Dyno numbers and the effects of high altitude

[Fenixfire]

So some can gain a better understanding of how high altitude affects a naturally aspirated or supercharged motor I figured I would post some info.

Here are my final dyno numbers. We dialed it back abit because my fuel pump(Svt focus pump) is near maxed. Its pretty conservative timing and a/f wise. This is a 3.1 pulley unported eaton, stock heads and stock cams, but they were advanced 4 degrees. Motor is bored .030 over and stock compression (10.1:1). Other mods include C&L CAI w/ 95 mm MAF, 1 and 5/8" longtubes with 3" collectors, an o/r x pipe and stock catback with the mufflers cut out and straight pipe welded in their place.

With a 3.1 pulley I should be seeing around 11-12 lbs of boost at sea level. Im only seeing 8 lbs up here, which is stock pulley boost numbers.

Actual altitude is 5300 ft. above sea level. Density altitude on the day of the dyno was 6500.

First, the corrected SAE dyno sheet.

Now the actual numbers I made here are:

Same altitude, but with a DA of 6200ish the car ran [email protected] mph with a 2.12 60 foot. Only made 8 passes but it was trapping 116-117 all day with 87-90 mph 1/8 mile traps(ya pretty crappy i know, but no traction). 245/45/17 Nitto 555s all the way around.

Its slightly worse for N/A cars. Turbos and nitrous need not apply, lol.

As you can see the thin air makes it hard for engines to breath up here. Hope these comparisons help.

 

[scotty98]

ya the da in abq sucks big time. but the one good thing is everybody you race has the same air up here.:beer:

 

[Fenixfire]

ya the da in abq sucks big time. but the one good thing is everybody you race has the same air up here.:beer:

Except for turbos and nitrous.....they have an advantage.

 

[Mach828]

True, damn turbos

 

[97desertCobra]

Except for turbos and nitrous.....they have an advantage.

Exactly. Alot of dyno graphs from turbo cars in high altitude are over inflated because the dyno program makes an over correction with the numbers when in reality its not needed. Thats why you see cars making 900rwhp at 20psi when in reality they would only be making 750rwhp at sea level.

 

[WutApex]

Thanks for posting - I'm at ~6500ft

Man I wish going turbo wasn't so expensive

 

[Fenixfire]

Exactly. Alot of dyno graphs from turbo cars in high altitude are over inflated because the dyno program makes an over correction with the numbers when in reality its not needed. Thats why you see cars making 900rwhp at 20psi when in reality they would only be making 750rwhp at sea level.

Yep.........thats why when someone tells me about their turbo cars dyno I ask them what the UNCORRECTED numbers were, because the corrected ones dont mean shit!

Thanks for posting - I'm at ~6500ft

Man I wish going turbo wasn't so expensive

Ya true that. I wouldnt mind a twin turbo setup, but I should still be able to make around 650+ rwhp at my altitude with a whipple 2.9L and ill be happy with that.

 

[Roll Race Rob]

Exactly. Alot of dyno graphs from turbo cars in high altitude are over inflated because the dyno program makes an over correction with the numbers when in reality its not needed. Thats why you see cars making 900rwhp at 20psi when in reality they would only be making 750rwhp at sea level.

still jealous??? lollll:lol:
do you have any hard evidence of such a case or just 'speculation' because you or your friends automobile's make inferior numbers?
dynojets, WITH correction factors, are generally within -/+ 2% whp/wtq regardless of altitude.
if you'd like, i am willing to drive my car to a dynojet at sea level, if the numbers are anywhere near your 750whp mark at 20psi i eat the time/cost, however if the numbers are in fact 'accurate' you front the bill and my time?
i know, kinda far fetched, but im in a shit talking mood and figured id throw it out there just to see if you want to back up your shit talking mouth.

 

[97desertCobra]

still jealous??? lollll:lol:
do you have any hard evidence of such a case or just 'speculation' because you or your friends automobile's make inferior numbers?
dynojets, WITH correction factors, are generally within -/+ 2% whp/wtq regardless of altitude.
if you'd like, i am willing to drive my car to a dynojet at sea level, if the numbers are anywhere near your 750whp mark at 20psi i eat the time/cost, however if the numbers are in fact 'accurate' you front the bill and my time?
i know, kinda far fetched, but im in a shit talking mood and figured id throw it out there just to see if you want to back up your shit talking mouth.

Thats true for n/a cars but thats not the case for turbo cars.

A turbocharger also helps at high altitudes, where the air is less dense. Normal engines will experience reduced power at high altitudes because for each stroke of the piston, the engine will get a smaller mass of air. A turbocharged engine may also have reduced power, but the reduction will be less dramatic because the thinner air is easier for the turbocharger to pump.

Howstuffworks "How Turbochargers Work"

As opposed superchargers driven by the engine itself, turbochargers are driven using the exhaust gases from the engines. The amount of power in the gas is proportional to the difference between the exhaust pressure and air pressure, and this difference increases with altitude, allowing a turbocharger to compensate for changing altitude without using up any extra power.

[ame=http://en.wikipedia.org/wiki/Supercharger]Supercharger - Wikipedia, the free encyclopedia[/ame]

The way it works is that at higher altitudes there is less atmospheric pressure. Atmospheric pressure at sea level is 14.7psi. At altitude that changes, it reduces the higher up you travel. So where its 14.7 psi at sea level it may be closer to 11 psi at 6,000ft. Because of this difference n/a cars will lose power, roughly 20%. A turbo however, is set up to produce a specific manifold pressure. At sea level the turbo car may be set to produce 10 psi. In total the engine at sea level with the turbo would be making 24.7 psi. Your boost guage would only be registering 10 psi though because they set to read pressure AFTER 1 ATM(14.7psi). Now at 6,000ft that same turbo car is still set to make 24.7 psi total manifold pressure, so where it starts at 11psi due to the increase altitude it will compensate and therefore produce 13.7psi in order to achieve the 24.7 psi total manifold pressure. Your boost guage would still only read 10 psi though because the boost guage is set to read pressure AFTER 1 ATM.

So to sum it up, turbo cars make up for the loss of atmospheric pressure. They still lose power though, because a turbo is still increase the pressure on a n/a engine but the amount of power loss is significantly less than that of a n/a car. When the dyno at altitude makes the correction it adds an additional 20% more horse power(more or less) to compensate for the altitude. This is fine for a n/a car but grossly over inflated for a turbo car, nearly 20% over inflated in fact.

There was a reason why jet fighters in WWII used turbo charged engines, they could make up for the higher altitudes and thus keep performance consistent. Same with the Pikes Peak Hillclimb cars, they use turbos to compensate and keep performance consitent.

Don't be so angry or defensive about the issue. Your car would still make 7xx rwhp at sea level which is alot of power for a 4.6 and would still be ****ing fast.