These Snow Days are the Days I love My Car......

[asp_125]

I have the new A3 with S-tronic. I'll never go back to manual again. I really enjoy it over both traditional manual and the much slower tiptronic (or any other single clutch application)

Oh and Pirelli Sottozero 3's murder snow

+1 the DSG in my A3 3.2Quattro was actually fun to drive, paddle shifting and left foot braking like a go-kart.

[tecknojoe]

and they still secretly have launch control too. not as impressive in the a3 as it is the S4, but still fun

[Spooph]

IIRC the turbo is better for elevation.

Whatchoo talking about? Sure, a turbo is scavenge/waste powered, and a super charger uses some of the power, but doesn't suffer from turbo lag. The turbo's need a dual setup, either in series or parallel (not sure what the mechanical/engine terms are here) - IE, either 2 small turbos for less cylinder or a smaller turbo feeding a bigger turbo, all of which makes plumbing very tricky.

How does that relate to elevation?

[birchyboy]

Whatchoo talking about? Sure, a turbo is scavenge/waste powered, and a super charger uses some of the power, but doesn't suffer from turbo lag. The turbo's need a dual setup, either in series or parallel (not sure what the mechanical/engine terms are here) - IE, either 2 small turbos for less cylinder or a smaller turbo feeding a bigger turbo, all of which makes plumbing very tricky.

How does that relate to elevation?

Why do you say turbo's need to be a dual setup? Many cars have single units and work extremely well.

[GMR]

I think he was talking in relationship to minimizing turbo lag a dual setup is used. Most people seeking big power gains switch from twins to a large single turbo though, which is probably what I'd do as well.
And now I just saw shortline has a blue 6 speed manual WRX in their lot...fuck me! Why did I get a truck?
I've driven a few paddle shifter cars, some terrible, the GTR great. Footbraking with the left foot may sound fun, quicker to brake/accelerate through a corner in the right gear but I don't drive track so I better like the idea of somewhere to rest my right hand..that's a true cruise

[Wrider]

Whatchoo talking about? Sure, a turbo is scavenge/waste powered, and a super charger uses some of the power, but doesn't suffer from turbo lag. The turbo's need a dual setup, either in series or parallel (not sure what the mechanical/engine terms are here) - IE, either 2 small turbos for less cylinder or a smaller turbo feeding a bigger turbo, all of which makes plumbing very tricky.

How does that relate to elevation?

N/A cars lose the most power from elevation, S/C cars lose a bit less, but turbo cars lose the least from elevation changes from what I've read.

[Spooph]

N/A cars lose the most power from elevation, S/C cars lose a bit less, but turbo cars lose the least from elevation changes from what I've read.

Tell me more! Very curious about this...

[Wrider]

Tell me more! Very curious about this...

From what I've read, it's simply because S/C cars use every ounce of boost they make while turbos have to bleed off excess boost (via wastegate). At altitude, the S/C is still going to suck in the same volume of air, but seeing as the air is less dense, the PSI is going to be decreased.

The turbo on the other hand, is going to maintain its PSI as the wastegate is set to the PSI, and not limited by what volume is being shoved into the engine.

Both are clearly more efficient than a N/A engine, but they still lose some power.
A little google-fu turned up that the average drag racer with an N/A engine in Denver loses 1 second vs sea level, whereas the average turbo car loses about .4 sec.

This link claims that N/A cars lose approx 3% of power for every 1000 ft whereas turbo cars lose approx 1.5% for the same altitude gain.

If I'm incorrect or phrasing this wrong, someone else please feel free to jump in and correct me!

[Ezzzzy1]

What yall need to do is spool the turbo with nitrous.... Its like having a super charger and a turbo all in one, no lag.

Another option for some good gains without messing with the motor too much is to fog nitrous to the intercooler. Colder air always equals more HP.


Most people dont "like" like nitrous but over the years I have started to believe thats due to most people being either scared of it or not knowing the first thing about it.

I have had 2 cars with nitrous and there is nothing more fun dollar for dollar than responsibly adding it to any motor.

[Aaron]

I just like rowing my own gears. I know the DCT is quicker and more efficient, but I prefer manuals. I'll still consider the RS5 and C63, but the Corvette and BMW gain big points with their manual options.

I believe Audi's reasoning for sticking with superchargers is for space restraints and cost. Superchargers are cheaper, take up less space, and last longer. Turbochargers are more efficient and thus will make more power per psi of boost.

At altitude, a supercharged car will suffer the same as a N/A car, figure about 21% at 7,000ft. A turbocharged car will only suffer half of that loss, about 10.5% at 7,000ft. However what you'll also notice in the turbo car is that the timing and lag are drastically affected by altitude. The 335i does not have any noticeable lag at sea level, it's response is instant. Like Jeremy Clarkson says, I know it has lag because it's a turbo car so it must, but it doesn't. At altitude, that's a different story. It's still really good for a turbo car, but you can feel it for sure, and full boost doesn't come in until 2500rpm, where it's 1400 at sea level.

[Wrider]

At altitude, a supercharged car will suffer the same as a N/A car

Ummm, not true. Read anything about supercharged/turbo vs n/a and it'll say that s/c suffers less than n/a.

[DriverDave]

From what I've read, it's simply because S/C cars use every ounce of boost they make while turbos have to bleed off excess boost (via wastegate). At altitude, the S/C is still going to suck in the same volume of air, but seeing as the air is less dense, the PSI is going to be decreased.

The turbo on the other hand, is going to maintain its PSI as the wastegate is set to the PSI, and not limited by what volume is being shoved into the engine.

Both are clearly more efficient than a N/A engine, but they still lose some power.
A little google-fu turned up that the average drag racer with an N/A engine in Denver loses 1 second vs sea level, whereas the average turbo car loses about .4 sec.

This link claims that N/A cars lose approx 3% of power for every 1000 ft whereas turbo cars lose approx 1.5% for the same altitude gain.

If I'm incorrect or phrasing this wrong, someone else please feel free to jump in and correct me!

The boost gauge on my Celica all-trac always showed 4-5 psi around Denver. When I took a road trip to CA, it showed 8 psi at sea level and felt waaay faster...just my 2 cents from my own experience...just an fyi - this was 20 years ago.

[Spooph]

so this then be my question: A super charger and turbo charger with equal amounts of peak boost - would they suffer differently?
Or is the loss because the turbo isn't directly linked to engine RPM's that it has a near infinite amount of boost as it can spin faster and faster, whereas the supercharger is limited to the engine's redline?

[Ezzzzy1]

The boost gauge on my Celica all-trac always showed 4-5 psi around Denver. When I took a road trip to CA, it showed 8 psi at sea level and felt waaay faster...just my 2 cents from my own experience...just an fyi - this was 20 years ago.

Thats because the wastegate was electronically controlled. Basically controlled by its environment. As far as feeling faster, it was. 3lbs of boost is a lot for a car like the Celica.

[Grim2.0]

so this then be my question: A super charger and turbo charger with equal amounts of peak boost - would they suffer differently?
Or is the loss because the turbo isn't directly linked to engine RPM's that it has a near infinite amount of boost as it can spin faster and faster, whereas the supercharger is limited to the engine's redline?

Short answer to your question: yes


Altitude effects everything in different ways, cars, humans electric motors...anything that demands POWER is directly effected. You will see minimized losses in Turbo VS S/C because the Turbo is producing greater air intake/fuel via the exhaust (heat and pressure) producing energy which in THEORY could be infinite but is obviously limited to what the cars can produce exhaust wise.

The Supercharger is reliant on the Engines RPM so it relies on the pulleys and is considered a "step up" transformation.

Because you have to DE-rate the engine at higher altitude due to atmospheric pressure you lose power, loss in power via engine = lose of power directly to the supercharger as well as it demands power.

Because the Turbo creates and relies on exhaust while there is still power lose in the engine there is no lose in the turbo.

I hope that confused you

[Spooph]

awesome, thanks Grim!

[madvlad]

Superchargers take power to make power. Altitude power loss on top of power transfer loss is a bitch for sure lol... N/A at altitude is seriously drunk and needs to go home lol

[Aaron]

Ummm, not true. Read anything about supercharged/turbo vs n/a and it'll say that s/c suffers less than n/a.

You're wrong, and here's the numbers. Now first, I'll say in general. There are electronically controlled, ambient pressure adjusting wastegates. They are extremely rare in automotive applications, used mainly for aircraft. In fact I've never heard of one being used in an automotive application. There are also ambient pressure supercharger bleed-off valves, that basically spin the supercharger faster than needed all the time, and bleed off excess boost. Again extremely rare, and never been in an OEM application as far as I'm aware. This is for 99% of automotive applications, including the Subarus, BMW's, and my Fiero.

Sea level = 14.69psi
Colorado Springs = 11.7 (That is the cells that my piggyback is at with ign on, engine off).

Anyways, we lose about 3psi ambient pressure due to altitude. For an N/A car, this is a 20.4% loss in air pressure, which would equate to a 20.4% loss in power (Assuming same ignition timing maps, which is likely).

