Sea Level vs Altitude Tuning

[soutthpaw]

In celerbration of my 200th post, I decided to start another thread

being that I am at 6000 ft and that there are obvious differences between Flatlander and Mountain Man tuning, I would like to get more input on this subject...

seems to play a role in Fueling and injection timing as there even separate settings for sea level and altitude in the programming... even for WOT shifting...

The Turbo in general is supposed to offset the effects of altitude found in naturally aspirated engine. So I am wondering why the altitude parameters are needed...
Oh, and at what elevation does the altitude parameter start to function? is that adjustable?????

For Jack I think the parameters would be even more significant for the Gassers being they are naturally aspirated

[Jackpine]

Originally Posted by soutthpaw

In celerbration of my 200th post, I decided to start another thread

being that I am at 6000 ft and that there are obvious differences between Flatlander and Mountain Man tuning, I would like to get more input on this subject...

seems to play a role in Fueling and injection timing as there even separate settings for sea level and altitude in the programming... even for WOT shifting...

The Turbo in general is supposed to offset the effects of altitude found in naturally aspirated engine. So I am wondering why the altitude parameters are needed...
Oh, and at what elevation does the altitude parameter start to function? is that adjustable?????

For Jack I think the parameters would be even more significant for the Gassers being they are naturally aspirated

I can talk about what I've highlighted:

Any kind of air compressor can only boost pressure relative to the outside (ambient) pressure. At sea level, the compressor is going to push more air into the engine than it can at 6000+ feet. (Up on Pikes Peak, the effect would be even more pronounced). So, you are still getting the effect of a change in altitude even with the blower and, the fueling will have to be adjusted for it.

To give you "numbers", at 18,000 feet, (only 4,000 above Pikes Peak), you are at 1/2 standard sea level atmospheric pressure (14.7 psi), so at 18,000, the pressure is only 7.35 psi. A good turbo might give you a 40% boost, I think. At sea level, this means your intake "sees" about 20.6 psi, which really improves the engine's power. But, if you could take that turbo to 18,000 feet, the same 40% boost gives you a total of only 10.29 psi, much less than an unblown engine at sea level.

A turbo DOES allow you to run your engine at a higher altitude than an unblown one, which is why reciprocating aircraft engines might have them. But, as with all things, there is still an upper limit.

- Jack

[cleatus12r]

Originally Posted by soutthpaw

and at what elevation does the altitude parameter start to function? is that adjustable?????

4500 ft.

There is a "baro transfer" listing in the definitions. That would change the PCM's perception of your elevation but I am not sure how it works (as far as how to change it to correct for anything), but I know how the "map transfer" works.

Notice that the high altitude SOI is not changed for you........

[soutthpaw]

Ok I found a calculator for Barometric pressure online and it says I am at 11.77psi at 6000 ft. being that most of my driving is at 5000-8000 feet how do i get the turbo to add that extra 3lbs of boost.
what sort of change should I make to these settings
low boost fuel (altitude)
Injection timing (altitude)
I would think with less air pressure the boost is going to come on later so less fuel (lower boost fuel settings) should go into the engine and go in earlier (more advanced timing) as less oxygen to support combustion

Torque Table Altitude & Torque Friction Table Altitude: do these need to be changed or are they already compensated from the factory... and what purpose do these maps serve... (i don't see how friction loss changes at altitude) same goes for the sea level map... do other parameters use the values in this map to calculate other factors like mass fuel desired etc?

There is also the Barometric Multiplier and Torque Multiplier vs Baro not sure what these do either
I already set the altitude offset for the WOT shifting higher by 200rpm as I lowered the WOT shift point anyway

[soutthpaw]

Originally Posted by JackandJanet

I can talk about what I've highlighted:

A good turbo might give you a 40% boost,


- Jack

Well You can't really look at boost as a percentage esp with diesels as there are quite a few diesels runing upwards of 50 PSI boost pressure

[Jackpine]

Originally Posted by soutthpaw

Well You can't really look at boost as a percentage esp with diesels as there are quite a few diesels runing upwards of 50 PSI boost pressure

I don't think you're right here. Everything I've read on turbos says the good ones give a 50% boost, not 50 psi, but that since you don't get perfect efficiency out of it, you might see a 40% boost. 50 psi is about 3.4 atmospheres! That would be an enormous amount of air. You'd be burning 3.4 times the unboosted fuel volume just to maintain the correct A/F ratio!

And, there's simply no way a turbo could maintain that 50 psi boost as ambient air pressure drops. (How much boost would you get in space?) The boost value HAS to be a percentage of the ambient pressure, not a fixed pressure value.

I see I forgot to congratulate you on passing the 200 post milestone. :o I meant to, and I enjoy your thoughts.

- Jack

[soutthpaw]

Jack we are talking Diesel here, NOT wimpy gassers heck the old 5.9 cummins on my RV can hit about 28 PSI of boost.. remember Cody's post about air/fuel mixtures for diesel vs gas????

[Jackpine]

Where the heck are you getting the power to drive this blower? It's got to come from somewhere, and I doubt a turbine in the exhaust could supply it.

Is it a belt driven supercharger? And, even then, that much boost (at sea level) takes an enormous amount of power. You're talking a 340% increase!

You're dead right, southpaw. I know next to nothing about diesels, but the numbers you're quoting just seem way out of line.

I'm happy to have my opinion changed though. Just point me to one of these beasts that can produce those numbers and I'll crawl back under my rock.

- Jack

[soutthpaw]

Well just look at the boost gauge in any stock or modified diesel there is a reason you can buy 60PSI boost gauges.. But we are really getting off topic and would be better in a new thread as I would really like to get some feedback on the subject of this thread

[cleatus12r]

Originally Posted by soutthpaw

Ok I found a calculator for Barometric pressure online and it says I am at 11.77psi at 6000 ft. being that most of my driving is at 5000-8000 feet how do i get the turbo to add that extra 3lbs of boost.You're not going to get it with a stock turbocharger.
what sort of change should I make to these settings
low boost fuel (altitude)You can up this one, but be prepared for more black smoke before the turbocharger has a chance to "light".
Injection timing (altitude)This table will USUALLY be filled with higher values due to lower atmospheric pressure. Having less air means that more advance can be used to help in the combustion process.
I would think with less air pressure the boost is going to come on later so less fuel (lower boost fuel settings) should go into the engine and go in earlier (more advanced timing) as less oxygen to support combustion

Torque Table Altitude & Torque Friction Table Altitude: do these need to be changed or are they already compensated from the factory... and what purpose do these maps serve... (i don't see how friction loss changes at altitude) same goes for the sea level map... do other parameters use the values in this map to calculate other factors like mass fuel desired etc? I've never seen one touched.

There is also the Barometric Multiplier and Torque Multiplier vs Baro not sure what these do either
I already set the altitude offset for the WOT shifting higher by 200rpm as I lowered the WOT shift point anyway

Bill will have to answer the rest. I don't know.