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Discussion Starter #1
I'm running a K&T set up on my XP with 9-1 CP pistons & was told I could run 12 psi on pump gas without a problem at the dunes, well that got me thinking when I'm in Colorado more around 6000' elevation I should be able to bump the boost up a bit to make up for the loss of air! My question is, if I'm correct how much? Thanks, Troy
 

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Discussion Starter #3
I should have mentioned the dunes I run are the Imperial Sand Dunes which is more or less sea level! I was thinking I should be able to run @ 14 up here in CO!
 

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Atmospheric Pressure at Sea Level is 14.696 PSI.

Atmospheric Pressure at 6000' is 11.777 PSI.

14.696 - 11.777 = 2.919 PSI

In round terms - At 6000' elevation .. .. Crank up the Boost 3 PSI to eqaual cylinder pressure running at Sea Level.

Hows that for a specific answer .. .. .. :rofl3:

:ride:
 

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TURBO'S RULE
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Not so fast everyone...

Does boost change significantly at elevation?
Will it matter what ambient atmospheric pressure(elevation) the turbo is operating in as far as the waste gate is concerned?
Does Wastegate set point need to be changed to reach similar boost pressure at greater elevation than sea level?

Wastegate diaphragm is boost pressure dependent not atmospheric pressure dependent.
Wastegate opening is mostly determined by the spring in the wastegate diaphragm.
Its all about absolute pressure, not gauge pressure.
Wastegate runs on absolute pressure, not gauge pressure. Even when wastegate is set using a normal boost gauge(zero'[email protected]_sea level atm)
example:
atmospheric pressure @ sea level 14.7psi
boost gauge [email protected] set point @ sea level +15.0psi
total 'absolute' wastegate set point pressure =29.7psi
(not boost gauge pressure)

So the variables are atmospheric pressure and absolute boost pressure.
In the above example we must reach 29.7lbs absolute' to satisfy the wastegate set point. The turbo has to supply this additional "absolute pressure difference in order to satisfy the wastegate.
You won't be able to read this on your boost gauge because a boost gauge is zero'd out at atm 14.7. If we go to elevation and change our ambient ATM to 12.0 psi instead of sea level 14.7, then your turbo will have to make up that 2.7lb difference before you can even read 1lb of gauge boost. In other words your gauge is starting with a 2.7psi deficit compared to sea level. The same holds true for the wastegate spring opening pressure. IT does not change. Turbo has to and will, make up the deficit and will do it with a regular spring Diaphragm operated wastegate, and no other controller needed.

On a side note...
At some point in altitude the compressor(turbo) will reach max and not have the capacity to deliver the volume of air needed to reach set point of wastegate. This is critical pressure altitude. But this doesn't seem to effect most rzr kits at elevations.The turbos used in most RZR kits are more than capable of supplying enough air at 8000' to reach normal 'absolute' boost limits.

The turbo has to work harder to keep the same boost as in lower altitudes. This means it runs at a higher pressure ratio, which creates more IAT…How does raising boost effect high elevation IAT ?

Engines need air mass, not volume, to operate. A non-intercooled RZR might run the same boost and volumetric efficiency (volume of air moved vs. displacement of the engine), but produces a lot less power than the same engine with intercooling. Higher temperatures make the air "thinner", which means you have less mass per volume (lower density), so the air mass entering the engine is lower.
Higher altitudes also make the air thinner (lower density), same effect as higher intake temps.


What I'm saying is 12 psi gauge boost is 12 psi gauge boost at any elevation. All our gauges are zero'd at 14.7 atm. We are not using absolute pressure controllers or gauges. All ours are zero'd at 14.7psi atm.
So no need to change anything. You might see it take more time to reach boost since the turbo is starting with a deficit. But that extra work the turbo compressor must make up, won't disappear no matter how you set the waste gate or boost.
 

