Factory Limits Torque in 1st and 2nd
JK Junkie
Joined: Jul 2008
Posts: 3,017
Likes: 0
From: Lakewood, OH
The only power cut off I've noticed with mine is in first gear at 5000 RPM. It seems to be more noticable with the tuner because the rest of the power increase is that much greater.
I don't normally red line mine, but it revs so fast in first gear I've noticed that a few times. The 4.10s plus the manuals very low first gear makes it rev fast in first.
I don't normally red line mine, but it revs so fast in first gear I've noticed that a few times. The 4.10s plus the manuals very low first gear makes it rev fast in first.
Thread Starter
JK Newbie
Joined: Oct 2009
Posts: 4
Likes: 0
From: Hermosa Beach, CA
I have owned over a dozen manual trans cars, trucks, and motorcycles, with both carbs and fuel injection. I mention carburated, in that other than transient issues like the accelerator pump, there is consistent output gear to gear.
I am certain of what I feel, which is particularly annoying in 2nd, at least on my Cali emissons manual JK. By 5000 rpm, it is putting out reasonable power, so I would not be surprised if it is truely WOT by that rpm.
At least in the stock state, the PCM knows what gear it is in by simply comparing wheel speed to crank speed. I understand that axle gearing changes this.
As everyone knows, the horsepower peak occurs at a higher rpm than the torque peak. At the peak horsepower rpm, the torque is well below the peak torque value achieved at lower rpm.
I state this fact to point out that it is possible to limit the max torque in lower gears to the torque value at max horsepower. In this scenario, there is no reduction in peak horsepower, but the torque and power at lower rpm is reduced. This is easy to imagine when looking at a dyno chart. This reduces acceleration through the gear until the engine hits the peak HP rpm and above.
Sorry to ramble on. My JK is one of the best vehicles I have ever owned!
I am certain of what I feel, which is particularly annoying in 2nd, at least on my Cali emissons manual JK. By 5000 rpm, it is putting out reasonable power, so I would not be surprised if it is truely WOT by that rpm.
At least in the stock state, the PCM knows what gear it is in by simply comparing wheel speed to crank speed. I understand that axle gearing changes this.
As everyone knows, the horsepower peak occurs at a higher rpm than the torque peak. At the peak horsepower rpm, the torque is well below the peak torque value achieved at lower rpm.
I state this fact to point out that it is possible to limit the max torque in lower gears to the torque value at max horsepower. In this scenario, there is no reduction in peak horsepower, but the torque and power at lower rpm is reduced. This is easy to imagine when looking at a dyno chart. This reduces acceleration through the gear until the engine hits the peak HP rpm and above.
Sorry to ramble on. My JK is one of the best vehicles I have ever owned!
JK Super Freak
Joined: Jan 2009
Posts: 1,462
Likes: 3
From: Aurora, CO
That's funny because it's an exact rewind of what I did with my first 0-60 test. After doing it with the stock set up, I used the Superchips 93 tune, blew through first gear faster than I was prepared for, hit the rev limiter and still bettered the stock 0-60 time by 7/10ths. of a second
Granted, this was when I first got it and its possible that they've changed the tune again since then. I noticed a difference after my last update and I don't know that I've gone past 5000 RPM since then...
JK Super Freak
Joined: Jan 2009
Posts: 1,462
Likes: 3
From: Aurora, CO
I have owned over a dozen manual trans cars, trucks, and motorcycles, with both carbs and fuel injection. I mention carburated, in that other than transient issues like the accelerator pump, there is consistent output gear to gear.
I am certain of what I feel, which is particularly annoying in 2nd, at least on my Cali emissons manual JK. By 5000 rpm, it is putting out reasonable power, so I would not be surprised if it is truely WOT by that rpm.
At least in the stock state, the PCM knows what gear it is in by simply comparing wheel speed to crank speed. I understand that axle gearing changes this.
As everyone knows, the horsepower peak occurs at a higher rpm than the torque peak. At the peak horsepower rpm, the torque is well below the peak torque value achieved at lower rpm.
