Banks experiment - altitude and hp

valhalla360 wrote:
I stand corrected that there are supercharged production vehicles...of course, none listed look like typical tow vehicles. Most aren't even typical passenger vehicles but specialized performance vehicles sold in tiny numbers. So while technically true, you aren't likely to see many of these towing a 30' TT.

Out of curiosity are they permanently on and at max boost? If not, you might see a similar effect to turbos.
- Cruising at highway speeds on level ground at sea level, my assumption is they turn off the supercharger as it's simply not needed...similar to a turbo charger not boosting under light load. Only it's worse as superchargers eat up some of the HP to power them.
- Under heavy load climbing at altitude, a supercharged engine intended for towing would be putting out max boost.

It would probably be a little more choppy in terms of effect (on vs off rather than a more smooth matching of boost to needs) but the general effect would still be there. Or as someone suggested, they may have some sort of gearing (or equivalent function) to adjust boost to need...but again, none of the examples are intended for serious towing.

To the second part of your comment: it's nice to see the math but nothing beats actual testing as unexpected issues can come into play.

Now that you've mentioned it, I believe the Range Rover 3.0 V6 and 5.0 V8 supercharged engines have a "boost bypass" function, which allows the blower rotors to freewheel.

But even on a normal supercharger, you're not putting how max boost constantly, because the throttle body is in front of the blower. So at partial throttle, you're feeding the blower a vacuum, and getting slightly less vacuum out of it. That's why I made up that simplified 50% throttle example.

I agree they're not ideal for towing - you have a lot of parasitic loss, and heat rejection (roots and screws not as efficient as a centrifugal compressor, and OEM only use roots/screw).

4x4ord wrote:

ShinerBock wrote:
Haven't watched the video, but that is about right doing the math. An N/A engine drops about 3% power every 1,000 ft above sea level.

3 x 5.6 = 16.8

347 hp - 16.8% = 289 hp

Not too far off.

Not that it makes a huge difference but if the power drops off 3% every 1000 feet the power would have dropped to:
.97^5.6 x 347 = 292.6 HP

To determine what percent hp drop there is per 1000 feet of elevation gain when the engine went from 347 down to 285 hp over 5600 feet of elevation gain you would set up an equation like this:

x^5.6 * 347 = 285 so x^5.6 =.8213 and therefore x = .8213^(1/5.6) or .965 which means that the power drops off 3.5% per 1000 feet of elevation gain.

I guess I should have explained it better, but I figured the math I stated would have. It is a cumulative 3% every 1000 ft from hp at sea level, not 3% off from every value at each 1,000 ft in elevation. That is the way it was explained to me from an engineer at Cummins that will get you the closes to actual. It seems that they were correct based on the cumulative percentage being closer to the actual number stated. It just used as a general rule of thumb, and not exact science.

ShinerBock wrote:
Haven't watched the video, but that is about right doing the math. An N/A engine drops about 3% power every 1,000 ft above sea level.

3 x 5.6 = 16.8

347 hp - 16.8% = 289 hp

Not too far off.

Not that it makes a huge difference but if the power drops off 3% every 1000 feet the power would have dropped to:
.97^5.6 x 347 = 292.6 HP

To determine what percent hp drop there is per 1000 feet of elevation gain when the engine went from 347 down to 285 hp over 5600 feet of elevation gain you would set up an equation like this:

x^5.6 * 347 = 285 so x^5.6 =.8213 and therefore x = .8213^(1/5.6) or .965 which means that the power drops off 3.5% per 1000 feet of elevation gain.

RoyJ wrote:

valhalla360 wrote:
- I don't think any production vehicles are running superchargers...so not really relevant but even there, you are assume they are on 100% of the time. Assuming there is a control mechanism, there can be a difference.

As mentioned, many vehicles run superchargers.

No, I didn't assume superchargers run wide open. They're throttled just like NA and turbo gas engines. But regardless of how much you open the throttle, they have a fixed pressure ratio (boost ratio).

