Delica Canada | Mitsubishi Van Club

jwfchase wrote:Couldn't resist my 1.5 cents...

This is a POV from someone who only understands the basics of how a turbo works-- I'm am definitely not an expert, in fact, not even quite competent . However, here's how my (also limited) understanding of physics seems to support the idea that a turbo COULD automatically compensate for increase in altitude TO A POINT (though I DON'T know where that point is- based on the limitations of individual turbos. The following is an uneducated hypothesis that could either be supported or shot to shart by those of you more informed than me:

As you go up in altitude, atmospheric pressure on the intake side decreases- supplying less oxygen through the intake. However, atmospheric pressure on the exhaust side also decreases, resulting in a decrease of backpressure through the exhaust, equal to the decrease on the intake side. Would this not cause the turbo to spin faster in this "thinner atmosphere", with the end result being that post-turbo intake psi going into the engine would be more or less exactly the same?

Also, not particularly understanding how an IP works, would a decrease in atmospheric pressure on the IP cause it to deliver too much fuel, even if the turbo is operating more or less as it would at sea level? It seems to me (and hopefully someone COULD explain this better) that atmospheric pressure could affect the operation of the engine, but that the turbo and the IP are two separate issues.

You got 'er. If there were such drastic change by altitude, if you monitor your boost guage, you would never be able to reach the same level of boost as you could at sea level. If you are reaching the same level of boost then you ARE experiencing altitude compensation.
Further to your last statement at altitude fuel along with air becomes LESS dense.
To argue anything other than the fact that TURBO'd engines experience altitude compensation is purely through ignorance.

Delica's at high altitudes :

http://www.delica.ca/forum/the-altiplan ... -6472.html

The Delica managed better then we did almost. Besides quite a bit of black smoke, and difficulty starting when cold in the morning (needed to bump it, fortunately we were parked on a decent hill!) it was great. Power was still decent too.

Altimeter was accurate to about 3500m (the town of Putre), but I think once it rolled over, we never saw the 4500m the lake is supposed to be at.

http://www.delica.ca/forum/delica-sets- ... -1444.html

Also, not particularly understanding how an IP works, would a decrease in atmospheric pressure on the IP cause it to deliver too much fuel, even if the turbo is operating more or less as it would at sea level? It seems to me (and hopefully someone COULD explain this better) that atmospheric pressure could affect the operation of the engine, but that the turbo and the IP are two separate issues.

The link between the turbo and the IP is the boost compensator. As boost increases the compensator increases the amount of fuel the IP delivers over and above its basal rate (the amount of fuel delivered at 0psi boost). The rate at which the fuel increase changes over the boost range is controlled by the boost ramp. In a mechanical compensator the boost ramp is typically set with a simple sloped pushrod that moves up/down depending on the boost pressure acting upon the diaphram above it (or below depending on design).

This pushrod is one of the things you can play with on the compensator if you plan on tuning your engine (you can also adjust things like the preload but thats a lot more of a delicate fine tune adjustment). If you are lucky the pushrod has various ramp slopes already on it from the factory so you can easily play around. If not you would have to have new pushrods machined with alternate slopes.

Here is a picture of a typical boost compensator. Sorry it is in French but it should still make sense.


Here are a couple pictures of the pushrods (from a Toyota Surf 2LT) so you can see the slope. Notice how it is asymetrical around the circumference, meaning I could alter the boost ramp in my old Surf simply by twisting the pin to the left or right. (Also note that the ramp reverses rapidly back to a pre-boost setting at the end...this is an overboost protection on the Surf...not sure if the Delica would have this since your vehicle already has that pressure relief valve as an overboost safety...)



I imagine the mechanical boost compensator in teh Delica should be quite similar similar in design but is likely not exact. Anyone feeling adventurous who wants to open theirs up and start playing with it...be sure to take some pics.

Wow, sorry Green1, no support from me, but thanks for the entertainment. I noticed that no one said the basic statement that the change in oxygen level is simply due to a decrease in atmosphereic pressure, which I am sure is stating the obvious to most of you. The wondorous thing about that statement is that if you are making 8psi or 20psi at sea level and you are still making that same respective boost level at altitude your oxygen content will be the same as it was down at sea level. There is no need for more boost to compensate, the only problem you will have was shown in the post Jesse copied from that delica in Chile; hard starts with extremely black exhaust until on boost, then it goes away as Green1 would have me say "magically". Since the wastegate only opens when it sees a certain boost level the turbo simply spins faster until that boost level is seen and you need fuel to get your turbo to spin, so in my opinion you should just live with the black fart until you get into boost because even at low boost levels you are suddenly at the same oxygen levels you would see at that boost at sea level.

wake up green...the turbo has a limit on rpm's eventually...there fore there is a limit, but driving through the rockies has almost no affect, says all six different diesels ive owned!

This is laffable, sorry manitoba-he sounds like a lawyer!

mac_stang wrote:wake up green...the turbo has a limit on rpm's eventually...there fore there is a limit, but driving through the rockies has almost no affect, says all six different diesels ive owned!

This is laffable, sorry manitoba-he sounds like a lawyer!

Green 1 has been gone from this forum for quite some time.

Didn't think I'd see this thread bumped back up this year

jfarsang wrote:

mac_stang wrote:wake up green...the turbo has a limit on rpm's eventually...there fore there is a limit, but driving through the rockies has almost no affect, says all six different diesels ive owned!

