High altitude performance

[BSchulte]

My family and I are planning on taking a vacation in the mnts. this summer. When I was out there years ago, I remember following diesels up the high passes. I also remember that I couldn't see much because of the smoke billowing out of their rigs and holding up the line. Obviuosly, our engines are much better in performance and technology. My question is. What can I expect for performance and mileage when we're up above 10k feet?

 

[RTillery]

I got my 04 just before Christmas and have taken it to California over Donner pass, and crossed the Rockies a couple of times. Going over I70 you get up over 10000ft and it is a fairly long pull. I passed everything in sight and was going as fast as I could negotiate the curves. Didn't have gauges yet so I don't know egts but there was no visible smoke. I filled up in Rifle and came home about 200 miles over the top. Driving hard uphill and feather footing it down, I got just over 21 mpgs. What a great truck.

 

[Gonzo 1066]

You should have full rated Horsepower up to the 10,000' level. The turbocharger is pulling in extra air by spinning faster at higher elevation. The diesel trucks you saw last time holding up trafic and belching black smoke were no doube non turbo 6. 9 and 7. 3 fords. They were a good engine on the flat but any grade and there was not enough power to get out of thier own way. All of the new turbo diesels will do the same as our Dodges that is full power at altitude.

 

[KBennett]

The only problem I have had is trying to count the number of cars I pass that are in the right lane.



When pulling the passes my wife says it's like a wild horse. This truck just likes to run!

 

[Prairie Dog]

You will have a slight loss of power at those altitudes because although the same amount of air is being pumped into you engine, it's thinner. Your not going to have any trouble getting arround though - trust me

 

[BarryG]

My truck has never seen sea level so I cant say how it would run down there but up here it sure does run fine even at 10k it will go faster than I am willing to go up those roads. Surely there is some hp loss due to the less dense air turbo or not but your truck will run fine and any loss will be small.

 

[goodwid]

I took a trip last fall pulling the T. T. (6K) over the rockies. Not a bit of trouble and got really good milage (Approx 2 x's better than my 5. 9 gasser the year before and I got passed all the time even by semi's).



I had to down shift a couple of times going up some step grades and spun the Turbo a little to quick and she let me know... . so watch out for that!



Safe Driving!

 

[JNutter]

I was thinking about this subject last week.



Here's my theory:



The waste gate opens at about 24 psi on a stock truck (I got my gauges installed last week). That should be 24 psi + whatever ambient pressure is. Total absolute pressure should be around 38. 7 psi (14. 7 + 24) at full throttle at sea level.



At sea level ambient air pressure is about 14. 7 psi, and I'm pretty sure you lose about 7% per 1000 ft of altitude gain. Someone please correct me if that is wrong. That works out to about 7. 1 psi of ambient pressure at 10,000 ft. That 7. 1 + the 24 psi from the turbo equals 31. 1 psi, or about 80% of the pressure available at sea level.



80% doesn't sound that good, until you realize that a gas engine is only making 48% of it's sea level power when it's at 10,000 ft.



You wouldn't have to try to hard to convince me that the power of a diesel doesn't fall off at the same rate as the air pressure, becuase diesels always have excess air. Actual power loss may well be less than the 20% that I calculated.



Am I way off base with this theory, or does it make sense?

 

[Gonzo 1066]

The math and theory sound good to me. But I think you will find that ther is NO LOSS OF POWER TO 9,000' and very little up to 10,000'. This is what Cummins has been advertising for years on the Industrial 5. 9s The little Holset is a great compensator for thin air. IMHO

 

[Forrest Nearing]

Originally posted by Gonzo 1066

The math and theory sound good to me. But I think you will find that ther is NO LOSS OF POWER TO 9,000' and very little up to 10,000'. This is what Cummins has been advertising for years on the Industrial 5. 9s The little Holset is a great compensator for thin air. IMHO

at stock power/boost levels, this is true... it will take longer for the turbo to spool up, but the truck will pretty much run the same power levels...



but, when you've got the thing turned up and you're getting closer to the edge of the compressor's efficiency range, there'll be a considerable difference in performance... nothing like an NA engine, but noticable.



Forrest