I state this fact to point out that it is possible to limit the max torque in lower gears to the torque value at max horsepower. In this scenario, there is no reduction in peak horsepower, but the torque and power at lower rpm is reduced. This is easy to imagine when looking at a dyno chart. This reduces acceleration through the gear until the engine hits the peak HP rpm and above.
Sorry to ramble on. My JK is one of the best vehicles I have ever owned!
I am certain of what I feel, which is particularly annoying in 2nd, at least on my Cali emissons manual JK. By 5000 rpm, it is putting out reasonable power, so I would not be surprised if it is truely WOT by that rpm.
At least in the stock state, the PCM knows what gear it is in by simply comparing wheel speed to crank speed. I understand that axle gearing changes this.
As everyone knows, the horsepower peak occurs at a higher rpm than the torque peak. At the peak horsepower rpm, the torque is well below the peak torque value achieved at lower rpm.
I state this fact to point out that it is possible to limit the max torque in lower gears to the torque value at max horsepower. In this scenario, there is no reduction in peak horsepower, but the torque and power at lower rpm is reduced. This is easy to imagine when looking at a dyno chart. This reduces acceleration through the gear until the engine hits the peak HP rpm and above.
Sorry to ramble on. My JK is one of the best vehicles I have ever owned!
Maybe that's why we're all so happy with our Flashpaqs? Maybe they do something in their programming to address that issue...
JK Junkie
Joined: Jul 2008
Posts: 3,017
Likes: 0
From: Lakewood, OH
Well, some times it's better to know where to get the information than to discover it yourself.
I sent an email to the Chrysler lead engineer at Superchips on this topic and there are throttle restrictions on both automatic and manual transmissions out of the factory in the lower gears. The Superchips Flashpaq for both platforms does remove that limitation and allows you to run at WOT in first and second. That goes a long way in explaining why on my first test I didn't need to get out of first gear to notice there was an increase in power.
I still want to test it for myself, but don't feel as compelled by the urgency that I put on it yesterday. Perhaps over the weekend when I can get some cleaner freeway on ramp blasts.
Also, some new SC announcements for the Jeep Flashpaq coming at SEMA, so as they say, stay tuned.
I sent an email to the Chrysler lead engineer at Superchips on this topic and there are throttle restrictions on both automatic and manual transmissions out of the factory in the lower gears. The Superchips Flashpaq for both platforms does remove that limitation and allows you to run at WOT in first and second. That goes a long way in explaining why on my first test I didn't need to get out of first gear to notice there was an increase in power.
I still want to test it for myself, but don't feel as compelled by the urgency that I put on it yesterday. Perhaps over the weekend when I can get some cleaner freeway on ramp blasts.
Also, some new SC announcements for the Jeep Flashpaq coming at SEMA, so as they say, stay tuned.
JK Super Freak
Joined: Apr 2009
Posts: 1,633
Likes: 0
From: Forsyth County, GA
Well, some times it's better to know where to get the information than to discover it yourself.
I sent an email to the Chrysler lead engineer at Superchips on this topic and there are throttle restrictions on both automatic and manual transmissions out of the factory in the lower gears. The Superchips Flashpaq for both platforms does remove that limitation and allows you to run at WOT in first and second. That goes a long way in explaining why on my first test I didn't need to get out of first gear to notice there was an increase in power.
I still want to test it for myself, but don't feel as compelled by the urgency that I put on it yesterday. Perhaps over the weekend when I can get some cleaner freeway on ramp blasts.
Also, some new SC announcements for the Jeep Flashpaq coming at SEMA, so as they say, stay tuned.
I sent an email to the Chrysler lead engineer at Superchips on this topic and there are throttle restrictions on both automatic and manual transmissions out of the factory in the lower gears. The Superchips Flashpaq for both platforms does remove that limitation and allows you to run at WOT in first and second. That goes a long way in explaining why on my first test I didn't need to get out of first gear to notice there was an increase in power.
I still want to test it for myself, but don't feel as compelled by the urgency that I put on it yesterday. Perhaps over the weekend when I can get some cleaner freeway on ramp blasts.
