Sea Level vs Altitude Tuning

[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

[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