Auto transmission, exhaust brake, EGT questions

[CoastyAV8R]

I've owned a couple of 3rd gens but they were both 6 speed manuals. My 03 has the 48re transmission with a temp gauge and an EGT gauge. The transmission has been rebuilt with a billet torque converter and has a shift kit in it. The truck also has a PacBrake exhaust brake.

Questions:
1) what type of EGT numbers should I see for an EGT probe that is installed after the turbo? Previously my EGT probes were installed prior to the turbo so I"m not sure what I should be looking for numbers wise.

2)What temps should I be seeing for transmission temps both loaded and when towing? I know ambient temps as well as the load I'm towing (7000 lbs camper) will affect it but I'm looking for ballpark temps and what are considered to be too high?

3) The truck has had the pac brake in it since 04 and there is a box that isn't standard that I think maybe a controller for the transmission so the line pressure is high enough for the torque converter to lock up when using the exhaust brake but this is only a guess as I'm still waiting for a relay to come in so I can get the exhaust brake to work. Would my truck require a box like this to ensure the line pressure is high enough so the exhaust brake will work? Also the truck has a 3 position switch, any idea what all positions are for? I know one is to turn it off but i"m not sure what the other two modes are for.

Thanks in advance
Patrick

 

[AH64ID]

I ran a pre and a post pyro on my 05. General rule of thumb is that my post temps were 10° per psi of boost lower than pre temps. i.e. 800° pre with 10 psi would be about 700° post. This was fairly accurate as long as I wasn't lugging, which I tied to avoid anyhow.

 

[cerberusiam]

Move the EGT probe, or keep it, pre-turbo for best results. These engine shave to wide an operating band for consistent readings on EGT post turbo, post turbo works much better with the lower revving lower pressure turbos. Just too many ways the difference can way off acros trucks, especially MY's. What John saw with his 05 won't be what you see with an 03, throw programming in there and you can throw out the norms.

7k is not much of a load unless you are running some big tires or trying to run OD at 55-60 mph and lugging it. The operating range on the 48RE is 140 to 240 degrees, dash light and downshifting come into play at 260 degrees. As a rule, 190-195 degrees in lockup all the time when temps are over 70 degrees is normal. That temp will drop with ambient temps and load. If you are doing stop and go in warm ambient temps not unusual to see 220 degrees. No problem if it cools back down when lockup is applied, just the result of fluid coupling energy loss.

What is the box actually hooked up to, that is the question. On an 03 there is no way to electronically control TV pressure which is what is needed, the only way to do that is advance the TV lever to full or almost full manually. It cannot be anything that controls pressure, but, maybe it is an OD lockout controller. BD used to market a mechanical cylinder that pushed the TV open when the EB applied but they have discontinued it now. EB in OD is mostly useless, the sprag clutch in the OD section will not allow and EB to slow the truck. You will have to test it but it might to knock the trans out of OD when the EB comes on, or, just a controller to allow EB activation when APPS is at 0%.

You will have to test trans pressures at various rpms and throttle positions, but, unless it will hold 90 psi with throttle closed you run a real risk of burning up the clutches in the trans and the TC. It would much preferable to hold the pressure at 120-130 psi when EB activates to promote trans life expectancy. You are probably fine with a rebuild as long as the shift kit boosted the pressures enough and the updated thrust washers were used, no way to tell unless you get pressure readings and know what was used in the rebuild. About the only other way to make it work is a constant pressure VB and a controller like the AntEater to get rid of the mechanical pressure control. You ar enot heavy on the expected load so good chance your existing setup will perform well for an adequate time.

 

[AH64ID]

Specs I’ve seen on other engines also follows suit to what I’ve seen. Programming doesn’t change much, if anything, for temp drop across the turbine. Programming has a big effect on pre-turbo temps, but the drop across the turbine is based on the cooling rate of expansion due to the massive pressure drop.

There will be minor variances based on turbo size, but nothing crazy.

Moving it pre-turbo is the best option for sure.

It took me quite a while to get used to what the post was telling me, but pre is always decipherable.

That being said most OEM pyros are post, so the readings can’t be that bad or hard to figure out.

 

[CoastyAV8R]

Specs I’ve seen on other engines also follows suit to what I’ve seen. Programming doesn’t change much, if anything, for temp drop across the turbine. Programming has a big effect on pre-turbo temps, but the drop across the turbine is based on the cooling rate of expansion due to the massive pressure drop.

There will be minor variances based on turbo size, but nothing crazy.

Moving it pre-turbo is the best option for sure.

It took me quite a while to get used to what the post was telling me, but pre is always decipherable.

That being said most OEM pyros are post, so the readings can’t be that bad or hard to figure out.

Thanks guys, I just want a ball park idea on temps for the transmission and EGT. The engine will remain stock and I'm not pulling anything real heavy so I don't expect crazy EGT temps but I know on hot days on a long grade pulling our trailer things will still warm up.

