2015 Pentastar V6 Towing [SUPERCHARGER SUCCESS!]

[ramffml]

Vern, the reason why gears is a waste is because you can get the same effect with a downshift. We have 8 speed transmissions now, and if you do the math you discover that 3.21 is just 1 gear ahead of the 3.92, but both rear ends end up having almost identical gear ratios for the 5 main highway gears, just offset by 1 numerical gear (so 5th = 6th, 6th = 7th, and 7th = 8th etc).

Different story in the old days with a 3 or a 4 speed, but with todays 8 and 10 speeds it's a waste of money unless you're making a very large jump like 3.21 to 5.xx

You don't necessarily get anymore torque from a gear swap: RPMs are RPMs, and gear ratio is gear ratio. If you're driving the same speed (3.21 vs 3.92) and both trucks are at 3000 rpms, then both trucks are putting down the same amount of torque (because the gear ratio is the same, regardless of the numerical gear number you are in). All you're doing is moving the gear ratio to a lower numerical number, meaning, if you didn't swap and instead downshifted, you'd be in the same position. So it's like rearranging your tranny such that your gear ratio "X" which used to be in 5th, is now in 4th. You're giving yourself better take off torque (especially first gear), but not helping anything really on the highway.

Just my pair of pennies.....

 

[ramffml]

It seems that rear-gears will change the transmission gears but in the end - the RPM's will need to be really high for the steep grades. Gears exchange RPM for torque, right?

To get the extra torque required for an uphill run - the RPM has to go up. My Death Valley example was the most extreme so far - I had to go really slow and was still needing big RPM's to get that.

Will gearing really help at highway speeds (with big drag) and hills? Different transmission gears, but still 4-5k RPM?

Exactly. You can have a 3.21 or a 5.30 (if such a rear end exists). If the 3.21 needs to be at 4500 rpms to climb up a hill at 40 mph, then your truck with the 5.30 will also downshift to whatever gear that gives you the same RPMs; the trucks will be in totally different numerical gears (maybe the 3.21 is in 3rd and the 5.30 in 5th, or whatever), but both trucks will put you in the same gear ratio (or as close as possible; the math might not work out identically, but it will be in the same sort of range for RPMs and gear ratio; the one truck might be 4600 and the other 4400 but you get the idea).

Bottom line; you'll never walk up that hill at 2500 rpms just because you switched to a 5.30. You're still going to get as close as possible to 4500 rpms.

 

[engineering]

Bottom line; you'll never walk up that hill at 2500 rpms just because you switched to a 5.30. You're still going to get as close as possible to 4500 rpms.

That is why I am after an additional 100ft/lb of torque from the engine. Still shy of the ecoDiesel, but good enough for a ~5000# TT

 

[Robeffy]

Exactly. You can have a 3.21 or a 5.30 (if such a rear end exists). If the 3.21 needs to be at 4500 rpms to climb up a hill at 40 mph, then your truck with the 5.30 will also downshift to whatever gear that gives you the same RPMs; the trucks will be in totally different numerical gears (maybe the 3.21 is in 3rd and the 5.30 in 5th, or whatever), but both trucks will put you in the same gear ratio (or as close as possible; the math might not work out identically, but it will be in the same sort of range for RPMs and gear ratio; the one truck might be 4600 and the other 4400 but you get the idea).

Bottom line; you'll never walk up that hill at 2500 rpms just because you switched to a 5.30. You're still going to get as close as possible to 4500 rpms.

Hi, I think I disagree, atleast with some of this, not all of it. Just suggesting we look at this from my engineering background.

If you consider the power hits the road at the rear tires. So, if you are trying to pull a load ( do work ) and need a certain amount of forward effort from the tires ( where they meet the road ), to keep the load moving up a hill, at a constant speed, you are generating a force between the tire and road sufficient for the situation.

Now, that force becomes a torque, and if we ignore acceleration, so, you are doing a constant speed, we really simplify the situation. That torque, ie, the distance from the center of the rear axle to the road, times the force, is the torque.

