[partyhardryan16]

Hey Guys. I just moved to Fort Collins, Colorado about 5400 ft up, from New York basically at sea level. I've only been on my 954 for about 5 minutes, but I definitly noticed a difference in power. Is this normal? Also, they only sell 91 octane up here and I had a little 93 octane left from the last fill up in NY before I trailored it out here. Please let me know if you guys know of any complications with this. I didnt think it would mess with the bike considering it is fuel injected. Any help is appreciated. THANKS!!

[ghbzorro]

Yeah, lower power at elevation is normal. You will lilkely find the gas mileage improves, too.

I'm not going to touch the octane issue (except to say tht if it was me I wouldn't worry about it).

[sb1000rr]

yeah no power at altitude is normal, no need to mess with it....

[BALDGONZO]

With mine the power loss is huge. I go from sea level to around 6000 ft. Every step of the way is noticeable above 2000 ft; but especially above 4000 ft.

[DUX]

I just read an article about a Range-Rover test high into the mountains on their new turbo diesel.

Different engine and much higher elevation, but if I remember correctly the guide told the reporter to expect to lose about 3% of the power for every 1000ft climbed.

[bladeracer]

You have less engine compression.
Your compression is a _ratio_ of the ambient pressure.
I don't recall the figures but at 5400ft ambient is probably down around 11.5psi compared to 14.5psi at sea level.
A 12:1 engine simply multiplies the ambient pressure so 12x14.5 is a lot higher pressure than 12x11.5.

[red08]

to put it bluntly ... higher altitude = less oxygen = less power.

[bladeracer]

This is true in as much as if you have only 80% of the air density/pressure then you also have 80% less O2 content in the combustion mix.
Even re-jetting for this though you're still going to have less compression.
I assume you can run significantly higher compression ratios at higher altitudes without detonation to bring the compression back up equivalent to sea level - 15:1 at 5000ft would bring you back to the 12:1 ratio. I've never lived anywhere where's there's mountains so can anybody confirm this?

[red08]

Originally Posted by bladeracer

This is true in as much as if you have only 80% of the air density/pressure then you also have 80% less O2 content in the combustion mix.
Even re-jetting for this though you're still going to have less compression.
I assume you can run significantly higher compression ratios at higher altitudes without detonation to bring the compression back up equivalent to sea level - 15:1 at 5000ft would bring you back to the 12:1 ratio. I've never lived anywhere where's there's mountains so can anybody confirm this?

I am no engineer but isn't it the oxygen that supports combustion and not the pressure? So theoretically if you had sea level pressure with the same low oxygen level of high altitude wouldn't you still have a decrease in power?

[bladeracer]

Of course.
The pressure merely determines the amount of power produced from the charge in the combustion chamber.

[08silvercbr]

Their gas should be oxygenated to compinsate for the higher altitude. Your gas mileage should improve also. My truck got 60-70 miles more out of a tank of gas in Arizona then here in Michigan.

[joema]

Originally Posted by partyhardryan16

Hey Guys. I just moved to Fort Collins, Colorado about 5400 ft up, from New York basically at sea level...I definitly noticed a difference in power. Is this normal? Also, they only sell 91 octane up here...

It's completely expected a normally aspirated engine will produce less hp at higher altitude.

The general rule of thumb is you lose 1% hp for ever 333 ft altitude gain. You also lose 1% hp for each 11F temperature increase, and lose more from humidity increase.

To pick a worst-case example, the hp difference between a low humidity 50F day in New York City vs a 90F humid day in Ft. Collins could be:

3.6% hp loss from increased temperature
3% hp loss from increased humidity
16.2% hp loss from higher altitude
================
22.8% total hp loss

IOW a bike producing 150 rear wheel hp on a cold, dry day at sea-level would only produce 115.8 hp on a hot, humid day at high altitude.

The effect is called "density altitude". There is little you can do to regain the lost hp except for forced induction.

Rejetting a carb will only minimize the loss to the above amount. It will not regain sea-level power or even approach that.

Most fuel injected engines have a barometric pressure sensor and will automatically reduce injected fuel to match the diminished oxygen level at high altitudes. Increasing engine compression ratio won't significantly help.

The engine must run at a certain air/fuel ratio to produce best power. There is simply less oxygen at higher altitudes, so the fuel must be reduced to maintain the same a/f ratio. Without this change the engine runs overly rich, and the loss is even greater.

Even with fueling changes, less fuel is burned per unit time, which means less power produced.

[bladeracer]

Originally Posted by joema

Increasing engine compression ratio won't significantly help.

Why not?
Two otherwise identical engines running the same perfect air/fuel ratio but one with 12:1 and the other with 9:1 compression ratios then the higher ratio engine will produce more power from the same air/fuel mix.

[joema]

Originally Posted by bladeracer

Why not?
Two otherwise identical engines running the same perfect air/fuel ratio but one with 12:1 and the other with 9:1 compression ratios then the higher ratio engine will produce more power from the same air/fuel mix.

The poster was asking what practical changes he could make to mitigate his 954's hp loss at high altitude. The simple answer is increasing his bike's compression ratio is not a practical solution for the magnitude of power loss he's experiencing.

There is a relationship between thermodynamic efficiency and compression ratio, such that a 1-point increase will produce an approximate 1% increase in thermodynamic efficiency: 7.2 What is the effect of Compression ratio?

However: his 954 is already running 11.5:1 compression ratio. You theoretically might increase this by 1 point to about 12.5:1 (the new CBR1000RR runs 12.3:1). It would require new engine components, and wouldn't be practical for him, but it theoretically could be done.

That increase might buy him 1-2% more hp. But (as shown above) he's probably down 20% in hp vs sea level. A 2% increase isn't nearly enough.

Also higher compression ratios also require higher octane fuel, which the poster already said was a problem. Hs new location has *lower* octane fuel.

So in addition to the cost of major internal engine mods, he couldn't run pump gas anymore.

If practicality, cost and engineering were no obstacles, there are various internal engine mods that could increase hp: increased displacement, higher compression ratio, different valve timing, increase redline, etc.

But none of those are addressing the core problem: reduced oxygen per unit volume at altitude. Rather they increase hp at both sea level and altitude.

The only long-term solution (on that bike) is forced induction. Nitrous injection might be a short-term solution.

[BALDGONZO]

bladeracer I agree with you most the time, but this time your explanation isn't quite right.

red08 was blunt and correct.

joema is spot on and should given extra kudos for taking the time and sharing his knowledge with all of us. Thanks joema!

[rokitt51]

Same thing happened to me when i moved from dallas to west tex. I couldnt find the problem til i checked the difference in altitudes. I think that im about to move to Tallahassee in a few months though. BRING ON THE POWER.

[93CB750]

higher altitude = less oxygen
same thing happens with car or any motorized vehicle, no brainer

i'm in laramie, wy at over 7200 ft., just be thankful ur not me lol

[partyhardryan16]

Wow guys thanks for all the info. Def helps. I used to be able to power wheelies up in first, now I may have trouble cluttching it up in second. I am not looking to do any expensive mods, I just wanted some feedback on the issue. Fortunately, the humidity is significantly lower up here rather than in NY and the temp. is usually a little lower. So, I may be gaining a few % of hp in those catagories. But, I cant believe I am losing about 15% because of the elevation. Thats nuts. Glad I dont have my 600 any more.

[MT929]

Originally Posted by 93CB750

higher altitude = less oxygen
same thing happens with car or any motorized vehicle, no brainer

i'm in laramie, wy at over 7200 ft., just be thankful ur not me lol

i am very happy i don't live in laramie....or any of wyoming....haha

[93CB750]

Originally Posted by MT929

i am very happy i don't live in laramie....or any of wyoming....haha

haha, i am originally from Denver CO but when I was like 7 my dad got transferred to WY and life has been crappy since . Wyoming isn't that bad, just everything is to far away and there aren't enough sport bikes around. everyone is just a grumpy harley rider.

[Redfiddyfo]

Go out and run a mile. you'll see how your bike feels.

Rick

[bladeracer]

Originally Posted by joema

The poster was asking what practical changes he could make to mitigate his 954's hp loss at high altitude. The simple answer is increasing his bike's compression ratio is not a practical solution for the magnitude of power loss he's experiencing.

There is a relationship between thermodynamic efficiency and compression ratio, such that a 1-point increase will produce an approximate 1% increase in thermodynamic efficiency: 7.2 What is the effect of Compression ratio?

However: his 954 is already running 11.5:1 compression ratio. You theoretically might increase this by 1 point to about 12.5:1 (the new CBR1000RR runs 12.3:1). It would require new engine components, and wouldn't be practical for him, but it theoretically could be done.

That increase might buy him 1-2% more hp. But (as shown above) he's probably down 20% in hp vs sea level. A 2% increase isn't nearly enough.

Also higher compression ratios also require higher octane fuel, which the poster already said was a problem. Hs new location has *lower* octane fuel.

So in addition to the cost of major internal engine mods, he couldn't run pump gas anymore.

If practicality, cost and engineering were no obstacles, there are various internal engine mods that could increase hp: increased displacement, higher compression ratio, different valve timing, increase redline, etc.

But none of those are addressing the core problem: reduced oxygen per unit volume at altitude. Rather they increase hp at both sea level and altitude.

The only long-term solution (on that bike) is forced induction. Nitrous injection might be a short-term solution.

I don't see the original poster asking anything at all about regaining his lost power. He merely asked for an explanation of where it went. I wasn't offering increased compression as an option. I was asking if it's possible to run a higher ratio than is possible as sea level due to the lower ambient pressure. I'd still be interested in an answer if anybody has one.
I took my GSXR750 from 11.8 to 13.05:1 without having to run higher octane fuel and it made significantly more than 2% more power.
I agree that increasing his compression ratio from 11.5 to 12.5 wouldn't be cost-effective which is why I asked about going to 15:1 instead as that should give roughly equivalent compression ratio as 12:1 at sea level.
Also, even forced induction via a turbo still only multiplies the ambient pressure doesn't it and probably require higher octane fuel?

[BALDGONZO]

Blade-- Your still beating your dead horse buddy. If he merely asked for an explanation of where it went---joema--- answered it.

Come on... Try something like a "flux capacitor" or something! 86MPH blah, blah, blah!

[bladeracer]

If you mean because nobody is going to answer the questions I've asked then I guess I am indeed :-)
I think I made a decent effort at explaining it myself although I concur that Joe did a better job. All I'm interested in now is answers to the questions I asked.
As I said, not having ever been around mountains this is not something I've been (or am ever likely to be) able to experiment with for my self.

[lanbrown]

No need to argue; have a beer and at high altitudes they work better too.

[bladeracer]

I wasn't aware anybody was arguing.
And I find life far too interesting to warp my view of it with alcohol :-)

[lanbrown]

Originally Posted by bladeracer

And I find life far too interesting to warp my view of it with alcohol :-)

You can have a Shirley Temple then.