Turbo Caused Back Pressure

[CareyWeber]

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.picturetrail.com/gallery/view?p=999&gid=4595059&uid=2337941

Carey

[ 08-19-2004, 01:13 PM: Message edited by: CareyWeber ]

[MTTwister]

Carey - I thought it was more a function of the restrictions in the exhaust system...?

[CareyWeber]

MTTwister,

I thought it was the exhaust side of the turbo.

If a 6.5 is running an after market exhaust I would not think the exhaust pipe would be the issue.

Carey

[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 it.

[CareyWeber]

Try try this link I'm hosting it.

http://www.picturetrail.com/gallery/view?p=999&gid=4595059&uid=2337941

It looks like the wastegate is larger though.

Carey