Turbo or Supercharging vs Altitude

[Vreracing]

This is not just for the Viper, but for performance in general.

Where I live its 3800 feet in altitude. Not much, but it does make a little difference.

If a turbocharged car is advertised 0-60 at sea level of lets say 7.2 sec and another car is 0-60 at 7.5 sec with a difference of .3 sec. If you take these two cars up to altitude and then test them, will the turbo charged car get a significant advantage, thereby increasing the difference in 0-60 times.

It seems that way to me, but I have not seen any published tests.

 

[Vreracing]

I guess no one knows.

I guess I've been pondering this ever since I took a 944 Turbo S up over BobCat pass in New Mexico. The car was going 95+ at about an 10% grade at an altitude of about 9800 feet.

The turbo lag was pretty long (since it had an Autothority stage 2 chip is was pretty bad anyway) but the peak performance was there.

Obviously the Viper has no turbo lag, but the performance is definitely down at altitude. So the question still in my mind is whether the increased turbo lag will offset any gain in horsepower.

Interestingly enough when you look at running and cycling. The running gets slower at altitude, but the cycling stays the same. This is due to the fact the decreased resistance in air pressure allows you to compensate for the lack of power.

I guess I felt I had to answer my own question since no one else would. I sort of hate orphan questions sitting out there. Its so sad.

 

[MES]

Here is my understanding, it's by no means 100% accurate.

With a STOCK forced induction car you WILL loose some power going to altitude. I don't know exactly why but it has to do with the computer/electronics and the maximum amount of boost they will let the car make. So it will loose some power but the % is not as great as a normally aspirated engine.

If you go with a MODIFIED forced induction car then you will not loose power if you compensate for the thinner air. For example if a car is making 10 lb of boost at seal level then it might make just 7 lb at 3500 ft. But if you have a boost controller that can boost the car back up to 10 lb, then no you will not loose any power at higher elevations. To the car it's still seeing 10 lb of boost just like at sea level. Now if you take the car back down to sea level it might make 13 lb of boost which may be too much which would cause detonation therefore the boost would need to be reduced back to 10 lb.

So a turbo/supercharged car will have a big advantage if it can be tuned for the altitude it's being used in.

Well there you go, this is no longer a orphan post and maybe my comments will spark others.

 

[Russ M]

Ok here goes,

A turbo charged factory vehicle will loose just as much power as the naturaly aspirated one. The problem is not in just the psi level but in the density of the air coming in. So even if the ecu does bump the boost to say the factory 10 psi, it is still going to loose hp due the the lack of volume.

On a modified car turbo cars can make up for the loss of power in higher boost pressures, which does make them more ideal for higher altitudes. However they still loose hp on the same level as normaly aspirated cars. You can make up for the loss by bumping the boost beyond what you would run at sea level, but you will damage your motor if its not set up to run that boost.

A good example would be a pikes peak car say Rod Millens celica/tacoma powered by the Toyota 2.1 litre GTP motor. It makes roughly 1100hp at sea level, and at the top of the peak it makes about 600-700hp, and the lag is horible.

 

[Makara]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Vreracing:
This is not just for the Viper, but for performance in general.

Where I live its 3800 feet in altitude. Not much, but it does make a little difference.

If a turbocharged car is advertised 0-60 at sea level of lets say 7.2 sec and another car is 0-60 at 7.5 sec with a difference of .3 sec. If you take these two cars up to altitude and then test them, will the turbo charged car get a significant advantage, thereby increasing the difference in 0-60 times.

It seems that way to me, but I have not seen any published tests.

<HR></BLOCKQUOTE>


I remember reading that a stock turbo car should retain it's performance untill the altitude is over 3000 feet. I have no evidence to back that up, it's just what I read a few years ago.

 

[Tim]

A normally aspirated engine (Viper) will lose 3% of its power per 1000’ increase in altitude. If your day is warmer than normal (allow a 2 deg Celsius drop in temperature per 1000’) even more power is loss. All measurements are based from sea level at 15 deg C and a barometric pressure of 29.92 inches. At 4000 feet you will be down 12% and if the day is warmer than 9 deg C more power is lost from the stock rating.
A 450 hp Viper will now be making 396 hp or even less depending on temperature.

A forced induction system will not lose as much power and in some cases it can be set up to maintain a rated power to much higher altitude to where even it will start to lose power due to all of the inefiencies of the system.

Here is a little story against a Mercedes AMG. My stock 94 RT10 with 25,000 miles on it, the car makes 400 HP at sea level. Edmonton is 2200' ASL with a temperature of 80 deg f. With the high density altitude my loss in HP would put me somewhere around the 350 HP (estimated, I will put calculated numbers in next week). There is a long story that goes with this but at the end of the day these cars were neck and neck (my jaw had dropped to my chest) until 150 MPH and then I started to pull quickly on him at this point where his car governed out. These guys have got all the goodies including traction control and with the super charger they normally maintain full power until a much higher altitude. Not like our normally aspirated engines that drop 3% in power per 1000-foot change in density altitude. Be careful with anything that is supercharged or turbocharged that makes close to your power at high altitudes and or hot days you could lose.