MPI Low Boost Turbo: PSI vs Altitude

[98Slim]

Low Boost MPI Kit: Assuming the kit is calibrated for sea level at 4.5 PSI what would one expect to see at 1000, 2000? I was just running at 2210 ft and seemed to be at least 5 psi, No EBAC so this is just what the waste gate is set at. thanks

 

[twyztid]

Did you ever get an answer elsewhere?

 

[cannondale27]

The Boost should be the same at any Altitude right? Isnt that the point of a Turbo?

 

[petey_sx700]

I think he is looking for a recommended safe number at his normal 2200 feet. I would think that 5 is in the safe range. As that's what my Hurricane runs at 800 or so feet. Someone with more experience in MPI fueling could possibly give him a higher recommendation for that height? As cannondale said the max boost will be the same at all heights until you turn the wastegate rod.

 

[Mike P]

Low Boost MPI Kit: Assuming the kit is calibrated for sea level at 4.5 PSI what would one expect to see at 1000, 2000? I was just running at 2210 ft and seemed to be at least 5 psi, No EBAC so this is just what the waste gate is set at. thanks

I found this artical on the SnoWest Snowmobile forum, not sure if its what your looking for.

"Heres a post that was put up in another thread.

I'd really like to see this out at sea level in Maine or Quebec. That's the turbo run terrible grounds. Not sure they have the perimeters for that as they come.....also clutching included? Or clickers on primary work?

Good topic.

Here is my take, my opinion.

A turbo on a low elevation sled needs to be looked at in a different way. :face-icon-small-con

Since the charge pressure, as MAP, on a sea level sled are already higher from ambient atmospheric pressures.... the change in HP is not as apparent to a flatlander because he has more hp on tap to start with.

Lets say you have an N/A engine that is making 165 hp at low elevations... You put a turbo on it to bump up your HP...
Add say, 6 lbs of MAP to make it 20.7 (1.4 bar) after turbo, ambient 14.7 + 6 = 20.7... You will still be making the same power as that same sled at 10,000 feet that has a MAP of 1.4 bar (+/- a small fraction).

But here is where the Perception plays a roll... The guy that rides at 10,000 feet may have 120 hp on tap on his NA sled because he's removed around 4 psi of atmospheric pressure. That '10,000 foot guy' adds a turbo to the same sled as you have to get that 1.4 bar MAP and VIOLA!!... he now has that 180 + hp that you have on your sled at low elevation (+/-)...but the difference HE feels is 50% more Horsepower.... BIG Difference.

Compare this 50% gain at 10,000 ft to your situation... You have gained 15 hp at the same boost level (1.4 bar)... which is only 11%.... Many would perceive this as 'less bang for the buck'. You don't feel as much of a difference as your buddy on HIS stock machine riding next to you at sea level as the guy who is riding at 10,000 ft next to his buddys same N/A sled.

If you want to pump up the hp beyond "reasonable" MAP pressures... which seems to hover around 1.3-1.5 bar for practical purposes with our 2-stroke sleds and a well designed turbo systems... you are going to have to really push the engine and turbo system.

If you wanted to feel that same 50% kick from your same sea level sled... you are talking about a sled that will have around 250 hp on tap... That sled probably would be running north of 1.8 bar... which will require different fuels, intercooling, bigger injectors etc etc... IMO... you would become a tuning guru by necessity in that scenario.

In short...getting 180-200 hp from a given 2-cylinder 2-stroke is a whole different story than getting 250 hp from the same engine....IMO.

The job of the turbo system here is to provide as CONSISTENT as possible charge-side pressure (MAP) and temperature as possible.
The best turbo systems provide the most consistent MAP/Temps throughout the range of elevations, and rider input for the desired HP level.

Have a look at the helpful chart from gmmustangt below... it may put this into perspective.
Note: I've changed his title of 'Turbo PSI" to "Gauge PSI"

See this thread for a description of what I mean by "gauge psi"
Clickable link
http://www.snowest.com/forum/showthread.php?p=4000543


Simply put if you are running "6psi" at sea level. With an altitude compensating feature. Rough numbers:
Typed on my phone .. Hopefully it lines up.

Elevation. / Atmosphere PSI. / Gauge PSI. / PSI Absolute

0ft ...... ...... 14.7 .................. 6 ............ 20.7

1000ft. ...... ...... 14.2 ...... ...... 6.5 ...... ...... 20.7

2000ft. ...... ...... 13.7 ...... ...... 7 ...... ...... 20.7

3000ft. ...... ...... 13.2 ...... ...... 7.5 ............ 20.7

4000ft. ...... ...... 12.7 ....... ...... 8 ...... ...... 20.7

5000ft. ...... ...... 12.2 ...... ...... 8.5 ............ 20.7

6000ft. ...... ...... 11.8 ...... ...... 8.9 ............ 20.7

7000ft. ...... ...... 11.3 ...... ...... 9.4 ............ 20.7

8000ft. ...... ...... 10.9 ...... ...... 9.8 ............ 20.7

9000ft. ...... ...... 10.5 ...... ...... 10.2 ............ 20.7

10000ft. ...... ...... 10.1 ...... ...... 10.6 ............ 20.7"