2012 Pentastar - not the torque we had hoped for....
11-16-2010, 06:09 AM
#21
JK Enthusiast
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What fools they are at Jeep!: they tuned the engine to the type of driving that 99.9% of GC drivers do. They really missed the mark by not tuning their SUV for offroad use.
11-16-2010, 06:24 AM
#22
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Hmm... I haven't heard that argument before. 
I don't think that's right. All the pushrod does is tell the cam when to open and close the valves. It's the valves' actions that affect the torque output; the pushrod is just the messenger. So, I'm going to say that this is not correct. And, pushrods do their jobs inefficiently, so I'll so far as to say that a pushrod engine creates less torque than the more advanced (pushrodless) engine. There was evidence of this years ago, such as the Ford 427 SOHC engine. Eliminating the pushrod made a world of difference.
I don't think that's right. All the pushrod does is tell the cam when to open and close the valves. It's the valves' actions that affect the torque output; the pushrod is just the messenger. So, I'm going to say that this is not correct. And, pushrods do their jobs inefficiently, so I'll so far as to say that a pushrod engine creates less torque than the more advanced (pushrodless) engine. There was evidence of this years ago, such as the Ford 427 SOHC engine. Eliminating the pushrod made a world of difference.If you compare Hemi's, Corvette and Camaro engines to the new Ford 5.0 engine .. you will see much differently shaped torque curves. Pushrods engines torque comes on in the low RPM range and gradually builds to holds steady. OHC engines generally have steeper TQ curves and have higher torque only at higher RPM's ..
A jeep needs to have as much TQ as possible below 2500 RPM ... and that is gonna be hard to do with a Overhead Cam engine ... unless specifically designed for that specific purpose. Pushrods engines are already designed for that purpose because they are lower revving engines.
11-16-2010, 06:25 AM
#23
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Hmm... I haven't heard that argument before. I don't think that's right. All the pushrod does is tell the cam when to open and close the valves. It's the valves' actions that affect the torque output; the pushrod is just the messenger. So, I'm going to say that this is not correct. And, pushrods do their jobs inefficiently, so I'll so far as to say that a pushrod engine creates less torque than the more advanced (pushrodless) engine. There was evidence of this years ago, such as the Ford 427 SOHC engine. Eliminating the pushrod made a world of difference.
I don't think that's right. All the pushrod does is tell the cam when to open and close the valves. It's the valves' actions that affect the torque output; the pushrod is just the messenger. So, I'm going to say that this is not correct. And, pushrods do their jobs inefficiently, so I'll so far as to say that a pushrod engine creates less torque than the more advanced (pushrodless) engine. There was evidence of this years ago, such as the Ford 427 SOHC engine. Eliminating the pushrod made a world of difference.
There's a story on how GM engineers were allowed to retain pushrods in the Gen III/IV LS engines. When working on the redesign of the entire Corvette from C4 to C5 they let the big wigs at GM drive 2 cars: a Vette with a pushrod LT4 and an 'old' ZR1 with the Lotus built OHC LT5. Every one preferred driving the pushrod LT4 due to its bottom-end torque, kick-in-the-pants acceleration.
It is quite common that pushrod engines tend to develop more low-end torque, generally at a small sacrifice of high-end hp...more so with increased displacement.
Torque is a measurable number, horsepower is a calculation....basically for bragging rights.
11-16-2010, 06:57 AM
#24
There may be hope for the 3.6L. How much heavier is the Durango vs. the Wrangler?
That being said, I plan on sticking with my 2010 for a while.
11-16-2010, 07:14 AM
#25
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Actually, I was being sarcastic. Like you (and most of us), I drive almost exclusively on-road. I like the iconic look, feel, and image of the JK, but don't drive it for the purpose for which it was designed. In reality, it's the perfect urban assault vehicle - it sits high over traffic, goes well in the snow, laughs at curb rash and pavement imperfections, and the fenders/running boards make it door ding-proof. But...it needs more power and fuel mileage.
There - I said it - and it's true for the VAST majority of all JK drivers. That said, we can have our cake and eat it too. With a stick and 4-wheel low, the new engine should be just fine for off-roaders.
There - I said it - and it's true for the VAST majority of all JK drivers. That said, we can have our cake and eat it too. With a stick and 4-wheel low, the new engine should be just fine for off-roaders.
Last edited by Rick in Colorado; 11-16-2010 at 07:20 AM.
11-16-2010, 07:33 AM
#26
JK Freak
The type of engine has absolutely nothing to do with the horsepower/torque numbers, plain and simple. The reason that pushrod engines have different power delivery (torque and horsepower curves) than overhead cam engines is because they are built for two completely different purposes.
