Improving low end torque
Guest
Posts: n/a
yeah, and enough back pressure can boost TQ numbers a little... but at the cost of higher RPM power...
from what I can tell, when we hit the tow/haul button. It feels like the truck just locks the torque converter... Like the chevy's used to do. (and still may for all I know)
The tow tune on the superchips tuner is not the same thing as pressing the button. You can still hit that button while using the tow tune, and it acts the same way as it does now... holds shifts longer, down shifts sooner. but everything is bumped way back, since that tune does some of that already.
I agree with superdak. Gears are the best thing you can do for towing. Especially if you have 3.55's. Putting in a set of gears will let you use that power more efficiently. Just remember that if its a 4x4, you have to do both the front and rear diffs.
I would also suggest a tuner, if its in the budget.
my list would be...
1. Intake (breathing easy cant hurt your cause)
2. Gears (not number 1 due to cost... but are the best option)
3. Superchips Tuner (or SCT custom flash)
4. FastMan Throttle body (again with the breathing)
the reason I didnt mention exhaust, is because most "kits" move the band up in the RPM's. If you do decide to go with some gears, a free flowing exhaust can help off set the mileage loss at highway speeds. (notice how I said help and not just off set...) But right now, working on making low end power means keeping some restriction in the system to keep back pressure up.
I hope that makes sense, these pain killers are starting to kick in.
from what I can tell, when we hit the tow/haul button. It feels like the truck just locks the torque converter... Like the chevy's used to do. (and still may for all I know)
The tow tune on the superchips tuner is not the same thing as pressing the button. You can still hit that button while using the tow tune, and it acts the same way as it does now... holds shifts longer, down shifts sooner. but everything is bumped way back, since that tune does some of that already.
I agree with superdak. Gears are the best thing you can do for towing. Especially if you have 3.55's. Putting in a set of gears will let you use that power more efficiently. Just remember that if its a 4x4, you have to do both the front and rear diffs.
I would also suggest a tuner, if its in the budget.
my list would be...
1. Intake (breathing easy cant hurt your cause)
2. Gears (not number 1 due to cost... but are the best option)
3. Superchips Tuner (or SCT custom flash)
4. FastMan Throttle body (again with the breathing)
the reason I didnt mention exhaust, is because most "kits" move the band up in the RPM's. If you do decide to go with some gears, a free flowing exhaust can help off set the mileage loss at highway speeds. (notice how I said help and not just off set...) But right now, working on making low end power means keeping some restriction in the system to keep back pressure up.
I hope that makes sense, these pain killers are starting to kick in.
Professional
Joined: Sep 2007
Posts: 153
Likes: 0
From: Toledo, OH
Backpressure helps torque how?
I have heard this before, but am curious if anyone knows how this is supposed to help? It seems that anything that impairs the flow of exhaust out of the engine (ie backpressure) would increase the power/torque loss from the engine as it now has to "push harder" to clear out the burned combusiton gasses.
Growlor
Growlor
Professional
Joined: Sep 2007
Posts: 153
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From: Toledo, OH
Trying to answer my own post with some quick Google hits
I found a couple of interesting theories (not sure if either is true.) This one sounds really whacky (that carburated engines were designed to have the intake air get slowed (and thus get more fuel "rich") from air being pushed back in the carb due to incomplete exhaust venting (http://www.uucmotorwerks.com/html_pr...torquemyth.htm)
Whereas this one actually makes some sense: that in a confined exhaust system, if the exhaust exapnds too much it will slow/cool and thus decrease the overall exhaust flow. Although I would think after the initial slowdwn the exhaust would be hot/fast again - so this might be untrue (see the comments by "doodfood" in this thread - http://forums.maxima.org/3rd-generat...nd-torque.html)
Growlor
Whereas this one actually makes some sense: that in a confined exhaust system, if the exhaust exapnds too much it will slow/cool and thus decrease the overall exhaust flow. Although I would think after the initial slowdwn the exhaust would be hot/fast again - so this might be untrue (see the comments by "doodfood" in this thread - http://forums.maxima.org/3rd-generat...nd-torque.html)
Growlor
Captain
Joined: Mar 2006
Posts: 531
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From:
if u want something that sounds good on these 4.7 dakota,get a mac performance muffler and put on it, when i got my 2 mufflers for my gt i stuck them on the tips of the truck just to see what it sounded like and i was really amazed by the low rumble it gave it,i will be puttin one on it very soon
Rookie
Joined: Sep 2008
Posts: 60
Likes: 0
From: Ontario Canada
Growlor, the second theory is correct. The rapid expansion of the hot gasses cools it quickly thereby causing it to slow. The slow exhaust gasses act to impede the path. What you're concerned with is exhaust flow velocity, as opposed to back pressure.