If you reduce the rear gears enough, you "could walk up that hill" at 2500 rpm. It really depends on the work being done, and the rear end gear. But, at what speed? This is where I agree with your comments.

Hope you don't mind this, but, honestly, I used to design rough terrain forklifts, with Cummins 4B3.9 and 4BT3.9 engines, Allison transmissions, moving a deadweight of machine at 24000 lbs, with a 10,000 load, and its all about this..

How much work are you trying to do? HOw fast do you want to go up that hill, How much load are you overcoming. Our top speed was only about 15 mph.. lol.. but, we could move 34000 lbs thru 2 ft of mud, in 4 wheel drive, with tractor grader tires, that stood nearly 5 ft tall.

Load - friction, air resistance, factor in the grade, tire rolling resistance, etc etc.

I agree, partly with your comment. I doubt you could get a compromise gear set that lets you "walk up that hill" at 2500 rpm, and also get 65 mph on a flat surface. Not sure how many forward speeds you would need. A gear vendors overdrive??

The only way would be to crunch a lot of numbers, make a lot of educated guesses, on the factors I mentioned, and there are likely some I don't know about, like how much power the trans absorbs at a given rpm. ( Chrysler 727 trans used to suck up around 55 hp at 6000 rpm. ) Factor in the hp curve for the trans, the cooling fan, air resistance, the trailer air resistance ( take a guess ?? ), and all of them are dependant on the air speed ( is there a headwind ?? )..

So, gear will make a big difference, but, not sure the top speed will be adequate.

 

[VernDiesel]

ack

 

[VernDiesel]

Engineering Your point is really diminishing returns at highway speeds. Truth but its first - "I had to go really slow and was still needing big rpms to get that." Your motor could only use the first three gears then had to stay in 3rd winding because it could not make the jump to fourth.

It would have been quicker and easier for it to accelerate the load to whatever speed you reached utilizing more gears to find where it could either hold that same speed at a lesser rpm or a higher speed at the same ish rpm. Usually the latter.


Edit I fully understood what you guys are saying long before this thread. Peak torque is where peak torque is, rpms wise, and with 8 gears its normally going to end up about there. But under this load the motor could only use 3. So their is gains to be had in rate of acceleration, reduced sustained motor load, reduced cooling system load, and more speed at the same ish rpm because its more optimised. More smaller steps to a more exact end. Better utilizing the work that the motor will do. In this case you cannot get the same effect by a downshift. At least not fully as with using only 3 gears he has left lots of work efficiency on the table. And yes this would have been even more dramatic if he only had a 3 speed transmission to work with but that's not the case.

If this is still insufficient for your goals (probably not I think from what you have said this would meet your needs) then add the supercharger. Plus after a gear swap your truck would be better able to handle the added torque from the supercharger. The 4.56 would allow your truck to tow that TT dramatically better, utilizing 5 or 6 gears instead of 3 or 4. Unless you want to tow to higher speeds perhaps 80 instead of the 60-65 on a flat then you would be reaching past the point of a diminished return.

"Bottom line; you'll never walk up that hill at 2500 rpms just because you switched to a 5.30. You're still going to get as close as possible to 4500 rpms." Correct and in this case the 4.56 through utilizing 2 more gears will allow him to get closer to that example 4500 rpms and at a higher speed. It will climb that hill either faster or easier your choice.

 

[VernDiesel]

Curious to what speed did that grade drag your truck down to? And I take it without much wind it would hold 60 - 65 reasonably well?

 

[RLJ10X]

You can try to convince someone else that the 8/3.21 is ok. Not me. I test drove one with a Hemi in a RCSB, no less, and I still didn't like the 3.21.

I pull trailers for a living. I have a ProCharger in a V6 Mustang 3.7. I have 4.10s in my Hemi 1500. All that doesn't make an expert on anything but my own opinion.

I am here to say: I would give up my ProCharger LONG before I'd give up my 4.10s.