Pushrod engines are generally designed for longevity, low maintenance, and work truck type applications. Thus the entire engine (valvetrain, fluid dynamics in the cylinder, clearences, etc) is designed around this concept. For the lowest maintenance RPMs will be kept as low as possible (as higher RPMs wear engines out faster) and in order to be used in a work truck the low RPM torque is thus maximized.
Overhead cam engines are generally designed to be as light as possible and maximize the fuel efficiency and the amount of power (not torque) out of a given engine. In order to maximize power and fuel efficiency, the easiest way to do this is make a smaller displacement engine rev as high as possible. This way if you are cruising on the highway in a high gear you only have a 1.8L engine turning at 2K RPM and getting 40 MPG. But if you need power, you have the little engine turn as fast as possible and use a super high-ratio (low) gear for the mechanical advantage to accelerate the vehicle. The downfall to this is that the engine wears out faster due to higher engine RPMs in addition to lighter weight components to allow higher RPMs (like timing belts and chains in place of pushrods) AND you have less low-end torque. The reason why torque curves must change if your engine is designed for high vs. low RPM performance (even given the same exact displacement engine) is that the fluid dynamics (air/fuel charge delivery) is very different.
At high RPMs the intake valve is designed to close after bottom dead center of the intake stroke, maximizing the air/fuel charge that can be taken into the engine (due to usually super-sonic, or choked, flow past the intake valves). However at low RPMs, since the fluid flow into the cylinder is not limited/choked by a super-sonic flow, causing the intake valves to close after bottom center of the intake stroke actually causes less air/fuel charge to be inducted into the cylinder before the intake valve closes (because part of it gets pushed back out as the piston starts the upward stroke).
So for this reason it is not the type (pushrod or OHC) engine that causes these differences in power delivery. It is the fact that Chrysler wants to get better fleet averaged fuel economy (thanks green weenies controlling the government!
), thus they are going to smaller displacement engines that rev higher. Also unfortunately the auto companies in the pursuit of revenue are going away from building engines that will last forever (nice high-torque, low-RPM engines) and toward engines that will merely survive for the "expected average life" of a vehicle which is approximately 100K miles / 10 years. Really an all together sad state that results in us torque lovers getting smaller and less torquey engines.
And I would be fine with this if we got diesels over here....but oh yeah....they give off too much NOX and particulate matter for the green weenies in the government as well (too bad they don't realize it would give us JKs that have the torque most of us want while getting 25 - 30 mpg on the highway). So we can't have those either! By the way I worked at GM as an engineer for a little while (thankfully got out before they went bankrupt) and have ~10 years of automotive engineering experience, so this is not someone promoting a conspiracy theory against big engines
Pushrod engines are generally designed for longevity, low maintenance, and work truck type applications. Thus the entire engine (valvetrain, fluid dynamics in the cylinder, clearences, etc) is designed around this concept. For the lowest maintenance RPMs will be kept as low as possible (as higher RPMs wear engines out faster) and in order to be used in a work truck the low RPM torque is thus maximized.
Overhead cam engines are generally designed to be as light as possible and maximize the fuel efficiency and the amount of power (not torque) out of a given engine. In order to maximize power and fuel efficiency, the easiest way to do this is make a smaller displacement engine rev as high as possible. This way if you are cruising on the highway in a high gear you only have a 1.8L engine turning at 2K RPM and getting 40 MPG. But if you need power, you have the little engine turn as fast as possible and use a super high-ratio (low) gear for the mechanical advantage to accelerate the vehicle. The downfall to this is that the engine wears out faster due to higher engine RPMs in addition to lighter weight components to allow higher RPMs (like timing belts and chains in place of pushrods) AND you have less low-end torque. The reason why torque curves must change if your engine is designed for high vs. low RPM performance (even given the same exact displacement engine) is that the fluid dynamics (air/fuel charge delivery) is very different.
At high RPMs the intake valve is designed to close after bottom dead center of the intake stroke, maximizing the air/fuel charge that can be taken into the engine (due to usually super-sonic, or choked, flow past the intake valves). However at low RPMs, since the fluid flow into the cylinder is not limited/choked by a super-sonic flow, causing the intake valves to close after bottom center of the intake stroke actually causes less air/fuel charge to be inducted into the cylinder before the intake valve closes (because part of it gets pushed back out as the piston starts the upward stroke).
So for this reason it is not the type (pushrod or OHC) engine that causes these differences in power delivery. It is the fact that Chrysler wants to get better fleet averaged fuel economy (thanks green weenies controlling the government!
