On another forum there's a bunch of guys discussing how engines lose power with altitude.
The bloke that started the thread read that at the WRC round in Mexico, the cars are running about 2km up and so they'll lose about 20% power.
I reckon that's a crock, as the boost on the cars would be set as an absolute, not relative. So they'll still make the same power (at least) than they would at sea level. I actually argued that they'd make a little more power because of the decreased air temperature over the sea level temps.
But they're still carrying on about all sorts of stuff and I can't see a flaw in my reasoning. I understand that increase/maintain in power won't continue as you keep going up as you'll get to a point where the wastegate is shut and the turbo just isn't pumping enough air.
The other factor is the inlet restrictors - I can see how they may choke the turbo more with the thinner ambient air but I simply cannot see anything like a 20% reduction in power from a 2km hike in elevation.
On this discussion on yet another forum, it has been mentioned that the compressor stall line would be closer with the higher elevation, thus limiting the turbo. I reckon the teams would know this and compensate with a bigger turbo.
Comments?
WRC cars and high elevation?
Started by
Bill Sherwood
, Apr 21 2007 14:48
1 reply to this topic
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#2
J. Edlund
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- 1,323 posts
- Joined: September 03
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Posted 21 April 2007 - 18:47
In WRC the power output is determined by the maximum flow through the restrictor from about 3000 rpm and up. As air density drop, maximum flow though the restrictor goes down, meaning that engines will lose power with altitude, something that WRC drivers also have mentioned.
A turbo engine can normally compensate for a lower air density, but it can only compensate to a certain degree. Sooner or later a turbo (without restrictor) will reach choke or maximum turbo speed (due to high pressure ratios) thus limiting the power output.
In races such as Pikes Peak hillclimb engines are equipped with oversize turbos. But this also have disadvantages, pick a too big turbo and you will suffer at low altitudes (at the start) and going to small and you will lose power at the end of the race.
In addition to the mandated restrictor in WRC, the size of the turbo is also limited.
A turbo engine can normally compensate for a lower air density, but it can only compensate to a certain degree. Sooner or later a turbo (without restrictor) will reach choke or maximum turbo speed (due to high pressure ratios) thus limiting the power output.
In races such as Pikes Peak hillclimb engines are equipped with oversize turbos. But this also have disadvantages, pick a too big turbo and you will suffer at low altitudes (at the start) and going to small and you will lose power at the end of the race.
In addition to the mandated restrictor in WRC, the size of the turbo is also limited.