Everybody has their own perspective from their own application. I can respect that.

But I would do 4.10 gears first. All the power in the world ain't worth jack if you don't have the leverage to utilize it. And tha

 

[engineering]

Curious to what speed did that grade drag your truck down to? And I take it without much wind it would hold 60 - 65 reasonably well?

The Death Valley 11% stuff got me in the mid 30's or so, 2nd gear, roughly 4k RPM. Trying to hold much higher required near wide open throttle and 5k+ RPM and still in 2nd gear. Pretty rough.

 

[NewBlackDak]

I think the best example we have is the 6.4 6-speed 2500s. Those of us with 4.10s can cruise at highway speeds with the MDS kicking on fairly often, and we motor up most inclines in 6th. The 3.73 trucks almost never see MDS on the highway, and they kick down to 5th more often than anyone would like.


Sent from my iPhone using Tapatalk

 

[engineering]

I am here to say: I would give up my ProCharger LONG before I'd give up my 4.10s.

Everybody has their own perspective from their own application. I can respect that.

But I would do 4.10 gears first. All the power in the world ain't worth jack if you don't have the leverage to utilize it. And tha

3.21 to 4.10 is essentially one gear difference on the 8 speed transmission. In terms of total leverage - there is no difference at highway speeds. There is, however significantly better torque available in 1st gear but that is not a problem for me. This is not really an opinion, it is just the way it is - the total ratio is what matters and the total ratio is the sum of the transmission gearing and the rear-end. With an 8 speed trans - there are a LOT of gears to choose from. What is the difference if I move from gears 3-4-5 to gears 4-5-6 at the exact same RPM's to get up the hills?

The only argument for a gear change on this project is to unload the transmission a bit after the supercharger throws it an additional 100ft/lbs of torque. That would help with trans temps as well.

 

[VernDiesel]

Thanks for your reply. It’s pretty unusual to hit more than a 6 or 7 percent grade on any road that has a long stretch that would allow for speed. 8 percent or more is usually short often with switchbacks. I’ve towed TTs through parts of Death Valley a few times and yes the heat can be legendary.

“With an 8 speed trans - there is a LOT of gears to choose from.” Yes but you have been discussing when your motor is so underpowered or over geared (tall 3.21) that it can only utilize 2 or 3 of them. The 4.56/4.88 that I linked allows you to fully utilize at least two more gears. It would accelerate faster or more easily, climb at a higher speed, and cruise at a higher speed more easily. I’m not saying it would be radically different but it would still be substantially & measurably different. Their are reasons Ram rates even just the 3.92 to tow more than the 3.21 in the same truck with the same transmission.

The unloading of the transmission (and time spent at max engine load / cooling system) as you mentioned is also substantial and should help make the head room so to speak for some boosted towing with the supercharger when necessary but certainly it’s not the only benefit. Being able to utilize two more gears should on its own allow for reasonable towing of that TT with the 3.6. Also on the other end of the spectrum it’s not the ole 3 speed you still have two overdrives to use. Highway travel unloaded while not as fuel efficient will be fine probably even more responsive & enjoyable.

Okay spent my two coins best to you and do let us know your future experiences with this.

 

[2003F350]

3.21 to 4.10 is essentially one gear difference on the 8 speed transmission. In terms of total leverage - there is no difference at highway speeds. There is, however significantly better torque available in 1st gear but that is not a problem for me. This is not really an opinion, it is just the way it is - the total ratio is what matters and the total ratio is the sum of the transmission gearing and the rear-end. With an 8 speed trans - there are a LOT of gears to choose from. What is the difference if I move from gears 3-4-5 to gears 4-5-6 at the exact same RPM's to get up the hills?

The only argument for a gear change on this project is to unload the transmission a bit after the supercharger throws it an additional 100ft/lbs of torque. That would help with trans temps as well.

Okay, I have weighed in before, and I'm going to again.

