[workerONE]

Where I live it's over 100 degrees half of the year. I've only had my M2C for a couple of weeks and am in the 1200 mile break in period so can't tell for sure how much power the M2C loses with AC on. Does anyone know or have any experience testing?

[allthatisntnow]

Probably something like 3hp. The answer you probably want is: nothing noticeable. its a 400hp/550nm engine.

[verysideways]

I'd expect between 2 and 3hp.
Negligible.

[nioh_lbbm2]

This isn't a 1999 Civic with 10 horsepower at the crank. You won't feel a difference with AC on/off lol

[David1]

Under acceleration the compressor is off anyways so nothing under full throttle.

[AUSf22]

Originally Posted by nioh_lbbm2

This isn't a 1999 Civic with 10 horsepower at the crank. You won't feel a difference with AC on/off lol

Nailed it

Imaging turning off AC in the m2 and it feels like you just changed it into sport + ...

[workerONE]

That's awesome 😎

[SilverScotty]

I agree. Butt dyno says Zero. I tested it all summer.

Now, in my WRX, that's another story...

[M2Cmtl]

This is something I've always noticed on less powerful car, but absolutely zero butt dyno difference with the M2C.

[maxcbrdriver]

How much does the AC affect the rev drop in upshifts assuming you've turned off the cars auto rev matching? In every manual car I've driven, none with auto rev match, the ac always seemed to result in a much faster rev drop that complicated a smooth 1-2 shift until you've ”relearned”.

[rcouchh]

Originally Posted by nioh_lbbm2

This isn't a 1999 Civic with 10 horsepower at the crank. You won't feel a difference with AC on/off lol

My 2016 Subaru WRX had a MAJOR power loss with the AC on. It's not that uncommon for modern cars.

It was tuned and around 300whp, with the AC it felt like it was 200 literally.

[Moflow]

Originally Posted by David1

Under acceleration the compressor is off anyways so nothing under full throttle.

Yup. My old 350z did this as well.

[Davil]

Originally Posted by rcouchh

My 2016 Subaru WRX had a MAJOR power loss with the AC on. It's not that uncommon for modern cars.

It was tuned and around 300whp, with the AC it felt like it was 200 literally.

WRX turns off AC under full throttle. But yes, you notice it when pootling around.

[akkando]

I dunno but I did get around an autocross course faster with it off.

[Noh Wan]

A little late to class, and new to the forum, but the average auto A/C compressor pulls around 20HP. That said, I'm pretty sure the compressor is disengaged at certain throttle positions (>70% maybe) so you shouldn't notice it much doing a dig at a stop light or hammering it on an on-ramp every once in a while. Multiple runs though, an autocross or HDPE, anything with idle time or sustained loads it will absolutely eat into the total ability of the cooling system to shed heat and will start to effect IAT's and the like.

[grl.racr]

I'll gladly trade a few HP for a warmer climate!

[MR RIZK]

Originally Posted by akkando

I dunno but I did get around an autocross course faster with it off.

Maybe cause it is hot in the cabin and you want to get to the end faster.

[pz619]

The AC really only consumes maybe 2-5 hp depending on the efficiency and capacity. A large window AC unit runs off around 7 hp (converting watts to HP) and you don't have that in your car. Certainly no where near 20 hp otherwise you wouldn't even be able to operate the AC at idle. The reason you feel the difference on lower powered cars is because of the percentage of power it consumes based on the power the motor is making at any given time. It takes about 10-20 hp to maintain 65 mph depending on weight, aero, etc. So at those speeds if you turn on the AC you could lose 20% of the available power your motor is currently running. This is more prevalent on lower powered cars or even turbo cars with small motors operating out of boost.

I wouldn't think about in terms of 400 hp and AC uses 5 hp. AC consumption is relatively consistent whereas the amount of power the motor makes it dependent on boost, rpm, etc.

[Noh Wan]

Originally Posted by pz619

A large window AC unit runs off around 7 hp (converting watts to HP) and you don't have that in your car. Certainly no where near 20 hp otherwise you wouldn't even be able to operate the AC at idle.

A typical window unit A/C is around 10,000 btu's. The typical car A/C is about 40,000 btu's. The window unit needs to cool a 90F room to about 70F (delta 20) in a half hour with mostly recirculated air. The car needs to cool the cabin from maybe 140F on a hot sunny day to 70F (delta 70) in a few minutes usually without recirculation. Automotive A/C's are also designed to be operated at cruising speed (~2000RPM) so high revs take them WAY out of their efficiency zone meaning you will put way more energy into it than is actually useful. On a hot day, freshly started, under full load, and at speed I guarantee you the compressor pulls as much as 20hp. After cooling the cabin or at lower engine speeds (i.e. idle) the compressor will pull less than that. So I guess the real answer is "it depends." Here is a link to a YouTube video of a guy dynoing an IS-F with A/C on/off. It shows about 10hp difference though I don't take him as an authority.