If the ratio is 2:1, at sea level, 100% throttle, then you manifold pressure is 14.7 psi. At an elevation of 0.8 atmosphere, you'll be at 11.76 psi.

At 50% throttle, you'll be at 7.35 psi, and high elevation 5.88 psi (grossly simplified, but you get my point).

Theoretically both NA should see similar percent reductions and both turbo should see similar percent reductions but actual field tests can bring to light issues not readily apparent (like small turbos only partially negating the thin air).

With NA, I bet test results = math.

To guess a turbo's "room" left to boost at altitude, you could look at how much top end hp a vehicle gains with only a tune.

On small turbo engines like my lil Mini Cooper, a tune can gain 30% of torque in the mid range, and only 10% above 5000 rpm. We can make an educated guess at say beyond 3000 feet (0.9 atm), it'll probably start to lose power. Because at that altitude, it requires the turbo to generate 10% more boost ratio.

I stand corrected that there are supercharged production vehicles...of course, none listed look like typical tow vehicles. Most aren't even typical passenger vehicles but specialized performance vehicles sold in tiny numbers. So while technically true, you aren't likely to see many of these towing a 30' TT.

Out of curiosity are they permanently on and at max boost? If not, you might see a similar effect to turbos.
- Cruising at highway speeds on level ground at sea level, my assumption is they turn off the supercharger as it's simply not needed...similar to a turbo charger not boosting under light load. Only it's worse as superchargers eat up some of the HP to power them.
- Under heavy load climbing at altitude, a supercharged engine intended for towing would be putting out max boost.

It would probably be a little more choppy in terms of effect (on vs off rather than a more smooth matching of boost to needs) but the general effect would still be there. Or as someone suggested, they may have some sort of gearing (or equivalent function) to adjust boost to need...but again, none of the examples are intended for serious towing.

To the second part of your comment: it's nice to see the math but nothing beats actual testing as unexpected issues can come into play.

valhalla360 wrote:
- I don't think any production vehicles are running superchargers...so not really relevant but even there, you are assume they are on 100% of the time. Assuming there is a control mechanism, there can be a difference.

As mentioned, many vehicles run superchargers.

No, I didn't assume superchargers run wide open. They're throttled just like NA and turbo gas engines. But regardless of how much you open the throttle, they have a fixed pressure ratio (boost ratio).

If the ratio is 2:1, at sea level, 100% throttle, then you manifold pressure is 14.7 psi. At an elevation of 0.8 atmosphere, you'll be at 11.76 psi.

At 50% throttle, you'll be at 7.35 psi, and high elevation 5.88 psi (grossly simplified, but you get my point).

Theoretically both NA should see similar percent reductions and both turbo should see similar percent reductions but actual field tests can bring to light issues not readily apparent (like small turbos only partially negating the thin air).

With NA, I bet test results = math.

To guess a turbo's "room" left to boost at altitude, you could look at how much top end hp a vehicle gains with only a tune.

On small turbo engines like my lil Mini Cooper, a tune can gain 30% of torque in the mid range, and only 10% above 5000 rpm. We can make an educated guess at say beyond 3000 feet (0.9 atm), it'll probably start to lose power. Because at that altitude, it requires the turbo to generate 10% more boost ratio.

The Volvos on your list are in face both Turbo Charged, AND Supercharged. I'm not certain they all are, but some of the S and V 60 models are.

valhalla360 wrote:
I don't think any production vehicles are running superchargers...so not really relevant but even there, you are assume they are on 100% of the time. Assuming there is a control mechanism, there can be a difference.