This is laffable, sorry manitoba-he sounds like a lawyer!

Green 1 has been gone from this forum for quite some time.

Didn't think I'd see this thread bumped back up this year

That just shows the powerful affect of "Green1". I wonder if it comes in a handy 350ml size?

That just shows the powerful affect of "Green1". I wonder if it comes in a handy 350ml size?

LOL!

Having said that, I do miss the guy. A good deal of my decision to buy what I bought was based on his posts. He was the first person I knew of in Canada with a Royal Exceed.

Nothing like bumping old threads....

mararmeisto wrote:That just shows the powerful affect of "Green1". I wonder if it comes in a handy 350ml size?

HAHAHA.... nothing like a good degreaser... I saw him not too long ago at CVI, he was on his way up north to the Yukon with his girlfriend.

Falco.

sorry for drudging up old threads...but ive spent the past few days thumbing through everything in here and something just set me off!!

-forgot how old this thread was! LOL!

Wow, this thread was pretty intense. There is some correct and incorrect information, so in the interest in of the general quality of technical information on this forum, I will clarify some things.

*Long Post Warning!

Lets call this Example #1. Ignoring pressure (PSI), if the same number of air molecules, and the same amount of fuel enter the combustion chamber, (at the same temperature, timing etc) then the same amount of power is made (assuming the same backpressure form the exhaust). Your engine does not know how high or low it is. This is theory, then there is reality.

As altitude increases, if this (same # of molecules per intake stroke) remains true, the downward force will actually INCREASE, due to the increased pressure differential across the piston. IE the lower pressure in the oil pan due to the altitude will have an affect. However this is offset by the upward force (compression) also requiring an increased amount of force due to the lower pressure in the oil pan relative to the same # of air molecules in the combustion chamber. This point is worth mentioning however, as you may get more "blow by" at higher elevations in turbo motors due to this affect.

Now, at the turbo inlet, the same thing happens, assuming the number of air molecules on the outlet side, the pressure differential across the turbo will increase as altitude increases. Meaning the turbo will have to work harder to "acquire" those air molecules, meaning there will be more backpressure from the turbo, increased exhaust restriction, ie less HP, for the same number of air molecules gathered.

Now all of this is ASSUMING the same # of molecules... however the amount of air molecules entering the engine is determined by temperature (IE A 2.0L bottle of COLD air has more air molecules then a 2.0L bottle of warm air, the same goes with a 2.8L bottle.. or engine) and pressure (PSI). Temperature is obvious as its automatically relative and finite in measurement (degrees Celsius or Fahrenheit)... but pressure is less relative.

What you are boosting your turbo to 8psi... how is that measured? The 8psi is a reference, or relative to something. IE my tires are 32 psi relative to outside pressure right now, and I am near sea level.

If I bring my tires up to 8000 FT ASL, they are going to be alot more then 32psi (perhaps around 40psi not including expansion). This is the same reason weather balloons pop when they get to a certain altitude. The pressure around the balloon drops, affectively increasing the pressure differential on the inside of the balloon vs the outside, EVEN though there is the same number of air molecules in the balloon (aprox) as before.

Let’s call this Example #2. The 8psi in older engines like the 4M40 is typically measured by the intake manifold pressure vs outside air pressure. This is because the boost control is mechanical in nature, and the mechanical reference for the wastegate is intake manifold vs environment pressure. IE the force across the wastegate spring is not relative to sea level, but to the conditions surrounding the springs at this very moment.

Now... on modern cars the MAP sensor (Mass Air Pressure) is typically relative to sea level. IE if you installed a modem MAP sensor on a 4M40 (as a measurement tool and not a control tool) engine and measured the boost at different altitudes you would see the "boost" change with altitude. I will get to why…

While the boost is 8psi intake manifold vs environment no matter what, the MAP would see that relative to sea level, we are hitting less then 8psi. At 5000 ft, the MAP may only read 5psi of boost, even though your boost gauge and wastegate are seeing 8psi of boost (relative to environment). This is because outside air pressure is now -3psi relative to sea level. The numbers are arbitrary approximations for this example.

In that example, the backpressure at the turbo would remain the same, or actually decrease slightly from simply moving thinner lighter air around (debateable). This is example #2.

Now to obtain similar results to Example #1, I could calibrate my electronic boost controller (or MAP controlled system) for 8psi of boost (relative to sea level) it will not open the wastegate until it sees 8psi relative to sea level. That may be actually 12psi relative to the environment at 6000ft ASL. So we have Example #1 approximately. It will acquire the same number of air molecules approximately (APROX, see below for why its not the same).

The reality is it will have to work harder to do it, so two things will happen as aforementioned. One more backpressure from the turbo (less HP), two when the turbo works harder, IAT's (Intake Air Temperatures) go up. When temperatures go up, pressure increases, but air molecule count goes down. So the 8psi relative to sea level will be hit sooner, but with less air molecules due to the temperature. The boost controller sees thr 8psi and opens the waste gate, but the IAT's are a little higher from the turbo having to work harder, so the air molecule count is lower then the sea level example.

The reality of ALL of this is, that no matter what example above (boost relative to sea level, or boost relative to environment), HP will go down. In the relative to sea level example, it will drop much slower (lose less) then the relative to environment example.

I hope that helps,

Steve