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Old 01-26-2011, 10:26 AM   #1
Bluefoton
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Default 190 HP on Monday!

165 HP at -28C, 60% humidity, 50 m altitude and 1020 hpa air pressure...... 15.6% increase in power = 190hp

http://wahiduddin.net/calc/calc_hp.htm
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Old 01-26-2011, 10:35 AM   #2
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Old 01-26-2011, 11:33 AM   #3
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Wtf?????
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Old 01-26-2011, 11:47 AM   #4
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Oh, I get it. OP is pretending HP calculators are accurate on outlier inputs like -28 degrees C. If they were, an NA Subaru could make 190 bhp. At which point axles and/or wheels would shatter from the cold brittle.
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Old 01-26-2011, 11:53 AM   #5
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Quote:
Originally Posted by BAN SUVS View Post
Oh, I get it. OP is pretending HP calculators are accurate on outlier inputs like -28 degrees C. If they were, an NA Subaru could make 190 bhp. At which point axles and/or wheels would shatter from the cold brittle.
So that's why i was bouncing off the rev limiter in top gear on Monday morning, early on it was actually -28 with a -38 wind chill here in Montreal
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Old 01-26-2011, 12:03 PM   #6
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-28c isnt that cold? nothing would shatter LOL
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Old 01-26-2011, 12:21 PM   #7
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It was meant as an utterly silly post, but why wouldn't it be accurate? Colder = more dense = more fuel = more power. Feed -30C air into an intake of an engine on a dyno and the resulting power/tq curves should rise by 15%..
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Old 01-26-2011, 12:48 PM   #8
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-28c isnt that cold? nothing would shatter LOL
Hush.
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Old 01-26-2011, 05:01 PM   #9
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It was meant as an utterly silly post, but why wouldn't it be accurate? Colder = more dense = more fuel = more power. Feed -30C air into an intake of an engine on a dyno and the resulting power/tq curves should rise by 15%..
lol. The simple formula used to estimate changes in HP by temp, humidity, etc are simple because they are taking a lot of factors out assuming that the user will be within a certain envelope.

To put it short, if things are extreme the formulas don't apply anymore.
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Old 01-26-2011, 07:20 PM   #10
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^ sure, but i'd still be curious to know the accuracy range. The only factor unnacounted for is the increased friction loss, which would occur mainly in the drivetrain - bearings, differential, etc. THe engine being at normal operating temperature, the rest is in principle unaffected...
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Old 01-26-2011, 07:37 PM   #11
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Well, your engine would have to have the overhead on fuel delivery and air metering to actually deliver the power, plus your cams and manifolds would have to work at the new flow rates. None of which would actually be true.
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Old 01-26-2011, 08:49 PM   #12
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Why would the manifold and cams care about the mass flow rate? The volumetric flow rate should be the same. Although, the wave tuning might be different if the stiffness of the air changes.
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Old 01-26-2011, 09:04 PM   #13
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If that were true, all manifolds and cams would make the same power in the same RPM ranges right?
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Old 01-26-2011, 09:15 PM   #14
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Two manifolds and two sets of cams that are made the same should produce roughly the same VE curves, yes.
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Old 01-26-2011, 10:18 PM   #15
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Why would the manifold and cams care about the mass flow rate? The volumetric flow rate should be the same. Although, the wave tuning might be different if the stiffness of the air changes.
The mass flow rate is more important than the volumetric flow rate because we are dealing with difference in air density. The volume is fixed. More dense air has more molecules of oxygen meaning it has a higher mass flow rate but there are several things that still need consideration.

Again, this is too simple of an approach to a very dynamic system...

let's just look at the air for example:

1. How much is the air heating up from conduction before it gets into the engine? Remember, the higher the difference in temperature, the higher the rate of heat conduction...

2. How does the denser air flow through the system compared to less dense air assuming it is constantly expanding from the rising temperature?
(and remember the flow is almost completely turbulent which can't even be predicted without modeling or huge assumptions)

3. As your engine heats up, will the air temperature entering the engine taper up to an equilibrium point from the thermal mass of everything around it? How much will this established "steady state" temperature really differ from standard inlet air temps on days when it isn't balls cold?

4. Etc

Last edited by Rudgers73; 01-26-2011 at 10:25 PM.
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Old 01-26-2011, 10:26 PM   #16
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Quote:
Originally Posted by Rudgers73 View Post
Again, this is too simple of an approach to a very dynamic system...

let's just look at the air for example:

1. How much is the air heating up from conduction before it gets into the engine? Remember, the higher the difference in temperature, the higher the rate of heat conduction...

2. How does the denser air flow through the system compared to less dense air assuming it is constantly expanding from the rising temperature?
(and remember the flow is almost completely turbulent which can't even be predicted without modeling or huge assumptions)

3. As your engine heats up, will the air entering the engine taper to an equilibrium in temperature from the thermal mass of everything around it? How much will this "steady state" temperature really differ from standard inlet air temps on days when it isn't balls cold?
No, I agree, he won't have 190 horsepower. I'm saying the manifold and cams would work just as good as they always did.
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Old 01-26-2011, 10:29 PM   #17
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All I know is my butt dyno absolutely see's difference between a -30C day and a 30C day. Feels like I'm driving a whole different car at that low temperature! I'll have to run an Airboy on it some day as I'm curious now.
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Old 01-26-2011, 10:44 PM   #18
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All I know is my butt dyno absolutely see's difference between a -30C day and a 30C day. Feels like I'm driving a whole different car at that low temperature! I'll have to run an Airboy on it some day as I'm curious now.
well -30 to 30 is a pretty big difference, so yeah, of course there is an increase. All I'm saying is that you aren't gaining 30 horses. If there were giant gains to be made from really cold intake air people would be spending money on refrigerated intercoolers and skipping the forced induction
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Old 01-27-2011, 02:40 AM   #19
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People do spend money on refrigerated intercoolers. It's just less effective than FI because the air isn't in contact with the cold thing for that long.


And air temps that low would cause the manifold and cams to "respond differently". The speed of sound would change, among other things affecting resonant tuning behaviors.
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Old 01-27-2011, 10:24 AM   #20
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This would call for a dyno test.. especially that there is only one variable involved and no changes to the engine itself... I didn't think about the change in speed of sound. Combustion is probably affected as well. Nevertheless, if the predicted HP gain based only on air density is 15%, I'd still assume I gained at least 10%.

To be anally correct though, my IATs never went down to -30C. With the engine and engine bay warmed up (30 min + of freeway driving), at WOT my IATs are about 15C (30F) higher than ambient air temperature - which means that I never went below -15C (5F).
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