I may be wrong here, but I'm assuming (as someone stated before) that the real question is whether the power produced by a given car/setup at sea level is the same as it is as altitude?

I can say without question that in my case the answer is NO! Whether this should or should not be based on the laws of....well ......i'm guessing physics....is not relevant. Fact is (my) Z at 5,280 ft does not perform the same as (my) Z at sea level.

 

Originally Posted by GurgenPB
Hey Guys

The discussion, before i posted, went into the why's and the how's, which is why i tried to be thorough. Anyway, better more info than less.... writing all this down helped me organize my own thoughts on the subject.

On to you question

Well, like i said if you tune the car only at one of those locations without using altitude correction, than your tune would be off, and that can lose you power in almost every case (being too lean or too rich from optimal afr). Now, assuming that you car is tuned perfectly for all eventualities, perfectly with altitude compensation, and that you have an adjustable boost controller which TN kits don't have, then two things will happen. At the same boost setting, or in your case, same wastegate spring, of 9psi at sea level, you will develop only 5.3psi at 5000' elevation.

Let me make a clarification/correction here..sorry for the confusion. It would be 6.1 psi over normal ambient of pressure of 1bar...so, it would make 9 psi over ambient, yes, but you would experience the same power loss that i talked about because the absolute pressure (MAP) has fallen from 9+14.7=23.7psi to 9+12.1=21.1psi by about that much, and MAP is what determines amount of air available for combustion. So, if you have one of the smart boost gauges, it will correct for the ambient pressure when you first turn on the car without cranking the starter, and give you true pressure over ambient.

How do you figure this? So your power will fall by about 16% just on the account of the lower boost. Why won't the wastegate compensate? You’re not explaining this. That is the job of the wastegate to read manifold pressure and route exhaust gas to or from the turbo. Your not explaining that. However, you will also experience power loss due to less compressor efficiency, so lose another 3-4% because of that. So, roughly 18-20% of total power. Explain to me why turbocharged airplanes are flat rated for a given horsepower up to a given altitude. But your stating that you will lose power as altitude increases.

I did explain this...the pressure that is exerted to the wastegate(s) is gauge pressure, not absolute, so it normalizes in reference to that. When they say “1bar spring” they mean 1 bar gauge pressure spring, or 1 bar over ambient. Look at the construct of the wastegate. What does the pressure that controls it (manifold pressure) have to push up against? That's total exhaust pressure, which of course, being open to the atmosphere, is a function of ambient pressure, hence pressure that needs to be put on is equal to the sum of that needed to overcome the spring and the pressure behind the wastegate 'door'. The latter, is approximately ambient pressure + exhaust backpressure, the point being is it's directly proportional to ambient pressure, which is not always 1bar. Hence, the total pressure to open the wastegate decreases with altitude, a decrease that is equal to the decrease in ambient…. hence it always takes the same gauge pressure in the manifold that it did at sea level. As you gain altitude in an airplane, or go to a higher elevation in a car, with a "0.5bar spring", it is 0.5 bar over ambient that of pressure (gauge pressure) that will be required to open the wastegate. So, the compressor at 5000’ elevation compresses the intake air until it reaches ambient pressure (0.82bar) + pressure req’d to overcome the spring (0.5 bar here) = 1.32 (btw…sorry about my error in addition in the big post 0.82+0.5=1.32 not 1.22). The wastegate opens and pressure is maintained at 1.32 bar absolute.

Let’s take the turbonormalized pressure system for the bonanza made by Tornado Alley Turbo in Ado, OK, that is wastegate spring controlled and not a manual wastegate control. I used to own a bonanza, so I have looked into it extensively a few years back. It will maintain 30" of pressure to its critical altitude of 26,000' (can't remember the altitude exactly). The installation includes an ‘automatic controller’ that controls the wastegate to maintain 1 bar absolute as it rises through the altitudes. Look it up. I am sure something very similar is available for the Socata, as it is for the B36TC and others.

Read the following if you want to know more:
On the account of compr efficiency change, your car would run richer, but you will also have higher intake temps (IF the temperature was the same at two elevation). It's cooler at higher elevation at a rate of 2degC per 1000', Dry adiabatic lapse rate is 3 degrees celcius per 1000'. ICAO lapse rate which you are quoting is for an atmosphere containing ZERo moisture and is unrealistic in making real world calculations. so you would have 10deg C (or 18 deg F) lower temps, which would help you (and cancel the effect of richer mixtures i just talked about if you don't have proper IAT compensation). So, in all likelihood, 93 octane would not help, since the cooler temps already would be a deterrent against detonation, and you would be running richer. Now, if you had a boost controller and turned your boost back up to 9 psi, then your mixture would be closer to what was tuned, except the compr efficiency change would be slightly higher due to the higher PR, which would still throw things off just like i discussed above, but to a greater degree. So, it all depends what kind of EMS you have, and what compensations it's got. Let's remove the EMS from the equation which complicates things greatly and discuss manual waste gates which levels the playing field. The physics involved are the same.


