Kung 4.2

Curious if any has some stats/physics on the reduction in horsepower as you go up in altitude. I live in the front range of Colorado at about 6 thousand feet. Even more curious of the reduction in Turbo versus non Turbo. I have a 4.2 and am interested how the performance difference changes between a 4.2 and a 2.7T.

DWC_2.7T

Power is a function of the air/fuel mix the engine burns. Naturally aspirated engines, by definition, rely on atmospheric pressure and have no way to increase inlet air volume. When the air is thinner, you simply can't mix as much gas with it, so power will be lower for a given rpm. There are mechanical limitations to how far the ECU and associated sensors can go to compensate for altitude in a non-turbo engine. Generally, its enough of a task to maintain smooth engine operation, let alone preserving power. I can't give you figures, but the power loss can be considerable.

In comparison, the turbo engine's ECU can just tell the turbos to pump more air (adjust dump valve) to achieve the volume the ECU expects/wants. There are limits, but the advantage of a turbo (or S/C) is even more significant at altitude.

Your questions reminds me of watching midwestern tourists who'd shut off their carburated engines on top of the pre-tunnel Loveland Pass Hwy (14000+ feet) while taking snapshots, and have a hell of a time restarting 'em.

Richard Solomon

In short: the most conservative numbers I've seen are 3% loss / 1000' so your 300HP V8 is <b>at best</b> 300 * .97 * .97 * .97 * .97 * .97 * .97 = 250HP at 6000'.

Modern turbocharged engines regulate the wastegate off ABSOLUTE manifold pressure, so develop the same horsepower at any altitude within the flow capabilities of their turbocharger(s). So my 250HP is only 250HP at 0', but it's still 250HP at 14,000'. (Yes, there are losses and lag increases, but peak HP is roughly constant.)

Are you in Colorado Springs by any chance? I'm guessing from your e-mail address that you're just down the road from me

Bollinger

I'd love to sidetrip to take some pictures. Can you give me some general directions?

mikef4.2

<ul><li><a href="http://www.firstrax.com/120.htm">http://www.firstrax.com/120.htm</a</li></ul>

Kung 4.2

Yes I am ... Melange A6 4.2. I have both the Tip chip and the Engine chip along with a K&N airfilter. It's made a world of difference over stock. Thanks for the info ...

audiconvert

At sea level turbocharging increases pressure which increases density as long as you cool the air - which is what intercoolers do.

P=qrt. P is pressure, q is density, and t is temperature.

At higher altitudes the air density is lower than at sea level. The pressure and temperature of the incoming air charge might be the same as at sea leve if the turbochargers have enough capacity to pump enough of the less dense air into the intake plenum. I'm not sure if the 2.7t turbos have that capacity to cover altitudes higher than say 10k feet. I think you'll get a lesser response. Certainly the turbos will have to spool higher to produce the same power. And more spining creates more heat which makes more work for the intercoolers.

DWC_2.7T

Sorry...12,000...its been 20 years!

mikef4.2

I wasn't being picky! Just jealous. It is a two day drive for me to get there. Looks great!

Bollinger

But didn't know it existed. I've been through the Eisenhower tunnel several times and noticed there was an alternative for trucks, but never checked it out. Maybe next time I get out there.

Sadly, I never get out there in my car, so I'll be in some wheezy rental car.