Effects of elevation on turbocharged vehicles

[glhs875]

First of all I don't intend for this thread to be bashing anyone or to make anyone mad. Although I am sure there will be members that disagree with what I have to say on this topic! But that's okay!
This topic was recently brought up on another thread after my statement that Milk Carton's car which has run 7.06 (1/8th) @ 5000+ feet in elevation would easily run in the 6's at a lower elevation. And I still believe that way and think that the E.T. would drop .2 to .3 tenths in the 1/8th at sea level or just a little higher. The reduction in E.T. would make Milk Carton's car run 6.70 to 6.80's with no changes to his combo.

I know there is math/theory that says this shouldn't happen,but one question I have is the math/theory taking into account a mechanical device that should be thrown into the equation?

I provided a link (there are many) that hits on my line of thinking. After clicking the first link, 189210 will have to be entered in the search box that appears and then hit search for the link to work. A new link will appear,click on that.

www.6speedonline.com/189210

www.honda-tech.com after clicking this link put 1235461 in the forum search box hit search then click on the new links that appear.

[black86glhs]

I think part of the problem is misunderstanding on both sides. It wasn't that elevation won't have an effect on a turbo/supercharged engine, it will be much less than an N/A engine. That is what I read from other posts. I am not being inflammatory in any way, just pointing out what I saw as a third party.

[Vigo]

Neither link worked for me.

The effect of elevation on a turbocharger is basically to move it up on the compressor map. Anyone who has looked at compressor maps will notice that the farther you get from the 'efficiency island' or happy place of the compressor, the faster shaft rpm goes up trying to give that next little bit of pressure ratio or mass flow, and the faster your adiabatic efficiency drops (charge air gets hotter/less dense).

So, if you are near the center of the efficiency island, the slight increase in PR the compressor has to make is only a slight increase in shaft speed and charge temp.

However, if you are already far from the efficiency island of the compressor, adding a tiny increase in PR may require a large change in shaft speed which means more pumping losses on the exhaust strokes along with hotter/less-dense charge air and less 'net' power at the same PSIA in the intake manifold.

This concept also applies to turbo intakes in general as they also effect how easily the compressor ingests air. Over the years there have probably been a lot of people who upgraded stock airboxes to cone filters or CAIs and wondered why they didn't gain much power. They were still in the 'happy' part of the compressor map and the slight drop in shaft rpm requirements didn't free up much power from exhaust pumping losses or gain much power from charge density. On the other hand there have been people who are pushing their compressors hard and upgrading from already 'big' 3" to 4" intakes got noticeable gains.

[glhs875]

To get the link to work first click my link then put the (number) of my link in the search box shown and hit search. A new link will appear, click on that. I know it is weird! Had trouble with the link! LOL

I redid the Honda-Tech link. Follow my new instructions for each link. It worked for me.

[glhs875]

Neither link worked for me.

The effect of elevation on a turbocharger is basically to move it up on the compressor map. Anyone who has looked at compressor maps will notice that the farther you get from the 'efficiency island' or happy place of the compressor, the faster shaft rpm goes up trying to give that next little bit of pressure ratio or mass flow, and the faster your adiabatic efficiency drops (charge air gets hotter/less dense).

So, if you are near the center of the efficiency island, the slight increase in PR the compressor has to make is only a slight increase in shaft speed and charge temp.

However, if you are already far from the efficiency island of the compressor, adding a tiny increase in PR may require a large change in shaft speed which means more pumping losses on the exhaust strokes along with hotter/less-dense charge air and less 'net' power at the same PSIA in the intake manifold.

This concept also applies to turbo intakes in general as they also effect how easily the compressor ingests air. Over the years there have probably been a lot of people who upgraded stock airboxes to cone filters or CAIs and wondered why they didn't gain much power. They were still in the 'happy' part of the compressor map and the slight drop in shaft rpm requirements didn't free up much power from exhaust pumping losses or gain much power from charge density. On the other hand there have been people who are pushing their compressors hard and upgrading from already 'big' 3" to 4" intakes got noticeable gains.

I agree! The closer you are to the edge of the combo/turbo the effects of elevation will be be more noticeable.

[1BADVAN]

All i can say is that my turbo cars run a few tenths faster in Vegas every time i go there, which is about 2,200 ft lower in altitude, so I imagine getting all the way to sea level would net even more gain. i have seen it on other cars too, like Corby's minivan (from utah with a track of 4,400 ft) first broke the record when it was taken to Phoenix.

[Vigo]

I read the links. The effect is not nothing, but it definitely depends on where you are in your turbocharger's capabilities. If you are in an efficient 'usage regime' i guess you would say, then you will gain less coming down to sea level than someone whos setup was being run near the 'limits' of their compressor.

[glhs875]

All i can say is that my turbo cars run a few tenths faster in Vegas every time i go there, which is about 2,200 ft lower in altitude, so I imagine getting all the way to sea level would net even more gain. i have seen it on other cars too, like Corby's minivan (from utah with a track of 4,400 ft) first broke the record when it was taken to Phoenix.

Thanks for posting some personal results!

[glhs875]

NHRA correction factors for supercharged/turbocharged cars.

1600ft of elevation ET: 1.0057 MPH: .9945

5800ft of elevation ET: 1.0307 MPH: .9726 - per NHRA correction for MILKCARTONS Shadow with ET of 7.06 @ 5800ft would be ET of 6.85 @ sea level

The NHRA correction factor for supercharged/turbocharged vehicles is half of the correction factor for NA vehicles.

[1BADVAN]

NHRA correction factors for supercharged/turbocharged cars.

1600ft of elevation ET: 1.0057 MPH: .9945

5800ft of elevation ET: 1.0307 MPH: .9726 - per NHRA correction for MILKCARTONS Shadow with ET of 7.06 @ 5800ft would be ET of 6.85 @ sea level

The NHRA correction factor for supercharged/turbocharged vehicles is half of the correction factor for NA vehicles.

That's interesting to see, that there is some corrections but not exactly linear as altitude increases

Sent from my SM-G900T using Tapatalk

[Vigo]

And only a vague guideline when one car could be in a completely different part of its compressor map vs another car.

[glhs875]

TA/D and TA/FC cars have no NHRA correction factor. I assume because of the oxygen content in the fuel.