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Discussion Starter · #1 ·
The old rule of thumb was that the AC units dragged HP down by 30-20 hp. So my question is has anyone done this comparison ?
 

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laws of physics
20 HP = 14,920 Watts
14,920 / 3.412 = 4,372 BTU's
The Challenger needs about 15,000 BTU's to successfully cool the interior.
On the dyno, kill the AC
-John
 

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Discussion Starter · #5 ·
Years ago I rented a 4 cyl POS. I'd floor the gas and when I turn off the AC it was like a nitro kick. Living in SW FL my AC is on 70% of the time. So I'm looking for real time experience on the dyno.No dyno's anywhere near me sad to say.
 

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2020 Dodge Challenger Hellraisin Scat Pack
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laws of physics
20 HP = 14,920 Watts
14,920 / 3.412 = 4,372 BTU's
The Challenger needs about 15,000 BTU's to successfully cool the interior.
On the dyno, kill the AC
-John
My 90hp VW Golf TDi had an excellent automatic climate control system and if at any time it required 20hp to operate I think I would have noticed it.

Even before I bought my VW (back in March 2002) admittedly I was curious as to how much A/C load there was. So with another car this one equipped with what proved to be a very nice autoclimate system, my experience with monitoring engine load -- via an OBD2 scan tool -- in real time with the automatic climate control system A/C off or on is the engine load changes very slightly. This at idle. Even if the cabin is hot and the A/C is running full blast -- in automatic mode -- the load is not even 1%. For this car 1% engine load would be just under 2hp.

In normal hot engine idle the engine load -- sans A/C -- is but a few percent, representing 4hp or 5hp.

Under hard acceleration -- this with other cars but I believe this should apply to Dodge vehicles as well -- the engine controller deactivates the A/C compressor.

Initially there were posts by drivers who complained about warm moist air coming from the A/C vents when subjecting the car to hard acceleration. I have felt this myself on occasion.

Regardless on the dyno I'd leave the A/C off. And even turn off the cabin vent fan to reduce -- if even only a tiny bit -- the parasitic load this results in by having the alternator generate the electricity to power this fan.
 

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Discussion Starter · #8 · (Edited)
I'm STILL waiting for dyno reports !

Last late fall with my AC off I hit the gas [ not to hard ] while rolling from a red light, my car went sideways. That was in the AUTO mode traction control on.
 

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Discussion Starter · #9 ·
The fact please not guesses, thank you. Printed dyno results, anyone can guess.
 

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It’s been pretty well discussed that the ac kicks off so unless you can figure out a way to over ride that it’s all a moot point.
 

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It’s been pretty well discussed that the ac kicks off so unless you can figure out a way to over ride that it’s all a moot point.
In my Scat Pack yesterday with the dyno display up. At 45mph engine HP read around 20. With A/C off no change. With A/C on and at max cool no change.

At a stop light with engine idling turning the A/C off then on and all the way up to max cool the HP display didn't change from 0hp. And there was no reaction from the engine like some big load was suddenly applied or removed as I turned the A/C on then dialed it to max cool then dialed it back down again and turned it off.

This agrees with what I have observed with other cars viewing the engine load via an OBD2 scan tool in real time the A/C system requires very little HP to operate.

For me no need to figure out how to prevent the A/C from being deactivated during hard acceleration or a dyno pull to see if the A/C load could even be measured. Based on my investigation being it is so small likely the amount of HP required is at the noise level of the dyno instrumentation.
 

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Rockstar, just a guess here because I don’t know how they come up with a hp display, but I bet it’s a computed number. For example, maybe speed vs throttle position it computes a hp number possibly. I’m pretty sure the ac does use up some hp. Someone with a Lexus found the ac was using about 10 hp and he ran it on a dyno. Google it and you will see some estimates which 10 hp would be the most and most likely less.
 

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Discussion Starter · #13 ·
Only a dyno comprasion run will tell. As I've had my other car on a dyno for a tune, the runs are over very quick so a few run would answer this question of the the affect of the AC on hard acceleration HP numbers. My experience here in SW FL is that my engine really comes alive with the AC off but the effect isn't instantaneous as it seems the CPU is readjusting ?

What really irks me is all the dyno runs with the hood OPEN. Yes I know about the heat issue but the air flow over the CAI system will give a false positive. I believe in real world tests not lab results. When I get home after a trip around town in 90+ temps and then open my hood it's like opening an oven. So how does the CPU tune for that heat vs controlled conditions of denser coolair flowing over the engine ot air affected by engine heated air ? ?

And I've found a way to really seriously lower the air intake temps which helps but seems to affect my MPG numbers ?
 

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AC on of off really don't matter because these variable displacement pumps never run at full displacement at high engine speed. The wobble plate inside the compressor has very little offset over 3500 RPM. Where the real HP is measured, the AC on should make little difference. I would bet maybe 2 HP at most. To beat this to death is pointless.
-John
 
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