 

[cerberusiam]

Programming doesn’t change much, if anything, for temp drop across the turbine.

Nuh uh, I have seen a 50 degree increase in post turbo temps translate to 300 degrees pre-turbo. The rate of heat loss across the turbo is going to be fairly constant at some point and the post turbo temps will rise accordingly. The problem being the rate of change is NOT constant so it is hard to build any kind of consistency that x temp pre is going to translate to y temp post. The programming will affect both drastically by how close to stoich the tune is trying to get. Change a cam the relationship changes, wrap the exhaust manifold and turbo, the relationship changes, change driving style and the relationship changes.

Post turbo EGT readings are only useful if the pre turbo temps are a known quantity and do not vary much across a range. That is going to limit usage to engines that run close to a constant rpm and constant load a significant portion of the time, in others NOT an engine a Ram truck. Any post turbo temp that is going to accurate has to be the result of extensive testing on a KNOWN CPL or it is really less than useful to gauge what is too hot and what is too cold.

 

[AH64ID]

Actually yes... cams, tuning, stoic, injectors, etc just don’t have any effect on the mechanical drop in temp from expansion. The single biggest effect is pressure ahead and acrosAt low drive pressure the pressure drop is lower, and so is the temp difference.

All of the above items will have a large impact on pre-turbo and post-turbo temps, just not the relationship between pre and post for the same exhaust flow/temp. Maybe that’s the difference and similarity in what we’re talking about

As stated pre-turbo is a much better number, but post is predictable too.

 

[cerberusiam]

That is correct to a point, there will be a max point at which drop in temp will be linear and could be mapped. Until that point is reached it won't be a linear difference. Saying that 700 post turbo will always equate to 1000 pre turbo won't be true UNLESS that is point at which pressure difference and radiant loss gains are close to flat line.

Based on what I have seen you don't get to that point until 1200+ pre turbo, then the correlation and rate of change is more linear and predictable. That is on ONE truck driven exactly ONE way with ONE tune and ONE set of components. It has to be mapped to existing conditions, driver, and truck or there are too many variations. Have never seen a post turbo expected temp for an ISB. The ISX's and older 10 liter engines you could find a number for that for a CPL but it wasn't really "official".

Hell, we can't even get Cummins to tell us what is too hot pre-turo let alone what post turbo temp would be. All we get is "Whatever it will do with in stock configuration is safe". I know of handful of 03 trucks that melted pistons at a constant 1100 degrees pre turbo under load, that is supposed to be a "safe" temp. Load too much fuel and timing into the engine and even 1000 degrees EGT might not a safe pre turbo temp. Hate to rely on a post turbo for anything critical when there is no good rule of thumb that applies broadly.

 

[AH64ID]

That’s where boost comes into play, but really it’s drive pressure. It is a variable differential, but predictable based on exhaust pressure.

 

[CoastyAV8R]

That is correct to a point, there will be a max point at which drop in temp will be linear and could be mapped. Until that point is reached it won't be a linear difference. Saying that 700 post turbo will always equate to 1000 pre turbo won't be true UNLESS that is point at which pressure difference and radiant loss gains are close to flat line.

Based on what I have seen you don't get to that point until 1200+ pre turbo, then the correlation and rate of change is more linear and predictable. That is on ONE truck driven exactly ONE way with ONE tune and ONE set of components. It has to be mapped to existing conditions, driver, and truck or there are too many variations. Have never seen a post turbo expected temp for an ISB. The ISX's and older 10 liter engines you could find a number for that for a CPL but it wasn't really "official".

Hell, we can't even get Cummins to tell us what is too hot pre-turo let alone what post turbo temp would be. All we get is "Whatever it will do with in stock configuration is safe". I know of handful of 03 trucks that melted pistons at a constant 1100 degrees pre turbo under load, that is supposed to be a "safe" temp. Load too much fuel and timing into the engine and even 1000 degrees EGT might not a safe pre turbo temp. Hate to rely on a post turbo for anything critical when there is no good rule of thumb that applies broadly.

Yall have convinced me to move my EGT probe...

 

[CumminsPuller]

@AH64ID[/USER] -

-John
I recall when we had our 99' w/47RE, towing in OD below roughly 2000 RPM was not recommended. Lugging/High EGT's, etc. Does this hold true with the 48RE? You can see in our signature below we recently sold our 97' and purchased an 07'. Yesterday we moved the travel trailer from the wife's place of work where we had been storing it, to a closer storage facility by the house. This time I opted to leave OD off rather than using Tow/Haul mode, 2200-2300RPM. When taking the trailer for new tires a couple of weeks ago I did use the Tow/Haul option @ 55-60MPH and did not care for it. RPM's would drop to 1500-1600. Granted we were driving through Portland, OR. So far this is all the towing we have done with the truck so far, no long trips as of yet. Previous owner installed 18" wheels and had 35's on them. I promptly removed those and had Michelin Defenders 265/70/18's installed at Costco.