What you need is balance, the exhaust needs to have a diameter small enough to keep the exhaust from expanding quickly after leaving the engine and big enough to eliminate any impedace. Smoothing out the exhaust path is the best way (high flow cats, mufflers, etc.).
Hope this helps!
What you need is balance, the exhaust needs to have a diameter small enough to keep the exhaust from expanding quickly after leaving the engine and big enough to eliminate any impedace. Smoothing out the exhaust path is the best way (high flow cats, mufflers, etc.).
Hope this helps!
Professional
Joined: Apr 2009
Posts: 170
Likes: 0
Growlor, the second theory is correct. The rapid expansion of the hot gasses cools it quickly thereby causing it to slow. The slow exhaust gasses act to impede the path. What you're concerned with is exhaust flow velocity, as opposed to back pressure.
What you need is balance, the exhaust needs to have a diameter small enough to keep the exhaust from expanding quickly after leaving the engine and big enough to eliminate any impedace. Smoothing out the exhaust path is the best way (high flow cats, mufflers, etc.).
Hope this helps!
What you need is balance, the exhaust needs to have a diameter small enough to keep the exhaust from expanding quickly after leaving the engine and big enough to eliminate any impedace. Smoothing out the exhaust path is the best way (high flow cats, mufflers, etc.).
Hope this helps!
VELOCITY, NOT back pressure
Exhaust is considered a fluid, like water when put through an exhaust system. If you're moving 4.7 liters of water through your exhaust (not actually doing that, but bear with the illustration) you want the first cylinder's amount of water to just be fully exited when the next cylinder's amount starts coming through. Thus, the first one essentially pulls the second one and so on, helping the motor out. This is done by the momentum from the piston exhaling the "water".
When you reach the perfect balance, (water isn't spread out, or all jammed through together, creating a bottleneck) you have the best mileage from your exhaust.
BACKPRESSURE: This just creates a bottleneck in the pipe for your exhaust gases and decreases both your HP AND torque. It does, however, move your overall power band lower, because your motor essentially can't move the "water" through any faster than it can at say, 3000 rpm. So, while the optimum exhaust tube may be 2.5", if it puts your workable torque at 5,000 rpm, then yes, putting 2" exhaust will lower your workable torque rpms, to lets just say 4,000 rpm. However, you will lose about that much percent in torque as well!!!
SO WHAT DO I DO???: Create more exhaust gases to fill your pipe at a lower rpm. Instead of going down in size on your exhaust (at least from stock) you need to create more exhaust at lower rpms than you are doing right now. There are several ways of doing this. The easiest is probably doing a Cold Air Intake. While the air going into your motor is a few degrees cooler, using denser air, once combusted, whatever is left will expand, and there will be more air left over, and more air/fuel combusted overall, createing more exhaust. Your engine's computer will read the cooler air and give it more fuel, so yes, the power will be better down low, as well as even better higher up. Other tricks and ideas are supercharging, adjusting your timing, and richening up your fuel mixture. Most of which are not available for our trucks right now, or are probably not what you're looking to do. (although, we'd all love to see you put a supercharger on!)
Ok, i'm spent, and I plan on writing up a FULL explanation of fluid dynamics of exhaust soon, and post it like on every forum i've ever been on... and tha'ts LOTS ( to include exhaust diameters and hp ratings, exhaust lengths, forms of induction inc. nos, intake dynamics, etc.)
TY for listening....
Blu3
Professional
Joined: Sep 2007
Posts: 153
Likes: 0
From: Toledo, OH
OK, velocity/flow = good, backpressure = bad.
That makes more sense. So now, I think our enemy is anything that impairs the flow. This means public enemy number one is that platinumed lined wonder, the catalytic converter, correct?
I am actually old enough to remember the days before catalytic converters were common (the air in Los Angles valley was sometimes PURPLE when my parents drove us there for summer vaction trips!), so I don't think completely eliminating them is good thing. However, maybe there ought to be some serious work done to redesign those things (maybe line the whole exhaust pipe with the catalyst and induce a swirl in the flow to ensure most/all of the flow can react with the catalyst?)
I've also wondered if using modern engine controls if the actual emissions would not be improved by just eliminating the darn things entirely (ie would the increased mileage - and thus decreased amount of fuel burned - offset the "quality" loss gained by adding a cat converter?)
Growlor
I am actually old enough to remember the days before catalytic converters were common (the air in Los Angles valley was sometimes PURPLE when my parents drove us there for summer vaction trips!), so I don't think completely eliminating them is good thing. However, maybe there ought to be some serious work done to redesign those things (maybe line the whole exhaust pipe with the catalyst and induce a swirl in the flow to ensure most/all of the flow can react with the catalyst?)
I've also wondered if using modern engine controls if the actual emissions would not be improved by just eliminating the darn things entirely (ie would the increased mileage - and thus decreased amount of fuel burned - offset the "quality" loss gained by adding a cat converter?)
Growlor