edwinsmith

I just had a thought. As dangerous as that is but could an intake air cutoff work to retard the engine when going downhill? If so, what would be the drawbacks of such a system?

Edwin

bgilbert

LOL, sure if you want to shut it down going down hill. Maybe if you had such a thing down stream of the turbo in the exhaust, create backpressure and that would retard the engine.

wannadiesel

I think it would cause massive oil consumption. Diesels are not typically set up to deal with vacuum on the valve seals, and the turbo seals wouldn't like it either.

Exhaust brake is a much better option.

rebal

I agree the engine would suck oil where ever it could

edwinsmith

OK please don't ridicule me for such a dumb question. I thought better of it as soon as I clicked the submit button.

But. Just as an academic exercise and as long as you kept the crankcase full, how bad would it be for oil to be sucked past the valve guides and compressor seal? AFAIK the compressor seal is just a slinger and the oil would just be burned or shot out the tailpipe as soon as you got back on it.

Curious in Kansas

Edwin

wannadiesel

Valve guides wouldn't be bad, and on a non-intercooled truck the turbo seal thing wouldn't be that big a deal (other than the nasty smoke and associted deposit buildup). On an intercooled truck you'd get oil puddling in the intercooler, and you might get a big enough slug of it to hydro lock a cylinder when you built some boost and blew it through.

Wasn't a dumb question.

gman07

Couldn't you also get runaway if you get oil through the compressor seal?

wannadiesel

No air = no runaway. Maybe when you opened the air shutoff the engine would rev up on the accumulated oil, though.

edwinsmith

Yeah but if it did just HIT THE BRAKE!

gman07

See, now my question was a dumb one! Wouldn't it be nice if my mind worked tonight...

edwinsmith

My boss always told me the only dumb question is the one you didn't ask.

Edwin

torquefan

It's not a bad idea at all, in theory. Unfortunately if you did it, it would suck in the preheater and intake manifold gaskets. You'd be replacing them all the time.

edwinsmith

Air pressure at sea level is 14.7 psi. Even with a perfect vacuum that would be the maximum pressure pushing the gaskets in. If they will hold 30 psi of boost in they'll certainly hold 14.7 psi out.

Edwin

JD730

This might be slightly off topic, but I have had the distinct pleasure of running a 1958 Mercedes Unimog once (25hp diesel, which I think is giving it alot of credit). The interesting part is that there is not throttle linkage hooked to the pump, only a shut down lever. Upon further investigation I traced a line going from the intake manifold to the injection pump, and before this line was a butterfly valve in the intake. The pump used vacum to throttle itself, what a goofy system, but it works (some how). Probably the only diesel I seen that runs vacum on the intake.

wannadiesel

Some diesels do have air governors instead of flyweight governors. That is what you were seeing. That "butterfly" was a vane that measured airflow. More air = higher RPM.