Lowest working RPM?

[DavesTractor]

Greg,
Wouldn't it be interesting to run a pyrometer on a little Yanmar? Has anyone done this?

What you said about heat while lugging is certainly true on my Banks Turbo'd 7.3l in my hauling truck. When pulling a long grade with a big load on, the pyrometer will sneak up to 1000 degrees or so, I shift down (raises the RPM) and drop a couple hundred degrees within 250 yards. I can only think that running a Yanmar at the proper rpm for the load would have similar results.

 

[gbirky]

Dave,
I agree it would be interesting. I work for Mack Trucks in the Powertrain Engineering department. For the past 3 years I have been developing engine controls for the 2002-2007 emissions regs. Most diesels are designed with a torque curve that increases with decreasing speed. In all cases, the peak torque point is lower in HP but better fuel economy. Your 7.3L is no different. Its lowest fuel consumption is at lower speeds, but you can't always run it there.

Is your pyro in the exhaust manifold or after the turbo? 1000 deg isn't bad for exhaust manifold, but it is high for tailpipe (after turbo).

 

[DavesTractor]

Greg,

It's in the manifold. Even then, I don't let it get over 900 very often, and never over 1050 even for a moment. It's an older truck (1989) and right now all my money is going into a new shop/warehouse/loading dock so the old beast has to go another couple of years. With the Banks and the pump turned up, it still does a fine job. I do wish for an intercooler and a 6 speed though. I pull a triple axle 24K lb gooseneck, so you imagine the loads we occasionally haul. /forums/images/graemlins/crazy.gif

Knowing what you do for a living helps explain the advice you often give posters on this board. Your mechanical ability and knowledge is excellent, and it is kind of you to take the time to help others.

 

[gbirky]

Dave,
Thanks for the kind words.

That engine in original form without the turbo may have had exhaust temperatures higher than 1000 deg. Remember that with the turbo, you can pump alot more air through the engine. At 15psi boost, you are basically moving twice the mass of air through the engine if the intake manifold temps are the same. Without the intercooler of course the intake manifold temps are higher, so the air charge is not as dense. But you can bet you are increasing mass flow by at least 50% over natural aspiration. Your intake manifold temps would have to be over 350 deg F to be less than a 50% increase in flow. Of course any increase in intake temps translates into an increase in exhaust temps.

I am told that back in the natural aspiration (no turbo) and even in the turbo but no intercooler days of Mack engine production, our exhaust manifold temperatures were in excess of 1300 deg F.