Back in high school, I had a friend who moved here from Texas, on the coast, who had a modded GTP. Via his data-logging software, he saw dead on 15psi. Added to the 14.69, he had 29.69psia. However here in Colorado, due to how a supercharger works, he only saw 12psi. Combined with the lower atmospheric pressure, he only got 23.7psia. He saw a 20.2% drop in psia, equating to a rough 20.2% drop in power, near identical to the N/A numbers.

Boost is pressure above ambient. Superchargers will show less boost as altitude increases. This is because they are set to run at a certain speed, which means a certain airflow. So on the inlet side of the supercharger, they are down 3psi ambient. Because there is less air going into the blower (3psi less), there's less coming out (3 psi less). So you've got a 3psi loss in boost pressure, mixed with a 3psi loss in ambient pressure, about a 6psi loss in total air pressure, which gets us our roughly 20% loss in power.

However, things are different for a turbocharger, since boost (Pressure above ambient), is kept equal at your peak power. So for me, it was 14psi. Added to the 14.69, at sea level, I'd have 28.69psia. Up here, that drops to 11.7 + 14 = 25.7psia. A 10.4% loss in power, roughly half that of the N/A and SC cars, exactly what we'd expect.

Superchargers suffer just as much power loss at altitude as N/A cars, with turbo cars being about half of those.

[Kim-n-Dean]

Altitude effects everything in different ways, cars, humans electric motors...anything that demands POWER is directly effected.

I'm curious as to how altitude affects electric motors. While I've never dyno'd my nitro or electric R/C cars at 11,000' when we are camping, I can see a lose in power on the nitro cars, but never on the electrics. I would think an electric car would be faster at altitude. No power lose, but the air is thinner. Therefore, less aerodynamic drag.

[Spooph]

You're wrong, and here's the numbers. Now first, I'll say in general. There are electronically controlled, ambient pressure adjusting wastegates. They are extremely rare in automotive applications, used mainly for aircraft. In fact I've never heard of one being used in an automotive application. There are also ambient pressure supercharger bleed-off valves, that basically spin the supercharger faster than needed all the time, and bleed off excess boost. Again extremely rare, and never been in an OEM application as far as I'm aware. This is for 99% of automotive applications, including the Subarus, BMW's, and my Fiero.

Sea level = 14.69psi
Colorado Springs = 11.7 (That is the cells that my piggyback is at with ign on, engine off).

Anyways, we lose about 3psi ambient pressure due to altitude. For an N/A car, this is a 20.4% loss in air pressure, which would equate to a 20.4% loss in power (Assuming same ignition timing maps, which is likely).

Back in high school, I had a friend who moved here from Texas, on the coast, who had a modded GTP. Via his data-logging software, he saw dead on 15psi. Added to the 14.69, he had 29.69psia. However here in Colorado, due to how a supercharger works, he only saw 12psi. Combined with the lower atmospheric pressure, he only got 23.7psia. He saw a 20.2% drop in psia, equating to a rough 20.2% drop in power, near identical to the N/A numbers.

Boost is pressure above ambient. Superchargers will show less boost as altitude increases. This is because they are set to run at a certain speed, which means a certain airflow. So on the inlet side of the supercharger, they are down 3psi ambient. Because there is less air going into the blower (3psi less), there's less coming out (3 psi less). So you've got a 3psi loss in boost pressure, mixed with a 3psi loss in ambient pressure, about a 6psi loss in total air pressure, which gets us our roughly 20% loss in power.

However, things are different for a turbocharger, since boost (Pressure above ambient), is kept equal at your peak power. So for me, it was 14psi. Added to the 14.69, at sea level, I'd have 28.69psia. Up here, that drops to 11.7 + 14 = 25.7psia. A 10.4% loss in power, roughly half that of the N/A and SC cars, exactly what we'd expect.

Superchargers suffer just as much power loss at altitude as N/A cars, with turbo cars being about half of those.

Good stuff right here, at least to get me digging deeper. Thanks Aaron!

[Grim2.0]

I'm curious as to how altitude affects electric motors. While I've never dyno'd my nitro or electric R/C cars at 11,000' when we are camping, I can see a lose in power on the nitro cars, but never on the electrics. I would think an electric car would be faster at altitude. No power lose, but the air is thinner. Therefore, less aerodynamic drag.

I'm curious as to how altitude affects electric motors. While I've never dyno'd my nitro or electric R/C cars at 11,000' when we are camping, I can see a lose in power on the nitro cars, but never on the electrics. I would think an electric car would be faster at altitude. No power lose, but the air is thinner. Therefore, less aerodynamic drag.

Ironically enough Electric Motors are my specialty!!

