Diesel vs gas......................

JIMNLIN wrote:

waynec1957 wrote:
Ok fellas, help me out here.

I'll take a shot at it.
From around '04.5 the Dmax uses a VVT (variable vane turbo) that restricts air through the turbo and acts as a exhaust brake. Programmed with the Allison which keeps the TC clutch locked which stops the slippage in the TC. Early models were called grade braking but were very weak when compared to a actual exhaust brake. The new '10 ?? and up Dmax/A with the VVT uses a very aggressive program and is at the top with the Dodge in turbo exhaust braking.

As far as I know the 6.0 gasser doesn't use or advertise a grade braking feature.
This from a engine braking wiki;
The term engine braking usually refers to the braking effect caused by the closed-throttle partial-vacuum in petrol (gasoline) engines when the accelerator pedal is released. While some of the braking force is due to friction in the drive train, this is negligible compared to the effect from the vacuum.

When the throttle is closed, the air flow to the intake manifold is greatly restricted. The concept can be illustrated by the amount of effort required to blow/suck through a thin tube vs. a thicker one. It is the work the engine has to do against this restricted air flow that provides the braking effect.

Who advertises a smart exhaust brake ?? I've heard of smart brake and a speed brake.

Thanks for the info on the Duramax/Allision. I sort of had the idea that when towing on a downhill grade if you take your foot off the accelerator the engine created some sort of backpressure (for lack of a better word) which combined with the software works with the transmission to keep the vehicle from speeding up. I know that’s not very technical, but if I’m understanding you correctly that’s more-or-less what happens.



As far as the gasser and the “Automatic Grade Braking” feature, I got that from the Chevrolet “build your own” website. When you get to the point where you choose the engine/transmission this below is how they describe the standard HD transmission:


6-speed automatic heavy-duty transmission

The standard equipment on Silverado® 2500HD, this 6-speed automatic heavy-duty transmission handles the power of the Vortec® 6.0L V8 engine. Electronically controlled Tow/Haul mode and Automatic Grade Braking to help you control those heavy loads.


This is how they describe the Allison 1000:

Allison® 1000 6-speed automatic transmission
With over a decade on the job, the legendary heavy-duty Allison® 6-speed transmission harnesses the power of the available Duramax® 6.6L Turbo-Diesel V8 engine.

Includes:
• Driver Shift Control (DSC), which allows the driver to manually select upshifts and downshifts with buttons on the column shifter
• Tow/Haul mode reduces shift cycling for better control and improved cooling when towing or hauling heavy loads
• Automatic Grade Braking uses the engine and transmission to slow the vehicle on downhill grades and help reduce brake wear (operates in Tow/Haul mode)
The durable Allison 6-speed puts you in control of all the intensity Duramax throws out. It requires the available Duramax 6.6L Turbo-Diesel V8 engine.

The both use the term Automatic Grade Braking, which is where I’m confused.

As far as the term “smart exhaust brake”, I thought that was a standard term for GM. “Smart exhaust brake feature on 6.6L Duramax turbo diesel that provides greater control on grades and reduced brake pad wear”. http://media.gm.com/media/us/en/gmc/vehicles/sierra_hd/2013.html

This is all new to me—this diesel thing. I’m on my 8th pickup since 1979 and they’ve all been gas motors. I’m seriously considering a diesel because we’re getting to the stage in life where we can pull the camper more (farther) and the extra power is appealing. But two things scare me, (1) my lack of knowledge about diesels and (2) the extra $8 grand for the DMax/Allison. That’s why I’m here asking questions.