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Discussion Starter · #1 ·
I just bought a 2003 zo6 from Michigan. 1100 miles. Moving it to Denver. Do I have to make any adjustments to the car since it will be running here at actually about 6000 ' higher ( I am just south of Denver and higher still) than it was in Michigan?
 

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No, the MAF will take care of it for you. Just get used to the idea of running about a second slower in the quarter, up here in the clouds...
 

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Adjustments? :-?

HMMMM: Technically, Tony may be right.

On the other hand, I have made a few adjustments aimed at getting that lost second back. :sneaky:

So far, these include Vararam, Long Tube headers and a Dyno Tune. Once I get my car back from Dragon, add Heads and Cam to the list. I expect to recover that second and a little bit more.

There is also a guy in town who specializes in adding the Magnussen supercharger kits to our car and he provides a complete package. I actually think his website is something like sealevelperformance.com.

Bottom line is that the car self-adjusts fuel mixture, etc. at high altitude but you will lose 15% of your sea level HP and Torque anyway and that really stinks.

The simplest way to get it back is forced induction, but after researching that, I chose the other route. Thanks to all the great info on this site, I was able to learn a lot and make informed decisions about my high altitude "adjustments". :z:
 

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Discussion Starter · #4 ·
Is the reason for the the performance loss because of the lower oxygen level. And do cars with turbo's experience the same drop in power?
 

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KipS said:
Is the reason for the the performance loss because of the lower oxygen level. And do cars with turbo's experience the same drop in power?
yes: The air pressure is lower so there is less oxygen, lower effective compression, etc. The ECM compensates be reducing the fuel accordingly.

Turbo cars usually lose less hp at altitude. My Audi runs closed loop boost control on a manifold absolute pressure sensor, so it will spin the turbo faster and compensate for altitude. However, the Audi factory ECM code actually throws in a boost reduction at altitude (yes, there is an altitude sensor on the car as well) to keep the turbo from spinning too fast and self-destructing. Nevertheless, it has been my experience that most factory turbo cars suffer less from altitude than normally aspirated cars. Some may experience less HP loss and some may experience minimal loss, if they have large enough turbos with enough head room. However, turbo lag is more pronounced at altitude since the turbo car will experience the same 15% loss in torque when off-boost but runs with closer to sea level torque when boost comes on.
 

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I agree with RalphP - turbo cars typically do not lose as much up here. So be careful with those STIs. AWD + not losing much power like we do, and they can eat you for lunch. Get used to having a mid 13 second car!

You will *really* notice the altitude if you drive up to higher elevations from Denver. At 10,000 ft, the car feels like a *#(&@ Civic.
 

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novetteyet said:
I agree with RalphP - turbo cars typically do not lose as much up here. So be careful with those STIs. AWD + not losing much power like we do, and they can eat you for lunch. Get used to having a mid 13 second car!

You will *really* notice the altitude if you drive up to higher elevations from Denver. At 10,000 ft, the car feels like a *#(&@ Civic.
You are right about the STIs. They are a big part of the reason I am modding my Z06. I just can't stomach having my doors blown off by a Subaru. My '94 S4 Audi has all of the Euro RS2 "go fast" mods including a bigger turbo and boost up to 24 psi. It pretty much rules on Vail Pass and the tunnel approaches.

I'll see how I like the H/C on the Z. For various reasons, I decided not to go with a SC. If I need more, then the next step may be a 427.
 

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It is all about pressure. At sea level or 1 ATP there is 760mmHg of air pressure total (all gases combined). Nitrogen makes up a bit over 78% of the gases, Oxygen is just under 21% and all the rest of the gases make up the difference (including CO2).

Regardless if you are at sea level or 30,000' the percentages are the same. The differences are in the total amount of pressure behind those gases.


Chris
 

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Found this it may help -- Oxygen is the same % in the air all the way up.




Oxygen Availability And Altitude
Moderate altitude is defined as 5,000-10,000 ft above SL. As the altitude increases, the barometric pressure (PB) decreases. This fall in the PB affects the available PO2. The O2% remains stable at about 21%. At sea level, the partial pressure of O2 available in the environment is equal to 0.21 times the PB (760 mm Hg), or 159 mm Hg. After saturation with water and expired CO2, the partial pressure of alveolar O2 (PAO2) is 103 mm Hg, as calculated by the following equation: PAO2 = FiO2 (PB - PH2O) - PaCO2 [FiO2 + (1 - FiO2/R)]

(PB is the ambient barometric pressure, PH2O is the pressure exerted by water vapor at body temperature, FiO2 is the fraction of inspired oxygen, PaCO2 is the alveolar carbon dioxide pressure, and R is the respiratory exchange quotient.)

