The Frustrations of Altitude

[mwiener2]

Stage 2 at sea level (50 degrees in shop)

http://i13.photobucket.com/albums/a257/mwiener2/IMG_0087.jpg

 

 

 

 

Stage 2+ at sea level (90+ degrees in shop)

 

http://i13.photobucket.com/albums/a257/mwiener2/mikewhptq.jpg

 

 

 

 

Stage 2+ at 5500 feet

 

http://i13.photobucket.com/albums/a257/mwiener2/scan0001.jpg

 

 

Stage 3 at 5500 feet

 

http://i13.photobucket.com/albums/a257/mwiener2/DiscoPotatoDyno.jpg

[chenc544]

I look at altitude as an advantage as oppose to a handicap.

It's all relative, with a FI engine I have an advantage over NA engined cars at altitude and no worst than other FI cars. So it really doesn't matter how much more whp I could make at sea level.

[Legend]

I look at altitude as an advantage as oppose to a handicap.

It's all relative, with a FI engine I have an advantage over NA engined cars at altitude and no worst than other FI cars. So it really doesn't matter how much more whp I could make at sea level.

 

Exactly! Our losses are what... 4-6% less than NA cars? So on a 300HP crank HP we have a 15HP advantage over a similarly powered non-turbo. Sweet. I want more altitude.

[mwiener2]

NA loses about 26%

 

Turbo loses about 18%

[chenc544]

NA loses about 26%

 

Turbo loses about 18%

 

I'm not getting into that discussion again...

[praedet]

NA loses about 26%

 

Turbo loses about 18%

You are wrong, again

[RockyMtnGT]

I read a Car & Driver article about altitude vs HP. It stated that NA cars lose about 3.3% of their HP for every 1000ft above sea-level you go.

 

So at 5.280 x 3.3% would mean that an NA car is down almost 18% on their HP vs a FI car. The article also stated that the effects on a FI car are "neglible" in comparison.

 

Those hits you take on your dyno results look to be considerabley more than what I wopuld call "neglible"! Still lookin like more than enough to me though! lol

[mwiener2]

On a stock car, the effects are neglible. Lets say the stock turbo can boost to 16psi without turning into a flame thrower. Stock boost target is 13psi (for example).

 

At sea level, it hits 13psi no problem. Up here we have ~2 psi less atmosphere. since the turbo can boost to 3psi past it's target, the 2psi loss in atmosphere is made up for by added boost from the turbo. Once you completely leave the efficency range of the turbo (stage 2) the car starts to loose power at altitude.

 

(Way overly simplified example)

[Prime Power]

I don't know about power, but my mpg went from 20 to 28 went I drove in Colorado. This oklahoma humidity, or something is killing my mpgs.

[mwiener2]

Higer Altitude = less air

less air = less fuel

less fuel = better MPG

[Prime Power]

If you have less fuel, and less air you have less power. But it takes x amount of hp to go a certain speed. So how does that work out. If you have less power at a given rpm, you would need to run @ a higher rpm to maintain say 70mph.

[mwiener2]

A school bus needs something like 15hp to drive 55mph

 

 

Thinner air at higher altitude is easier to push out of the way too

[Prime Power]

That I see, but I wouldn't have assumed the air resistance would be that much different.

[Prime Power]

So then I guess it really just comes down to less resistance.

[chenc544]

If you have less power at a given rpm, you would need to run @ a higher rpm to maintain say 70mph.

 

Nope, your rpm is fixed to speed by the gear ratio. You can't change that on the fly. What the ECU could do is increase the engine load to make more hp even though you are still at the same rpm.

[mwiener2]

except, as I was pointing out, unless you're going 100+ mph, there is more than enough power in our engines WITHOUT the turbo to maintain highway speeds.

[Prime Power]

Agreed, bad way of putting what I wanted to get across. You are correct, I should have put load. Been a hectic day, I am painting my calipers on my avalanche.

[chenc544]

except, as I was pointing out, unless you're going 100+ mph, there is more than enough power in our engines WITHOUT the turbo to maintain highway speeds.

 

How is that an "except"? Engine load is engine load, regardless of how many hp you need. I didn't say anything about the turbo. It's part of engine load equation but increasing engine load doesn't mean spooling up the turbo you know.

[RockyMtnGT]

On a stock car, the effects are neglible. Lets say the stock turbo can boost to 16psi without turning into a flame thrower. Stock boost target is 13psi (for example).

 

At sea level, it hits 13psi no problem. Up here we have ~2 psi less atmosphere. since the turbo can boost to 3psi past it's target, the 2psi loss in atmosphere is made up for by added boost from the turbo. Once you completely leave the efficency range of the turbo (stage 2) the car starts to loose power at altitude.

 

(Way overly simplified example)

 

Good info! Thanks man...

 

I love this forum...Any day now I'm gonna get it blocked for abuse by our new web filter from hell though

[praedet]

^^^^He is VERY wrong, check this thread, specifically post 13. Stock Subaru cars DO NOT push more psi to maintain the same absolute charge psi...

[LittleBlueGT]

^^^^He is VERY wrong, check this thread, specifically post 13. Stock Subaru cars DO NOT push more psi to maintain the same absolute charge psi...

 

I was thinking about how to explain the whole pressure ratio thing and, voila. Nice post!

[mwiener2]

^^^^He is VERY wrong, check this thread, specifically post 13. Stock Subaru cars DO NOT push more psi to maintain the same absolute charge psi...

 

I said the same thing, just without getting into PSIA and PSIG

[chenc544]

*sigh* here we go again.

[praedet]

^^^I know, I just would like to get the right info out there, instead of the wrong stuff over and over

[RockyMtnGT]

Thanks for the clarification praedet!