Altitude and engines
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Tuned
Joined: Dec 2007
Posts: 393
Likes: 0
From: Santa Clara, CA
Altitude and engines
I just past several days in Colorado and just have a quick question: how much does elevation change compromise engine performance?
Since there is less oxygen the engine should suffer, right?
Any differences between a N/A, Turbo or S/C engines? what about diesels?
Thanks
Since there is less oxygen the engine should suffer, right?
Any differences between a N/A, Turbo or S/C engines? what about diesels?
Thanks
Lead Driver
Joined: Oct 2004
Posts: 8,062
Likes: 35
From: Central Oregon
Got to be some differant in the way they run, the higher they go. I know my Bronco, with a carbed 460, does not like going from Prineville Or to Portland Oregon. It wants to run rough each way you go with her. It spends the summer in Portland and winters in Prineville, there is about 2500-3000 feet defferance.
Postmaster
Joined: Mar 2001
Posts: 4,968
Likes: 3
From: So Cal
In general the higher the altitude, the more power you lose. How much you feel it depends on your truck, what you are hauling and your buttometer.
Not enough really high roads around me but I recall years ago, my 1800cc Datsun mini truck barely had any power going over 7,000 feet on Angeles Crest. Could definitely feel the difference.
I hear going thru passes in colorado are a trial for a heavilly loaded truck.
I forget, so wild wild recollection, I think you lose 5 - 10% power for every 1,000 feet above sea level. ie 90% at 1000, 81% at 2000, 72% at 3,000 etc. Seems a bit high so probably a smaller percentage. But definitely feelable.
Just my opinion,
Jim Henderson
Not enough really high roads around me but I recall years ago, my 1800cc Datsun mini truck barely had any power going over 7,000 feet on Angeles Crest. Could definitely feel the difference.
I hear going thru passes in colorado are a trial for a heavilly loaded truck.
I forget, so wild wild recollection, I think you lose 5 - 10% power for every 1,000 feet above sea level. ie 90% at 1000, 81% at 2000, 72% at 3,000 etc. Seems a bit high so probably a smaller percentage. But definitely feelable.
Just my opinion,
Jim Henderson
Postmaster
Joined: Nov 2006
Posts: 4,517
Likes: 3
From: SE Wyoming
I can't remember the numbers off the top of my head, forced induction isn't effected near as much as the NA engines. I can feel a huge difference just dropping down to 4K feet from 6K-7K. I've only driven near sea level a few times and couldn't believe the power I had. I was lighting up my tires in Las Vegas constantly in my F150, not as easy to do here. We figure our tractors that are 85-90hp NA are equivalent to the 65hp Turbo'd ones at around7K', so that's a 25-30% loss over sea level.
Lead Driver
Joined: Jul 2007
Posts: 7,868
Likes: 9
From: Rhode Island
The power loss for N/A engines is 3-5% for every 1000 feet increase in altitude. Supercharged engines will have similar losses, but if you change the pulley sizes as you go up, you can compensate and still have the same power.
Turbo charged engines will pretty much automatically compensate and will have almost no losses.
Turbo charged engines will pretty much automatically compensate and will have almost no losses.
Post Fiend
Joined: Jun 2001
Posts: 5,228
Likes: 5
From: Running Springs CA
3% per 1000ft in standard conditions, which is 15C temperature and 29.92 in Hg barometric pressure at sea level. Unfortunately in Summer, it gets way hotter than that, so the loss is greater. Here at over 6000ft it has been over 80F every day this month.
The reason carbs lo0se more power than FI, is that the mixture becomes way too rich and falls off the maximum power range. EFI is constantly adjusted via the MAF or MAP sensor. Even 1980's "feedback" carbs with an O2 sensor only change the idle jet.
Having said that, some engines just do better than others for no obvious reason. The sequential multiport MAF system in the 1994 5.0 was a total dog above 4000ft. Compression was well within spec and everything checked out, but it needed second gear to get up here, without a trailer or any big load in the back.
The 1988 Ranger, on the other hand, with the cruder bank-fired MAP system on the 2.9 didnt seem to care. The BMW and Toyota also had no problem, but both of them had about 10:1 compression, which is a big help.
Jim
The reason carbs lo0se more power than FI, is that the mixture becomes way too rich and falls off the maximum power range. EFI is constantly adjusted via the MAF or MAP sensor. Even 1980's "feedback" carbs with an O2 sensor only change the idle jet.
Having said that, some engines just do better than others for no obvious reason. The sequential multiport MAF system in the 1994 5.0 was a total dog above 4000ft. Compression was well within spec and everything checked out, but it needed second gear to get up here, without a trailer or any big load in the back.
The 1988 Ranger, on the other hand, with the cruder bank-fired MAP system on the 2.9 didnt seem to care. The BMW and Toyota also had no problem, but both of them had about 10:1 compression, which is a big help.
Jim
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Cargo Master
Joined: Apr 2003
Posts: 3,476
Likes: 224
From: Frequently frozen MN
Just an interesting little side note. Some FI systems used to read barometric pressure only on startup and full throttle. This caused severe problems for one owner -- as reported in an auto service trade mag.
Guy took off one day, and made a large altitude change -- possibly went up a mountain (I forget). Car ran like crap as he went up. Shut it off and looked around for a while. Came down and it started running like crap as he descended! He apparently could have cleared up the problem along the way by flooring it or restarting.
Hope they don't use that technique anymore.
Guy took off one day, and made a large altitude change -- possibly went up a mountain (I forget). Car ran like crap as he went up. Shut it off and looked around for a while. Came down and it started running like crap as he descended! He apparently could have cleared up the problem along the way by flooring it or restarting.
Hope they don't use that technique anymore.
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Post Fiend
Joined: Mar 2002
Posts: 19,402
Likes: 38
From: Bonita Springs FL
We have taken numerous trips with the Bronco from sea level to 8000+ feet in a day, and the difference is huge. I think the speed density EFI systems had a barometric pressure sensor that they use to calibrate the mixture, but there is a definite and very noticeable power loss.
One weekend in Flagstaff, AZ (sits at about 7000 ft) a few years ago, I noticed that about half of the vehicles on the road were turbodiesels. I couldn't figure it out at first, but then it dawned on me that turbocharged motors aren't as susceptible to power loss caused by elevation changes.
One weekend in Flagstaff, AZ (sits at about 7000 ft) a few years ago, I noticed that about half of the vehicles on the road were turbodiesels. I couldn't figure it out at first, but then it dawned on me that turbocharged motors aren't as susceptible to power loss caused by elevation changes.