Altitude Issues

[Coyote]

I don't understand why idle MAP readings would change much from sea level to higher altitudes. I understand the WOT readings capping out lower at elevation but I would expect the idle area to remain almost the same. Guess I will have to test this next run up the hill.

[PoorUB]

Also, I don't think 30kpa is a realistic number for a land yacht to maintain 65mph level ground no wind. I may be wrong.
Bob

I have a bunch of data running in the Red Lodge MT area, 5,000+ feet. I see quite a few areas where I was running 2,500-3,000 RPM and the MAP is around 30 KPA, sometimes less, so it does happen in high elevations. possible it was on slight down hill runs, but at any rate the engine sees the conditions.

[Onthefence]

Also, I don't think 30kpa is a realistic number for a land yacht to maintain 65mph level ground no wind. I may be wrong.
Bob

I have a bunch of data running in the Red Lodge MT area, 5,000+ feet. I see quite a few areas where I was running 2,500-3,000 RPM and the MAP is around 30 KPA, sometimes less, so it does happen in high elevations. possible it was on slight down hill runs, but at any rate the engine sees the conditions.

Can you post a data log?  My adjusmtents were made with PV autotune which by default does not keep a log from AutoTune.  Just a value file to apply.

[FLTRI]

Also, I don't think 30kpa is a realistic number for a land yacht to maintain 65mph level ground no wind. I may be wrong.
Bob

I have a bunch of data running in the Red Lodge MT area, 5,000+ feet. I see quite a few areas where I was running 2,500-3,000 RPM and the MAP is around 30 KPA, sometimes less, so it does happen in high elevations. possible it was on slight down hill runs, but at any rate the engine sees the conditions.

Yep, but no difference at sea level. Only difference is max kpa is lower in altitude.
Not sure why this is so difficult to buy into.
Of course you can log low kpa when on level ground especially at low vehicle speeds.
Ya just can't push a bike through the air at 65mph @ 30kpa UNLESS you are going downhill.
Bob

[PoorUB]

Maybe I am missing what you guys are looking for, but I have looked at data runs at 900 feet and the only time it hits 30 KPA is at idle, the rest of the run the KPA bottoms out above 40. The 30 KPA above idle RPM cells will never get logged and tuned.

The question still arises, how do you tune for the lower KPA cells other than a educated guess, or cut and paste the 40 KPA cells to the lower KPA cells with no data?

I have a recording I can post, but it is too large to post here directly, any help with it??

[Onthefence]

I don't understand why idle MAP readings would change much from sea level to higher altitudes. I understand the WOT readings capping out lower at elevation but I would expect the idle area to remain almost the same. Guess I will have to test this next run up the hill.

According the chart here.  http://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html  at 10,000ft the atmospheric pressure is 69.7kpa.  Shouldn't that be within 2 kpa of what you will see at WOT. 

At sea level my bike idles at 37-40kpa.  Roughly 37-40% of atmospheric pressure.  Would the percentage not be similar at any altitude?  .37 X 69.7 = 25.789   .4 X 69.7 = 27.88. 

[Onthefence]

Also, I don't think 30kpa is a realistic number for a land yacht to maintain 65mph level ground no wind. I may be wrong.
Bob

I have a bunch of data running in the Red Lodge MT area, 5,000+ feet. I see quite a few areas where I was running 2,500-3,000 RPM and the MAP is around 30 KPA, sometimes less, so it does happen in high elevations. possible it was on slight down hill runs, but at any rate the engine sees the conditions.

Yep, but no difference at sea level. Only difference is max kpa is lower in altitude.
Not sure why this is so difficult to buy into.
Of course you can log low kpa when on level ground especially at low vehicle speeds.
Ya just can't push a bike through the air at 65mph @ 30kpa UNLESS you are going downhill.
Bob

I ran my bike at 8,000 feet and up between 2200 - 2500 RPMS in 6th gear and saw map readings consistently below 40k.  6th gear at 2500rpms is the same speed no matter what the map sensor reads.

