldn't breath up high. I ran better times short shifting instead of holding to readline. Additionally, I frequently raced a local guy who had a NSX. His car made about 17 more whp than mine, but my tq numbers were much higher (about 75) and power curve much flatter. The race was a driver's race, he won some and I won some, but according to your experiences, his car should have beat mine each time, especially since his car was lighter.
His trap was higher and if we raced farther, he would eventually walk away, but you see how this situation counters your statement.
This is very true of drag racing. What should win all the time doesn't always. What I'm refering to is, that if your driving your car, your best bet drag racing is to shift at redline. Your Z28 would have been faster if it could breathe at the top end. A new intake manifold with shorter runners and larger plenum would have solved that. THe long runners used on the Z28 mani make for huge torque but rob the motor up high. You would have spanked the NSX with only a few minor changes. Also shifting and how you launch are a lot of the equations. We still can't take out the human aspect of racing.

Quote:
Originally Posted by Mitch
My Acura RSX-s made 174 hp and 140 ft-lbs at the wheels when stock. After modifications it made 213 whp but tq ony increased by 3 ft-lbs. I currently own a Cooper-S used for daily dutuies, which makes 183 hp and 176 ft-lbs at the wheels. The cars have identical 1/4 times. The trap speed of the Acura is higher and on the highway at higher speeds, the higher reving higher hp engine wins, but in auto-x and in the 1/8 and 1/4, the broader power band and responsiveness mades up for the lower peak power.
Drag racing is really my specialty. With drivers and all other being the same, the higher HP Acura should have been faster. What made the difference is likely your skill is better now with more practice, or the Cooper-S is more your style of car so you drive it easier. Also weight is a concern, your Cooper-S is likely lighter than the RSX is as well. So with all other things being equil the higher HP car would have won. BUt not because it can rev higher, just that it has higher HP. Thats pretty easy to understand.

What I'm talking about is the title of this thread. Shift point for Maximum acceleration. You always shift at highest RPM. If your Camero was more setup for drag racing with a short runner manifold shiftinger higher would have made the car faster. You yourself said the downfall of the car, couldn't brethe up top. If you corrected that, what would your camero do to the NSX then? Right, mop the floor with it.

Quote:
Originally Posted by mitch
The power band is more important than peak power, and for someone who spends time at the track I'm surprised you don't see this. How many 700-800 hp Supras-MKIVs have you seen run slower than 500-600 hp ones. In order to make this much power, the twin turbo is swapped for a single larger one. It makes big power, but takes so long to spool up ( which means a peaky power curve ) that it's too late by the time is really kicks in. The lower hp cars use twin (actually sequential) turbos, which means power from low to high (flatter curve). I have two co-workers with Supras i described above, 550hp vs 920 hp and the lower hp usualy wins. This is also true for the Suby Sti. When modified to make more hp, they sacrifice a flat power band, which means they lose the hole shot and play catch up the rest of the race. This is a fairly common occurance to see at the tracks.
This should clearly illustrate that peak hp does not win races, in wins braggin rights.
I understand what your saying about Supra's but I build and dyno tune those very cars so your entering my world now.



What your talking about is pull the sequential turbo setup and replacing it with a Single unit like the Greddy T78 setup commonly used on these cars.. They don't acctually spool slowly as you can see on this graph. The supra engine is very efficient at moving air so it can spool a large turbo by 4500rpm or so. This graph is 631whp, see where the power starts and how far is goes?

In drag racing they use a two step to spool the turbo during the launch so you leave the line with 10psi or so. There is no spool up for the turbo then, and you never take your foot off the gas even when shifting so the re-spool is almost nothing, the supra powers down the track and runs a good number.

When you get to 800whp or so, you can't do that anymore. The Getrag tranny in the supra (sound familiar?) is quite good, but you can't two step a stock 800whp engine outta the hole nor can you power shift. Plus we all know the real reason for the Supra pehnomon is because they are all dyno queens and none of them really know how to drag race anyway lol...

I build and dyno tune drag cars for a living, I have also been drag racing imports for 10+ years now. My talon is built for that very purpose. I win the Street Import class every year, and took 3rd in the Steet Summit class which is all V8 powered cars last year as well. My dad has been drag racing for 35+ years and built an import to race in my class about 4 years ago.

One thing I do know is how to make a car run fast in a straight line and what wins races. I build cars dyno then then race them at the track many times before the owner of the car does because they want to see how fast the car should go before they drive it for bragging rights or whatever.

Seriously I'm not trying to start a fight, (tho I'm obviously not doing a good job) What I say is from practical experience at the track.

Hope that helps,
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Old 06-25-2006, 06:24 AM   #57
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Originally Posted by MNBoxster
Hi,

I've stayed away from this thread after the theoreticians entered the fray, but I have to say that I side with both 986Jim and mtch. This may seem a contradiction, but each completes a part of the total picture.

You can run calculations and sims all day long, but real life offers another dimension that cannot always be accounted for in the lab.

People know what they know, but that doesn't mean they know everything. I think I am well founded in the fundamentals of engineering, enough to have a passing knowledge of what I'm talking about. Should my resume' be in question, I have a BS in Materials Science (minor in Physics) from Purdue University. I have a BS in Aeronautical Engineering from Massachusetts Institute of Technology, I have an MS in Aeronautical Engineering from University of Minnesota (Courtesy of the US Taxpayer - Thanks!). In addition, I am a graduate of the US Navy Test Flight School - United States Navy Flight Test Center at Patuxent River Naval Air Station, and a Certified Test Pilot with in excess of 3700 Flying hours.

