Turbo Question???

[rjrkihap]

Does the turbo have to spin faster at a higher altitude to achieve the same boost as at sea level? Something I noticed last time I went to Wyoming was that the turbo tried to suck in (collapse) my air intake hose connecting the air box to the quarter panel of the truck. Does that imply the turbo must spin and therefore suck harder to get up to the 20 lbs. of boost?



Ron

 

[Alan Reagan]

It is not uncommon for the intake to suck closed even at sea level. That's why most members remove it from the box..... to reduce restriction. As far as spinning faster to gain 20 lbs of boost..... this should create a fire storm of answers. Theoretically, I say no, because you are only gaining 20 lbs of boost over what your ambient pressure is when you start. Theoretically the turbo would have to work harder at sea level because it is starting with 14. 7 psi ambient and therefore would have to provide 34. 7 psi with 20 lbs of boost. At altitude the psi pressure at the intake will be lower so the turbo should be working the same amount to build 20 lbs of boost. Notice it is 20 lbs of boost over what you start with. If your ambient was 10 psi, then 20 lbs of boost would be giving 30 psi which is 4. 7 psi less than sea level.

 

[MY6EATSV8'S]

yes the air is thinner=must spin faster to make the same boost

 

[Dane]

In addition to removing the inner fender to airbox connector and adding an AFE filter, I drilled four 1. 5" holes in the bottom of the airbox. No more strange howling noises and plenty of air to the engine. I don't mind the extra turbo music from the mods.

 

[DocStressor]

Yes, the turbo must spin faster to provide the same amount of boost at high altitude. But your gauge will not measure boost accurately since it measures the differential pressure between the inside of the manifold and ambient air pressure, which is lower at high altitude. So a reading of 20 psi at 10,000 ft will deliver less air volume than 20 psi at sea level. That's why some power and mileage is lost at high elevations

 

[Alan Reagan]

My thinking on this is that the exhaust flow is "thinner" so will it has less mass (at displacement volume) to spin it faster. So can you get 20 lbs of boost at high altitude? I'm thinking that you would get to 20 lbs of boost at altitude... ... it would just take longer to do so. If the turbo is spinning faster, there is going to be an EGT problem, not because the air is thinner and it won't cool as efficiently throught the intercooler (which is the case, somewhat), but the additional spinning time or faster spinning would cause the molecules of air to be beat together, creating more friction and generating more heat in the compressed air. This is definitely one of the best questions I've seen in a while. Doc Tinker must be feeling a little "down" that he didn't think of this one.

 

[Steve Campbell]

"Thinner air"

Does this have a lot to do with the poor fuel mileage that some complain of? Has anyone looked closely at the location of those posting poor fuel mileage? Cummins probably has some specs as to what to expect in performance loss at altitude!!!

 

[hawkerpilot]

hello guys

just my 2 cents, to maintain a constant 20psi with changing altituid, turbine speed has to change. A turbine engine is a derivitive of a turbo. If I take off with 50% thrust and if I want to maintain 50% thrust I have to increase turbine speed as i climb. not trying to flame anyone. b t w dont try a 50% take off it will put sk-id marks in your und-r- w-re.