HalltechSSM Installed and Baseline Dyno #
Drifting
Joined: Jul 2003
Posts: 1,796
Likes: 1
From: Annandale VA
Originally Posted by glennhl
Torque equals Inertia times Rotational acceleration. So if the acceleration is higher when you are in a lower gear, then the torque required to accelerate the moving parts in your car is higher and thus less engine torque is available to accelerate your vehicle.
It may sound confusing, but it's just physics. Come to think of it, that's why it sounds confusing!
It may sound confusing, but it's just physics. Come to think of it, that's why it sounds confusing!
What robs power is internal friction ---- parasitic loss. It takes more TQ (twisting power) to spin a 4.56 gear set than it does a 2.56. I've seen several threads on this forum and over in LS1TECH that provide exact figures for the amount of power that is lost.
It also takes more power to do a dyno pull in 1st gear than in 2nd gear, 2nd gear than 3rd gear, etc. Again, several guys have posted precise figures as to the loss.
Drifting
Joined: Jul 2003
Posts: 1,796
Likes: 1
From: Annandale VA
Originally Posted by glennhl
??? You'll have to explain this one to me. The engine will rev more quickly but the car won't? Are you saying that your car will accelerate more quickly in second gear than in first?
Let's say I'm in second gear, running at 4K RPMs. You're next to me in 1st gear, at 5500 RPMs. We both mash the gas pedal. Who pulls away? Answer: I do. My engine goes from 4K RPMs to 5K RPMs, right through the middle of the torque peak. Yours goes from 5500 RPMs to 6500 RPMs, well past the TQ peak. No contest. Your car will make more noise, but it won't accellerate as quickly.
Don't believe me? Get yourself side by side with a buddy with a car like yours, try it and see.
Physics don't lie......
Le Mans Master
Joined: Feb 2006
Posts: 5,762
Likes: 4
From: Chandler Arizona
Originally Posted by HITMAN99
It sounds confusing because you are confused. You don't understand torque, or physics. Torque IS rotational force, period. The force required to accellerate the moving parts in your engine from 2K RPMs to 6K RPMs is the same whether you are pulling a 2.56 gear or a 4.56 gear. The engine parts move exactly the same distance either way. The driveshaft turns the same number of RPMs. Actually, the biggest moving part is your rear wheels, and they are spinning LESS with a shorter gear.
What robs power is internal friction ---- parasitic loss. It takes more TQ (twisting power) to spin a 4.56 gear set than it does a 2.56. I've seen several threads on this forum and over in LS1TECH that provide exact figures for the amount of power that is lost.
It also takes more power to do a dyno pull in 1st gear than in 2nd gear, 2nd gear than 3rd gear, etc. Again, several guys have posted precise figures as to the loss.
What robs power is internal friction ---- parasitic loss. It takes more TQ (twisting power) to spin a 4.56 gear set than it does a 2.56. I've seen several threads on this forum and over in LS1TECH that provide exact figures for the amount of power that is lost.
It also takes more power to do a dyno pull in 1st gear than in 2nd gear, 2nd gear than 3rd gear, etc. Again, several guys have posted precise figures as to the loss.
No disrespect, but you are misunderstanding what I'm saying. If you have the car in first gear, all those parts in the engine and drivetrain are going to accelerate more quickly and that is what robs the torque. You are only thinking about things one dimensionally. Sure the parts have to travel the same distance, but in first gear they do it more quickly, hence the acceleration is higher. It does make a difference what rearend ratio you have because with a stiffer gear you are going to accelerate those engine parts more quickly. Do you understand T = I x Alpha? Plus the rotational inertia goes up with the gear ratio squared. I'm sorry you are confused, it is very confusing to understand the first time you come across it. If you don't believe me, then please do a search in a machine design engineering book. I'd recommend Shigley.
I do not argue the fact that there are inefficiencies in your engine/drivetrain, but that's not the point I'm trying to make.
Sorry,
Glenn
Last edited by glennhl; Jun 27, 2006 at 11:58 PM.
Le Mans Master
Joined: Feb 2006
Posts: 5,762
Likes: 4
From: Chandler Arizona
Originally Posted by HITMAN99
YES, that is exactly what I am saying. First, cars don't rev, engines do. Second, even though the engine may rev more quickly, it MAY not accellerate as fast. It depends on the two gear ratios in question, and the range of RPMs.