My degree is in mechanical engineering. My focus was powertrain engineering. I have been around RVs and towing my entire life, and I used to drag race a '67 Firebird with a Jim Butler Pontiac motor in it.

Trust me, if you're wanting to pull grades, you're going to want gears, THEN a power adder, not the other way around. If you do the power adder first, you're toying with costing yourself more down the road.

Here's why: While unloaded, you are technically correct about total gear ratio being what matters. But for longevity and towing with a load, the steps in between are what matter more. More gears in your transmission is GREAT for helping the motor find its peak power/torque output and putting it to the rear axle. But it comes down to how limited you are at the tires, and gears in your rear end will get you to that peak power, usually in a higher gear, and more often than not at a higher speed - WHICH IS VERY IMPORTANT FOR COOLING.

Nothing destroys drivelines like heat. Heat is your enemy. Heat will leave you stranded. Heat kills. Let's say you're screaming along up an 11% grade in 3rd gear at 30 mph and 4500 RPM. You're generating a LOT of heat (even more with the blower). You do that long enough or enough times, and that heat is going to cook your transmission clutches, smoke your main and/or rod bearings, wear out your rings, etc. etc. That motor won't last.

Let's say you do gears, 3.92/4.10/4.56, pick your poison, anything is better than that 3.21 highway gear. Let's say you're still hitting that 11% grade at 4500 RPM, but now you're in 4th and for the sake of argument you're at 40 mph (I'm taking a swag because I don't feel like doing all the math). You're still generating that heat, but now you've got a lot more airflow to get rid of it. You're taking strain off the transmission, you're getting rid of the heat you're creating, and your driveline is going to last a LOT longer.

I'm not saying don't do the supercharger. I'm saying gears will get you a LOT further, and are an added safety for the rest of your driveline and your pocketbook.

 

[VernDiesel]

Even though you can utilize 2 more gears to do it, you likely only have the “jump” of one full gear change of your current rear gear. Like where I’m going? Prove yourself right or at least get a better look into the somewhat limited difference of a gear swap right?

Perhaps some of the differences could be seen this way. Set the trans in 3rd. Run down the road at 5,000 rpms. Note your speed and how comfortable you & the truck / motor etc is at this cruise speed / rpm.

Now set the trans in 4th run that same speed. Note is it a lot less rpm and are you & the truck / motor a lot more comfortable? A more tolerable cruise rpm? Is that a substantial improvement? Now accelerate up to 5,000. How much more speed is it? Is that a substantial worthwhile improvement in climb speed or if need be cruise speed? Keep in mind this is only unloaded.

EDIT great post by 2003F350 while I was typing this post. Last I checked I believe it was your Firebird on Butlers site. Drag raced a bit myself and was into Pontiac Olds Buick & Cadillacs for fun & doing something different. Was always quite impressed with that car for seemingly getting 10 pounds out an 8 pound sack.

 

[ramffml]

Let's say you do gears, 3.92/4.10/4.56, pick your poison, anything is better than that 3.21 highway gear. Let's say you're still hitting that 11% grade at 4500 RPM, but now you're in 4th and for the sake of argument you're at 40 mph (I'm taking a swag because I don't feel like doing all the math). You're still generating that heat, but now you've got a lot more airflow to get rid of it. You're taking strain off the transmission, you're getting rid of the heat you're creating, and your driveline is going to last a LOT longer.

I'm having trouble following your argument. If you're in 4th gear at 40 mph at 4500 RPMs in the 3.21, then swapping to a 3.92 means you'd be in 5th gear, at 40 mph, at 4500 RPMs. Yes, that's how the math works out for the 3.92 and like you I'm to lazy to do the math for the 4.10 or whatever. But same idea. All you're doing is moving your numerical gear from 4 to 5, the effective gear ratio has not change, and you changed nothing when it comes to torque, power, or heat.


