Turbo Operation

[nikki girl]

I've had my 2003 GMC 2500HD, DMax/A, for about two months and have no idea on turbo operation since there are no gages/switches to know what the thing is doing.

How do you know when its operating?

[Minn-kota]

You hear a slight whistle and your butt moves slightly back into the seat.

[Idle_Chatter]

Welcome, nikki girl. There's no gauges and such (unless you add one) because the turbo kind of "does its thing" passively and all the time. Since it relies on exhaust flow to spin the compressor and pump intake pressure up, when exhaust flow goes up, turbo boost increases. The turbo pretty much "loafs" and doesn't begin to boost until there's some reasonably heavy demand. My boost gauge stays on the peg until there's some load or I get more than about 1/4 way into the throttle. Day to day driving, boost rarely gets much over 6 to 8 pounds and will drop right off as soon as things level off at the new speed or the hill is crested. Pulling my box trailer on the interstate at 65-70 mph, boost will run about 4 to 5 running steady and rise right up to 10 when climbing a grade in overdrive. The most noticable indication of turbo operation is the "whistle" as it spins down from boosting just immediately after letting off the throttle. It's pretty quiet, and it happens quick, so you really got to listen for it on a DMax. On the other hand, you can hear the same thing happening on a big (tractor trailer) turbo engine for a city block as they shift through the gears. When you're alongside one on a four-lane coming off a stop light you'll see what I mean: RRRRRRrrrrrrup! WHEEEEEEE! RRRRRrrrrrup! WHEEEEEE! :D