Let's say I'm in second gear, running at 4K RPMs. You're next to me in 1st gear, at 5500 RPMs. We both mash the gas pedal. Who pulls away? Answer: I do. My engine goes from 4K RPMs to 5K RPMs, right through the middle of the torque peak. Yours goes from 5500 RPMs to 6500 RPMs, well past the TQ peak. No contest. Your car will make more noise, but it won't accellerate as quickly.
Don't believe me? Get yourself side by side with a buddy with a car like yours, try it and see.
Physics don't lie......
Let's say I'm in second gear, running at 4K RPMs. You're next to me in 1st gear, at 5500 RPMs. We both mash the gas pedal. Who pulls away? Answer: I do. My engine goes from 4K RPMs to 5K RPMs, right through the middle of the torque peak. Yours goes from 5500 RPMs to 6500 RPMs, well past the TQ peak. No contest. Your car will make more noise, but it won't accellerate as quickly.
Don't believe me? Get yourself side by side with a buddy with a car like yours, try it and see.
Physics don't lie......
Don't forget, the tractive effort at the rear tires is the torque of the engine times the overall gear ratio. So in first gear I have 2.97 times 3.42 or a 10.2 to 1 overall ratio and let's say I'm at only 300 foot pounds. That gives me 3000 foot pounds at the rear wheels. Now you are in second and your engine is making 350 foot pounds. But in second the overall gear ratio is 7.08 so you have 2478 foot pounds of torque at the rear wheels. So I will win the race for a very short period of time until I have to shift to second.
Drifting
Joined: Jul 2003
Posts: 1,796
Likes: 1
From: Annandale VA
Sounds like "Professor" Irwin Corey to me --- "the rotational inertia goes up with the gear ratio squared". That's pretty creative!
BTW, I am the East Coast Manager of Systems Engineering for Northrop Grumman Corporation. I am familiar with Dr. Joseph Shigley, as we use CAD tools for our finite element design work. Who knew he was also into automotive performance!
BTW, I am the East Coast Manager of Systems Engineering for Northrop Grumman Corporation. I am familiar with Dr. Joseph Shigley, as we use CAD tools for our finite element design work. Who knew he was also into automotive performance!
Le Mans Master
Joined: Feb 2006
Posts: 5,762
Likes: 4
From: Chandler Arizona
Originally Posted by HITMAN99
Sounds like "Professor" Irwin Corey to me --- "the rotational inertia goes up with the gear ratio squared". That's pretty creative!
BTW, I am the East Coast Manager of Systems Engineering for Northrop Grumman Corporation. I am familiar with Dr. Joseph Shigley, as we use CAD tools for our finite element design work. Who knew he was also into automotive performance!
BTW, I am the East Coast Manager of Systems Engineering for Northrop Grumman Corporation. I am familiar with Dr. Joseph Shigley, as we use CAD tools for our finite element design work. Who knew he was also into automotive performance!
When you say you work for Northrup Grumman, is it on the aircraft side or the Marine side (Newport News)?
Drifting
Joined: Jul 2003
Posts: 1,796
Likes: 1
From: Annandale VA
I work in Herndon, VA for the Information Technology sector. I have engineers who support our Ship Systems in Pascagoula, MS and also at Newport News. We also support the Airborne Electronic Warfare folks up in Bethpage, NY, and the Air/Ground Systems and Battlefield Management Systems groups in Melbourne, FL. One of our AGS missile packages was recently responsible for knocking out Al-Zarqawi in Iraq.
Last edited by HITMAN99; Jun 28, 2006 at 08:38 AM.
Le Mans Master
Joined: Feb 2006
Posts: 5,762
Likes: 4
From: Chandler Arizona
Originally Posted by HITMAN99
I work in Herndon, VA for the Information Technology sector. I have engineers who support our Ship Systems in Pascagoula, MS and also at Newport News. We also support the Airborne Electronic Warfare folks up in Bethpage, NY, and the Air/Ground Systems and Battlefield Management Systems groups in Melbourne, FL. One of our AGS missile packages was recently responsible for knocking out Al-Zarqawi in Iraq.
Also, please forgive me about admitting that I'm an engineer. It's a curse!
http://home.pcisys.net/~tbc/hacks/knack.htm
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Drifting
Joined: Jul 2003
Posts: 1,796
Likes: 1
From: Annandale VA
No problem, & I'm not pissed off at all. However, I've found that most of the senior members of this forum and others like it (LS1TECH) are very knowledgable about automotive engineering as it applies to our cars. So when it comes to discussions about TQ, HP, dynos, parasitic losses, etc. it's best to do a search, and read the many learned threads about the subject. You will find some fascinating technical information, and often some fairly heated debates. Too often they turn into flamefests, which is unfortunate. In the long run, it's all good.