Lapse rate…I am not even conceding this. Dry adiabatic lapse rate refers to a pocket of rising/falling gas, not static atmosphere. So, it describes a dynamic process. I am not even going to go on… since it’s not even a bid deal if you are right, which you might me. So, it’s 15 degrees and not 10 deg Celsius difference… Again, I am not conceding that you are, I would have to do some research on this.

Wastegates… Are you talking about manual waste gates ala the Turbo Piper or manual boost controllers?

If your so thorough in your explanation why didn't you include intercooler efficiency in relation to decreased density altitude. It sounds like you cut and pasted this from various page on the internet. It's completely incoherent and doesn't make much sense or make me feel like you actually have any understanding of it no matter how technical you'd like to be.

I did say that there are other things in play, and anyone that knows me on this site knows that I am well aware of IC efficiency. The truth is that IC efficiency change due the lower density air fanning it, for the same MAP that the air flowing throw it supplies, is far less important than the compressor efficiency, lower boost MAP. In fact, temp decrease at higher altitudes will have a much greater positive effect to IC eff. than lower density. Now who’s trying to “look like they know what they are talking about”? I will bet anything that you weren’t aware of the internal EGR that I mentioned. IC efficiency, especially with an IC that is over engineered for a given setup, such as the case with Greddy TT, TN kit, and APS, will never be a real concern.

Also, just a note for the future, you with your 5000+ flight hours would be much better served by losing the “if I don’t get it, then I must be right” attitude, and it certainly doesn’t entitle you to accusing me or anyone else of plagiarism. My writing is not completely polished because it’s long, and I wrote it just to help out and NOT with the intention of publishing it in a science journal. If you think it’s incoherent, then I’d read it a few times, and not in the same fashion as one reads the newspaper.

I wasn;t going to get nasty, but i just hate being called what you called me, while still being wrong.

 

Definitely not, you are right. But SCs behave a little differently. You see, thay aredriven by the engine's rpm, which is constant with altitude. So, the reason that the SC lose more boost at altitudes than ST/TT's s because they can't be adjusted on the fly by delaying hthe wastegate opening, and hence increasing the tubine/compressor rpm. Say you are getting 8psi of boost on your SC..that means that at that given spin rate, controlled by the size of the pulley, you are getting a pressure ratio (PR) of (8+14.7)/14.7=1.54 at sea level. Regardless of your elevation, your PR is fixed, because it's a function of spin rate (and your spin rate is fixed because it's delivered by engine's rpm...which are the same everywhere). So, when you go to 5280' (1 mi) elevation, the ambient pressure is approximately 12.1psi, so with the same PR of 1.54, you will get 1.54*12.1-12.1=6.5psi of boost (instead of 8), but keep in mind that this is 6.5psi over the lower ambient pressure of 12.1..so it's a double-whammy. Again, what's important is MAP not relative/gauge pressure. Your MAP goes from 22.7psi (8+14.7) at sea level to 18.6 psi (6.5+12.1) mile high.

At the same time, in a turbo car (which we'll assume did not even have a boost controller, just an 8psi spring in it's wastegate) that makes 8psi of boost at sea level with the same PR=1.54, will go to 5280' elevation and make 8+12.1=20.1psi MAP...because it's driven by gases of the exhaust and is not tied to rpm. So, it will still make the set 8psi over ambient, and not 6.5 over ambient. And this is because it doesn't operate on a fixed PR principle, the turbine speed is adjusted, the PR goes up, to still make it's 8psi over ambient target. So, both cars make 8psi at sea level for a MAP of 22.7psi, but if they go to 5280' the SC will lose boost AND ambient, while the turbo only loses the ambient pressure component of the MAP, and consequently the power on the SC car will decrease approximately 18.1% (18.6/22.7), while the ST/TT car will experienice 11.5% loss (20.1/22.7). the beauty of the turbo car, is that you can recover ALMOST ALL of those loses by turnign the boost back up until you reach 22.7psi MAP again, whcih would be 22.7-12.1=10.6 psi of boost. Don;t let this number scare you, it's higher boost, over a lower starting/ambient. As far as your engine is concerned, you are seeing the same amount of air >>>>> MAP is what matters!

 

I am a frustrated scientist. I love reading these kinds of posts... until they always, inevitably, turn into nasty cockfights.

I don't want to mention any names, but, TODD:

It would probably be easier for JET and Gurgen to maintain a constructive conversational tone if "some folks" would not chime in with inappropriate, provocative comments, such as:

-That's all you had to say in response to that elaborate write-up!?!??!?!

