How much HP does 25 degrees give?

[majdoob]

Guys, I have a 91 stock NSX. I bought it in the spring and have not driven it in cold weather yet. I was out Saturday night in 20 degree weather and about 40% humidity and it felt like the car gained about 15 extra horses. I know the pysics behind cold air intake, but was quite impressed by how much faster the car felt. Is that what it feels like to upgrade the intake, headers and enhaust...I have read on here that you can expect about 15-25 more horses from that upgrade. I'm just trying to get a sense of how to compare the cold air drving last night to what it might feel like to get the I/H/E upgrade. Not looking for exact science, just your educated guess.

Thanks

 

[Gramps]

What the Lord giveth in cold air HP, He taketh away in tire adhesion.

 

[AdnanVCS]

Got a brain storm!
Why don't you make somthing around your intake that air cold!

Hmmm how can you get this done?
OR
It might already bean done!

 

[AdnanVCS]

Got a brain storm!
Why don't you make somthing around your intake that air cold!

Hmmm how can you get this done?
OR
It might already bean done!

Hmm have a plan on how to make a super colded intake

 

[majdoob]

Gramps, good point about tire adhesion. I don't know how much the additional HP helps when you can't stay on the road.

AdnanVCS, very funny. I've read a bunch on here about cold air intakes and the general consensus sounds like the gain is effectively zero. Now, if you could create a bolt on cold air intake that gave 15 HP, I think you'd be a rich man.

Anyone else? Any thoughts on how much extra HP you might be getting under these conditions vs normal (normal in the summer is about 80 degrees and 70% humidity).

 

[Bodhi]

Per you question: Ideally, the availabilty of oxygen and the density of air will increase slightly as the temperature goes down. The ideal gas formula describes the relationship: PV =nRT

Where;
P - pressure
V- volume
n - number of gas molecules (O2 = 0.20 x n)
R - universal gas constant
T - absolute temperature (degrees Rankine, not Farenheit)
80 deg. F = 540 deg. R
25 deg. F = 485 deg. R


So, as the temp declines and the volume is held fixed (displacement = 3.0 or 3.2 liters), the number of molecules in that volume increases and hence the greater number of oxygen molecules that are available for combustion). The power (HP) is proportional to the amount of chemical energy ((V)gasoline + (V)O2 + spark) that is converted to kinetic energy (force x moment arm x rotational velocity). This being said, the increase in HP is really an increase in torque as the RPM's are not increasing. I also think that the temp sensor allows for an increase in the volume of fuel delivered per stroke so that you have a more complete cumbustion of the air/fuel mixture as well as a slight increase in the volume of fuel combusted per power stroke. How much more? The math works out to about an 11% increase, not considering the increase in fuel which is handled by EMM, waste heat loss and frictional loss. So, at 8,000 rpm and at about 245 HP (NA1) at the wheels, you could expect about 25 hp increase minus the losses due to waste heat transfer (40%). In other words, you may notice an increase of about 15 HP (about what you thought!).

 

[majdoob]

Bodhi, you are the man! I was expecting some educated guesses and was pleased to see some exact science. Your analysis is very insightful. Thanks for taking the time to provide a thorough explanation. It confirms my original belief that the power increase I experienced is about the same that I could expect from new I/H/E. Thanks!!

 

[kreh]

Great back-of-the-envelope engineering analysis. This is what I would expect on Prime. Thanks

 

[BluryNSX]

holy crap Bodhi that some real life"Numbers" shit lol....I know I know that show isnt very realistic. But geez man thats pretty sweet

 

[Bodhi]

Aw, c'mon now. It really isn't rocket science. Just some basic gas relationships and thermodynamics. If you realy want to "know" about extracting every joule of energy from a small displacement engine, talk to the FI guys. They are very knowledgable about fuel/air/compression/heat transfer processes. BTW, the I/H/E path has more than performance to offer, it also sounds SO much better that OEM. Just MHO...:wink:

 

[clr1024]

for what its worth an 11 degree f change will net about 1% increase...or decrease in hp

 

[Bodhi]

Hmm, lets see if that is true?

1%/11 deg. F change
= 0.01 x (80-25)F
= 1% x 55 deg. F
= +5.5% x 245 HP (rear wheel HP)
= 13.47 HP

That is certainly within the range of error for this discussion!

clr1024; I like that relationship! Where did you find it? Simple, easy and pretty accurate.