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You can get technical till your blue in the face.You referred to pump gas so I would just go back up to 12 psi.Besides cylinder pressure theres the dynamic compression ratio (pump gas)At a higher altitude you will be running more turbo rpm moving your self on the compressor map affecting ratio,inlet temps,etc.K and T can tell you exactly what to run for boost as they know the compressor map,but in reality they probably tested at altitude and can give you real world results and what works best,or you can listen to all of us mentally masterbate through the key board.
 

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Interesting allcool, but if I take my old RZR with MCX turbo which is set 11 PSI at almost sea level and go ride in Sand Mountain, Nevada which is in 4000' elevation, my boost gouge star showing 14 PSI. The boost is adjusted be solenoid valve which is a part of MCX kit. But after go thru your post I am little confuse now.
milos
 

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Discussion Starter #11
Allcool thanks for the info I'm going to read it a few more times, because I'm a retard, to try a grasp all of it!
Noodles I was thinking more along the lines of cylinder pres also, if we go up in elev. theres less pres in the cylinder to start with which is where I was thinking it could be made up with boost!
Yes I realize I can call K&T & bug them, but I also enjoy all the input & opinions of the forum members!
I'm totally new to the turbo side of things & have no problems admitting to my ignorance, but I'm eager to learn!!!
thanks for all the info!! Troy
 

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TURBO'S RULE
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Interesting allcool, but if I take my old RZR with MCX turbo which is set 11 PSI at almost sea level and go ride in Sand Mountain, Nevada which is in 4000' elevation, my boost gouge star showing 14 PSI. The boost is adjusted be solenoid valve which is a part of MCX kit. But after go thru your post I am little confuse now.
milos
Not sure about that mcx solenoid, other than it bleeds off pressure to keep wastegate from opening, to increase boost at elev. Tried to get specifics on it a couple times but no one had details, or would give them out. From what I've gathered, mcx adds more boost to make up for increased iat, and less air density at elevation to keep hp up.

Anyway, without that mcx solenoid on a regular wastegate controlled turbo system, the max boost # will not change much, if any, at altitude. Other than take longer to reach max boost. HP will go down though.But the boost gauge psi # should stay close to the same once it reaches max boost set point on wastegate.
 

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TURBO'S RULE
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Wouldn't the boost gauge read less at altitude and you'd want to increase your boost to get it back to 12?
No, Not on a simple diagram controlled wastegate turbo system.
Its all about Absolute vs Gauge pressure.
Allcool thanks for the info I'm going to read it a few more times,
Sorry, not trying to confuse anyone, just fluid dynamics is my thing, or the less complicated parts of it are... :rofl3:
 

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Interesting allcool, but if I take my old RZR with MCX turbo which is set 11 PSI at almost sea level and go ride in Sand Mountain, Nevada which is in 4000' elevation, my boost gouge star showing 14 PSI. The boost is adjusted be solenoid valve which is a part of MCX kit. But after go thru your post I am little confuse now.
milos
Very interesting, I was curious how that worked.:popcorn:
 

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Hold the Presses!

This is certainly an interesting discussion. I have my 800 set to 10 psi of boost at 2800 feet. With no changes to the setup, it will boost about a half pound more at 1700 feet in Waynoka and the power is noticeably higher but nothing astounding.
Last month at Taylor Park, we were at 9000 feet. The first ride had me pleasantly surprised it would start at all as the install hadnever been run at that altitude. Everything is good right? Not, the boost would only hit 8 psi. I tightened up the wastegate controller a round or two and nothing in the way of an increase. Power had dropped off as well. It felt about as strong as a stock RZR 800 at 2800 feet and still ran good up to 12000 feet but there was the drop in horsepower no matter where you were.
I talked to two gentlemen who were with Aerocharger at Frank's big feed and they told me that my experience was typical for any turbo system with respect to power loss and the inability to maintain the same boost levels I was at home.
My Twin turbo pickup however didn't appear to suffer any such loss up to 12500 ft ulling the mountain passes so I'm left wondering if it might be the size and trim of my Rzr's turbo that is leaving the boost on the table or ????
Once back at 2800 feet, everything runs fine again. One more note. My A/F ratios did not change at all at Taylor Park as compared to the A/F here at home.
 
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