The nitty gritty is in fact air density which effects ambient temperature, the thinner the air the less the cooling capacity, electric motors MUST have a set amount of cool air blowing over them to push the heat dissipating on the cooling fins of the body. The hotter a motor gets the less performance it has, the solution is oversize and de-rate to account for the power loss. The principal per EASA is a 3% de-rate per 1,000ft after 3,300ft ASL (above sea level).

Those little RC cars dont have much power in them for you to even notice that 3% loss per 1000FT even if you have a 1hp operating at 6,000ft with a 9% loss you would have roughly .93HP not nearly enough to visually notice. The other thing you have to factor is you live in Colorado and in Parker along where I live we are already above 3300ft ASL you already have losses that you are accustom to and dont even know it. The motors i deal with range from 100HP to 500,000HP so the de-rate and loss is very significant.

I actually just had two 450HP motors at Cripple Creek gold mine in Victor Colorado overheat and fail three weeks ago because the original engineer did not account for altitude, the demand on the machine they were running was 450HP but because they only gave them a motor capable of 450HP at the 10,000 ft ASL they were at (21% de-rate) the motor was actually only operating at 355HP thus the demand was forcing the motor to work harder to keep up, the motor will do what is asked of it so it works harder, hotter until something either goes boom or burns up.

Result I sold them two 600HP motors operating at 474HP @ 10000ft ASL. Good day for me bad day for them

[Kim-n-Dean]

Ironically enough Electric Motors are my specialty!!

The nitty gritty is in fact air density which effects ambient temperature, the thinner the air the less the cooling capacity, electric motors MUST have a set amount of cool air blowing over them to push the heat dissipating on the cooling fins of the body. The hotter a motor gets the less performance it has, the solution is oversize and de-rate to account for the power loss. The principal per EASA is a 3% de-rate per 1,000ft after 3,300ft ASL (above sea level).

Those little RC cars dont have much power in them for you to even notice that 3% loss per 1000FT even if you have a 1hp operating at 6,000ft with a 9% loss you would have roughly .93HP not nearly enough to visually notice. The other thing you have to factor is you live in Colorado and in Parker along where I live we are already above 3300ft ASL you already have losses that you are accustom to and dont even know it. The motors i deal with range from 100HP to 500,000HP so the de-rate and loss is very significant.

I actually just had two 450HP motors at Cripple Creek gold mine in Victor Colorado overheat and fail three weeks ago because the original engineer did not account for altitude, the demand on the machine they were running was 450HP but because they only gave them a motor capable of 450HP at the 10,000 ft ASL they were at (21% de-rate) the motor was actually only operating at 355HP thus the demand was forcing the motor to work harder to keep up, the motor will do what is asked of it so it works harder, hotter until something either goes boom or burns up.

Result I sold them two 600HP motors operating at 474HP @ 10000ft ASL. Good day for me bad day for them

I had no idea. That's some cool info. My motors have fans on them for cooling. If the fan has enough CFM to cool the motor as if it were at sea level, would the altitude affect still be there? I'm assuming the altitude affect only happens after the motor heats up?

[Grim2.0]

I had no idea. That's some cool info. My motors have fans on them for cooling. If the fan has enough CFM to cool the motor as if it were at sea level, would the altitude affect still be there? I'm assuming the altitude affect only happens after the motor heats up?

Indeed it would and correct but keep in mind these motors get hot fast, there is low voltage but high current flowing through them and the harder the motor works the higher the current. On an RC car every time you stop you have to start again and starting or ramp up is the peak of the torque curve demanding higher current. The motors i work with are the same as your little motor, it has a TEFC enclosure (totally enclosed fan cooled). the CFM rating on the motor is set per that HP and speed rating however all electric motors have a standard insulation class and ambient temp rating, the higher the DE-rate the less the motor has to work thus less heat generated.

Regardless of the amount CFM flow over your motor you still have to account for Watts Loss through heat in the motor the motor will always generate the same amount of heat based on the function its performing and you will always supply the same amount of cooling air based on rotational speed, as long as you do not exceed the ambient rating no harm no foul. The biggest argument we have is "bigger fan more cooling air" which is wrong, you can gain the same amount of CFM with a fan half the size of a 10" DIA fan based on rotational speed. Its all about speed, and the fastest motor on the market that is coil wound and not a permanent magnet stator or rotor is 3600RPM or 2-pole, usually used for reciprocating Compressors.

Your RC cars have an advantage though....its a moving part, you have the cooling air from your fan on the motor but also the air over the vehicle when in operation.


Edit: One option there is to eleviate this issue is a Water cooled Motor however this is not cheap my any means and is much larger as well. Even still there will be slight losses due to atmospheric pressure and the motor having to work harder.

[birchyboy]

Cool info Grim.