Originally Posted by 333pg333

Is there a case of diminishing returns though? As we all know it gets colder up in the hills/mountains and when it gets colder our turbo cars run better. Is it merely that they benefit from the extra cooling of the air rather than a density matter? The air at Sea Level is denser but on a hot Summer's day down on the coast vs a cool morning in the Mountains, there is a voluble difference to the performance. I take it that this is merely temp not density. Having said that, isn't cooler air denser than hot air anyway?

Originally Posted by Rogue_Ant

Turbos that are near maxed out (flow or pressure) will not be able to make up the needed pressure and flow - making the altitude effect more dramatic. I agree.

However there are plenty of cars running up here with turbos that are not maxed. And they too run slower. Your GT30r car would have run slower here. Just because the turbo is not maxed, does not mean that it can make up the loss of atmospheric pressure for free. The turbo is working harder, that energy must come from somewhere (conservation of energy / 1st law of thermodynamics).

We can argue about it all day long, but the simple fact is cars run significantly slower up here - pull up youtube and watch videos of street cars at bandimere if you like.

Or take me up on my challenge, get a turbo car and bring it up here.

Originally Posted by 333pg333

Is there a case of diminishing returns though? As we all know it gets colder up in the hills/mountains and when it gets colder our turbo cars run better. Is it merely that they benefit from the extra cooling of the air rather than a density matter? The air at Sea Level is denser but on a hot Summer's day down on the coast vs a cool morning in the Mountains, there is a voluble difference to the performance. I take it that this is merely temp not density. Having said that, isn't cooler air denser than hot air anyway?

Originally Posted by 95ONE

Yes, you are correct Patrick. It is also a double edge sword in this argument. But all this can be worked out quite well in math to tell you the truth. I've done as many numbers and variables as I could when I saw some ridiculous correction factor on a dyno. something like 20%!!!!!??? -NOT one of Sid's Dyno's. Blew my mind no one questioned it. I took in consideration my set up. My intake temps off what the pressure and temp was for the day and used my exact compressor map to review how it would react at that city. I think the city was only about 4500 ft high though. It was a year or two ago. In the end. My car would have lost about maybe 5-6% power. (25hp) That's a strong percentage, but nothing like 20%. That number is just ridiculous.

To do the math again, would be a bit time consuming. I was just having to prove something to myself back then. And honestly, if you don't have a firm grasp of how a compressor map works,it will be tough to fully understand all the dynamics.Which Sid and Rogue clearly do, So I feel compelled to argue this with them to either learn from , or put this to bed and move on to the next fun facts.

Originally Posted by 95ONE

Complete and total sad face on this one. It is for this argument alone, I wish I still had one. Keep in mind, my argument is NOT that the power doesn't suffer at all. It certainly does, but very little. Definitely not a comparison of 8psi in Houston being like 12 psi in Colorado. (27.5%) Yes, the compressor works harder and builds more heat. It just doesn't lose that much.

I hope people understand that we are completely getting along. This is just an argument for information. In the end, everyone will take what they can from this and probably be bit smarter, or more confused Give me a little time tonight to try and cover everything I can, but I will of course, use every supporting tech / article I can to back it up.

Originally Posted by blown 944

Lol, it's not like it's cooler up here. It was around 95 degrees in areas here today.

To be honest I'm done with this conversation. I feel it's an insult to my tuning capabilities and combination to keep bringing it up. I'm not worried about it I'll come gown to some decent air and we shall see what's up!!

F it!!! I'll pay 2 grand for any 951 owner to run their car at sub 2000 ft and then bring it up here and match their trap without having to crank up the boost. That should cover their expenses. The only way you get the $$ is to match your mph with 5 mph without cranking it up or completely changing your combination.

Believe me I'm not worried about losing $$, it just won't happen.

There it is, prove me wrong!!!

When I see gt35 WRX's run 12's at 116 and gtrs have a hard time breaking into the low elevens after being heavily modified, I don't need much more proof.

Anybody game????

Originally Posted by 95ONE

EDIT: ...I clearly took this boosted power vs altitude thing too far on Sid's post. Apologies. Removed. Sid, I love what you did with this project and I wish all the best.

