So I know that a normally aspirated car loses power with every 1k feet in elevation. How does a turbo'ed car do at altitude? Is there a formula like with normally aspirated cars. Does it simply "spool" more air thus maintaining sea level output?

 

In theory, Turbo cars should lose ZERO power at altitude, given that the turbo pumps air into the engine up to a given, fixed value... i.e, .8 bar is .8 bar no matter if you are at sea level, or at 10,000 feet.. That's the theory... The reality is that the turbos have to suck a significantly greater volume of air in to accomplish this fixed level of pressure. Because the air is less dense at elevation, the turbo has to suck more cfm through it to pack the cylinder full of the same amount of air it would at sea level. I had a 550HP 944 turbo that I used to drive from San Francisco to Lake Tahoe.. Sea level in SF to 6400 feet and more in Tahoe. What I noticed was more lag, more heat generated by the engine leading to higher water temps etc... The calculations show that a normally aspirated engine loses approximately 27% of it's power at 6,500 feet. A Turbo would then have to suck approximately 36-37% greater volume of air (because of the lesser density) through it in order to pack the cylinders to the .8 bar value. This means that even though the engine SHOULD produce the same peak power.. it will take the system more time to suck that additional cubic volume of air into the engine, making the engine feel more laggy and sluggish...

I hope that makes sense...

 

Makes sense. Thanks.

So you probably lose some power through heat, friection, greater load, etc...
but the turbo's are able to substantially reduce the effects of altitude.

 

Yes.. you are correct... That's why turbocharged cars do so well in the Pike's Peak race and why turbos are used on Airplane engines (Turboprops).

One other issue with altitude is that because of the longer "fill rate" the engine mapping and fueling is a bit off sometimes as well as the MAF results...

 

That's the first sound explanation I've seen on any board. Thanks.

 

Oh and one other thing... Your tires will become ROCK HARD at altitude... Because there is less pressure at altitude to resist the pressure in your tires, your tires will reach RIDICULOUS psi at 5000 feet plus... Ask me how I know this...

 

[quote=80shilling;2581681]Yes.. you are correct... That's why turbocharged cars do so well in the Pike's Peak race and why turbos are used on Airplane engines (Turboprops).

Turboprops are not piston engines. They are jet engines with a prop attached and loose a great deal of power at altitude.

They make up for it as they produce more power than can be used at a lower altitude and just add more fuel as they climb.

 

Great explanation. If you want to know why they get hotter, just put your thumb over a bicycle pump with one hand and pump with the other.

 

I drove over the Swiss alps last year (over 9000 feet) and the turbo lag is MASSIVE at altitude! All the hairpins had to be taken in 1st gear as 2nd gear from 2000rpm you would be waiting for over 5 secs for the turbos to kick in under full throttle.

 

[quote=Sloopy;2582570]See... I learn something every day.. I was convinced that turboprops were in fact turbocharged...

 

While turboprops are indeed turbine jet engines which drive a propeller through a gear box, there are a great many turbo-charged piston engines in service in general aviation aircraft.

 

I've got a turbo'ed airplane but it is designed to produce sea level HP at alititude. It's not meant to create addtional HP just to preserve the HP it had at sea-level.

It runs hotter both in CHT's (350f range) and EGT's than its normally aspirated counter part.

With these porsche cars it sounds like that its more laggy but it maintains the same HP just takes longer for you to get it.
Interesting.

I snowmobiled last year with a guy who had turbocharged his 4 stroke. It was pretty impressive compared to my uncharged 800 2stroke.

J