On Tuesday, July 18, 2006, at 09:53 PM, Dick J wrote:
> A local dirt tracker that I know, who is also a truck driver, happened
> to pull up next to me in his big rig on the way home, and tried to
> demonstrate his racing technique. I couldn't get over the whir of
> that big turbo right next to my driver's window as he pushed it to the
> max.
>
> Just exactly how high do those great big turbos spin? I've seen the
> one on his rig and it must be a foot in diameter.
>
> DickJ
> In East Texas
Diesel turbos are a little different from gas engine turbos -- in that
they need to run at (or at least near) 100% most of the time so the
engine can make proper hp. Gas engine -- turbo idles along, not doing
much, 'til you mash the gas pedal. Diesel -- turbo makes boost as
you're cruising as well as when you're accelerating, so needs to be
able to take different loads and heat and have different bearings that
can live at high load for hours on end, day after day. They run at
mid-range speeds 'til you get to a hill or stand on it to pass -- then
you'll hear the turbo spool up the rest of the way to make more still
more boost. Our Caterpillar engines have electronic cruise control --
you can hear the computer call for horsepower by listening for when the
turbo whistle pitch increases. You hear the turbo dang near 100% of
the time going down the road.
And yes, they're (physically) big. They gotta last for hundreds of
thousand of miles, so need to be built right - and tough. We had a
Ford F-700 with Cummins 5.9 diesel -- got rid of the truck at something
past about 15,000 hours on the engine. Multiply that by 75,000 rpm (a
guess at average turbine speed) and 60 min/hour and then think that the
turbo never got touched -- no service whatever -- and in its' life it
spun something like 2 3/4 TRILLION revolutions. I guess that's a sign
of good bearings or something. . .
Jon Wennerberg
Seldom Seen Slim Land Speed Racing
Marquette, Michigan
(that's 'way up north)
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