Forum Discussion
158 Replies
4x4ord wrote:
Me Again wrote:
4X4ord. 2 gear(2:1) in a Aisin and 4:10's out back is going to hold back a lot on the full exhaust brake setting. If the VGT exhaust brake makes 75HP of braking, then in 2 gear wouldn't that equal 600+ hp of braking at the rear wheels?
AT that weight, what speed would 600 hp hold.on that grade. You seem to be able to compute the numbers going up, so you should be able to computer them coming down. I know at 24,500 in 4th(1:1) and 3.42 out back, I had to step on the throttle once in a while on 6% grades to not slow down to much. Would that not be 225HP of braking at the rear wheels?
Torque is multiplied through gears not power.
So if torque is what gets a load moving would in not also be needed to slow down a load?FishOnOne wrote:
The Ford and Ram exhaust brake system works independently of the cruise control unlike GM the exhaust brake system works in conjunction with the cruise control.
I cannot speak to the others, but you are spot on on how the GM works. And this is a major problem with their testing criteria.
I have never had to use the brakes on my truck on a down hill when the cruise is set, but when approaching I do reduce the cruise setting a few clicks. Mainly because it is more unsetteling for me to be 5 over the speed limit going down, than it is going up... And that is the variable it allows before shifting gears.
In most cases, especially on a unkown to me hill, I prefer to be 5 under, so that means 10 down clicks on the CC. If a slower posted section of highway comes up, I reduce the setting on the cruise accordingly, before getting into that section. It will downshift as needed to get the speed where I want it to be. After the slow section or the down hill ends, I simply raise the CC the same number of clicks I previously lowered it.
As you can see some driver input is needed, but to me, it is better on the brakes to do it this way. And I don't think CC should be used as an excuse to stop driving the truck.
IMO, the GM EB works best when used in conjunction with the CC, even though it is not a hands off experience.Me Again wrote:
4X4ord. 2 gear(2:1) in a Aisin and 4:10's out back is going to hold back a lot on the full exhaust brake setting. If the VGT exhaust brake makes 75HP of braking, then in 2 gear wouldn't that equal 600+ hp of braking at the rear wheels?
AT that weight, what speed would 600 hp hold.on that grade. You seem to be able to compute the numbers going up, so you should be able to computer them coming down. I know at 24,500 in 4th(1:1) and 3.42 out back, I had to step on the throttle once in a while on 6% grades to not slow down to much. Would that not be 225HP of braking at the rear wheels?
On a 6% grade a 24500 lb truck and trailer would require about 215 reverse horsepower to keep it from accelerating down the hill. At 55 mph about 100 of that 215 hp will be air and rolling resistance. The other 115 will come from the engine. Rotating the engine 2000 rpm might account for about 50 hp and the remaining 65 reverse hp could come from the exhaust brake.
In the case of Ron's unit I did some sloppy number crunching in my head without a calculater. The actual reverse hp to keep his unit held back is more like 430. At 35 mph air and rolling resistance don't account for a whole lot. So maybe the engine needs to make about 400 reverse hp.Me Again wrote:
4X4ord. 2 gear(2:1) in a Aisin and 4:10's out back is going to hold back a lot on the full exhaust brake setting. If the VGT exhaust brake makes 75HP of braking, then in 2 gear wouldn't that equal 600+ hp of braking at the rear wheels?
AT that weight, what speed would 600 hp hold.on that grade. You seem to be able to compute the numbers going up, so you should be able to computer them coming down. I know at 24,500 in 4th(1:1) and 3.42 out back, I had to step on the throttle once in a while on 6% grades to not slow down to much. Would that not be 225HP of braking at the rear wheels?
Torque is multiplied through gears not power.- 4X4ord. 2 gear(2:1) in a Aisin and 4:10's out back is going to hold back a lot on the full exhaust brake setting. If the VGT exhaust brake makes 75HP of braking, then in 2 gear wouldn't that equal 600+ hp of braking at the rear wheels?
AT that weight, what speed would 600 hp hold.on that grade. You seem to be able to compute the numbers going up, so you should be able to computer them coming down. I know at 24,500 in 4th(1:1) and 3.42 out back, I had to step on the throttle once in a while on 6% grades to not slow down to much. Would that not be 225HP of braking at the rear wheels? - I have posted the picture of the sign several times in the past. Is says “14% NEXT 4 MI”. I’m having trouble posting pics. It was several miles and it was STEEP.
It was second for sure. I can’t lock first and can’t go 30-35 in first. - The Ford and Ram exhaust brake system works independently of the cruise control unlike GM the exhaust brake system works in conjunction with the cruise control.
Cummins12V98 wrote:
4x4ord wrote:
Cummins12V98 wrote:
To have zero brake applications they need to be running at the speed they want to maintain then set cruise to say 5mph less but also lock the trans in the same gear you would have climbed that grade in. This will vary based on the grade and load. This takes a human to dial this in.
I easily maintained 30-35mph locked in 2nd gear on a several mile 14% grade at 33k combined simply by moving the cruise speed up or down with my thumb.
For the Cummins closer to 3k will give the best downhill braking.
Cool brakes along any big downhill grade = GOLDEN.
After appling a bit of physics to what you're experiencing I come away thinking your Ram must work similar to my Ford on cruise.... it applies the wheel brakes. Holding 33k on a 14% grade in second gear with 4.10 final gear ratio means about 1000 lbft at the crankshaft. If your engine is revving around 3000 rpm it would be producing about 575 reverse hp. The back pressure on your exhaust brake would need to be somewhere around 180 psi. So I think your truck must be automatically applying the service brakes.
It does not.
Something is not adding up. Could you possibly be in low gear? or could the grade be significantly less than 14% or you are accelerating down the hill? I've never been on a long 14% grade with a 25k trailer behind my pick up but I'm sure it would be a run away without using the wheel brakes in 2nd gear. 33k on a 14% grade would be like 66k on the steepest section of the Ike. The Duramax and Ford couldn't hold back 39k on the Ike.- ^^It does not, at least on our 2015 RAM's. FWIW that is a really stupid thing for them to do. The uninformed could get their brake REALLY hot and not know it.
4x4ord wrote:
Cummins12V98 wrote:
To have zero brake applications they need to be running at the speed they want to maintain then set cruise to say 5mph less but also lock the trans in the same gear you would have climbed that grade in. This will vary based on the grade and load. This takes a human to dial this in.
I easily maintained 30-35mph locked in 2nd gear on a several mile 14% grade at 33k combined simply by moving the cruise speed up or down with my thumb.
For the Cummins closer to 3k will give the best downhill braking.
Cool brakes along any big downhill grade = GOLDEN.
After appling a bit of physics to what you're experiencing I come away thinking your Ram must work similar to my Ford on cruise.... it applies the wheel brakes. Holding 33k on a 14% grade in second gear with 4.10 final gear ratio means about 1000 lbft at the crankshaft. If your engine is revving around 3000 rpm it would be producing about 575 reverse hp. The back pressure on your exhaust brake would need to be somewhere around 180 psi. So I think your truck must be automatically applying the service brakes.
It does not.
