Spied: 4.5-liter Duramax Diesel V8 Hummer H2T?
By: Mike Levine / KGP Photography Posted: 12-14-07 03:00 PT
© 2007 PickupTruck.com and KGP Photography

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Update #1: 12-18-07 15:05 PT

Found this partially blocked view of an H2T mock-up from a scan of the Hummer H3 (Launch Book) that's posted on the H2 Forums at Elcova.com.

A spy shot of what the boys at Winding Road say is the future Hummer H2T looks like it also might be the first half-ton truck from General Motors we've seen running with GM's new light duty 4.5-liter Duramax diesel V8 under the hood.

Here's what I think the 'tell' is.

The tailpipe on the truck (seen in the top picture and middle photo, left) appears to have a very large aperture - a sign that it's using a serial double barrel exhaust, with a gap between the two pieces, to quickly cool its exhaust.

Why would a diesel H2T needs this?

New 'clean diesel' vehicles require a device called a diesel particulate filter (DPF) to trap engine soot, so the soot doesn't pollute the environment in the form of black exhaust clouds that have long been associated with diesel engines. The DPF is placed between the engine and the tailpipe.

After a while the DPF gets gummed up with accumulated soot and has to be cleaned out. The only way to do this is to inject metered amounts of diesel fuel into the DPF to burn the soot up, like a self-cleaning oven, in a process called 'regeneration'.

DPF temperatures can hit 1,100-degrees during regeneration and, as you can probably imagine, the exhaust gets close to these temperatures too.

To not burn nearby vehicles (and people) the gap in the tailpipe creates a 'Venturi' effect that pulls fresh air through the split to rapidly cool the super hot exiting gases right before they pass the exhaust tip.

In the middle picture, you can see a slightly enhanced close-up of the H2T tailpipe for comparison against the exhaust portal of a 2008 Chevrolet Silverado Heavy Duty pickup with a 6.6-liter Duramax V8.

Both the 6.6-liter and 4.5-liter (when it debuts) have to comply with the same tough federal regulations that limit the amount of soot that can be emitted by a 'clean diesel'.

Here's another look (bottom) at a Venturi tailpipe, so you can see how the two pieces fit together straight on.