), thus they are going to smaller displacement engines that rev higher. Also unfortunately the auto companies in the pursuit of revenue are going away from building engines that will last forever (nice high-torque, low-RPM engines) and toward engines that will merely survive for the "expected average life" of a vehicle which is approximately 100K miles / 10 years. Really an all together sad state that results in us torque lovers getting smaller and less torquey engines. And I would be fine with this if we got diesels over here....but oh yeah....they give off too much NOX and particulate matter for the green weenies in the government as well (too bad they don't realize it would give us JKs that have the torque most of us want while getting 25 - 30 mpg on the highway). So we can't have those either! By the way I worked at GM as an engineer for a little while (thankfully got out before they went bankrupt) and have ~10 years of automotive engineering experience, so this is not someone promoting a conspiracy theory against big engines
11-16-2010, 08:18 AM
#27
JK Super Freak
The type of engine has absolutely nothing to do with the horsepower/torque numbers, plain and simple. The reason that pushrod engines have different power delivery (torque and horsepower curves) than overhead cam engines is because they are built for two completely different purposes.
Pushrod engines are generally designed for longevity, low maintenance, and work truck type applications. Thus the entire engine (valvetrain, fluid dynamics in the cylinder, clearences, etc) is designed around this concept. For the lowest maintenance RPMs will be kept as low as possible (as higher RPMs wear engines out faster) and in order to be used in a work truck the low RPM torque is thus maximized.
Overhead cam engines are generally designed to be as light as possible and maximize the fuel efficiency and the amount of power (not torque) out of a given engine. In order to maximize power and fuel efficiency, the easiest way to do this is make a smaller displacement engine rev as high as possible. This way if you are cruising on the highway in a high gear you only have a 1.8L engine turning at 2K RPM and getting 40 MPG. But if you need power, you have the little engine turn as fast as possible and use a super high-ratio (low) gear for the mechanical advantage to accelerate the vehicle. The downfall to this is that the engine wears out faster due to higher engine RPMs in addition to lighter weight components to allow higher RPMs (like timing belts and chains in place of pushrods) AND you have less low-end torque. The reason why torque curves must change if your engine is designed for high vs. low RPM performance (even given the same exact displacement engine) is that the fluid dynamics (air/fuel charge delivery) is very different.
At high RPMs the intake valve is designed to close after bottom dead center of the intake stroke, maximizing the air/fuel charge that can be taken into the engine (due to usually super-sonic, or choked, flow past the intake valves). However at low RPMs, since the fluid flow into the cylinder is not limited/choked by a super-sonic flow, causing the intake valves to close after bottom center of the intake stroke actually causes less air/fuel charge to be inducted into the cylinder before the intake valve closes (because part of it gets pushed back out as the piston starts the upward stroke).
So for this reason it is not the type (pushrod or OHC) engine that causes these differences in power delivery. It is the fact that Chrysler wants to get better fleet averaged fuel economy (thanks green weenies controlling the government!), thus they are going to smaller displacement engines that rev higher. Also unfortunately the auto companies in the pursuit of revenue are going away from building engines that will last forever (nice high-torque, low-RPM engines) and toward engines that will merely survive for the "expected average life" of a vehicle which is approximately 100K miles / 10 years. Really an all together sad state that results in us torque lovers getting smaller and less torquey engines.
And I would be fine with this if we got diesels over here....but oh yeah....they give off too much NOX and particulate matter for the green weenies in the government as well (too bad they don't realize it would give us JKs that have the torque most of us want while getting 25 - 30 mpg on the highway). So we can't have those either! By the way I worked at GM as an engineer for a little while (thankfully got out before they went bankrupt) and have ~10 years of automotive engineering experience, so this is not someone promoting a conspiracy theory against big engines
Pushrod engines are generally designed for longevity, low maintenance, and work truck type applications. Thus the entire engine (valvetrain, fluid dynamics in the cylinder, clearences, etc) is designed around this concept. For the lowest maintenance RPMs will be kept as low as possible (as higher RPMs wear engines out faster) and in order to be used in a work truck the low RPM torque is thus maximized.
Overhead cam engines are generally designed to be as light as possible and maximize the fuel efficiency and the amount of power (not torque) out of a given engine. In order to maximize power and fuel efficiency, the easiest way to do this is make a smaller displacement engine rev as high as possible. This way if you are cruising on the highway in a high gear you only have a 1.8L engine turning at 2K RPM and getting 40 MPG. But if you need power, you have the little engine turn as fast as possible and use a super high-ratio (low) gear for the mechanical advantage to accelerate the vehicle. The downfall to this is that the engine wears out faster due to higher engine RPMs in addition to lighter weight components to allow higher RPMs (like timing belts and chains in place of pushrods) AND you have less low-end torque. The reason why torque curves must change if your engine is designed for high vs. low RPM performance (even given the same exact displacement engine) is that the fluid dynamics (air/fuel charge delivery) is very different.