Also, some new SC announcements for the Jeep Flashpaq coming at SEMA, so as they say, stay tuned.
JK Junkie
Joined: Jul 2008
Posts: 3,017
Likes: 0
From: Lakewood, OH
Oh, and I have two cars available for drag racing and a Hemi Ram if I really feel the need for better acceleration on pavement.
Last edited by JPop; Oct 7, 2009 at 05:06 AM.
JK Freak
Joined: Jul 2009
Posts: 590
Likes: 1
From: State College, PA
More than likely it will not go WOT in first or second in order to allow effective use of EGR in the 3.8s. The old 4.0s were nice engines because they didn't need to pass any stringent emissions standards. And as everyone knows the reason they switched the new Jeeps to run the 3.8 is to pass emissions standards.
Part of these pesky emissions standards are NOx (which comes from high stoichiometric combustion temps, especially before the catalytic converters have a chance to get up to operating temps). One of the easiest ways to keep NOx down is to recirculate exhaust (EGR = exhaust gas recirculation) so that the "fresh" charge going into the cylinders have not only less oxygen available because the exhaust has displaced it (hence you inject less fuel for stoich combustion) but the mixture with all the CO2 and water has a higher specific heat, so you reach even lower peak combustion temps.
The reason why the throttle wouldn't open all the way for effective ERG use is to draw a vacuum in the intake to pull the exhaust gases through the EGR loop and back in the intake.
Modern diesel engines (D-maxes, powerstrokes, cummins, etc) all actually now have electronic throttles that close up at high load for higher EGR use to suppress NOx as well. Up until modern emissions standards diesels didn't even have ANY type of throttle.
Isn't it nice to have an mechanical/energy engineering grad student on the board
Also if anyone has any real technical questions feel free to ask as I've engineered stuff for the big 3 before and I enjoy giving the real reasons (as I often see complete BS answers to many engine/fuels questions circulating around but don't often get time to give the real answers to them 
)
Part of these pesky emissions standards are NOx (which comes from high stoichiometric combustion temps, especially before the catalytic converters have a chance to get up to operating temps). One of the easiest ways to keep NOx down is to recirculate exhaust (EGR = exhaust gas recirculation) so that the "fresh" charge going into the cylinders have not only less oxygen available because the exhaust has displaced it (hence you inject less fuel for stoich combustion) but the mixture with all the CO2 and water has a higher specific heat, so you reach even lower peak combustion temps.
The reason why the throttle wouldn't open all the way for effective ERG use is to draw a vacuum in the intake to pull the exhaust gases through the EGR loop and back in the intake.
Modern diesel engines (D-maxes, powerstrokes, cummins, etc) all actually now have electronic throttles that close up at high load for higher EGR use to suppress NOx as well. Up until modern emissions standards diesels didn't even have ANY type of throttle.
Isn't it nice to have an mechanical/energy engineering grad student on the board
Also if anyone has any real technical questions feel free to ask as I've engineered stuff for the big 3 before and I enjoy giving the real reasons (as I often see complete BS answers to many engine/fuels questions circulating around but don't often get time to give the real answers to them )
JK Junkie
Joined: Jul 2009
Posts: 2,343
Likes: 1
From: The San Andreas Fault
I have owned over a dozen manual trans cars, trucks, and motorcycles, with both carbs and fuel injection. I mention carburated, in that other than transient issues like the accelerator pump, there is consistent output gear to gear.
I am certain of what I feel, which is particularly annoying in 2nd, at least on my Cali emissons manual JK. By 5000 rpm, it is putting out reasonable power, so I would not be surprised if it is truely WOT by that rpm.
At least in the stock state, the PCM knows what gear it is in by simply comparing wheel speed to crank speed. I understand that axle gearing changes this.
As everyone knows, the horsepower peak occurs at a higher rpm than the torque peak. At the peak horsepower rpm, the torque is well below the peak torque value achieved at lower rpm.