Originally Posted by 333pg333

I think the better question to ask is; Ok so let's take it as fact that cars do run slower up where you guys are. Why is this so? If there's math to test or prove these results then we're all better off for it. What will be good is if you can get your car down the hill a bit and run it also. I find this interesting but it's not a deal breaker. Whatever our competition is, they have to run under the same climate as we do so...it's a bit like dyno's. They're good to test mods and tune with but my 350whp might be the same as someone else's 400whp. I still find when I read people with e.g. 400whp at 17psi totally incredible vs what I've seen on my car so these comparisons are just academic.

Originally Posted by 95ONE

YI've done as many numbers and variables as I could when I saw some ridiculous correction factor on a dyno. something like 20%!!!!!??? -NOT one of Sid's Dyno's. Blew my mind no one questioned it. I took in consideration my set up.

Originally Posted by Rogue_Ant

Bruce, that link has bit of marketing hyperbole, and definitely leaves out a lot of important assumptions & info.
I will match any math you want to put up, and I have the empirical data to back up the "theory" that vehicles, turbo or not, are less powerful up here.

Being at this altitude means that you are at a higher differential on the compressor. This means that the turbo is generally having to hit a higher RPM, to make up both pressure and flow. This is absolutely not a free-hp situation. As you know the classical kinetic energy formula E = ½ mv². The energy required to increase the turbo RPMs is not a linear relationship. The velocity is squared, so any increase in velocity is going to require a velocity change squared increase in power.

One might say that the "lower post-turbine pressure" equalizes this, but then they are forgetting entropy: that their is unusable energy losses any time energy changes from one form to another.
Additionally, as Shawn mentioned there is adiabatic losses from having a higher pressure differential. If we look at the compressor, even assuming an ideal compressor (100% efficient), compressing air produces heat (ideal gas law). Having a lower starting point (atmosphere), means we have to compress the air just to get back to sea-level. To achieve the same 15psi in Denver as sea-level, we generally have to compress the air an extra ~3psi. More compression = more heat.

On 99% of turbo cars, there is not a 1:1 manifold pressure relationship (post-turbo intake pressure vs pre-turbo exhaust pressure). Generally, the relationship is 1:1.5 to 1:2.5, specifics-dependent. This further diminishes the "lower post-turbine pressure" advantage. Even if we assume no entropy, no turbo RPM change, and no adiabatic losses (all are ridiculous assumptions), and just apply the intake vs exhaust pressure ratio, then we are still at a dis-advantage.
For example: Assume X setup has a good 1:1.5 ratio. At Denver altitude, there is 3.0psi less air pressure than sea-level. So we need to make an additionally 3psi of intake pressure to account for the lesser atmospheric pressure. Then by the 1:1.5 ratio, the turbine side needs an additional 4.5psi of drive pressure... 4.5 required is greater than the 3.0 gained from less post-turbine pressure. Therefore, we are, again, losing power.


So, anyone that feels different: I lay out this challenge. Run your car, 1/4mi, at/near sea-level. Then come up here (you won't find a better prepped track), and run your car again without any changes. I do not care what your setup is, you will run a slower MPH.

Originally Posted by 333pg333

Whatever our competition is, they have to run under the same climate as we do so...it's a bit like dyno's. They're good to test mods and tune with but my 350whp might be the same as someone else's 400whp. I still find when I read people with e.g. 400whp at 17psi totally incredible vs what I've seen on my car so these comparisons are just academic.

Originally Posted by Rogue_Ant

Bruce, both Sid and I know that you are being genuine with your opinion, but the context is wrong. This is Sid's thread about his unique stroker engine, showing its merits. By arguing that altitude has no effect, your are (intentionally or not) diminishing the results of his achievement. Sid has run, IIRC, 116mph at 12psi of boost with this engine. To hit 110mph, I had to significantly more boost (and more aggressive timing). I highly doubt anyone would suggest that my car is poorly tuned.

The end result is that Sid's 2.9L motor, even with a very conservative tune, is leaps and bounds more powerful than my 2.5L. (and his has more potential)

Originally Posted by DanaT

Now, there is one type of power enhancement that doesn't take the altitude hit: nitrous. It brings it own oxygen to the party.