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Altitude and Rx-8?

Old 07-15-2005, 04:08 AM
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Altitude and Rx-8?

Hi!

I live in New Mexico 6500 feet above sea level. I am thinking of getting an RX-8. Will high altitude give me problems with the car? Will it lose too much power?

Csaba
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Old 07-15-2005, 06:48 AM
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Get it..

Greetings, faffy. Nothing to worry about, pal. In fact, we're blessed with one of the better locations to have an RX-8... driving thru the mountains is such a blast.

:D ohh, and with that wonderful news that the State Police are having budget problems due to increased fuel costs...they don't bother chasing us anymore! hee-hee! J/K!!!!
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Old 07-15-2005, 09:18 AM
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Faffy, I live near Boulder, Colorado (7000 feet) and have not had any problems with my 8. It just turned a year old a few days ago, and it runs perfectly!
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Old 07-15-2005, 03:56 PM
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Thank you for the response. It is good to know that you don't have any problems. I guess it is also true during winter when it is really cold up there.

Csaba
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Old 07-16-2005, 09:19 AM
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I passed thru Cloudcroft (about 9000 feet) a couple of weeks ago. Slight power loss is apparent on steep climbs at that altitude, like with any normally aspirated engine, but no problems at all with the RX-8.

BTW, there's a fantastic mountain road east of Silver City (highway 152). Excellent pavement, highly twisty, so scenic it's hard to pay proper attention to the road. I stopped several times just to look around (and rest my arms, lol).

Central and northern NM is so beautiful I'm tempted to retire there. Yeah, I gotta go back in the wintertime so I remember how cold it is!
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Old 07-17-2005, 12:05 AM
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Csaba:

My Dear Wife bought hers in South Carolina 8 months before moving here to 8,200' in Colorado. Almost all of our driving is between 7 & 12,000'. We noticed that it does seem to suffer a bit more power loss due to altitude than other cars. Our Miatas for example, with roughly equivalent mass/torque ratios, feel like the're down maybe 15% or less. The 8 is surely down more than 20. My dumb-**** old Jeep, which was slightly slower than the 8 at sea-level is now a tick quicker. This is all just butt-dyno guesswork.

The RX-8 has worked quite well in winter, other than an odd idle fluctuation on startup when it's colder than about 10 below (which is pretty dang often up here). With Blizzaks, it's a veritable rocketship in snow, and the Jeep doesn't even come out 'till the white stuff is over a foot deep.

}}}}

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Old 07-17-2005, 12:31 AM
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I'm sitting here at 5500' as I type. I don't have any problems with it at all. The highest elevation I have driven it is about 8900', again no problems, no noticable reduction in power. I was running 3rd gear most of the time at around 6k rpms uphill through a great twistie run. I also haven't had any problems with it in the cold. I never changed the tires, so I parked it quite a bit this past winter. On Monday the 18th, I will have had it for a year. Total problems = 0 and I am averaging 19+ mpg, with very little highway driving.
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Old 07-17-2005, 08:03 PM
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I also live in New Mexico - Corrales, near Albuquerque and like NMShinka have experienced no issue with the altitude and I too love the mountain roads NMShinka is talking about.

I did take the 8 once to 14,100 feet and aside from the fact it didn't seem to want to start - took about 5 seconds of cranking to start that altitude - it didn't seem to bother it much. Of course like any vehicle you lose some horsepower with altitude - about 2% per thousand as a nice round number.

Now in its (the 8) defense there have been a few times when it took a bit more cranking to start at 5000 feet. I just decided not to conduct any testing while at 14,000 feet to see if the long crank time was altitude related...

Where in New Mexico are you? We try to get NM 8 owners together every couple of months and we would love to have you join us.
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Old 07-17-2005, 11:09 PM
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Well I guess it's about time I chime in on this one... I've had my 8 over Trail Ridge Road in Rocky Mountain National Park, (elevation 12,000'+); several times - (due to size restrictions, I can't post the photo of my 8 at the top - PM me your email and I'll send it; the photo clearly shows the elevation sign). I drive over Cameron Pass, (10,200'), in the Poudre Canyon at least once a month in the months when weather permits. I and my 8 currently reside at an elevation of 7200', (give or take 65' according to the ol' GPS :D ).
I've gone the other way too; have driven to St. Louis & San Antonio with no problems.
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Old 07-19-2005, 08:39 AM
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I think a better question is: "Will LOW altitude give problems with the 8? What with all that flat, boring, land and all!!"
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Old 07-19-2005, 02:54 PM
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Excellent point MadDog!! However, I think we already know the answer to that question is yes! Not so much for the car as for the driver.
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Old 07-19-2005, 05:37 PM
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Thankfully enough, on my recent trip to San Antonio, I drove across Texas at night in both directions. I'm convinced that's the only way to travel across barren, flat $#!thole places like that; oh, yea - and as fast as possible. :D
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Old 07-20-2005, 10:27 PM
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it's all altitude
 
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My trip over to Scottsdale and back was via Quemado, Showlow and Payson and NO problemas at all. Even survived that miserable heat in the Valley of the blistering Sun; although I worried at times about smoke inhalation from all the fires. Even with some extra weight in the trunk and my lead foot (averaged 80 mph) I still got over 20 mpg. I luv this car....just hope that stealth mod I installed keeps working!! hee-hee!
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Old 07-20-2005, 11:58 PM
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Well of course it CAN go to high altitude with no significant problem. Heck, my old VW van could climb Pikes Peak like nobody's bidness, passing tourists along the way. Truth is, an RX-8 will lose a LOT of power above about 7,000'. All internal combustion engines do this of course, but the 8 seems particularly vulnerable, perhaps because of its already rich mixture.