At high RPMs the intake valve is designed to close after bottom dead center of the intake stroke, maximizing the air/fuel charge that can be taken into the engine (due to usually super-sonic, or choked, flow past the intake valves). However at low RPMs, since the fluid flow into the cylinder is not limited/choked by a super-sonic flow, causing the intake valves to close after bottom center of the intake stroke actually causes less air/fuel charge to be inducted into the cylinder before the intake valve closes (because part of it gets pushed back out as the piston starts the upward stroke).
So for this reason it is not the type (pushrod or OHC) engine that causes these differences in power delivery. It is the fact that Chrysler wants to get better fleet averaged fuel economy (thanks green weenies controlling the government!
), thus they are going to smaller displacement engines that rev higher. Also unfortunately the auto companies in the pursuit of revenue are going away from building engines that will last forever (nice high-torque, low-RPM engines) and toward engines that will merely survive for the "expected average life" of a vehicle which is approximately 100K miles / 10 years. Really an all together sad state that results in us torque lovers getting smaller and less torquey engines. And I would be fine with this if we got diesels over here....but oh yeah....they give off too much NOX and particulate matter for the green weenies in the government as well (too bad they don't realize it would give us JKs that have the torque most of us want while getting 25 - 30 mpg on the highway). So we can't have those either! By the way I worked at GM as an engineer for a little while (thankfully got out before they went bankrupt) and have ~10 years of automotive engineering experience, so this is not someone promoting a conspiracy theory against big engines
11-16-2010, 09:01 AM
#28
JK Jedi Master
I always thought it was like this:
An overhead cam can open a valve, and close it, more rapidly than a push rod cam.
The less time in valve transition, the more efficient the charging process.
An overhead cam can open a valve, and close it, more rapidly than a push rod cam.
The less time in valve transition, the more efficient the charging process.
11-16-2010, 09:09 AM
#29
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That's too bad to hear, I too had high hopes for this motor. Not only does it appear that the new motor may underwhelm us but the buyers of 2012 JK's will not only have to live with the new "SUV" interior but also an exterior that could be potentially as disappointing as the new engine and interior are.
2010 the last great year of the JK...still has a Jeep interior and exterior and a motor that is very likely comparable to the upcoming 3.6.
I suspect that 2012 JK's will look very different I just hope they still are recognizable as a true Jeep and not something that is just another SUV. It's going to be interesting over the next 8 months or so as the news leaks out about the '12.
2010 the last great year of the JK...still has a Jeep interior and exterior and a motor that is very likely comparable to the upcoming 3.6.
I suspect that 2012 JK's will look very different I just hope they still are recognizable as a true Jeep and not something that is just another SUV. It's going to be interesting over the next 8 months or so as the news leaks out about the '12.
Mabar
11-16-2010, 09:26 AM
#30
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Two points about this thread:
1. The Durango curb weight is 4838 lbs according to the article. A 2011 2-door Rubicon weighs in at 4129 lbs. That is a HUGE 709 lbs difference. A Rubicon with this Pentastar engine will have a LOT more power than a much heavier Durango with the same engine.
2. The Durango had a 3.06 axle ratio. Wrangler axle ratios range from 3.21 to 4.11, depending on the configuration. That will also make a huge difference when comparing Durango/Pentastar with a Wrangler/Pentastar.
That having been said, I personally am very leery about a brand new engine. What type of "bugs" will show up within the next couple of years in the Pentastar. Also, check out the way the spark plugs are installed here: http://www.pentastars.com/engines/tech.php
The spark plugs are buried inside a long thin tube. Seems weird to me, and hard to work on.
I am not sold on this Pentastar engine, and much prefer the current 3.8L V-6, which is a time-proven engine that has been around for many years.
Mabar
1. The Durango curb weight is 4838 lbs according to the article. A 2011 2-door Rubicon weighs in at 4129 lbs. That is a HUGE 709 lbs difference. A Rubicon with this Pentastar engine will have a LOT more power than a much heavier Durango with the same engine.
2. The Durango had a 3.06 axle ratio. Wrangler axle ratios range from 3.21 to 4.11, depending on the configuration. That will also make a huge difference when comparing Durango/Pentastar with a Wrangler/Pentastar.
That having been said, I personally am very leery about a brand new engine. What type of "bugs" will show up within the next couple of years in the Pentastar. Also, check out the way the spark plugs are installed here: http://www.pentastars.com/engines/tech.php
The spark plugs are buried inside a long thin tube. Seems weird to me, and hard to work on.
Spark plug tubes are pressed into the heads and sealed in place; the tubes have thin walls, and mechanics were advised to be careful when working with them.
Mabar