.965*.965*.965......965*.965 = .652 1.000-.652 = .348 ~35%

 

Exactly right. My intention is to maintain rated horsepower (sea level). There will be very little difference around home but when we head for Leadville, CO I'll have the benefit of of an extra 30% (10,000 ft) over what I would otherwise, all while operating precisely within OEM parameters...no overload of any kind...the ECM will think we're in Houston...

 

Will the compressor map will be pushed right a little bit since the air density is thinner 10000 ft up compared to sea level? May slow response a little bit ?

 

Rube Goldberg would be proud.
There has already been more effort into thinking about this "turbo to sea level" thing then it would have taken to drink a couple beers and a few hundred bucks to make 5 pounds and be happy.

When does the cat tip over the candle to open the waste gate when the barrometric pressure gauge has already scared the bird out of the cage?

 

Lmao

 

If you're interested the solid state control it will work something like this. There are four main components: two pressure transducers registering 0~30 psia, an Arduino board, and a stepper motor. There will be other bits and pieces to tie it all together but that's basically it. One transducer will be located in the pressurized flow and the other outside. The stepper will be coupled to the waste gate shaft. The stepper will require ducted fan cooling as it is only capable of 150F. Transducer outputs will have to be first measured at the referenced pressure settings. The pseudo code will look something like this...

While pressure inside is > 16.7 psia
Rotate +1 step (open waste gate fractionally)
If pressure outside > 12.7 psia then
If pressure inside - pressure outside < 2 then
Rotate -1 step (close the waste gate fractionally)
If pressure outside is <= 12.7 psia then
If pressure inside is not > 14.6 psia and < 14.7 psia then
Rotate -1 step (close waste gate fractionally)
Delay 40 ms (wait for pressure to stabilize)
Loop

For all intensive purposes this will execute in 40 ms. If the stepper has 100 steps per rotation and the waste gate rotates 90 degrees then the waste gate has the potential of going from open to closed in 25 executions or 1 second. Is that quick enough under the worst circumstances?

As a fail safe maybe the BOV should be set to 6 psig.

 

I don’t think so simply because I’ve not seen any caveat to that effect on any compressor map. As far as response time, the circumstances will always be one where I head up a steep grade, gradually depressing the foot feed. Surely, response time will not be a problem but if it is I’ll live with it. It’ll just add a couple os seconds getting up the hill.

 

While pulling loads, everything happens so slowly, response time seems like it would be a moot point.

 

Altitude (density) does effect the compressor, and a given plot will move right on a map with elevation. Its even noticable with big temp swings at a given altitude.

 

Except not. Your putting huge load on the engine, especially if it downshifts spool is going to happen very quickly. My ecoboost will hit 23 PSI almost instantly with a 9500LB travel trailer at 10k+ elevation

 

HAHAHAHAHA!!! I give you credit man. Definately a thinker. lol

Are you going to artificially add pressure to the crank case? After all if you don't, the pressure drop across the piston will be higher then when you are at actual sea level and that is going to cause you to make more power then at sea level! We can't have that!

 

This is the kind of input I was looking for! I know some of you guys are having fun with this and that’s OK. I understand that my thinking is off-the-wall.

So, it adds more power. Is this power incidental to the ECM? More power just means less throttle in my scheme. I just don’t want to operate outside the OEM parameters.

 

Again, good information. So, I have a lag on a downshift. How long a delay? One second, two?

 

Thinking is what I did for a living. The engineer had a problem, I came up with a solution. I was a senior mechanical designer. FEA, solid modeling, I did it.

In this case I need some help with the thinking. That’s why I’m here.

 

It depends... The engine may already be loaded and producing boost, just depending on the nature and design of the system, in my case 0-10PSI happens so fast the needle wont keep up, 20PSI is in the first second. You will see posts describing boost being "like a lightswitch" you really can go from vacuum to a high level of boost very quickly.
I think you should start playing around with matchbot, get an understanding of the factors that goes into one of these systems that way. It will give you an idea of how much exhaust your going to have to be gating, and how quickly. I do not believe your stepper will be fast enough to make the turbo controlled or smooth. You should look at what the OEM's are doing, most modern turbos are computer controlled. Again, I think setting a 5psi spring and calling it good is your best bet. Even if you could keep the pressure artificially at sea level there are many other factors that you can't easily control. Your going to try to fool a modern ECM, I don't think its going to play nicely, you should be working with it symbiotically.

 

All that you say is correct...BUT...my system is not load dependent. It is strictly dependent on atmospheric pressure. The change is very slow. Very slow. When a down shift occurs it will likely be at full boost already. It will be important that the waste gate opens quickly enough to avoid over-boost.

 

Your making some assumptions that may or may not be true. I do not believe a fooled system is as reliable as a properly calibrated and tuned one, if this is a vacation rig the last thing you want to be doing is worrying about the reliability of the stuff underhood.

Your assuming that the air coming in from the turbo is the same as ambient air pressure would be at sea level. It isn't, its going to have a different velocity and different turbulence, until you actually dyno the thing your not going to know how the plenum or heads react to positive pressure, it isn't as cut and dry as replacing missing atmospheric pressure.
Your assuming that your barometric pressure sensor is in a location it can be fooled.
Your assuming flow into whatever your mass air meter is will be measured properly
Your assuming the air intake temperature is going to be similar to stock, and it wont, its going to be quite a bit hotter, is your ECU going to be able to account for this, are you going to try to make up the power difference due to the air density?
Your assuming the exhaust side pressure increase will not have any effect on power production or engine behavior.
Your assuming your O2 sensors are going to be in the same place and unaffected
Your assuming your cat converters are going to be unaffected by the turbo in the exhaust stream.
Your assuming your stepper system can move the gate fast enough to keep the ECM thinking everything is ok
Your assuming the stock ECM will forgive all of this.

There is more, but i'm sure you can figure it all out.

Having the thing properly tuned gets around all of the assumptions, ensures longevity, reliability, allows you to get something from the investment of the turbo system.

 

^^^^ this.

 

But wait. Don’t your concerns come from experience with much more aggressive setups? We determined to run a minimum 2 psig ranging up to 5 psig. The progression from minimum to maximum will take place over the course of hours most likely. Yes, on a downshift it will be necessary for a near instantaneous response by the waste gate to dump the extra pressure. It seems unlikely to me that the response time of the waste gate (i.e. inertia and friction) can possibly keep up with the electronics. Keep in mind that the 40 ms delay was a somewhat arbitrary guess on my part and would ultimately be set to match the waste gate response, expecting the electronics to be faster.

Are the heat and the other variables really a concern in this benign setup? Just asking.

 

No disrespect to anyone here or their builds, but it is interesting to see 2 guys on totally different ends of the spectrum of how they approach their build.