Attention: TDR Forum Junkies 
Got back this afternoon from our RV trip up to Pollock Pines towing our 24 ft fiver... First time with a BUNCH af changes to truck, some to trailer... Largest upgrade was addition of the PS propane system:
Earlier testing empty, and around town were somewhat inconclusive, primarily due to the LARGE percentage of slippage designed into the stock torque converters used in the earlier Dodge/Cummins 727 3-speed automatics. The slippage causes much of improvements in power output to be consumed and lost in the TC, so while there IS significant improvement, it is hidden or lost thru TC inefficiency... 0-60 times improved by a minimum of 20% with the propane, but a more direct hookup in the drivetrain would undoubtedly free up substantially more power to the road!
Combined weight of our RV setup GCVW is somewhat over 12,000 lbs. The route used for test was a portion of hiway above Placerville on US 50 between Placerville and Pollock Pines - a distance of 8-10 miles with grade running from 5-7%. Prior to latest changes, I consistently take that grade at 60-65 mph, exhaust temp runs around 1100 degrees pre-turbo. I run in direct 3rd gear in the 727. (I also have the US Gear OD unit)
WITH the PS system, I EASILY was running 70 mph with the AC on maximum, outside temp seemed in the mid to hi 90's, and COULD have run substantially faster in OD if I had wanted, but was already WELL over road and traffic conditions...
Problem is that now I need a steeper and longer grade to more accurately test the capabilities of my truck - or a heavier trailer!
AGAIN, the biggest problem in obtaining max performance from the propane system centers on TC performance - at 65 mph or so on steep grades and under load, the Cummins is well up near the top of its RPM curve, and is near its 2500 rpm governered rpm - a stiffer TC delivering another usable 400 rpm or so would make ALL the difference in the world, and would eliminate the NEED to go to OD to bring the power back into a reasonable portion of the RPM band - along with the sluggishness the higher gearing would also bring with it!
The propane system works GREAT, and while a little final "tweaking" remains, the limiting factor will NOT be the PS system, but the stock TC in my truck - the engine is now powered about as much as is practical under current conditions... Exhaust temps remained about the same as before propane injection...
Bring on the Fords and GM stuff...
Similar note - the new "Double Deep transmission pan" is also installed - seems to deliver the promised 20-30 degree temp reduction in around town driving and when empty - but when PUSHED even in those conditions, temps WILL go up to their original highs! The same holds true when pulling - the additional fluid capacity provides a better buffer in temperature spikes under short bursts of applied power - but won't do much to help SUSTAINED high power under load. If that reduction under sustained power is what YOU need, spend your money on a good supplemental transmission fluid cooler instead!
For the record, my transmission fluid temps ran a max of about 230 under load, with the temp sensor in the fluid line immediately leaving the torque converter.
The new TC will be my next goal - I feel the transmission itself should live satisfactorily for a reasonable period longer - I don't push it during shifts, and DO service it regularly, and it is still operating perfectly - and it's OBVIOUS that additional power mods are pointless with the stock converter...
Earlier testing empty, and around town were somewhat inconclusive, primarily due to the LARGE percentage of slippage designed into the stock torque converters used in the earlier Dodge/Cummins 727 3-speed automatics. The slippage causes much of improvements in power output to be consumed and lost in the TC, so while there IS significant improvement, it is hidden or lost thru TC inefficiency... 0-60 times improved by a minimum of 20% with the propane, but a more direct hookup in the drivetrain would undoubtedly free up substantially more power to the road!
Combined weight of our RV setup GCVW is somewhat over 12,000 lbs. The route used for test was a portion of hiway above Placerville on US 50 between Placerville and Pollock Pines - a distance of 8-10 miles with grade running from 5-7%. Prior to latest changes, I consistently take that grade at 60-65 mph, exhaust temp runs around 1100 degrees pre-turbo. I run in direct 3rd gear in the 727. (I also have the US Gear OD unit)
WITH the PS system, I EASILY was running 70 mph with the AC on maximum, outside temp seemed in the mid to hi 90's, and COULD have run substantially faster in OD if I had wanted, but was already WELL over road and traffic conditions...
Problem is that now I need a steeper and longer grade to more accurately test the capabilities of my truck - or a heavier trailer! AGAIN, the biggest problem in obtaining max performance from the propane system centers on TC performance - at 65 mph or so on steep grades and under load, the Cummins is well up near the top of its RPM curve, and is near its 2500 rpm governered rpm - a stiffer TC delivering another usable 400 rpm or so would make ALL the difference in the world, and would eliminate the NEED to go to OD to bring the power back into a reasonable portion of the RPM band - along with the sluggishness the higher gearing would also bring with it!
The propane system works GREAT, and while a little final "tweaking" remains, the limiting factor will NOT be the PS system, but the stock TC in my truck - the engine is now powered about as much as is practical under current conditions... Exhaust temps remained about the same as before propane injection...
Bring on the Fords and GM stuff...
Similar note - the new "Double Deep transmission pan" is also installed - seems to deliver the promised 20-30 degree temp reduction in around town driving and when empty - but when PUSHED even in those conditions, temps WILL go up to their original highs! The same holds true when pulling - the additional fluid capacity provides a better buffer in temperature spikes under short bursts of applied power - but won't do much to help SUSTAINED high power under load. If that reduction under sustained power is what YOU need, spend your money on a good supplemental transmission fluid cooler instead!
For the record, my transmission fluid temps ran a max of about 230 under load, with the temp sensor in the fluid line immediately leaving the torque converter.
The new TC will be my next goal - I feel the transmission itself should live satisfactorily for a reasonable period longer - I don't push it during shifts, and DO service it regularly, and it is still operating perfectly - and it's OBVIOUS that additional power mods are pointless with the stock converter...
Last edited:
