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anybody care to take a guess how much power i lost going from 1000' to 6300' ? anybody know how much compression i lost ?

100hp honda wrote: anybody know how much compression i lost ?

Altitude has little to do with it, Barometric pressure does.

1. Find a local weather report, and get the barometric pressure forecast. It will be something like 29.92"

2. Go to this website: http://www.srh.noaa.gov/elp/wxcalc/pres ... vert.shtml

Enter the barometer reading into the conversion table to read out in PSI

3. Do the math, multiply the PSI by 10.5. ( The compression ratio on a CR500 is about 7:1.. However, this is a static number. Heat induced by the compresion action further expands the gas and makes the actual compression ratio about 10.5:1)

Here , in Aliso Viejo today....The Barometer is 29.85".. that equals 14.66 psi, which should provide 153 psi cylinder pressure.

If I was in Boulder CO today... where the elevation is MUCH higher, you would think the barometric pressure would be lower..... not today....the barometer is higher ( than in Aliso Viejo) today at 30.03". I could expect 155 psi cylinder pressure.

In a extreame example, on Mt. Everest, the barometric pressure is 11.5", or 5.65psi. This would be a n easy kicking CR500, with only 59 psi of cylinder pressure...

Clear enough Clyde?

AlisoBob wrote:

100hp honda wrote: anybody know how much compression i lost ?

Altitude has little to do with it, Barometric pressure does.

1. Find a local weather report, and get the barometric pressure forecast. It will be something like 29.92"

2. Go to this website: http://www.srh.noaa.gov/elp/wxcalc/pres ... vert.shtml

Enter the barometer reading into the conversion table to read out in PSI

3. Do the math, multiply the PSI by 10.5. ( The compression ratio on a CR500 is about 7:1.. However, this is a static number. Heat induced by the compresion action further expands the gas and makes the actual compression ratio about 10.5:1)

Here , in Aliso Viejo today....The Barometer is 29.85".. that equals 14.66 psi, which should provide 153 psi cylinder pressure.

If I was in Boulder CO today... where the elevation is MUCH higher, you would think the barometric pressure would be lower..... not today....the barometer is higher ( than in Aliso Viejo) today at 30.03". I could expect 155 psi cylinder pressure.

In a extreame example, on Mt. Everest, the barometric pressure is 11.5", or 5.65psi. This would be a n easy kicking CR500, with only 59 psi of cylinder pressure...

Clear enough Clyde?

So I'm confused. I can tell a marked difference in performance with altitude changes. I shot around looking at the barometer readings from sea level to 8500ft and the barometer is with in 1 inch. What gives? Another example I'm at 5280 I own a few things that have high enough compression to use premium. If I run regular I have never heard detonation. I assumed that was because of the altitude. Am I just not hearing bad things happening? Enlighten me Bob?

Most of the time, barometric pressure DOES fall when you increase altitude.

I'm just showing an example of when it didnt.

Most of the performance loss with altitude changes is because the bike is becoming "richer". If its not leaned out to compensate, performance will suffer.

As fas as knocking, what "things" do you own? If they are computer controller, they wont knock no matter what gas you put in them.

theres alot less oxygen at altitude. less oxygen=less power. im not sure if they still do it but in nhra drag racing they used to be allowed to run a higher nitro % at the denver track to compensate for the altitude power loss

100hp honda wrote:theres alot less oxygen at altitude. less oxygen=less power. im not sure if they still do it but in nhra drag racing they used to be allowed to run a higher nitro % at the denver track to compensate for the altitude power loss

Exactly, but if the pressure is the same at sea level and denver the oxygen content should be the same, right?

The question was:

Clyde wrote: How much cylinder pressure do I lose at altitude?

quantum500 wrote: So I'm confused. I can tell a marked difference in performance with altitude changes. I shot around looking at the barometer readings from sea level to 8500ft and the barometer is with in 1 inch. What gives? Another example I'm at 5280 I own a few things that have high enough compression to use premium. If I run regular I have never heard detonation. I assumed that was because of the altitude.

