EGT's and altitude

[JCleary]

I took a trip up towards Lake Tahoe last weekend, and I noticed that at altitude:



1. Cruise EGT's were 100-150 degrees hotter than at sea level



2. The truck had major lag off idle (box on or off), accompanied by a cloud of smoke with my box turned on. Once the turbo spooled, the truck was quick (and clean) as normal.



Is this what happens to all trucks in the altitude? If so, a laggy turbo would be terrible to have!

 

[CLAYTON]

For every 1000 feet of elevation you loose 1% hp. So a 300hp engine at 10,000 ft you would have a 10% lose in power = 30hp

 

[CJEliassen]

For every 1000 feet of elevation you loose 1% hp. So a 300hp engine at 10,000 ft you would have a 10% lose in power = 30hp

Actually, it is closer to 3% for a natually aspirated engine. If you do not exceed EGT or wastegate limits, a turbocharged engine will actually produce more power at 10,000 feet than sea level do to a reduced back pressure.



A little extra lag is normal. Since you have almost no boost at idle and less air is getting into the cylinder, you produce less exhaust gases to drive the turbo, and you need to spin the turbo a little faster to compress the same amount of air.