Guys, I need your help on this one before I make a decision to press ahead. I'm planning to go with TTs, but the install shops I'm considering are in cities at a much lower altitude and with availibility of 93 octane gas. What should be my plan for making sure the car runs correctly at Albuquerque's 5,000 ft altitude and 91-octane gas when I return home?

Additionally, the local corvette expert doesn't have a dyno and not much experience tuning TTs.

Your thoughts?

Thanks, looking forward to joining the FI Club!

Gordon

 

It'd be great if you could log at your altitude after the initial tune and get a final w/ adjustments..

Either way, good luck..

 

Have a full tank of 91 octane in the car when you get it tuned, that way it's tuned for 91. With the altitude the only problem you should have is the loss of a few psi. There really isn't much you can do about that though that I can think of in your situation. You may seek the help of a member of Corvetteforum that is in your area that may help with logging data once you get your car back. Good luck.

 

Help me understand something. I was under the impression that air density is not real important with TT simply because the turbo will only make a set amount of boost at any altitude. So long as the boost is set at let's say 7psi the wastegates will control the boost at that level and 7psi is 7psi. That's why aircraft use them to get around the variable air density at different altitudes. In comparison to a SC where the blower will keep boosting based on engine speed and in that case, air density is a concern. I think as long as you have a good tune done by someone who's done it before like FLP, you'll be fine where ever you drive. The key is a good tuner.

 

hmmmmmm... now I don't know a whole lot about turbos but I thought that the problem with altitude is not only is the air thinner, but less plentiful in oxygen. So say at a lower altitude, these numbers won't really represent real life but just to get the point across, you flow 7psi of air. Say at the lower altitude the air is 50% oxygen. Say at 50% oxygen it would equal a million units of oxygen for each psi. Say when you get to the higher altitude it's only 25% oxygen. You're still boosting 7psi of air, but now instead of pumping the million units for each pound you are pumping 500,000 units for each pound, same boost, diffrent amounts of oxygen. And with a supercharger the loss is even greater becasue the above occurs, less oxygen per unit, but also the supercharger doesn't compensate for air density changes. So as the air thins out it can't pump the 7psi with the same amount of revolutions, so now your 7 psi just dwindled to say 4 and in that 4 there's half the oxygen, so it's like pumping 2psi. These numbers don't represent actual values, they are just put in to get the point across. Like I said, I don't know much about turbos but this is just what makes sense to me. Thanks, Dan

 

At high altitude, the proportion of oxygen doesn't change relative to the other gases. Everything just needs to be compressed more to reach the same density.

I'm not sure a turbo really compensates for altitude changes. I think the wastegate is referenced to outside air pressure, so you'd always have "X" amount of boost over ambient, and ambient is lower with increased altitude.

 

Back in the day, I raced turbo Eclipses at Bandimere Speedway in Denver Colorado. 25-30psi, what a ball those were. And we were consistently a full second slower at Bandimere than at sea level. Anyways, the issue with higher altitude is the air is less dense. The air has less oxygen, so every gulp of air by the motor has less 02. Less 02 needs less fuel, so overall you get less power. Now, fuel injection makes a lot of compensations, but at WOT the ECM ignores the 02 sensor and goes by the fuel map (correct?). I would think that a tune done at sea level would be rich at higher elevations at WOT. Or am I missing something?

Colby

 

I may be and usually am wrong but I was thinking the manifold pressure would ba an absolute pressure and not ambient plus. The mixture of gasses is still the same but as you said, the unit volume at higher elevations is less due to the lower pressure exherted on the air. That said, if you compress air to 7psi, it would be an absolute pressure and the wastegates would maintain that level. It may need to work harder to do so but it will still compress the air all the same.

If you think about it, when you travel in an airplane, the air is pressurized to sea level to make it possible to breath freely. Same thing with a turbo. It compresses the air to the governed pressure. You may have trouble out of boost but in boost you should be alright. Again, I'm probably wrong.

 

Gordon.

I have been to Alb numerous times and there is a place called the dyno edge there that should be able to tune it without a problem. I had mine tuned at HP in Roswell. If all else fails, you can bring it here to the dyno and I will help with the tuning. Just let me know if I can help, or you can go to Texas Speed in Lubbock and they can tune it for you also.

 

Guys - fantastic discussion; see why I want to get this right?!

Any other thoughts our there on this subject? I think the bottom line is that I need to get the car to a "high altitude" competant LS tuner and use the gas I will have available in Albuquerque.

Gordon

 

Texas Speed in Lubbock. Excellent tuner with 2 turbo vettes himself.

 

Gauge pressure (manifold) should stay the same because of the wastegate referencing ambient pressure. The absolute pressure would be lower because of the lower ambient pressure, so you have less mass air flow for a given psi of boost (at altitude). Because of this you would make less power at altitude.

I think this depends on how much power you are making and whether or not you are maxing out your MAF. If you are running within the limits of your MAF, your WOT AFR should stay about the same. However, if you are exceeding the MAF (you're beyond the measuring capabilities of airflow and are just dumping in fuel), then you would end up more rich at altitude (dumping in the same amount of fuel, but you have less air to go with it).

 

I don't know why none of the posts above have said it, but I'll say it! Don't bring your car to just an install shop. He's gotta have a dyno AND be able to properly tune your car. Turbos rely on balance between the exhaust in intake, and you'll need someone who knows about TT's and has done plenty of installs before. A dyno is a necessity!!!!

 

Although I didn't say it in my initial post, the plan is to do the install which will include a dyno tune. That should get me in the ballpark, but I need to know how to proceed once I head to my home in higher altitude - ABQ, 5000'.

Gordon