High Altitude Turbo

[mwjcyber]

At almost 6000 ft, according to altitude calculators, I'm getting 36 less bhp than someone at sea level. This has left me desiring something...more

Altitude BHP calculator
http://www.wallaceracing.com/braking-hp.php

I've been contemplating NA upgrades versus boost, and have come to the conclusion that with my altitude the best bang for the buck would be with a turbo setup (turbo > supercharger for high altitude).

Ideally I'd like a system that makes ~250whp on 91 octane, can't get 93 at this attitude, and doesn't require other component upgrades such as a clutch, injectors, pump, etc. From what I've read, turbos need to spool more at high altitude to compensate for the thinner air, thus increasing their heat and reducing their performance. I really like the AVO system, for its athletics and proven reliability, but I'm concerned about its performance at my altitude. Would something like the FA20Club 57 trim perform better than the AVO 18/49 at 6000 ft?

Thus my question to the community is what turbo setup do you recommend for my altitude that will provide ~250whp?

Thank you in advance!

[1086]

Why have you already come to the conclusion that a S/C is inferior to a T/C at high altitude? Because of the parasitic nature of the S/C, therefore you're losing HP because of altitude and you're losing HP because of the S/C?

It seems as if a S/C would be better at high altitude due to the fact that boost would hit much sooner in the power band than a T/C. Per your quote,

turbos need to spool more at high altitude to compensate for the thinner air, thus increasing their heat and reducing their performance.

S/C run 'relatively' cooler than a T/C, and when you bring up your quote, the T/C will be working 'X' times as hard, it seems like a T/C would be counter-intuitive to what you want to achieve. Then again, I am sure there is something I haven't yet considered. I am spoiled I live 62 ft above sea level >_<

Lastly, if close to sea level cars are dynoing around 160 whp, that means your getting roughly 124 whp - so you want to gain an extra 126 whp with a T/C - hmmm

[wulfgang]

I live at 6700' out in the East Mountains, so I feel your pain. There is no good answer for getting back that 20%. You can always turn up the boost more to make up for the difference, but even with a 100% efficient intercooler, you will still run into the 91 octane problem and therefore still make less power than people running the same absolute boost pressure on 93 octane. There are a few E85 stations around ABQ, so if you are in town, that would help.

There is no difference at high elevations for the S/C versus the turbo argument -- that is, the arguments for S/C versus turbo are still the same arguments. The same rules apply as apply at sea level except that now you have to run more boost to make the same amount of power. As always, the turbos start looking better and better the more boost you run, and so that would be an advantage for the turbo IF you are turning up the boost further to get back that 20% loss.

In a nutshell: both setups will be running higher effective pressure ratios, and so yes, the turbo will spool slower. But the S/C will have similar issues.

Having said that, you could just accept your 20% loss, get the turbo or S/C kit, and have fun. At 8 psi boost in ABQ, you'll still be making significantly more power than a stock engine at sea level.

[AVOturboworld]

Technically, you don't have to turn up the boost on a turbocharger to compensate for altitude because it will do it for you. If you drive from 0 feet to 6000 feet, the boost pressure read by your boost gauge will show the same peak boost levels being reached. That's because the wastegate spring pressure doesn't change, and since it was calibrated for, say, 6psi, it will just bleed less and less air pressure off until it runs too far out of it's efficiency range. So if you were running at 6psi at sea level, it'll hold that 6psi to the mountains and back. In our particular case, the turbocharger is good up till 16psi, so you'd be very unlikely to run out of boost pressure up to typical elevations.

I know this because we tested at altitude, and I remember the drop in ambient pressure at 4000~6000 feet wasn't really that great, only 2~3psi I believe. So your 6psi at sea level setup would be running at 8~9 psi, and it should be ok up to 12 at the wastegate.

[mwjcyber]

Originally Posted by 1086

Why have you already come to the conclusion that a S/C is inferior to a T/C at high altitude? Because of the parasitic nature of the S/C, therefore you're losing HP because of altitude and you're losing HP because of the S/C?