I state this fact to point out that it is possible to limit the max torque in lower gears to the torque value at max horsepower. In this scenario, there is no reduction in peak horsepower, but the torque and power at lower rpm is reduced. This is easy to imagine when looking at a dyno chart. This reduces acceleration through the gear until the engine hits the peak HP rpm and above.
Sorry to ramble on. My JK is one of the best vehicles I have ever owned!
I am certain of what I feel, which is particularly annoying in 2nd, at least on my Cali emissons manual JK. By 5000 rpm, it is putting out reasonable power, so I would not be surprised if it is truely WOT by that rpm.
At least in the stock state, the PCM knows what gear it is in by simply comparing wheel speed to crank speed. I understand that axle gearing changes this.
As everyone knows, the horsepower peak occurs at a higher rpm than the torque peak. At the peak horsepower rpm, the torque is well below the peak torque value achieved at lower rpm.
I state this fact to point out that it is possible to limit the max torque in lower gears to the torque value at max horsepower. In this scenario, there is no reduction in peak horsepower, but the torque and power at lower rpm is reduced. This is easy to imagine when looking at a dyno chart. This reduces acceleration through the gear until the engine hits the peak HP rpm and above.
Sorry to ramble on. My JK is one of the best vehicles I have ever owned!
More than likely it will not go WOT in first or second in order to allow effective use of EGR in the 3.8s. The old 4.0s were nice engines because they didn't need to pass any stringent emissions standards. And as everyone knows the reason they switched the new Jeeps to run the 3.8 is to pass emissions standards.
Part of these pesky emissions standards are NOx (which comes from high stoichiometric combustion temps, especially before the catalytic converters have a chance to get up to operating temps). One of the easiest ways to keep NOx down is to recirculate exhaust (EGR = exhaust gas recirculation) so that the "fresh" charge going into the cylinders have not only less oxygen available because the exhaust has displaced it (hence you inject less fuel for stoich combustion) but the mixture with all the CO2 and water has a higher specific heat, so you reach even lower peak combustion temps.
The reason why the throttle wouldn't open all the way for effective ERG use is to draw a vacuum in the intake to pull the exhaust gases through the EGR loop and back in the intake.
Modern diesel engines (D-maxes, powerstrokes, cummins, etc) all actually now have electronic throttles that close up at high load for higher EGR use to suppress NOx as well. Up until modern emissions standards diesels didn't even have ANY type of throttle.
Isn't it nice to have an mechanical/energy engineering grad student on the board Also if anyone has any real technical questions feel free to ask as I've engineered stuff for the big 3 before and I enjoy giving the real reasons (as I often see complete BS answers to many engine/fuels questions circulating around but don't often get time to give the real answers to them )
Part of these pesky emissions standards are NOx (which comes from high stoichiometric combustion temps, especially before the catalytic converters have a chance to get up to operating temps). One of the easiest ways to keep NOx down is to recirculate exhaust (EGR = exhaust gas recirculation) so that the "fresh" charge going into the cylinders have not only less oxygen available because the exhaust has displaced it (hence you inject less fuel for stoich combustion) but the mixture with all the CO2 and water has a higher specific heat, so you reach even lower peak combustion temps.
The reason why the throttle wouldn't open all the way for effective ERG use is to draw a vacuum in the intake to pull the exhaust gases through the EGR loop and back in the intake.
Modern diesel engines (D-maxes, powerstrokes, cummins, etc) all actually now have electronic throttles that close up at high load for higher EGR use to suppress NOx as well. Up until modern emissions standards diesels didn't even have ANY type of throttle.
Isn't it nice to have an mechanical/energy engineering grad student on the board
Also if anyone has any real technical questions feel free to ask as I've engineered stuff for the big 3 before and I enjoy giving the real reasons (as I often see complete BS answers to many engine/fuels questions circulating around but don't often get time to give the real answers to them )It's probably out of the question to get Jeep's official documentation on how the PCM is programmed, but any insight into the "typical" behavior and operation of this module would be very useful. I've searched the SAE website and only found very generic papers on the subject, but both of you probably understand the current trends in this technology.
Welcome to both of you. Hope you can help shed some light on how to improve the performance of the anemic 3.8L.