The barometer reported at various altitudes via weather sources isn't the true measured BP, it's corrected to an equivalent value at sea level.

Sea level = 29.5-ish inHg +/- based on weather conditions
5000 feet = 24.5 +/- based on weather conditions
top of pike's peak (14,110) = 18.0 +/- based on weather conditions

You've got lower pumping losses at lower barometer values, but it's overshadowed by the loss in compression since less oxygen is available. We usually see a 20% loss in horsepower on a modern fuel injected engine in Denver, and almost 40% at 10k, in comparison to sea level.

-Nick

Blusmbl wrote:

quantum500 wrote: So I'm confused. I can tell a marked difference in performance with altitude changes. I shot around looking at the barometer readings from sea level to 8500ft and the barometer is with in 1 inch. What gives? Another example I'm at 5280 I own a few things that have high enough compression to use premium. If I run regular I have never heard detonation. I assumed that was because of the altitude.

The barometer reported at various altitudes via weather sources isn't the true measured BP, it's corrected to an equivalent value at sea level.

Sea level = 29.5-ish inHg +/- based on weather conditions
5000 feet = 24.5 +/- based on weather conditions
top of pike's peak (14,110) = 18.0 +/- based on weather conditions

You've got lower pumping losses at lower barometer values, but it's overshadowed by the loss in compression since less oxygen is available. We usually see a 20% loss in horsepower on a modern fuel injected engine in Denver, and almost 40% at 10k, in comparison to sea level.

-Nick

im no expert on this subject but this is what i was thinking. %10-%20 hp loss at 5000'-6000'. altitude has no effect on a deisel with turbo? is this correct ?

Buy any performance prediction computer ( for mostly the ET classes in NHRA like any of the .90 classes ) and they take a variety of factors into account.....such as temp, humidity, corrected altitude etc.

What this has to do with this discussion-I don't know, but I do know that there are many atmospheric variables to consider when calculating power loss or gain.

It's been my personal experience that humidity plays a larger factor than most people acknowledge. Warren Johnson has said for years that normally aspirated engines can't pump water. Blown stuff makes its' own atmosphere.

This whole thread and you were asking about a diesel with a turbo charger?

teemtrubble wrote:This whole thread and you were asking about a diesel with a turbo charger?

no. i was asking how much power the average cr500 would lose at altitude. the deisel comment was just thinking how altitude affects various different engines. i heard turbo deisel doesnt suffer the same affects of altitude as other types of engines ? the turbo is essentialy a altitude compensator is what i heard, not sure what that means though

piston planes with a turbocharger can go to much higher altitudes

nmdesertrider wrote:piston planes with a turbocharger can go to much higher altitudes

altitude still affects turbo engines but not as much as non-turbo ? i sort of understand how a turbo works but ive never had to mess with one

If you had a turbocharged diesel running at full boost (wastegate closed @ all times), it would also be down on power at higher altitude. However, most turbodiesels have boost managed by the wastegate, and in someplace like Denver the wastegate is closed a further amount compared to sea level, bringing power back to levels you'd expect so it isn't anywhere near as noticeable...compared to a naturally aspirated engine.

10,000 ft is roughly the ceiling for turbo compensation on most turbo'ed diesels.

this is pretty cool thread about 2stroke with a turbo. its a saber with turbo, not sure of the exact cc but im guessing its around 500cc. i seen photos somewhere of turbo saber and how they plumed everything in, but im not sure if it was this exact bike or if someone else made a similiar machine but this is badass

http://forums.atvdragracers.com/index.php?showtopic=66

With snowmobiles we go through up to 4000 foot of elevation changes depending upon the location. Like Exnav said, the humidity plays a huge role along with press like Bob said, and like Bob said the fuel changes are the best defense for power loss has been first, power jets and as of late EFI.
The same altitude at Mount Baker in Washington gives better performance than Utah, most of the time, due to thicker marine air.

humid air is less dense and has less oxygen available than than dry air. Not sure what you mean by 'thicker'