Comments like these do not add to the discussion, and (surprise, surprise) could get some folks riled up. I think the discussion started to turn "nasty" right about there...

That's all I'm saying.

 

Hi GurgenPB,

I agree with everything you have said. You certainly have earned my respect with your follow up postings.

Let's look at the big picture. The question is will a turbocharged engine lose power with an increase in density altitude. As you are aware turbo normalized aircraft powerplants are able to produce flat rated power to a given altitude. If we both agree on that, which we have done, then we can agree on a concusion to this discussion. The generalized conclusion being that the real world loss or status quo of power in a turbo charged motor is directly dependent on the type of system maintaining boost pressure. Would you agree that this statement is correct?

JET

 

Thanks for the feedback bullseye...my comments were not meant to "rile" anyone up... this was an intellectual dicussion from the get-go...I was a bit suprised how quickly the gaurd goes up, instead of saying :"Gurgen, thanks for spending so much time trying to help explain some things in detail and in lay terms"....people are quick to try to find a flaw in what he was saying and discredit him....
since you are so quick to point out where this discussion went bad...look a bit more carefully

....Gurgen wrote a ton of info...info was then misquoted and attacked as false...I chimed in...Gurgen addressed being misquoted...

I have known Gurgen for a long time, back when I blew up my first motor He was the guy that so generously told me to cal him if I needed any help (as he was in the middle of a motor build at the time)...he spend time then trying to help me out... so, not to get all Montel Williams on you, but we need to put our gaurd down and try to help one another, not bicker and try to prove who knows more...

-TODD

 

Jet,

I am glad how this turned out... for the sake of everyone including science itself, lets just be constructive in the future, like I always am. Thanks for the kind comment above. I truly do do all the research and do not post with taht kind of authority unless I am sure of what i am saying. If I am not, than I say so. In this case, the discussion went from hte rather simple idea of will you make the same amount of power at higher altitude, to the much much more complicated idea of why not and how come? lol And the wastegate control mechanism in turbo cars IS not very intuitive, since gauge pressure, MAP, PR come into play...in reality it is very veyrr complex... and i tried to integrate EM into the discussion as well.

Turbocharged engiens will lose power, but we are are addressing her in excatly what manner. Turbocharged aircraft maintain the power on a given segment of altitudes (notice, NOT all the way to critical altitude) by always controlling the preload on the wastegate spring, which is increased more and more and more as you reach critical altitude, which is defined as altitude that corresponds to the maximum pressure ratio of the compressor. And yes I agree with that statement, the matter before in this discussion was that the wastegate spring alone, will maintain a given MAP, which is what I was reponding to as being incorrect. You requirea more complex sustem, because a wastegate spring only maintains a certain gauge pressure not map, necessitating an additional boost control system to get to constant MAP, which is what's done in the airplanes.

This was a good one... and i just hope that people read it since there is a lot to be learned.

 

Thanks for the kind words, Todd. The FI blown engine club is how this is all started.

And bullseye, I think that last quote kind of attacking Todd was perhaps a little misplaced. It got nasty, before it got resolved like it did now (i am glad about that), between Jet and I after Jet's post and on his accord, and I think all of it was brewing under the surface before this. It';s all good now, and lets move on and keet it constructive.

Todd is a great friend of mine and a great enthusiast on this board. He has been part of several breakthroughs in the infancy of this car's modification life along with several others on this board. I got his back. He was simply interpreting what he was reading, which i agree with him on.

 

Here's another added theory on top of it all strictly non-scientific...

since you stated that the turbos have to work harder at high altitude due to the thinner air it would take longer to reach the same power levels. Hence on a 1/4 track you reach peak power later than on a sea level track and based on that your ET's will suffer explaining the difference in performance

 

I can tell you two (Gurgen, Todd) are friends; You obviously stick up for each other, which is what friends do. I have nothing but respect and admiration for you both. Whenever you guys post (JETPILOT, Q45TECH, and a few others, too!), I know I can look forward to learning more about my car. That's why I visit here.

I feel I should commemorate this occasion in some way: I think it's the first time I ever typed in a mild rebuke where it was not only interpreted as such, but also had the desired effect. Group hug, everybody!

Thank you for your input, too.

 

Bullseye, I agree with you. This at the end turned out to be a pretty contrucrive thread. Those who really wanted to, followed the discussion, and I think they'd be better for it. It helped myself organize all my thoughts that i wanted to synthesize in thit manner for a long time.

 

cool..let's keep it civil guys...evryone is here to help! glad it ended well...ok, group hug

 

Gurgen, thank you for taking the time to answer my question. Very well explaned. You definitly have my respect!

 

2fast...no problem.

Love your signature!

 

Great discussion. Just to add a tiny detail, humidity also plays a small factor because the more humid the air is, the less dense it is. H20 water vapor is lighter than the N2 and 02 particles it displaces.