M Theory: Code Red

I am trying to shed some light on something I haven't noticed before.. over the break I drove to New Mexico from Los Angeles. On my way there, I noticed that my 8 was having trouble staying up to speed when climbing any sort of hill/mountain on the freeway. I could be in 6th at 85mph on cruise control and my rpms would be dropping as well as my speed. I would have to downshift just to keep my speed/rpms up. When I arrived I checked my air filter and it was dirty and filled with junk so I replaced it hoping that my power would come back and the car could breathe once again. It seemed to do the trick at the time. However on the way home, once I was below about 3000 feet elevation my power started to return and it has fully returned now that I am relatively back at sea level. The last time my car crossed state lines was 60k miles ago when I purchased it in Ohio and I definitely never noticed losing power when I gained elevation.

So, here's my question: does the RX8 just not get enough air to keep it's normal low end power at higher elevations or is it simply that my car is getting old and can't run like it used to? I'm almost to 100k miles, is it just that simple? I was always under the impression (and still am) that the rotary motor doesn't lose it's power as it ages.

Does anyone that lives in a high altitude location notice an increase in power if they drive to sea level and visa versa?

Thanks and happy new year everyone!

8 Maniac

iTrader: (1)

To answer your general question: Yes, cars have less power at higher elevation. The air is thinner and the engine can't get as much oxygen as it can at lower elevations.

M Theory: Code Red

That's not really my general question... I understand that higher elevation = less oxygen. I mean do 8 owners that live in higher elevations notice the change when they come to sea level? It was a pretty drastic change and that's why I am curious.

9krpmrx8

iTrader: (46)

Ther is an increased load on the engine when you go up a hill and the RX-8 is not great on steep inclines (unless you are turbo ). Whether you are experiencing power loss depends.

DarthRX8

I bought my 8 in CO and owned it there for 3 years. During that time I bought an AP from Jeff and went through his tuning service. While doing my logs I never saw my MAF go above 200g/s.

I moved from CO to Germany and had to drive my 8 to CA; during the drive I did some data logging and once I got to AZ noticed that my 8 was pulling much harder. After reviewing the data I noticed that my MAF was ~230g/s. My AFRs were also a little leaner as such.

I live in D.C. now and appreciate my 8 at sea level so much more than at 6000ft ASL. Its like a modification...

Bladecutter

Yes, it is the same question, just worded differently.

Engines lose between 16 and 20% power at 5k feet in altitude.
When you climb up those big hills to get to 5k feet, your car will slowly lose power the higher up you get. When you go back down the hill, your car slowly gains in power.

So, an engine that makes 200 hp at sea level will only have 160 hp at 5k feet.
40 hp is a very noticeable drop/increase in power.

There's also the fact that your engine has nearly 100k miles on it, and I'm not quite sure why you got that idea from. These engines are famous for losing compression in under 100k miles.

You're most likely low on compression, also, so you might have even less hp than if your engine was freshly built, with perfectly gapped seals on the rotors.

BC.

04RX8man

I doubt elevation change would be a noticeable power drop.

Bladecutter

Dude, I just did a drive yesterday.
I started out at 5300 feet in my Home town of Arvada, drove up to the Peak to Peak Highway, which brings me through Nederland, CO (over 8200 feet) and Ward, CO (9500 feet).

In third gear, at WOT, there's a big difference in power, climbing from 3k rpms to 8k rpms at home, vs Ward.

And I can go to roads with even higher altitudes, if I felt like it.

You live in Maryland, where there aren't altitude changes like there are here.
The highest point in your entire state is under 3400 feet.
I climbed higher than your entire state going from one city to another.

BC.

RadRedR3

...and you'd be wrong. *shrugs*

HiFlite999

iTrader: (2)

You don't fly airplanes.

In outer space, there's no oxygen, so no power.

At sea level, there's ~30 inches Hg of pressure. At 18,000 feet ~15", so half the oxygen per cc of air, so half the power one has at sea level. The available oxygen falls off at roughly 1" per thousand feet for under 10,000 feet. So you lose ~1/15th of your maximum horsepower per thousand feet of altitude.

Turbocharging can restore this loss (up to a point).

monchie

That's why rx8 owners don't live in higher elevations...

M Theory: Code Red

Thanks for all the info guys. I figured altitude with have some sort of affect on the cars performance, but had no idead how much.

DarthRX8

I shot you a quick email, but did not stay in the area long.

Wish I could have stayed longer, but I had to get to DC and start my new job

Next time you come to our nations capital drop me a line; I'll give you a tour of the Pentagon and all its wonders!

Tell me about it! When I got out of the mountains it was like a totally different car....

Sorry but I can vouch that it is and my datalogs support this fact! ~30 g/s of air more to be precise!

HiFlite999

iTrader: (2)

On the bright side, your mpg's will be better! (Ignoring the effects of getting up there.)

For any a given hp output, the throttle plate will be more open up high than at sea level, so pumping losses will be lower. Drag at a given speed is also lower.