The only thing altitude will affect turbo cars is thinner air for the intercoolers. The turbo compresses the air to become dense air. The stock turbo will runs harder but unless it runs out of steam the engine should not make any less power. For oversized turbos i believe this should not be a problem. I since my car is detuned from the GT2 I believe the altitude should not make as much difference as to an undersized turbo car such as the Subaru Wrx.

Would someone else please give a third opinon.

 

Altitude does matter, regardless of what sort of power adder you run. I also got 1.7x 60's out of a stock Turbo, on 19"s. Practice makes perfect, thats all.

 

You're barking up the wrong tree.

 

Altitude matters! Period.

 

At higher altitude, the turbos have to work harder to generate the same combined manifold pressure as at sea level, pushing them away from their range of maximum efficiency, resulting in more parasitic drag per pound of boost, therefore lower power. The effect is smaller than with a NA car, but it is real.

At some altitude, the turbos would simply run out of air to compress, even spinning their little turbine hearts out.

 

Thanks for all of the responses guys. Yeah, I know my 60' times are dog****, but 2.0 is about as good as it's going to get without a clutch drop. First of all, I don't like the wheel hop, and secondly it's the stock clutch. So, I'll deal with it by taking out the extra weight and lowering the tire pressures to 20psi all around (thanks MARKSKI) - that should get me a 1.9, or at least stop the spinning in the top of 1st.

To answer some of the other questions:
- It was chilly, in the upper 40's when I made my first runs. It warmed up to low 60's when I made the best ones. Car also ran best on a hot motor. Cooled it down twice and made no difference.
- The track preparation was garbage. Track was slippery and we were running against a 20-30mph headwind all day (they only let bikes run 1/8 it was so windy). Had an effect for sure, but who knows how much. 2mph? Could be... [I WISH I had been at Atco, or better yet the "slightly" downhill MIR... lol]
- Shifted at 6500rpm in every gear
- New PZero tires
- VP 109 octane unleaded
- Boost held 0.7bar from what I could tell, but I still have to hook up a boost gauge to see what's going on. Div valves could be leaky (26k miles), but I don't get the "honking" associated with the failing ones.

AP silicone hoses and BOV go on this week, exhaust next, and then back to the track in 2 weeks to see what's up.

Thanks guys

 

That's actually not true, Ari.

MT ran a 11.9 @ 116.1 in a NON-X50 car in November of 2000.

MT *also* ran a 11.86 @ 119.9 in a X50 car in 2003.

I have both times listed in the 1/4 mile list. Those boys at MT can drive.

 

Exactly. Great post, PMac.

 

gtr,

Indeed pressure and temperature do determine energy. This has no relationship to the number of oxygen molecules per unit volume of measure when you are consulting steam tables.

I think where some of the confusion may arise is that if a turbo creates 1.01 bar of pressure at sea level and 1.01 bar of pressure at 10,000 feet, the number of molecules of oxygen per unit volume of measure will be less at 10K feet and hence less will be available for combustion. The parasitic drag issues and reduced intercooler efficiency mentioned previously also figure into the total picture of less engine power output as altitude increases. If you thin out the amount of gasoline per unit of volume of fuel, there will be fewer btu's available for the heat of combustion. If you thin out your oxygen per unit volume of air, ther will be less available for combustion.

The last aircraft I flew had 4 turbochargers and a service ceiling of somewhat over 25,000 ft. The reason for that service ceiling is that at that altitude there simply aren't enough available molecules of oxygen for proper combustion. A/F ratios become the limiting factor.

 

I understand other issues that causes a decrease in hp but your saying "if" the turbos is able to hold 1 atmosphere to the engine it is still dependent on altitude? In another words your saying air is not 21% oxygen, 78% Nitrogen and 1% at 1 atmosphere?

 

gtr,

I am not saying that air is not 21/78 at 1 atmosphere.
That IS the approximate composition of air at 1 atm. One atmosphere is the weight of a 1 in. by 1 in. column of air (14.7 pounds at sea level) being exerted on each square inch of any and everything. You see, everything is already at one atmosphere of pressure (sea level and standard temp) before you create any boost.

One bar of boost (approx 14.5 psi) is exerted over and above the pressure already on everything. When that one bar of boost is created at higher altitudes there are less molecules of oxygen contained in the inlet charge. 18,000 ft = approx. 1/2 atmosphere, just as approx. 33 ft. below sea level is approximately 2 atmospheres. I'm not referring to the % composition of air at a given altitude, it's just that as altitude increases, you are doing your 1 bar of boost on less than one atmosphere of air, and hence fewer oxygen and nitrogen molecules in that compressed charge. The air weighs less up there and has fewer molecules of both oxygen and nitrogen per unit of volume.

Why do you think our engines make more power when the air is cold. One of the reasons (there is more than 1) is that the air density is greater (density being the weight of a given volume of substance) and therefore there are more molecules of oxygen and nitrogen for a given volume of air at that lower temperature. That allows 1 bar of boost to bring in more oxygen and nitrogen molecules each time the intake valve opens. With more oxygen, we get more power, assuming the ECU adjusts the A/F ratio properly.

I hope that helps.

 

You don't need to drop the clutch on an AWD car to get a good 60'. I have been drag racing AWD's for 5-6 years now. I NEVER drop the clutch. You just need to slip it, relatively quickly. If you dump it you WILL get wheel hop and you will break ****. I got those 1.7x 60's on an all stock TT (including at 85000 km stock clutch) on 19's without much hassle. Like I said, it just takes practice. On other AWD cars with street tires I am able to get 1.5x 60's without dropping the clutch. People just think thats the most effective way, when in actuality its not.

 

Awesome advice, I'll have to try tha, actually my best 60' was a 1.98 and I didnt drop the clutch I just got up there and went (11.73 @ 124). Still sucky but if I can get a 1.70 60' in my car I would go 11.30's



EDIT: LMAO at how this thread turned to science class, get em Al. Altitude affects every car because turbos are only POWER ADDERS, the motor still has to breath the same air and is affected by high altitude, the turbos feed off of the exhaust gasses emmited by the motor so if the motor isnt breathing efficienctly, the turbos arent getting the full effect of the motor, whether they are affected themselves or not, maybe less so than NA or SC but still present nonetheless.

 

LOL, yeah talk about threadjack

Seriously, thanks for all the advice guys. FYI I'm no rookie at this either - I have well over 400 passes under my belt with about half on AWD vehicles. I have no excuse for not ripping off better times, but there's something about abusing this car and wheelhopping that makes me cringe. I guess I should just "trust the German engineering" like one of you said. We'll see next time...

 

Guilty as charged. I ask your forgiveness.

Al