It seems as if a S/C would be better at high altitude due to the fact that boost would hit much sooner in the power band than a T/C. Per your quote, S/C run 'relatively' cooler than a T/C, and when you bring up your quote, the T/C will be working 'X' times as hard, it seems like a T/C would be counter-intuitive to what you want to achieve. Then again, I am sure there is something I haven't yet considered. I am spoiled I live 62 ft above sea level >_<

Thank you for the response 1086! Superchargers have a fixed boost level that's dependent upon the engine rpm, the size of the S/C pulley, and the resultant S/C's rpm. Atmospheric pressure at Sea level is 1 bar = 15psi. At 6000 ft the atmospheric pressure is 11.7psi, or 22% less than at sea level. Thus because a supercharger boost level is dependent on the engine rpm and air density, it doesn't have a way to compensate for the thinner air, so its hp loss ratio would be similar to a NA setup at altitude.

From the research I've done (lots of sites, even though I reference wiki), turbo's can provide engine performance similar to Sea Level, because at altitude a turbo will spin ever faster to compress the ever thinner air to achieve the original target boost. The limit here is the wastegate and the turbo's maximum rpm; of course the turbo takes longer to achieve the same boost levels since its having to reach higher rpm's, which means increased lag.

So the main difference is that the supercharger will produce less boost with the same pulley combination up here than compared to sea level. Where as a turbo can spin faster to produce more boost (but not necessarily the same amount of power), a supercharger can't unless you change pullies to spin it faster.

"A turbocharger remedies this problem by compressing the air back to sea-level pressures, or even much higher, in order to produce rated power at high altitude. Since the size of the turbocharger is chosen to produce a given amount of pressure at high altitude, the turbocharger is over-sized for low altitude. The speed of the turbocharger is controlled by a wastegate."
[ame="http://en.wikipedia.org/wiki/Turbocharger"]Turbocharger - Wikipedia, the free encyclopedia[/ame]

Originally Posted by 1086

Lastly, if close to sea level cars are dynoing around 160 whp, that means your getting roughly 124 whp - so you want to gain an extra 126 whp with a T/C - hmmm

Shiv@vishnu's test car dyno'd at 170 whp stock. So lets use that as our reference.

170whp/200bhp = 15% (drivetrain loss)

200bhp-36bhp = 164bhp at 6000ft
164bhp*85% = 139.4whp at 6000ft

Either way, with your number or mine, that's considerably less than Sea Level; which is why I'm looking for more.

[mwjcyber]

Originally Posted by AVOturboworld

Technically, you don't have to turn up the boost on a turbocharger to compensate for altitude because it will do it for you. If you drive from 0 feet to 6000 feet, the boost pressure read by your boost gauge will show the same peak boost levels being reached. That's because the wastegate spring pressure doesn't change, and since it was calibrated for, say, 6psi, it will just bleed less and less air pressure off until it runs too far out of it's efficiency range. So if you were running at 6psi at sea level, it'll hold that 6psi to the mountains and back. In our particular case, the turbocharger is good up till 16psi, so you'd be very unlikely to run out of boost pressure up to typical elevations.

I know this because we tested at altitude, and I remember the drop in ambient pressure at 4000~6000 feet wasn't really that great, only 2~3psi I believe. So your 6psi at sea level setup would be running at 8~9 psi, and it should be ok up to 12 at the wastegate.

Thank you for the response Paul!

I just found @gdrider77 's AVO "Stage 2" Build thread, and he's posted some impressive results with your system at Denver's altitude.
http://www.ft86club.com/forums/showthread.php?t=39839

Back to my original post, I know a turbo will have to spin faster to meet it's specified boost psi level with thinner air at altitude; which means increased lag. That would lead one to believe a smaller turbo would be better to counter that increased lag, but then one would have to account for the increased rotational rate of the turbo, and can that same small turbo handle it. Thats what led me to question if I should be going for a larger turbo for my altitude, or if something like the Avo18/49 could handle it.

Seems like this might be my answer:
@gdrider77 's BRZ with AVO turbo running 8.5psi in Denver, tuned by "TheBoostCreepLtd"

[wulfgang]

Originally Posted by AVOturboworld

Technically, you don't have to turn up the boost on a turbocharger to compensate for altitude because it will do it for you. If you drive from 0 feet to 6000 feet, the boost pressure read by your boost gauge will show the same peak boost levels being reached. That's because the wastegate spring pressure doesn't change, and since it was calibrated for, say, 6psi, it will just bleed less and less air pressure off until it runs too far out of it's efficiency range.

