Engine braking Gas Vs Diesel
Just wondering why gas engines have better engine braking than diesel. No real reason, just wondering. With the higher compression of the diesel I would think that diesel would be better but understan...
Forum Discussion
brulaz wrote:
Thanks for this. What I'm hearing is that a diesel engine without an exhaust brake has less engine braking than a same sized gas engine.
My 2011 F150 with the 3.5L EcoB has good engine/tranny braking in Tow/Haul mode, but on some steep and windy Appalachian trails I've needed to let it wind up to 4000-5000 rpm in first gear so as not to cook the truck+trailer brakes. From what I'm reading here, a similarly sized diesel without an exhaust brake would be worse.
Have read here that even the RAM 2500 with the I6 Cummins doesn't brake that well on these same trails in first gear because the exhaust brake is disabled when the auto tranny is forced into first. But in auto 2nd, the exhaust brake kicks in and works well. This makes more sense now.
It also makes sense that the RAM Ecodiesel has weak engine braking, from what I've read in the forums probably worse than my 3.5L EcoB, because it does not implement an exhaust brake.
And although nobody seems to know for sure, it's possible the Nissan Titan XD with the Cummins 5L has not implemented the turbo's exhaust brake feature, just an engine/tranny Tow/Haul mode. That would be a major disappointment for sure.
Of the smaller diesels appearing these days, the only one I know for sure has an exhaust brake is the Colorado's Duramax.
1) In order for a diesel turbo exhaust brake to work in an auto transmission the torque converter has to be locked. If I am not mistaken, none of the current truck makes have TC lock up in first gear.
2) The pickup version of the ISV 5.0L that will be in the Nissan and Toyota trucks use a compound turbo setup while the non pickup ISV 5.0L found in medium duty trucks use a VGT. One of the draw backs to a compound turbo set up is the fact that you cannot utilize an exhaust brake like a variable geometry turbo. This is why Ford switched to a VG turbo on the 2015 and up Powerstrokes. The 2011 to 2014 Powerstroke have a compound turbo.
3) The 2.8L Duramax in the Colorado/Canyon does have a VG turbo and does have an turbo exhaust brake.
4) Although the 3.0L Ecodiesel uses a VG turbo, it was not designed with an exhaust brake. I suspect this is due to the fact that the engine was initially designed to go in a Cadillac sedan which would not need an exhaust brake since it was not meant to go into a vehicle that tows.
