I know that turbos help and I hear that diesels do not wheeze out as bad as gassers, but am interested in knowlegeable opinions on what % I am losing at say for instance 5,000, 8,000, 10,000 ft.
Another difference I see is with EGTs...They go pretty crazy here at 8-10,000 ft.!

 

i know my egts were much higher crossing the rockies towing the trailer, but that was with the stock turbo.

 

With the turbo I doubt if you are losing much up to about 10,000 feet ASL. Mine lives at an altitude of 6,000 feet and occasionally goes from sea level to just under 10,000 feet ASL. Have not towed above 6,000 feet, but empty, I can't feel any difference. The only difference I see is that at altitude it tends to smoke a little at WOT.

 

I noticed that going down to 2500 ft from my normal 6500 ft my turbo spooled like the stocker and I had a hard time getting my egts hot on settings where I usually have no trouble burying the gauge. My truck felt stronger and my boost was up 5-10 psi. My truck liked the lower elevation.

 

There is an article in this months issue of Diesel Power Magazine discussing this very issue. Turbos may have work harder in high elevations, but there shouldn't be much of a difference. If you're making 20 PSI at sea level you'll still be making 20 PSI at higher elevations. What I mean is 20 PSI is 20 PSI no mater what.

 

I am not a engineer so pardon me for any ignorance communicated. I live at 6400alt. My lungs have the same capacity at any elevation, I think. However when I climb a hill while hunting in NM mountains I am pulling in air and filling my lungs to capacity but am short on oxygen anyway. When I climb a hill at lower elevations back in MD I am not as lacking on oxygen even though the pressure build up has my lungs fully expanded. So 20psi on mt everest is the same as 20psi at sea level? Does oxygen rich enviroments feed better

 

Our lungs can only draw what air is available; air is not being forced in to them, just "drawn". In order to more oxgen into the lungs they must work harder, ie pump faster. But the lack of air/oxgen will still be noticed. Same for a naturally aspriated engine. It can only "draw" the available air into it. So it must work harder to run somewhat properly.

In thinner air, a turbo or a supercharger will take the available air and COMPRESS that to make the 20 PSI or what ever PSI. It just has to work harder in thinner air then in does in denser air. Basiclly we're talking about "forced induction". So, yes, I believe 20 PSI produced by a turbo or a supercharger is the same whether at sea level or high altitude.

Edit: Heck I'm probably wrong. I'm not an engineer either. But I do read, read and read. And I've built and run naturally aspirated and supercharged engines at different elevations.

 

You are right on the money JPR. You are too Sweeney. 20psi read from a mechanical gauge at sea level is 20psi at elevation and contains the same amount of air molecules. However, a larger volume of outside air must be drawn into a turbo charger at elevation to create the same amount of psi as sea level. I think this is what you mean by working harder JPR. I would think a turbo would spool faster at lower elevations, but I'm not entirely sure how they operate and what controls the amount of boost they generate. As far as I know, turbos build boost up until they reach a pressure determined by the waste gate.

When your lungs fill with air up in the mountains, they are drawing in the same volume of air as the lower elevations, but the difference is that there are less oxygen molecules in that volume of air. In other words, the oxygen is less dense at higher elevations.

Radiators of any sort would not cool as efficiently at elevation because there are less molecules of air to transfer heat to.

Other interesting facts about elevation are that things weigh ever so slightly less than at sea level. Also, there is less drag from wind resistance.

 

Very interesting, I am learning from you fellows today. SO, if oxygen density is less would that mean that 20psi in the mountains does not cool as well as a more oxygen dense 20 psi at sea level. Maybe I am still a little thick(due to lack of oxygen up here ). Heck, Ive already come to terms with that fact.

 

I live in Colorado and live @ 6500ft, when i go up to the mountians 9000-10000ft my truck doesn't run any different. I have not pulled anything at high elevations. I have lived here my whole life and the elevation does not effect me unless i get over 10000ft, maybe our trucks are like that, they get used to the elevation (just a thought). One thing i can tell you is my gas truck (Titan) was a different truck at higher elevations, it was a slow!!!

 

Yeah, any naturally aspirated motor will not run the same at higher elevations. You can re-jet or re-calibrate lean out the fuel amount, but the engine can only draw so much air................... Gotta just love our turbo induction Cummins.....................

 

A naturally inspired piston engine in an airplane can't get much higher than 12,500 ft. But put a turbo on it and it can basically double that altitude.

 

I live at 6300' here and routinely get up to 10k and above. Running empty I do not notice much difference except more smoke and higher egts and more lag when going slow . Towing a trailer up that high I still dont have a problem power wise but the egt issue is worse and the smoke is even more pronounced due to the increased turbo lag. When my truck has been at sea level I was quite suprised at how much less lag there was, lower smoke and my egts were much easier to control when towing heavy.

Now I am no engineer but did sleep at holiday inn the other night . So take this for what its worth(which by the way is very little). 20 psi at altitude is not quite the same as 20 psi at sea level. The pressure at sea level that reads zero on your gauge is higher to begin with than it is at altitude. At sea level the atmospheric pressure is like 14.2 or something close to that. Here it is 12.5 or something close due to the fact that the air is less dense(ie less o2)the higher the altitude. Your boost gauge is comparing the ambient pressure or whatever that technical term is not the pressure at sea level(unless you are at sea level). So at sea level your engine is really seeing 14.2 psi at idle or zero boost condition. At altitude here for example it is 12.5 at idle or zero boost condition. While that is only about a 1.7 psi difference that equates to approx 12%. So there is approx 12% less 02 at altitude regardless of boost pressure compared to the same boost pressure at sea level. A good example of this when you are here or anywhere in the mountains at altitude go in the local store and check out a bag of potato chips or can of pringles. If they were packaged at sea level the bag will be really puffed out ready to explode or the lid may be getting ready to blow off the pringles and when you open it you will hear the air pop or rush out of the bag or can. They didnt blow the air in there it is just the pressure differential from where it was packed to where it is now. Even scuba diving here you have to make allowances for the increased altitude for no reason other than the lower air pressure as the dive tables are made for diving at sea level.
That being said I have never had a problem power wise but it is noticeable in some ways ie lag and its brothers smoke and egts. I have had difficulty starting at 12k after sitting overnight unplugged in below zero temps but never at home at even colder temps.

 

BarryG seems to confirm my theories on performance. I think that comment was correct about boost because a waste gate would be affected by outside atmospheric pressure. After more thought I would think a boost gauge would have to be calibrated to the elevation you are at and then you would find you are getting less boost.

 

That's not quite right, think of it this way...

An air compressor working at 10k feet would need 12% more strokes to get 20 psi than one at sea level.

But once both tanks are filled to 20psi, the number of molecules in them is the same at a given temperature, which means it has the same oxygen content and power making ability. The tanks of air are equal in every way no matter where they were compressed.

It takes more work to compress air at 10k feet to 20psi than that at sea level (think of the compressor running longer, it uses more energy).

Higher EGT's are a result of having to "work harder" to get the same amount of boost at higher altitudes (whether its a turbo or a supercharger, it still creates power losses) this means there will be a power loss in forced induction vehicles. If I remember right, the NHRA correction factors for all forced induction engines at altitude are 50% that of naturally aspirated vehicles. That is not an exact figure and it differs for a turbo vs supercharged engine, but it's probably closer to reality.