Yes you might have one more gear to play with (so now you can play with gears 1 to 5 instead of 1 to 4), but I'm pretty sure these 8 speeds already have a low jump in rpms from gear to gear, something like 500 rpms. And I get that moving to a 4.56 would change the numbers, and maybe if you go really high to a 5.x you might even gain another gear for that range, so now you get gears 1 to 6. But then unloaded your truck becomes horrible to drive around on the highway, screaming in 8th gear and going nowhere.

I don't see the point, and I think some of you are taking your knowledge and experience from "the old days" where you had 3/4/5 speeds at play, and still trying to apply that to a world of 8 and 10 speeds. It's just no longer effective.

 

[ramffml]

One final thought, highlighting how important and game changing our 8 speeds are:

The 3.21 in first gear has a gear ratio of 16.05
The 4.30 in first gear of Toyota's 6 speed, has a gear ratio of 14.33

The 3.21 in 8th gear has a gear ratio of 2.05
The 4.30 in 6th gear of Toyota's 6 speed, has a gear ratio of 2.52

That means the 3.21 has more torque off the line, and yet still lower RPMs in final cruising speed, than the Toyota 6 speed with the 4.30. It's better in every way to have the 8 speed 3.21, then it is to have the Toyota 6 speed with 4.30.

Just throwing that out there, because like I said I feel some of you are still thinking and applying knowledge from old transmissions without actually doing the math and seeing where we are now with 8 speeds.

 

[RLJ10X]

Well said Vern and 2003!!
You saved me a lot of time!!

 

[engineering]

SOLID points from people with far more knowledge than me! I am very thankful for the participation in this thread. Really appreciated.

I'm not saying don't do the supercharger. I'm saying gears will get you a LOT further, and are an added safety for the rest of your driveline and your pocketbook.

I agree with all of that which is why gears are still on the table. Heat is indeed my biggest single concern and I don't want to ignore that.

With that in mind, I am trying to figure out if just monitoring the stock gauges are enough. Just before I start wrenching, I was going to take the truck on some data collection drives. There is a specific path I have in mind that takes me up some fairly long and steep hills over a 2 hour round trip. I was going to log the oil, coolant, and trans temps at specific points on the drive to get a baseline.

I will do the drive totally unloaded, again fully loaded with travel trailer and cargo. Then, of course, after the super charger is installed. It is a lot of driving, but I REALLY REALLY want to have some data that tells me how well the stock cooling systems are coping before it is too late. I am under the assumption (tell me if I am wrong), if the trans temps on the digital gauge do not rise much - I don't have much too worry about. I will keep the 3.21 gears. If the temp rises a lot (there is a 'red line' on the gauge for what that is worth), I have the option of going to a 4.10 gear to reduce the load on the transmission, lowering the temps.

If the engine is at risk of overheating, there are other remedies for that. I suspect the engine cooling system will be able to keep up. If not, it will probably only need a little help - perhaps just a fan upgrade. The nuclear option is a larger radiator, but that seems unlikely. At least there is enormous amount of room for upgrading the engine cooling on the V6.

 

[Larry Rambo]

I have a 2015 with 3.6 and 3:55 rear end. This ratio came stock in my truck. I pull a 6800 lb camper. I have pulled it all over tUS including Alaska. Up grades 8% and an altitudes of over 12000 ft in the Rocky Mountain NP.. Over 30000 miles of towing this trailer with this truck. No heating issues or any other problems at all. Plus it gets 21 MPG when not pulling a trailer. About 10 MPG when pulling this camper. Keep the truck and go with a taller gear.

 

[engineering]

I have a 2015 with 3.6 and 3:55 rear end. This ratio came stock in my truck. I pull a 6800 lb camper. I have pulled it all over tUS including Alaska. Up grades 8% and an altitudes of over 12000 ft in the Rocky Mountain NP.. Over 30000 miles of towing this trailer with this truck. No heating issues or any other problems at all. Plus it gets 21 MPG when not pulling a trailer. About 10 MPG when pulling this camper. Keep the truck and go with a taller gear.

What RPMs do you typically see on 8%, 12,000ft altitude, 60mph - while fully loaded?