Although the O2% in inspired air is constant at different altitudes, the fall in atmospheric pressure at higher altitude decreases the partial pressure of inspired oxygen and hence the driving pressure for gas exchange in the lungs. An ocean of air is present up to the ends of troposphere layer. The weight of air above us is responsible for the atmospheric pressure, (100 kPa at SL). This atmospheric pressure is the sum of the partial pressures of the constituent gases, oxygen and nitrogen, and also the partial pressure of water vapour (6.3 kPa at 37°C). (8)

The decrease in PB with increasing altitude results in a fall in the PaO2. Atmospheric pressure and inspired oxygen pressure fall roughly linearly with altitude to be 50% of the SL value at 5500 m and only 30% of the SL value at 8900 m (the height of the summit of Everest). For example, the PaO2 decreases from 103 mm Hg at SL to 81 mm Hg in Denver, Colo (5,280 ft, 1,610 m), and 48 mm Hg at the top of Pikes Peak (14,110 ft, 4,300 m). (9)

A fall in inspired O2 pressure reduces the driving pressure for gas exchange in the lungs and in turn produces a cascade of effects right down to the level of the mitochondria, the final destination of the O2. (8)

The lungs are a delicate interface between the atmosphere and our bodies across which O2 diffuses from the air we breathe to the blood. In healthy lungs at SL where there is a surfeit of O2, this process occurs easily, whereas, in lungs with disease it becomes a task, which may not be fully successful and hypoxemia may ensue or worsen. At high altitude where the PB and thus the supply of O2 is lower, the job of getting O2 to the blood, even in the healthy lung is more difficult, and in the diseased lung it may be impossible. (10)


Chris
 

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Turbos and superchargers depending on boost can make up for the pressure loss at higher altitudes and basically makes the car or aircraft act like it is at sea level pressure.



Chris
 

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Chris310P said:
Turbos and superchargers depending on boost can make up for the pressure loss at higher altitudes and basically makes the car or aircraft act like it is at sea level pressure.

Chris
Chris: Thanks for all the information. The only other thing to remember is that a turbocarged vehicle is primarily designed for sea level performance. To compensate for altitude, it has to take in a greater volume of air, compress it and provide the sea level equivalent volume and pressure at the inake manifold. The only way to do it is to spin the turbo faster. Most factory cars use the smallest turbos possible since larger turbos take longer to spin up and induce unwanted turbo lag. Hence, there is a limit to how fast the small turbo can spin and to how much air it can compress and deliver though the intake system. That limit will dictate a maximum altitude at which the car can maintain its' sea level performance. Above that altitude, the car will perform worse than sea level, but still better than its' normally aspirated cousins. BTW: compressing all that air heats it too, and most of the factory intercoolers can't keep up on hot days in Colorado (the air to air intercooler loses heat transfer efficiency at altitude) so pick a hot day to mess with an STI.

What does all of this have to do with our cars? Well, the good news is that I bet the STI is already making less HP than sea level when it is in Denver, and will only continue to lose as it climbs. So, I think a moderately "breathed on" Z will hold its' own just fine. :D
 

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Discussion Starter · #12 ·
That's all great info. Thanks. Do you have any recommendations other than a supercharger that are easy to do to regain some of the losses.
 

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RalphP said:
You are right about the STIs. They are a big part of the reason I am modding my Z06. I just can't stomach having my doors blown off by a Subaru.
I know whatcha mean. I've long wished Chevy offered a version of the Vette with a mid sized TT V8. Maybe 4.8L TT or thereabouts. Forced induction seems to rule at high altitudes.

I'll see how I like the H/C on the Z. For various reasons, I decided not to go with a SC. If I need more, then the next step may be a 427.
Cool. Be curious to know how you like the H/C. I had a SC on an old 96 Z28 I used to have, and I was never happy with it. The car seemed to run rough, like a strange wobbling sensation, at low RPMs and I think it was due to the lateral force on the engine shaft from the SC belt. If I left everything alone but removed the belt, it ran smooth as silk at any RPM. Also the SC blew my head gasket, and added weight to the front end of the car.

H/C sounds nice. I thought about it for my Z but finally elected to leave it stock. I would go TT if I could afford it.

novetteyet
 

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KipS said:
That's all great info. Thanks. Do you have any recommendations other than a supercharger that are easy to do to regain some of the losses.
Kip: Frankly, a supercharger is probably the most bang for the buck, albeit a big buck. However, originally, I did not want to spend that much or deal with various complications.

