Re: Turbo cool down

Posted by RodInNS on March 23, 2006 at 20:04:54 from (142.177.9.34):

In Reply to: Re: Turbo cool down posted by NC Wayne on March 23, 2006 at 19:20:38:

Hi Wayne,

What I was getting to with the idle speeds and cooling. Hmmm. To eloborate more. Think of the engine as a big air pump, right? So for every rev, it moves so many CFM, and that would be it's air exchange. Turning at 1250 is roughly twice 650, so it should have roughly twice the air exchange. I couldn't tell you the exact parameters of how much heat the engine and manifold etc. is giving off, but the basic idea is that the more air that goes through the engine, the more heat it's going to carry off.
Now, off to pump theory. An engine like the Ford 268 turbo that I used as an example will have and idle fuel delivery of 2-3 cc/200 shots. At high idle I think it was something like 4-5cc/200 shots. Wheras the factory delivery at maximum on that engine was ~21cc/200 shots, and I'm thinking I've got it somewhere around 25cc/200 shots. So basically there is a very very small amount more energy going into the engine to turn it at 1250 rpm than at low idle, and really not much more heat being generated. So with the higher air movement, it should cool itself much quicker. This I have observed on the pyro on that tractor. If I let her idle at 650, it might take 10 minutes and it's still around 300 F. Idled up a bit, and she goes to ~100F in a couple minutes, depending on how hot it was. As I said, I've seen that thing hit 1150F in the pipe after the turbo. The info from Hewitt that came with the pyro suggested a 200-250 F drop across the turbo.... so that's 1350+ in the manifold. I try not to go there to often, or for too long. Aluminum has that smell about it..... To take your question further, it doesn't heat back up noticeably at low idle on that engine, because it's not making much heat. Just the higher rate of heat removal at a fast idle that causes the quicker cooling.
To answer the other question. The turbo we lost on that tractor was an AiResearch. It was replaced with a Garret branded turbo.... but basically the same turbo. Came through Ford, so it should be. Again, it was just a matter of whoever was in the seat would drive into the yard, after dragging who knows what, full bore, and the cooling and spooldown time it had was the amount of time it took to set the brakes. Then out comes the shutoff. I'd like to see how long that spun. Probably quite a while. One turbo I do know that spins and spins is on the 3204. Often hear that for 20 seconds or more. Talking 3306's reminds me of the milk trucks that used to pick up here. Dairy was big on Cat's. Run nothing else in recent years. I guess in days gone by, they used to rag the drivers about ideling the old Detroits... Shut them off. shut them off. So, they shut them off. Up the driveway the come, lugging and blowing smoke. The key went off 10 feet from the door, and roll to a stop. WWWWHHHHHIIIIIRRRRRRRrrrrrrrrrrrr. I can still hear the damn thing. They ate a few turbo's over the years too, and never learned. Oh well.
Anyway, I'll give you one thing. You got a good discussion going. Take er easy.

Rod

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