GMCTD,


It's know that the GM 4-8 turbo's are small and cause to much back pressure.


My question is why does the Duramax turbo not due the same thing from this pic the outlet does not look much bigger.


http://www.uscom.com/%7Ehoot/cars/duramax/gmc/headgaskets/index_8.htm


CareyEdited by: Carey Weber

I can't get that page, Carey - but, the GM-X series are designed for ~250-300cuin engines, which gets 400cuin Boost up quickly off-idle.

This is where working trucks need the torque, but exhaust energy - heat and volume - are minimal.
Using a small turbo which responds to lower exhaust energy on a larger displacement engine will generate low rpm torque.

Doesn't take long for the larger engine to start producing exhaust energy much greater than the smaller engine, and the turbine becomes a bottleneck as exhaust flow and pressure rises above design specs.

A 5" exhaust pipe may impress the ladies, but does nothing to help reduce exhaust back pressure inside the small turbine.

To compare the two turbo's would require measurements of turbine housing 'snail', nozzle area and radius dimension (A/R), wheel diameter, number of blades, angle of blades, turbine outlet diameter, wastegate port diameter, etc.

Turbine 'snail' perspective in pictures does not allow a good comparison.

The DuraMax was designed as a turbo motor system - the 6.5L, designed to be naturally aspirated, got a turbo as a tack-on when NavStar and Cummins released their systems.

And that's the truth, as far as I know ithttp://www.dieselplace.com/forum/smileys/Cool.gif Edited by: gmctd

I can't get that page, Carey - but, the GM-X series are designed for ~250-300cuin engines, which gets 400cuin Boost up quickly off-idle.

This is where working trucks need the torque, but exhaust energy - heat and volume - are minimal.
Using a small turbo which responds to lower exhaust energy on a larger displacement engine will generate low rpm torque.

Doesn't take long for the larger engine to start producing exhaust energy much greater than the smaller engine, and the turbine becomes a bottleneck as exhaust flow and pressure rises above design specs.

A 5" exhaust pipe may impress the ladies, but does nothing to help reduce exhaust back pressure inside the small turbine.

To compare the two turbo's would require measurements of turbine housing 'snail', nozzle area and radius dimension (A/R), wheel diameter, number of blades, angle of blades, turbine outlet diameter, wastegate port diameter, etc.

Turbine 'snail' perspective in pictures does not allow a good comparison.

The DuraMax was designed as a turbo motor system - the 6.5L, designed to be naturally aspirated, got a turbo as a tack-on when NavStar and Cummins released their systems.

And that's the truth, as far as I know ithttp://www.dieselplace.com/forum/smileys/Cool.gif


Sorry about the link.


http://www.dieselplace.com/forum/uploads/Duramax_Turbo_Exhaust_Outlet.JPG

for comparrisonhttp://www.dieselplace.com/forum/uploads/AZ2_turbo121.jpg

No comparison possible - note the threaded bolt-hole diameters - what is actual dimension?


Perspective is a hard taskmaster........


But thanks - imo the DM is much larger.Edited by: gmctd

It's definitely refined, waste gate is 2" looks beefier. Are those taps the water jacket fittings? any idea what something like that costs? used even? I see the exhaust comes in two ports. Is this where they bring the driversside exhaust to now?

No comparison possible - note the threaded bolt-hole diameters - what is actual dimension?


Perspective is a hard taskmaster........


But thanks - imo the DM is much larger.





I don't have a way to measure it I found the pic on Hoots web site about his duramax headgasket R&R.


It really kind just suprised me I thought it would have been bigger.


Maybe a duramax guy/gal could measure one for us sometime.


Carey

It's definitely refined, waste gate is 2" looks beefier. Are those taps the water jacket fittings? any idea what something like that costs? used even? I see the exhaust comes in two ports. Is this where they bring the driversside exhaust to now?


There are some pictures of a loose engine in this post: http://dieselplace.com/forum/forum_posts.asp?TID=13183&PN=1

Or a GM parts dude, with one in hand.....