 

[clr1024]

Hmm, lets see if that is true?

1%/11 deg. F change
= 0.01 x (80-25)F
= 1% x 55 deg. F
= +5.5% x 245 HP (rear wheel HP)
= 13.47 HP

That is certainly within the range of error for this discussion!

clr1024; I like that relationship! Where did you find it? Simple, easy and pretty accurate.

I have known this approximation for years...I suppose reading, but proved it to be a good approximation years ago in thermodynamics:wink:

From another post:
The SAE correction factor is proportional to ((Temp + 460)/536.4)^0.5 when Temp is in degrees Fahrenheit. So a 10.6 degree reduction would increase the power approximately 1%.

 

[nsxotic911]

Are there any consequences to this effect? EG If I have a high-boost SC putting out about 400RWHP and now I'm driving in 30 degree weather and essentially gain more HP, does this incerease my chances of the engine going kabluy?

 

[Bodhi]

Boy, does this open a can of worms!!! First: I am not an FI knowledge rich person Two: This is based on a couple of simple relationships, and Three: A high boost engine is more likely to go *&^% than a NA engine (all thing being equel).

My first thought is that with cold air (dense) your boost is simply increased when compared to temperate or warm air (i.e., more O2 available). Detonation is more likely since your "net" compression is higher, but this may be mitigated by the reduced ambient temperature. I would ask the SC manufacturer about this! I would also consider a more complete warm up period as temperature differentials in engine components WILL add thermal stress to an allready highly stressed component(s) (think entire drive train).
Personally, I wouldn't run a SC engine in extreme cold - period.

I would still ask the FI boys about this one, they have mucho experiance! I don't... :redface:

 

[clr1024]

Are there any consequences to this effect? EG If I have a high-boost SC putting out about 400RWHP and now I'm driving in 30 degree weather and essentially gain more HP, does this incerease my chances of the engine going kabluy?

Like Bodhi said, I could speculate for a while on this as well, but I am probably better of leaving it to those that have experience in the FI tuning and building. I guess it matters how close to the edge of your engine limits you are before the temp drop.

 

[nsxotic911]

Like Bodhi said, I could speculate for a while on this as well, but I am probably better of leaving it to those that have experience in the FI tuning and building. I guess it matters how close to the edge of your engine limits you are before the temp drop.

Any FI folks to catch on this thread?

I usually let the engine warm up a lot, at least 20 minutes idl'ng, sometimes pushing towards 30. I usually check to make sure the SC is at least warm to the touch before taking it out and drive 'nicely' for at least another 10 15 minutes, so the SC is fairly warm... I'm in Seattle and the nights are cold (especially this time of year..) so it looks like I have to give it some more consideration.

 

[TURBO2GO]

Per you question: Ideally, the availabilty of oxygen and the density of air will increase slightly as the temperature goes down. The ideal gas formula describes the relationship: PV =nRT

Where;
P - pressure
V- volume
n - number of gas molecules (O2 = 0.20 x n)
R - universal gas constant
T - absolute temperature (degrees Rankine, not Farenheit)
80 deg. F = 540 deg. R
25 deg. F = 485 deg. R


So, as the temp declines and the volume is held fixed (displacement = 3.0 or 3.2 liters), the number of molecules in that volume increases and hence the greater number of oxygen molecules that are available for combustion). The power (HP) is proportional to the amount of chemical energy ((V)gasoline + (V)O2 + spark) that is converted to kinetic energy (force x moment arm x rotational velocity). This being said, the increase in HP is really an increase in torque as the RPM's are not increasing. I also think that the temp sensor allows for an increase in the volume of fuel delivered per stroke so that you have a more complete cumbustion of the air/fuel mixture as well as a slight increase in the volume of fuel combusted per power stroke. How much more? The math works out to about an 11% increase, not considering the increase in fuel which is handled by EMM, waste heat loss and frictional loss. So, at 8,000 rpm and at about 245 HP (NA1) at the wheels, you could expect about 25 hp increase minus the losses due to waste heat transfer (40%). In other words, you may notice an increase of about 15 HP (about what you thought!).

I thought the kid was just good at photoshop...