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Discussion Starter · #1 ·
Everyone knows that the hotter the air, the harder it is for an engine to produce power. Especially with turboed cars. N/A cars are effected but not nearly as much. For my big turbo setup, I refuse to even drive the car if it's too hot outside. And if it's above 75-80 degree range out, it never sees boost. My difference is night and day, huge amounts of lost power when it's too hot. I have a 180 degree stat and it maintains that as long as it's cool enough out. Once the summer comes, it runs at stock 195-200ish temp even at highway speeds. How much of a difference does it make for everyone else? I swear I lose 50+ wheel horse if not more when the weather gets sticky. Does everyone else have that much of a drastic change? I think it's pretty interesting every car responds differently. Any stories comment :)
 

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The heat is making your tires super duper sticky so no more chirping...

Seriously though, there is a formula, I will attempt to demonstrate:

Considering that a fixed volume of air passes through your engine each stroke, it will be our constant. The variable is density of the air which you burn. Dense air = More oxygen, duh. "The change in horsepower is proportional to the inverse square root of the ratio of the two temperatures."* For example, I will assume my car produces 235whp on a 50* December day. On a steamy 100* day, there should be a difference in power of -4.79% which would mean my car would hypothetically make 223.75whp. I think a 11hp difference is not negligible.

Here's what I read: Kansas: Temperature and Horsepower »
*Their words, not mine.
 

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Discussion Starter · #3 ·
Ahhhhh I see. Now is that % loss always a consistent number? My guess is the senario changes depending on all the factors. But you def gave me a broad outlook on it. Example... My buddies stock srt that I have rode in/driven in the winter at below freezing, as well as 90s in the summer, felt all but identical to me. But my other friends 1993 supra that has a 88mm turbo on it has a huge difference when it's hot. He even had to have a special fan system constructed for him to have his fan constantly running when it's above a certain temp outside. Same with my other friends 1997 GTS viper single turbo 106mm. Both of them have told me they feel like they lose gobs of power when it's to hot outside. I can say the same for my car, maybe it has Sumtin to do with bigger blower, making more heat, sucking higher volume of hot air, effects temps more and in turn, effects power more. Now I'm not assuming that this is the case with every car and or every motor, but it sure is strange that guys with smaller turbos/superchargers seems to have less of a problem when it's hot out then the guys with bigger ones. In my experiance at least and based on who has discussed it anyways lol. Either that or baby Jesus wants certain cars to suck worse then others when it's hot who knows :)
 

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Since it is a percentage loss of power, high power engines do have more to lose. I may lose 11hp, but big turbos upwards of 23...hypothetically, of course.
 

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Discussion Starter · #5 ·
And if we convert whp to crank, 11whp = 12.54 crank hp loss. And 23whp = 26.22 crank hp loss (assuming drive train loss is 14% and adding to whp) and if that's the difference between an ideal temp of around 60 degrees up to 90-100 when that much is lost... I would imagine on the other side of the playing field of your going from 60 degrees down to 20-30 degree temps your gains would be similar to the loss at high temps??? In theory possibly! That would be a diff of 22whp from summer time to winter time for a stock turbo srt, and about 46whp for a big turbo, based on the % values. It's all very interesting to me trying to break it all down technically. Keeps me wondering
 

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Other factors that would affect you are altitude, humidity, # of trees present, cleanliness of air and quality of fuel. Engine knock can come out of no where with just one bad tank of gas. What's your mod list?
 

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And if it's above 75-80 degree range out, it never sees boost. My difference is night and day, huge amounts of lost power when it's too hot.
LOL, your car wouldn't have very many miles on it if you lived where I do. It's supposed to be 110*+ all week here in Phoenix.
 

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Discussion Starter · #12 ·

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Large displacement N/A cars are affected the most with atmospheric changes. Boosted cars can compensate somewhat. For anyone that does flying this is critical because depending on humidity, temperature, elevation, and barometric pressure effects the power output of your engine. With less engine performance could extend your takeoff distance and lower your climb rate substantially.

Black Magic has posted something that many forget about in addition to just simple atmospheric conditions. Thanks for that bit of info, it can make a pretty big power difference.

Here are some interesting reads...

Old NHRA altitude correction factor table:
Lucas Oil Drag Racing Series News: NHRA adjusts altitude factors for 2002 (02/15/2002)

Density altitude calculator (if you want to plug in your own variables):
https://wahiduddin.net/calc/calc_da.htm

If you only care about the real-time dyno correction factor in your city, horsepower loss, and density/pressure altitude, I created a quick calculator tool thingie - it's a rough estimate using the basic formulas:
Current Dyno correction factor, density altitude per city.

For example, in my home town Tucson, AZ it's hotter than the sun right now. We are high elevation, so as of right this second (12pm June 15th 2015), our dyno correction factor is a whopping 1.18. We are loosing nearly 20% horsepower. I monitored my IAT's today - the road temps are 135 degrees, so in town traffic can be magnitudes worse, like a billion or more horsepowers have escaped.
 

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Discussion Starter · #15 ·
Holy Mary mother of god :eek: that's insane! Wowwww that makes me feel as though a 100 mile road trip high up in the mountains is enough to make you feel like your driving an entirely different vehicle if you started at sea level. There is so many variables no wonder why every top drag team always retunes there cars EVERY time they pack up and move to another track. I have literally heard guys dyno tuning there cars the night before, trailoring them to the track... Then logging and street tuning at the track. It's all needed if your looking for maximum efficientcy
 

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I think a Water/Meth injection kit would be a great next mod for you considering your problem and your setup sounds like it would really benefit from it as well. I've been considering swapping to a 160 thermostat for the summer, I live in South Jersey so we've been experiencing the same temps and my 180 thermostat still runs 195 on the highway and 210 in stop and go traffic. I even popped out the hood scoop insert to let the engine get some wind on it.
 

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Discussion Starter · #18 ·
Now here's a ? ... When you install a meth kit does it need retuned? The reason I'm asking is I wanna make sure it doesn't cause knock. I realize it cools intake temps and makes a little more power (and a good amount more torque) but because of that does it completely throw the tune off? Or is my guess on this the opposite way? Will it help cure knock if there is any, and or only protect the engine more if you just slap it on and call it a day without retuning? I realized to get maximum efficiently you want to retune, but is it 100% needed if your not worried about maximizing hp and only worried about cooling your temps down? If it's not a danger to slap it on and it can only help and not hurt, then i will defiantly get it like now lol. But I just recently spent alottttt of time dialing the car in as it is right now, and I'd hate to go through that entire process again if I definitely need to retune if it's a danger to the motor...
 

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If you're only concerned about using injection as an anti-detonant, you can probably just inject a small amount of distilled water without needing to retune. It depends how much your knock count is currently. For example:

If you're ECU is pulling a little bit of timing or limiting boost because of knock counts, then most likely you're losing power. To gain this power back you could run a small amount of water injection. It'll basically trick your ECU into thinking you're running a higher octane fuel and in better weather conditions.

If you start injecting a lot of water, or water + meth then this changes the in cylinder burn rate characteristics or AFRs (if you use meth), so you'll need to retune for optimal power if you want it.

As a disclaimer I'm not an expert in water/meth injection.
 
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