My first step was long tube headers, a vararam and a tune. Everyone on this site seems to agree that headers make a difference and that was my experience too. The car felt faster and more free breathing. People on this site argue about how much good a Vararam does. Unfortunately, I never had a "stock" dyno run. However, based on what my tuner told me a stock Z runs on his Mustang Dyno, I picked up about 20 lb-ft across the power band with the bolt-ons and another 15 lb-ft after tuning. The car felt substantially stronger than stock and was pretty satisfying to drive. Did I mention it sounds awesome?? I figure these gains recovered about 60% of the altitude loss in Denver. Of course, I was not satisfied and I sprung for a fairly aggressive head/cam package that is being installed now. I expect to be slightly beyond sea level HP and torque at this point but I plan to post details and dyno curves in the Pit Road forum when I have them in a week or so.

BTW, I did my own header/Vararam install to save money, but by the time you get a tune, it still ain't real cheap. At this point, with the H/C cost, I could easily have started stock and self-installed an A&A supercharger kit for the same or less $$.

HTH :)
 

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So far, I haven't been convinced that headers are good bang for the buck on these cars. They are just too damn expensive. 30-35 hp for $2K is weak. The cheapest solution is almost $1500... That said, it's probably my next mod. :)

I'm actually very pleased with the Z's performance, stock. I'm adding a 100 shot of N02 for those times I want to blast it down the track. I went crazy with the safety stuff on the nitrous and am still under $1K. That's bang for the buck! 450 at the wheels, but only when I want it. I can also pull the setup and sell it if I change my mind.

Some folks like to have the power under tap at all times, but I'm not really a street racing fan. That's not to say I've never done it, but it's really pretty irresponsible... Although, I have to admit probably drive the 'vette faster than the f-body, on a daily basis. The 'vette handles so well, it feels really safe.

The supercharger is probably one of the best mods for these cars, but it just feels contrary to their original design. These are high compression, high-reving, n/a motors. Perfect for nitrous, not so perfect for s/c... Now, if you're going to do a rebuild, my thinking flips. Forge the bottom end, lower compression and add some serious boost. Now you're back into some serious buck bang.
 

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TonyJ said:
So far, I haven't been convinced that headers are good bang for the buck on these cars. They are just too damn expensive. 30-35 hp for $2K is weak. The cheapest solution is almost $1500... That said, it's probably my next mod. :)

I'm actually very pleased with the Z's performance, stock. I'm adding a 100 shot of N02 for those times I want to blast it down the track. I went crazy with the safety stuff on the nitrous and am still under $1K. That's bang for the buck! 450 at the wheels, but only when I want it. I can also pull the setup and sell it if I change my mind.

Some folks like to have the power under tap at all times, but I'm not really a street racing fan. That's not to say I've never done it, but it's really pretty irresponsible... Although, I have to admit probably drive the 'vette faster than the f-body, on a daily basis. The 'vette handles so well, it feels really safe.

The supercharger is probably one of the best mods for these cars, but it just feels contrary to their original design. These are high compression, high-reving, n/a motors. Perfect for nitrous, not so perfect for s/c... Now, if you're going to do a rebuild, my thinking flips. Forge the bottom end, lower compression and add some serious boost. Now you're back into some serious buck bang.
Tony: I agree with you on all points. Also, I don't mean to imply that I street race because I really don't (kinda sorta mostly). For me, it is usually enough to be able to smile and know I can kick butt. But, the real question here is how to get the cars to run the way they do at sea level. I forgot Nitrous as probably the most economical solution - so thanks for adding that! Is it practical for occasional street use?
 

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Nitrous is only practical for street use, if you plan to use it. If I'm going out for a fun afternoon of driving, I'll switch on the heater and open the bottle. As long as it's up to pressure and open, you can arm it at a stop light. Depending on the weather it can take a while to get up to pressure, though. It's a little like the t/c settings. Some folks just turn it off when they want to race and others turn it off as soon as they get in the car. :)

For me, the nitrous is just a toy. I'll play with it when I'm in the mood. I just want to know how to run the car under big power and get some experience racing. It will also serve as backup for my drag car (s/c'd Z28) when it's down. I run Club Clash at Bandimere, so the Z will keep me from losing points.
 

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RalphP said:
Of course, I was not satisfied and I sprung for a fairly aggressive head/cam package that is being installed now.
Ralph -- Do you get your work done in Denver? If so, where, and would you recommend them?
 

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novetteyet said:
Ralph -- Do you get your work done in Denver? If so, where, and would you recommend them?
The work is being done at Dragonrace Engineering. I will be able to recommend them, I hope, after the completion of this work as it is really the first work they have done on my car. I visited at least 1/2 dozen Vette shops in Denver. I chose Dragon, most simply, because he has his own dyno and nobody else does! He also has a flow bench. If you are serious, you have to get the tools, right? Anyway, if you are seriously thinking of having work done in Denver, PM me and I will be happy to pass on what I learned. :z:
 
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