There are plenty of supercharged cars available since the 80's:

Volvo XC90, S90, S60 T6
Land Rover Range Rover, Sport
Chevrolet Camaro ZL1, Corvette Z06, Impala SS, Cobalt SS
Cadillac CTS-V, STS-V
Buick Riviera
Pontiac GTP
Ford SVT Lightning, Saleen Mustang, Mustang Cobra SVT, Thunderbird SC
Chrysler 300 SRT8
Dodge Challenger & Charger SRT Hellcat
Jeep Grand Cherokee SRT8
Audi A6, B8, S4
Porsche Chayenne Hybrid
Jaguar F-Pace, F-Type, XF, XJR
Mecedes-Benz E55 AMG, SLK32 AMG
Mini Cooper S
Toyota Previa LE S/C, MR2
Scion TC TRD

RoyJ wrote:

valhalla360 wrote:
It would be fun to see a series of similar tests with diesel and turbo vs non-turbo.

As you say it matches the math but it's always nice to see confirmation.

A naturally aspirated diesel would have the same ratio of loss as an NA gasoline. A supercharged engine, despite popular belief, also loses just as much power with elevation gain as NA, as the supercharger is spinning at a fixed rpm. Unless the supercharger is purposely bleeding off boost at sea level, and then doing full boost at elevation.

With turbos, it depends on the size of the compressor. If they're undersized, like say an Ecoboost (for throttle response), then at high elevations you'll run into the limit of the compressor, and lose some power. Usually significantly less than NA though.

With a "performance" turbo, where the compressor has plenty of room left on the compressor map, then at elevation it may retain near 100% of power. Trade-off is a relatively laggy throttle response.

As I said, I understand the math but it's always nice to see how it turns out in reality.
- I don't think any production vehicles are running superchargers...so not really relevant but even there, you are assume they are on 100% of the time. Assuming there is a control mechanism, there can be a difference.
- As you indicated, the turbo may run out of blow at some point, so how close to the theoretical no impact does it get?

My intent was actually 4 options:
- NA gas
- turbo gas (production style turbo)
- NA diesel
- turbo diesel

Theoretically both NA should see similar percent reductions and both turbo should see similar percent reductions but actual field tests can bring to light issues not readily apparent (like small turbos only partially negating the thin air).

RoyJ wrote:

valhalla360 wrote:
It would be fun to see a series of similar tests with diesel and turbo vs non-turbo.

As you say it matches the math but it's always nice to see confirmation.

A naturally aspirated diesel would have the same ratio of loss as an NA gasoline. A supercharged engine, despite popular belief, also loses just as much power with elevation gain as NA, as the supercharger is spinning at a fixed rpm. Unless the supercharger is purposely bleeding off boost at sea level, and then doing full boost at elevation.

With turbos, it depends on the size of the compressor. If they're undersized, like say an Ecoboost (for throttle response), then at high elevations you'll run into the limit of the compressor, and lose some power. Usually significantly less than NA though.

With a "performance" turbo, where the compressor has plenty of room left on the compressor map, then at elevation it may retain near 100% of power. Trade-off is a relatively laggy throttle response.

Exactly. I'm not sure everyone realizes turbodiesels do well at altitude because of the turbo, not because they are diesels. Gas turbos reap the same benefits.

Interesting fact regarding superchargers and altitude. Some supercharged airplanes had two speed superchargers so they could spin the supercharger faster at high altitudes to gain some power back.

valhalla360 wrote:
It would be fun to see a series of similar tests with diesel and turbo vs non-turbo.

As you say it matches the math but it's always nice to see confirmation.

A naturally aspirated diesel would have the same ratio of loss as an NA gasoline. A supercharged engine, despite popular belief, also loses just as much power with elevation gain as NA, as the supercharger is spinning at a fixed rpm. Unless the supercharger is purposely bleeding off boost at sea level, and then doing full boost at elevation.

With turbos, it depends on the size of the compressor. If they're undersized, like say an Ecoboost (for throttle response), then at high elevations you'll run into the limit of the compressor, and lose some power. Usually significantly less than NA though.

With a "performance" turbo, where the compressor has plenty of room left on the compressor map, then at elevation it may retain near 100% of power. Trade-off is a relatively laggy throttle response.