The wastegate diaphragm responds to gauge pressure (psig), not absolute pressure (psia). The wastegate spring pushes against the intake manifold pressure, but there is atmospheric pressure on the other side of the diaphragm. Since the atmospheric pressure is lower at 6000', it takes less manifold pressure to push the spring than it would at sea level. Therefore, even though the boost gauge reads 6 psi in the mountains, it is not the same as 6 psi at sea level. (Sorry, not trying to lecture a turbo kit manufacturer; in my opinion, your post makes it seem like one will automatically make the same power at 6000' as one would at sea level just because the boost gauge still reads 6 psi.)

So I don't see how the turbo can automatically compensate for the elevation unless you use a boost controller that has an absolute MAP sensor. A simple wastegate won't do it. If it did, your boost gauge should be reading something like 8-9 psi in the mountains (the boost gauge also reads gauge pressure, not absolute pressure).

[mwjcyber]

Originally Posted by wulfgang

The wastegate diaphragm responds to gauge pressure (psig), not absolute pressure (psia). The wastegate spring pushes against the intake manifold pressure, but there is atmospheric pressure on the other side of the diaphragm. Since the atmospheric pressure is lower at 6000', it takes less manifold pressure to push the spring than it would at sea level. Therefore, even though the boost gauge reads 6 psi in the mountains, it is not the same as 6 psi at sea level. (Sorry, not trying to lecture a turbo kit manufacturer; in my opinion, your post makes it seem like one will automatically make the same power at 6000' as one would at sea level just because the boost gauge still reads 6 psi.)

So I don't see how the turbo can automatically compensate for the elevation unless you use a boost controller that has an absolute MAP sensor. A simple wastegate won't do it. If it did, your boost gauge should be reading something like 8-9 psi in the mountains (the boost gauge also reads gauge pressure, not absolute pressure).

@wulfgang what I've read confirms your statements. At 6000ft a 9psi turbo output would be almost equivalent to 6psi output at Sea Level. I say almost equivalent, because at 6000ft the turbo is spinning faster, creating more heat, and there's less air to cool the intercooler; thus the number I've seen numerous times is a turbo is 3% less efficient in Denver than Sea Level.

Sea Level
15psi (1 atm) + 6psi (boost) = 21 psi engine

6000ft
11.7psi (.78 atm) + 9.3psi (boost) = 21 psi engine

Then only thing that makes me question this reality is looking at @gdrider77 's dyno charts. Other AVO setups with similar boost levels at Sea Level are making the same whp. How can that be?

[wulfgang]

Originally Posted by mwjcyber

Then only thing that makes me question this reality is looking at @gdrider77 's dyno charts. Other AVO setups with similar boost levels at Sea Level are making the same whp. How can that be?

SAE dyno numbers are corrected to sea level. They add back in the 20% you lose at high elevation.

[Toyota86.ir]

Originally Posted by wulfgang

The wastegate diaphragm responds to gauge pressure (psig), not absolute pressure (psia). The wastegate spring pushes against the intake manifold pressure, but there is atmospheric pressure on the other side of the diaphragm. Since the atmospheric pressure is lower at 6000', it takes less manifold pressure to push the spring than it would at sea level. Therefore, even though the boost gauge reads 6 psi in the mountains, it is not the same as 6 psi at sea level. (Sorry, not trying to lecture a turbo kit manufacturer; in my opinion, your post makes it seem like one will automatically make the same power at 6000' as one would at sea level just because the boost gauge still reads 6 psi.)

So I don't see how the turbo can automatically compensate for the elevation unless you use a boost controller that has an absolute MAP sensor. A simple wastegate won't do it. If it did, your boost gauge should be reading something like 8-9 psi in the mountains (the boost gauge also reads gauge pressure, not absolute pressure).

Do you mean ?
Turbo at Sea level : 1bar + 0.5bar(boost) = 1.5bar
Turbo at 1200m altitude: 1bar*0.86 + 0.5bar(boost) = 1.36bar
Supercharger at Sea level: 1bar + 0.5bar(boost) = 1.5bar
Supercharger at 1200m altitude: 1bar*0.86 + 0.5bar*0.86 = 1.29bar