All I can say is that we were continually surprised at Pax River when real-world test data conflicted with our preconcieved calculations. And, this wasn't Ivory Tower Academia, this was hanging it out beyond the envelope 9-5, M-F.

What's interesting to me in this impirical discussion, is that no one has yet mentioned Drag Coefficients and Frontal Areas - surely you're aware that the effect of these is not at all negligible in the context of the discussion here - remember your inverse square laws governing Drag?...

Happy Motoring!... Jim'99

The reason drag hasn't been mentioned is that it will not have an influence on speeds in gears and not the torque made at the wheels, so the shift points are not effected. The time it takes to get to any speed is effected, but that's not relavent here.
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Old 06-25-2006, 06:35 AM   #58
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Originally Posted by 986Jim
Your Z28 would have been faster if it could breathe at the top end. A new intake manifold with shorter runners and larger plenum would have solved that....

Shift point for Maximum acceleration. You always shift at highest RPM. If your Camero was more setup for drag racing with a short runner manifold shiftinger higher would have made the car faster. You yourself said the downfall of the car, couldn't brethe up top.
This is the WHOLE point. I wish I could connect these dots somehow because you're saying it right here.

If you change breathing on the engine, then you've changed the horsepower and torque curves and the game is a new one.

What he's saying is that redline isn't best in EVERY situation with an actual example, which, if you look back at my responses, is also exactly what I said.


Quote:
Originally Posted by 986Jim
Seriously I'm not trying to start a fight, (tho I'm obviously not doing a good job) What I say is from practical experience at the track.

Hope that helps,
Debate and discussion is a useful learning tool. If it remains on subject and avoids getting personal, all it can do is enlighten.
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Old 06-25-2006, 05:49 PM   #59
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Just got back from a 2 hour romp. Man, I love this car !

Question, does anyone know ( or know where I can find ) the shift points for a 99 Boxster ?

Example ( fake numbers ) :

1st Gear : redlines at 30 mph
2nd Gear : redlines at 60 mph
3rd gear : redlines at 90 mph
4th gear : redlines at 120 mph
5th gear : redlines at 150 mph

Thanks !

Nick
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Old 06-26-2006, 05:17 AM   #60
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Originally Posted by blue2000s
This is the WHOLE point. I wish I could connect these dots somehow because you're saying it right here.

If you change breathing on the engine, then you've changed the horsepower and torque curves and the game is a new one.

What he's saying is that redline isn't best in EVERY situation with an actual example, which, if you look back at my responses, is also exactly what I said.




Debate and discussion is a useful learning tool. If it remains on subject and avoids getting personal, all it can do is enlighten.
Here's the thing about the camero. Even tho it lost steam up top, it still will accelerate faster if you take it to redline. Making the car accelerate fast has more to do with being where the engine can accelerate than where it makes the most power over the logest part of the curve. Changing the intake manifold would have just made it more efficient and could beat the NSX but he should still shift at redline.

Lets say the Camero has a redline of 6000rpm. But makes peak power at 4500rpm which is probablly pretty close to the truth. Lets also assume the gears are long which they are so switching to the next gear will induce a drop of 2000rpm from whatever point you are at. Based on the curve of that engine it would probablly be best to shift at 5500rpm and land at 3500rpm where your in the greatest part of the curve. The problem is the engine will not accelerate as fast even though your in the strongest part of the curve.

Shifting at 6000rpm even though your way over the curve is better. The engine accelerates faster at 6000rpm with less hp than it does at 4500rpm with a lot more, thats what I'm trying to say. So shifting at 6000rpm and landing at 4000rpm is in a point where the engine will accelerate faster even though your not in the maximum part of the torque curve. It's all about how freely the engine can accelerate.

It's for the same reason many companies say you can't spray nitrous on a motor at less than 3000rpm. This is true most of the time but not all the time. The engine car freely rev in 1st and 2nd gear in most cars so you can spray them right at 1000rpm outta the hole in drag racing. You can't do this in 3rd onwards however because the engine ability to accelerate is lower so the stress on the motor with all that power is too high and will melt a piston.

This is the same way the engine works when accelerating at the top. It will accelerate more freely between 5500-6000rpm even tho it's making less power so acceleration will be greater even with less hp. I know this doesn't sound right, but a quick trip to the strip with that Camero would prove this, short shifting the engine into a zone down low where it doesn't accelerate is worse.

There is a trade off. You have 2000rpm you must accelerate in no matter what. What will accelerate faster? The zone from 3500-4000rpm or the zone from 5500-6000rpm? Look at this graph and you will see what im talking about. The Green zone is better because it will accelerate in the last 500rpm faster than the first 500rpm in the red zone. This is only true because its up higher in the rpm band where it's easier for the engine to accelerate. Even though it's outta the curve, the last 500rpm (5500-6000) is just a faster spot for the engine than 4000-4500rpm spot at the beginning of the shift.

What we are really debating is which 500rpm are better? The 500rpm frpm 4000-4500 or the 500rpm from 5500-6000. The rest of the rpm in the middle we are both in regardless.

Hope that helps,


Last edited by 986Jim; 06-26-2006 at 05:22 AM.
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