Mad Dawg:

Lower than here = boring? Ever try, say US 129 (aka The Dragon) in western NC? Or maybe US 276 over Caesar’s Head, or SC 178 through Rocky Bottom, or just about any other road in that region? Shoot, our good "sports car roads" in the Rockies are much like the goldang Interstates in the Southern Appalachians!

}}}}
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Old 07-21-2005, 07:28 AM
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Originally Posted by Foureagles
Well of course it CAN go to high altitude with no significant problem. Heck, my old VW van could climb Pikes Peak like nobody's bidness, passing tourists along the way. Truth is, an RX-8 will lose a LOT of power above about 7,000'.
Really? I & my baby live and play @ 7200', (Laramie, WY). To get out of the valley here, every road takes at least 1000' in elevation rise. I travel out of town pretty regularly, and only when I went over Trail Ridge did I notice a very slight dip in power. :D
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Old 07-22-2005, 03:19 AM
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I'm not saying that jumping above 7,000' suddenly turns an RX-8 into a diesel Vanagon, but that this car does seem to drop power with altitude more precipitously than others in my experience. Let's look at a bit of what Ma Nature imposes.

Oxygen content drops at something like 4.5% per 1000' of elevation gain. Generally, just generally, an internal combustion engine loses power relative to that change in O2 availability. Depending on state and sophistication of tune, some fare better than others, but not by much unless you're talking carburetors or superchargers.

Say you have maybe 240 horses at sea level. By the time you reach 7,000' you might expect to drop 75 wheezing ponies (7*.045*240). To me, my 125 HP (at sea level) Miata feels very much like a 2,000 lb, 85 HP car at 7,000' -- maybe a bit better. Likewise, my old hotrod Jeep seems to have misplaced nigh-on a hundred horses in the move. Our RX-8, on the other hand, feels much more like it puts out something like 140 HP rather than the expected 165. This is a noticeable difference in a 3,000 lb car, and I think at least somewhat relevant to faffy's original question.

Why does the 8 behave this way in the high country? Beats the hellouta me! My uneducated guess is that its ECU tends toward conservative mixture richness, which makes it more vulnerable to a loss of O2. Heck, up here in the high country, air molecules are far enough apart that we can whiz between 'em on sticky tars, and easily justify their absence from sticky barstools, which is all I'm really doing now.!

}}}}

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Old 12-11-2005, 11:56 AM
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Oxygen depleted

"Conventional wisdom" is to subtract 10% of your horsepower at 3000 feet, and another 10% for each 1000 feet thereafter.

However, this is for piston engines. I believe rotaries don't have the same volumetric efficiencies. Rotary God or MazdaManic could probably shed some light on this...

Get a turbo. It's a great altitude-equalizer!
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Old 12-12-2005, 03:42 PM
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Originally Posted by JoeMamma
"Conventional wisdom" is to subtract 10% of your horsepower at 3000 feet, and another 10% for each 1000 feet thereafter.

However, this is for piston engines. I believe rotaries don't have the same volumetric efficiencies. Rotary God or MazdaManic could probably shed some light on this...

Get a turbo. It's a great altitude-equalizer!
When I visit my parents who live in the mountains at 7,000 ft does that mean my engine has half the horsepower than at sea level?

I thought 20% N/A 9% FI are the approx. losses for 1 mile above MSL.

I guess FI is my only choice.
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Old 12-14-2005, 01:39 PM
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Haha! Yes, you loose rediculous amounts of power up here! BEFORE my turbo my UNcorrected dyno was about 136HP!! WOO! Corrected, it was 168HP. still nothing to crow about.

the turbo will more than correct for this. Infact, a car at high altitude will gain more HP than a car at low altitude for the same boost.
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Old 01-26-2006, 12:26 AM
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Originally Posted by MadDog
...
the turbo will more than correct for this. Infact, a car at high altitude will gain more HP than a car at low altitude for the same boost.
Uh...could you explain that one? I got a brain cramp trying to figure out why.

(...you owe me two Motrins...pay up...)
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Old 01-26-2006, 12:36 AM
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Originally Posted by Former A4'er
When I visit my parents who live in the mountains at 7,000 ft does that mean my engine has half the horsepower than at sea level?

I thought 20% N/A 9% FI are the approx. losses for 1 mile above MSL.

I guess FI is my only choice.
Sorry, but it's pretty dang close to 30% knock in Denver. For those of us acclimated to driving in high altitude it's a major kick to take our vehicles down to at-or-near sea. I trailered my Valkyrie to Phoenix (1400 ASL?) to see my parents, and got air in second gear! That just plain doesn't happen up here.
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Old 01-26-2006, 12:25 PM
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Originally Posted by JoeMamma
Uh...could you explain that one? I got a brain cramp trying to figure out why.

(...you owe me two Motrins...pay up...)
Judging by the brain in your avatar, you need only about 1/4 of a motrin!

Lets say at 6kft the ambient pressure is 11psi. At sea level ~15psi.

The turbo increase pressure relative to ambient. If I'm running at 8psi, its 8psi above ambient. So, at 6kft, the intake pressure under boost is 19 psi, at sea level 23psi. The gain at altitude is 73%, at sea level its 53%.
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Old 01-26-2006, 01:07 PM
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Originally Posted by MadDog
Judging by the brain in your avatar, you need only about 1/4 of a motrin!

Lets say at 6kft the ambient pressure is 11psi. At sea level ~15psi.

The turbo increase pressure relative to ambient. If I'm running at 8psi, its 8psi above ambient. So, at 6kft, the intake pressure under boost is 19 psi, at sea level 23psi. The gain at altitude is 73%, at sea level its 53%.
Ow! Stop it!! Ow! Stop it!! Ow! Stop it!! Ow! Stop it!! Ow! Stop it!!

I get it...
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