Le Mans Master
Joined: Feb 2006
Posts: 5,762
Likes: 4
From: Chandler Arizona
Originally Posted by HITMAN99
No problem, & I'm not pissed off at all. However, I've found that most of the senior members of this forum and others like it (LS1TECH) are very knowledgable about automotive engineering as it applies to our cars. So when it comes to discussions about TQ, HP, dynos, parasitic losses, etc. it's best to do a search, and read the many learned threads about the subject. You will find some fascinating technical information, and often some fairly heated debates. Too often they turn into flamefests, which is unfortunate. In the long run, it's all good.
Drifting
Joined: Sep 2005
Posts: 1,775
Likes: 1
From: Rehoboth Beach Delaware
Originally Posted by glennhl
No problem. You are correct about the inefficiencies, but the rotational inertias do play a part. The first time a friend told me this, I responded with a "say what???" But when I thought about it, it made sense to me. The quote that you said was gibberish wasn't even mine, it came from a Mustang article, but I thought it did a better job than I did trying to explain the effect.
Much too much emphasis put on dyno numbers, seems to be a trendy thing to do. Great for tuning, but to indicate what a mod has afforded as far as increased power has no real value.
Competitive motor sports be it drag or road are a better indication of power mod results, but without a chassis and tires, then you are doing nothing to utilize any increased power.
Thread Starter
Team Owner
Joined: Sep 1999
Posts: 20,054
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From: Swansea IL
Originally Posted by RBYCC
Competitive motor sports be it drag or road are a better indication of power mod results
Wouldn't the track and ambient air temps have an impact on times?
I've been to the track and I am proud to say I am not skilled enough to pull off consistent and similar runs.
Tom
Le Mans Master
Joined: Feb 2006
Posts: 5,762
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From: Chandler Arizona
Originally Posted by RBYCC
What also must be considered in comparing dynamometer results is the amount of cooling air used in the test. I'm sure all shops don't use the same size fan. Heat retention in the car between runs will also alter the results, and finally the inherent .5-1.0% variation in acuuracy of the unit.
Much too much emphasis put on dyno numbers, seems to be a trendy thing to do. Great for tuning, but to indicate what a mod has afforded as far as increased power has no real value.
Competitive motor sports be it drag or road are a better indication of power mod results, but without a chassis and tires, then you are doing nothing to utilize any increased power.
Much too much emphasis put on dyno numbers, seems to be a trendy thing to do. Great for tuning, but to indicate what a mod has afforded as far as increased power has no real value.
Competitive motor sports be it drag or road are a better indication of power mod results, but without a chassis and tires, then you are doing nothing to utilize any increased power.
Drifting
Joined: Sep 2005
Posts: 1,775
Likes: 1
From: Rehoboth Beach Delaware
Originally Posted by AFVETTE
How is that any better than dyno pulls on the same dyno under the same conditions? I would guess there are just as many variables on the track, maybe more than on a dyno. Everyone keeps harping that the only true measurement is out on the track. With few exceptions I doubt any of us could execute the EXACT same launch, shift and track conditions repeatedly especially if the runs are made on different days.
Wouldn't the track and ambient air temps have an impact on times?
I've been to the track and I am proud to say I am not skilled enough to pull off consistent and similar runs.
Tom
Wouldn't the track and ambient air temps have an impact on times?
I've been to the track and I am proud to say I am not skilled enough to pull off consistent and similar runs.
Tom
You win the "game" by making the power usable, or getting it to the ground.
Track conditions do affect performance, but you have the ability to adjust to track conditions on any given day.
Once you adjust to what you believe is the optimum setup for the day, you can be very consistent.
Look at times turned by experienced quarter milers, usually can run with hundreths of a second on that day.
Road racing is very similar once you adjust the chassis and tires for the track.
Lap times will improve as you find your "line", and at some point you're locked in to consistent times.
Being consistent with what you have usually keeps you near the top in competitive motor sports !
Ed
Drifting
Joined: Sep 2005
Posts: 1,775
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From: Rehoboth Beach Delaware
Originally Posted by glennhl
I agree the track is the proof. We have a Quarter Mile Club here at work where we go out for a big meet once per year. We call it the "1320-foot asphalt lie detector." We have also found that trap speed is a better indicator of power than ET.
Couldn't agree more....
You might see someone post 1/4 time of 13.1 @ 112 mph and another at 12.7 @ 112 mph, oddly enough both cars are making about the same power !!!
Last edited by RBYCC; Jun 28, 2006 at 01:26 PM.