High elevation observations

[Vaughn MacKenzie]

Last weekend I took a trip into central Oregon to go snowboarding and stayed at a place around 4000ft. Although I don't consider that to be very high altitude, it does have a slight (and noticeable) affect on how my Cummins behaves compared to the 300ft elevation I live at:

1) Starts are smooth and much quieter, not the usual sharp clatter at the moment of lightoff.

2) Considerably less combustion noise at idle when cold. It is normal when warmed up.

3) Wait to start light only stays on 2-3 seconds when parked above 5000 feet for 6+ hours with temps in the low 20s. I noticed this happens every time I go up in the mountains, but it lights right off anyway, with barely any smoke. At home in warmer temps, the WTS light stays on MUCH longer when parked outside all day. Never have figured that one out.

4) It takes only 4-5psi boost to maintain 70mph cruise, compared to 5-6psi at sea level. Less air drag. I noticed last summer blasting along at 80mph @ 4000 feet I still got 21mpg in Nevada (not possible at home!).

Anyone else experience what I've seen? I like the way my truck runs and starts at higher elevations, it is a happy camper when riding in high places #ad


Vaughn
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'01 QC SB 2wd, ETH 6-speed, 3. 54 lsd, RV inj. , 3/8" fuel lines, straightpiped, Amsoil air filter, PS boost module


[This message has been edited by Vaughn MacKenzie (edited 02-27-2001). ]

 

[joesoot]

I could feel a signifigant difference(inversely), seat of my pants, going from 6600 to 4700 in my old '90. Dropping 1900 ft. gave me 1 to 2 psi more boost, less smoke and roughly 1 MPG
more on the highway. I really experienced the opposite of what you did.

[This message has been edited by joesoot (edited 02-27-2001). ]

 

[Diesel Freak]

I was in cheyenne, and it was real easy to hit 1000F in EGT (unloaded), smoked more than at sea level also. remember that boost gages reference to atmosphere, so indicated boost of 5 psi is less at 8000ft than 0ft. This would be easy to see with a gage that had a constant reference pressure.

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http://www.mudrunner.sites.cc

 

[John]

Originally posted by Vaughn MacKenzie:
Last weekend I took a trip into central Oregon to go snowboarding and stayed at a place around 4000ft. Although I don't consider that to be very high altitude, it does have a slight (and noticeable) affect on how my Cummins behaves compared to the 300ft elevation I live at:

1) Starts are smooth and much quieter, not the usual sharp clatter at the moment of lightoff.

Hey Vaughn, are you sure that your ears had popped once you reached the high elevation? #ad
Maybe the engine wasn't really quieter. Hmmm..... I've got it, someone installed a muffler on your Ram when you weren't looking. #ad


Fire away at will buddy. #ad

 

[jkern]

i took a trip to colorado last year in mine up pikes peak and all around the ski towns... average elevation about 10,000 ft. my truck ran like crap!!! smoked like crazy, would idle ok, but would not accelerate very well at all. one morning it was about -10*F, still at 10k ft, and it took 15 minutes of fooling around and hoping the batteries were gonna hold out before it finally stayed running. the WTS light would stay on for over a minute and when i would crank, it would only hit on on cylinder and then stall. however i did notice that it was much quiter when running that high. i did not have boost or EGT gauges then and the truck was totally stock, except for tires and the bumper, so i really don't know numbers... but i couldn't wait to get down a few thousand feet so it would at least run half decent again!!!


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Jeremy Kern
1999 2500HD 4x4 QC,SB, ISB, 5spd, 3. 54LSD, 33x12. 50 cooper STT's Denver off-road bumper with Ramsey RE12k, PIAA series 520 lights, Rancho RS9000's, heavy ft. springs, JVD Torque Enhancer, DiPricol boost and pyro gauges, and a bunch of other little things! www.geocities.com/phrn30 for pics!

 

[Vaughn MacKenzie]

John, I'll take a look and see if someone stuck a muffler on my rig when I wasn't looking #ad
LOL

I get it. . . the thin air doesn't transmit the combustion clatter to my ears as readily as the denser stuff at sea level. That must be it #ad


I did notice about 50-75F higher EGTs when climbing hills.

Vaughn

 

[John]

..... probably had a dead Duramax in tow huh? #ad

 

[PAYCHECK]

Hey guy's,i live in Wyoming i don't have any problems. my truck starts every morning even if not plugged in,whether 25 below or above. i do get about 1 to 1. 5 mpg better when i head to the flatlander's country! don't notice any difference in sound. all the other parameter's seem about the same.

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01 SLT+ 4X4,Q-CAB,SWB,3. 54,5spd,e-brake,tow package,camper special,all black,all leather,fully loaded,htd power mirrors,htd seats,full rhino lining bed and rocker panels,265/85r16 BFG ATs,nerf bars,everthing black,still stock engine.

 

[Bad340fish]

Correct if if i am wrong but doesn't a boost guage read PSI?? So i would assume that 30psi at 10000 feet is the same as 30psi at 700 feet?? Except the turbo is going to have to work harder to get to that 30psi. Am i on the right track here??
Clark

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Clark
1999 2500 QC SB 5spd Flowmaster 3 chamber, K&N Re-0880
1968 Barracuda Formula S Viper Blue 11. 98@112

NHRA member for life

 

[illflem]

Clark,what it is is that 0 on all pressure gauges is assuming sea level. One metric system for measuring pressure is atmospheres,14. 74(?) psi= 0 atmospheres =air pressure at sea level. As you rise in elevation the pressure gauge is no longer right,it should read lower than 0 but doesn't, used to know the formula,but... You are still on the right track though,as you rise in elevation the air is less dense(thinner)the turbo has too spin more to deliver the same amount of air as it would at sea level,so you would need more boost to equal the same power at high elevation as you would at sea level. You have to imagine a cubic foot of air getting bigger as you rise. That's what I've noticed at higher elevations,my boost is running higher to maintain the same speed than it would down in the lowlands assuming no hills.

 

[GSchlegel]

Bad340fish
I believe our boost gages read "boost" or increase in preasure over ambient, kind of a presure differential. 30 lbs. of boost at 10,000' is different then 30 lbs. of boost at sea level. In aircraft we read an absolute value called manifold presure (inches of mercury). This allows us to figure hp by checking MP (manifold presure) vs. RPM. We fly by power settings, as an example most non turbo aircraft engines us 25 square (2500 RPM x 25 in. MP) as a cruise climb setting. In a non turbo you slowly advance the throttle to maintain MP as the altitude increases.

Sorry about the long post, but I got to talk about 2 of my favorite subjects, Flying and CTD.

Gene

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'96' 3500, 5-speed, 3. 54 LSD, Ext. Cab, 180,000 plus miles, relay controlled back-up alarm and rear facing fog lights, K&N air filter, TST #11 plate . 010" forward of stock, AFC spring kit, lost cat, SPA digital EGT and boost gauge,20 yr. old marine air horns, bed liner, 5" monster exhaust tip, Geno's manual trans. filter.

 

[Bad340fish]

Thanks Illflem and Gene for clearing that up for me... i think #ad

Clark

 

[David_VT]

I did the 'road to the sun' in Glacier national park last summer. Ram sure kicked butt compared to my old gas 'burban during it's '91 trip.