[Coyote]

Whatever KPA you idle at represents the current motor load. If it's 40 kpa, that's an absolute manifold pressure measurement. You go up in elevation, that load does not change. So the KPA required to sustain that load does not change. The only deal with elevation is you have less air to deal with so you will top out at a lower KPA and make less power. At least this is what I understand from the reading I've done on this system.

I have read some that the load on the motor might drop slightly at elevation but this is due to the exhaust being a bit easier to push out into the thinner air. 

I hope the experts will correct me if I'm off on this.

[FLTRI]

I ran my bike at 8,000 feet and up between 2200 - 2500 RPMS in 6th gear and saw map readings consistently below 40k.  6th gear at 2500rpms is the same speed no matter what the map sensor reads.

You will regularly see under 40 KPA whenever you are basically in a no load state.
In other words, it makes no difference whether you are at sea level or 6000ft.
Again, 40kpa is 40kpa and can be observed no matter what elevation you are at.
I must sound like a broken record because I make the same statement over and over only to fall on deaf ears I guess. Nothing special at altitude other than less air to get to 100kpa.
Coyote, I'm no expert but maybe someone you feel is will come on here to straighten this argument out.
Bob

[Coyote]

Bob, if you're saying I got that part (sounds like so) then that's good enough for me. It would be interesting to know about how much power one loses at altitude when the max KPA drops to say 70. I know I can feel it.

[FLTRI]

Bob, if you're saying I got that part (sounds like so) then that's good enough for me. It would be interesting to know about how much power one loses at altitude when the max KPA drops to say 70. I know I can feel it.

Do a pull while maintaining 70kpa. It won't be exact but definitely close.
Plus air quality also plays a part. Take your bike to a smokey fire area and run it on a dyno and compare results with clear air runs.
May have the same temp and humidity but full of crap (particulates, etc) which kills power.
Bob

[Onthefence]

I ran my bike at 8,000 feet and up between 2200 - 2500 RPMS in 6th gear and saw map readings consistently below 40k.  6th gear at 2500rpms is the same speed no matter what the map sensor reads.

You will regularly see under 40 KPA whenever you are basically in a no load state.
In other words, it makes no difference whether you are at sea level or 6000ft.
Again, 40kpa is 40kpa and can be observed no matter what elevation you are at.
I must sound like a broken record because I make the same statement over and over only to fall on deaf ears I guess. Nothing special at altitude other than less air to get to 100kpa.
Coyote, I'm no expert but maybe someone you feel is will come on here to straighten this argument out.
Bob

No one is stating that 40kpa at 500 feet is somehow different than 40kpa at a higher elevation.  What I am stating and you obviously disagree with is that my bike will not hit map areas below 40kpa unless either idling or deceling while at or near sea level. 

However, when I was at elevation, I saw below 40kpa while I was cruising down the road.  That's just a fact.

All I was asking was whether this could be reproduced on a dyno at or near sea level.  Your response throughout has been that my data is wrong.  In a round about way I have my answer.

Maybe your bike has different readings than mine at 10,000 feet, which makes my numbers seem unbelievable.

[FLTRI]

Nope. Never doubted your data. Never.
What I have repeated was that you can go 65mph at sea level and turn the throttle until you see 40 KPA. Same goes for at altitude.
Now if you can show some data that supports your statement that you can hold steady state speed @ 65mph level ground at any altitude while only showing 40kpa I will stand corrected and apologize for arguing with you ok?
I've been wrong before and not ashamed to admit it, but I don't how you can be at 6000ft altitude and use less KPA to hold 65mph than at sea level.
Bob

[PoorUB]

I don't argue that a certain KPA is the same regardless of elevation. I just want to know the best way to tune for it when you can not reach it at the elevation you tune in. Tuning for lower KPA in lower elevations.

[Coyote]

If idle KPA stays the same as does the decel area, it would seem if you tune the bike at sea level, then the rest is already there. 

[wolf_59]

Idle KPA on both my bikes completly different builds at 6000' is in the 37-38 range
KPA at this elevation is 83.2 average atmospheric pressure is 11.7-11.8 compared to 14.7 at sea level
Dyno correction factor is 1.27 at 6500'

[FLTRI]

I just want to know the best way to tune for it when you can not reach it at the elevation you tune in. Tuning for lower KPA in lower elevations.

You're killing me! 
Once again, no difference whatsoever. I tune from 20kpa up to 100kpa or whatever max is.
There is no lower KPA at altitude except maximum?
I can reach any KPA at sea level as you can at 6000ft but you can't reach the high load/KPA I can at sea level.
Tuning is exactly the same.
Bob

[PoorUB]

I just want to know the best way to tune for it when you can not reach it at the elevation you tune in. Tuning for lower KPA in lower elevations.

You're killing me! 
Once again, no difference whatsoever. I tune from 20kpa up to 100kpa or whatever max is.
There is no lower KPA at altitude except maximum?
I can reach any KPA at sea level as you can at 6000ft but you can't reach the high load/KPA I can at sea level.
Tuning is exactly the same.
Bob

You are killing me!

Well, I looked at some data runs at home and at 5,000+ feet. The only time the engine saw 30 KPA at home was at idle. At 5,000 feet it would see 30 KPA running down the road and it hit the 20's once in a while at idle. Running down the road here at home it would barely make 40 KPA and was closer to 50 KPA at the low end. So go ahead and tell me how to reach 30 KPA part throttle cruise running down the road, because so far I can not get down that far at part throttle at home.

[glens]

I say everything scales with elevation.  Nothing to back it up yet but I'll see what I can do.

[whittlebeast]

Tuning does change with altitude.  The operating range of MAP shifts lower as you go up.

[glens]

Think about it.  Say 40 kPa at idle at sea level.  If you went high enough that only 50 kPa were available to fill the cylinders, would it still be 40 kPa at idle?  Or would it be more like 20 ?  I'd put money on the latter.

Get Ron in on this one.  I'll bet he's had piston engines at altitude.

[Onthefence]

I just want to know the best way to tune for it when you can not reach it at the elevation you tune in. Tuning for lower KPA in lower elevations.

You're killing me! 
Once again, no difference whatsoever. I tune from 20kpa up to 100kpa or whatever max is.
Bob

I don't know that I saw stated before that you were getting the 20kpa and up range.  You are hitting areas that to this point seem impossible to hit on the street.  And they cover the map ranges that we claim we were having troubles with.  So yes as you keep banging your head over a good 20kpa is good at any evlevation.   In our case, since we haven't collected any valuable data down there it didn't get exposed as bad data until reaching high elevations.  Which for me the problems were in the 8 - 10 range.  5 and 6 ran pretty decent.

Any guidance on how to nail down those lower ranges on the street.  Say the 2000-3000 in the 30 and 35kpa? 

[whittlebeast]

Simply log the motor going up one of those mountain passes and watch the long term fuel trims change as you go up in altitude.  If the altitude correction table is correct, the trims will not really change that much.

If your software does not expose this table or have the data available in the logs, have the company fix the software.

The same sort of trick works great on the warmup logic.  This has everything about hitting your AFR targets in all situations as consistently as you can.

Andy

[Onthefence]

Think about it.  Say 40 kPa at idle at sea level.  If you went high enough that only 50 kPa were available to fill the cylinders, would it still be 40 kPa at idle?  Or would it be more like 20 ?  I'd put money on the latter.

Get Ron in on this one.  I'll bet he's had piston engines at altitude.

My understanding is yes it will be lower by some factor.  Thinking any throttle setting below WOT is drawing a vacuum against whatever the atmospheric pressure is.  So at 5% throttle opening the density of 50kpa air should be lower than  the same throttle opening at 100kpa air.   

According to Wikepedia:
https://en.wikipedia.org/wiki/MAP_sensor

Engine vacuum is the difference between the pressures in the intake manifold and ambient atmospheric pressure. Engine vacuum is a "gauge" pressure, since gauges by nature measure a pressure difference, not an absolute pressure. The engine fundamentally responds to air mass, not vacuum, and absolute pressure is necessary to calculate mass. The mass of air entering the engine is directly proportional to the air density, which is proportional to the absolute pressure, and inversely proportional to the absolute temperature.

[joe_lyons]

I looked back through real quick but did you post your calibration?  It would be nice to take a peek at it.