I don't want to re-subscribe to SAE so I can't pull up the white papers, but Here is a link to an open source white paper studying A/C fuel economy effects on Hybrid EV's demonstrating an average HP draw of ~9hp through the test cycle. Their results are published in Kwh (not hp) though so I'd be happy to be corrected if my math is wrong. Their methodology seemed solid to me.

If anyone has gone to Wikipedia where it says a modern automotive A/C unit draws 4hp you'll find this citation which is a preprint presentation, not a published white paper, with no experimental data. Only simulations. In fact several of their own citations are papers they wrote themselves so take it for what it's worth. I'm skeptical.

All that said, modern cars are pretty good about disengaging auxiliary equipment under the right circumstances so, if I'm getting at what I think the OP was really asking about... No you won't notice the A/C driving around town and doing the occasional dig at a stop light. However, if you're trying to squeeze every last tenth out of your ET at the drag strip you should probably turn it off.

Now, the interesting part! (to me at least) Phase-change cooling systems move MUCH more energy than they consume. For example a 10,000 Btu window unit draws around 1,000 watts (1.3hp), but moves around 2930 watts (about 4hp). So taking A/C draw estimates from both ends of the range, running on a track with A/C pulling 4hp will be adding an equivalent heat load to the cooling system as a motor with 15.7 more hp. Assume the A/C pulls 10hp, it will run as hot a a motor with 40 more hp. (I'm making some assumptions about efficiency so don't take me too seriously). Over a thirty minute track session that heat load will make a difference. That said the CS version of the S55 already runs 50hp over and the GTS version runs 90hp over ours leading me to think there is enough heat shedding capacity built in already, though I'm not sure if they made any significant changes to the cooling systems.

It should now be abundantly clear that I have too much time on my hands. *sigh* I'm sorry... and bored.

[pz619]

Originally Posted by Noh Wan

A typical window unit A/C is around 10,000 btu's. The typical car A/C is about 40,000 btu's. The window unit needs to cool a 90F room to about 70F (delta 20) in a half hour with mostly recirculated air. The car needs to cool the cabin from maybe 140F on a hot sunny day to 70F (delta 70) in a few minutes usually without recirculation. Automotive A/C's are also designed to be operated at cruising speed (~2000RPM) so high revs take them WAY out of their efficiency zone meaning you will put way more energy into it than is actually useful. On a hot day, freshly started, under full load, and at speed I guarantee you the compressor pulls as much as 20hp. After cooling the cabin or at lower engine speeds (i.e. idle) the compressor will pull less than that. So I guess the real answer is "it depends." Here is a link to a YouTube video of a guy dynoing an IS-F with A/C on/off. It shows about 10hp difference though I don't take him as an authority.

I don't want to re-subscribe to SAE so I can't pull up the white papers, but Here is a link to an open source white paper studying A/C fuel economy effects on Hybrid EV's demonstrating an average HP draw of ~9hp through the test cycle. Their results are published in Kwh (not hp) though so I'd be happy to be corrected if my math is wrong. Their methodology seemed solid to me.

If anyone has gone to Wikipedia where it says a modern automotive A/C unit draws 4hp you'll find this citation which is a preprint presentation, not a published white paper, with no experimental data. Only simulations. In fact several of their own citations are papers they wrote themselves so take it for what it's worth. I'm skeptical.

All that said, modern cars are pretty good about disengaging auxiliary equipment under the right circumstances so, if I'm getting at what I think the OP was really asking about... No you won't notice the A/C driving around town and doing the occasional dig at a stop light. However, if you're trying to squeeze every last tenth out of your ET at the drag strip you should probably turn it off.

Now, the interesting part! (to me at least) Phase-change cooling systems move MUCH more energy than they consume. For example a 10,000 Btu window unit draws around 1,000 watts (1.3hp), but moves around 2930 watts (about 4hp). So taking A/C draw estimates from both ends of the range, running on a track with A/C pulling 4hp will be adding an equivalent heat load to the cooling system as a motor with 15.7 more hp. Assume the A/C pulls 10hp, it will run as hot a a motor with 40 more hp. (I'm making some assumptions about efficiency so don't take me too seriously). Over a thirty minute track session that heat load will make a difference. That said the CS version of the S55 already runs 50hp over and the GTS version runs 90hp over ours leading me to think there is enough heat shedding capacity built in already, though I'm not sure if they made any significant changes to the cooling systems.

It should now be abundantly clear that I have too much time on my hands. *sigh* I'm sorry... and bored.

Very interesting. The first source I looked at showed about 10,000 BTUs for cars. Looked deeper and found some are in the 60k range, with the average being in 30-40k range, which is something I would have never guessed!

[richard in NC]

So we've gone from common sense assumptions to wild guesses to detailed analysis which proves out the common sense assumptions.
1. Yes there is some consumption of HP.
2. You won't notice it in most circumstances.
3. When eeking out the last 10ths of seconds at the drag strip, turn it off.
4. Yes it puts more load and cooling requirements on the motor.
5. Again not an issue but if on track, turn it off if concerned about overheating the motor but turn it on if concerned about overheating yourself.