Using AC system as blow-through intercooler?

Over the weekend I picked up a 1998 Buick Riviera to hopefully use as my Challenge car this year. The Riviera- at least the later models like this one- uses the L67 supercharged 3800 engine, so I'm hoping it will at least be fun to sling around the autocross and run down the drag strip.

In looking at options to up the power on it, cooling the air charge coming out of the blower is something that is obviously worth considering- but the manufactured ones are rather pricey and would eat up a larger portion of my budget than I think is reasonable. I initially looked at making one from scratch using a heater core, but in thinking about this it dawned on me that the car already had something similar- and even better at cooling air- on it: the AC evaporator.

The question is though (assuming I could reroute all of the lines properly and get it all to fit- spot me that for the moment...), will the drop in temperature in the air charge provide more power than the AC compressor will draw running the system? Obviously you can't get more out than you put in- but it's possible to up the fuel going in with the cooler air would it come out better than not having it at all?

Interesting idea. You will have to figure out how to keep the AC on while at full throttle, but that shouldn't be too hard.

Bigger issue is probably boost leaks through the dang thing. HVAC is meant to move a lot of air at very near atmospheric pressure, so a leaky evaporator would be almost no issue.

Probably easier to just do a 150 shot and keep the AC working in the cabin. I've heard of people doing RPM switches for the nitrous and then calling it vtec.

Meth injection. Thats the answer you are looking for. Cheap, simple, and effective.

25hp shot is sufficient at cooling intake charge.

Ford had a similar idea that I'm pretty sure never made it to production, but was on a Lightning concept truck. That one used the AC to chill a tank of antifreeze to well below freezing, then when the driver wanted to use it the really cold coolant would be fed through the intercooler instead of the regular temperature coolant. A 3 gallon tank was supposed to last about 45 seconds on the 5.4L engine.

Here's a link to a story about it: autoweek story

I'm not sure a regular car AC puts out enough cold air to really make an impact in real time, but maybe it could pre-chill the intercooler while you're lining up for a quarter mile or autocross run.

Schmidlap wrote: Ford had a similar idea that I'm pretty sure never made it to production, but was on a Lightning concept truck. That one used the AC to chill a tank of antifreeze to well below freezing, then when the driver wanted to use it the really cold coolant would be fed through the intercooler instead of the regular temperature coolant. A 3 gallon tank was supposed to last about 45 seconds on the 5.4L engine. Here's a link to a story about it: autoweek story I'm not sure a regular car AC puts out enough cold air to really make an impact in real time, but maybe it could pre-chill the intercooler while you're lining up for a quarter mile or autocross run.

That's an interesting variant of the idea... just route a line into the cabin with a metal line around the evaporator core and set it up so the AC can run while idling and then shut off the AC before the run. Would need a normal a2w intercooler setup as well, but I can go back to my 'heater core' intercooler idea and effectively do both...

It probably would not work during a run but I could see it as a staging cooling device to keep the IC from heat soaking

http://killerchiller.com/products/2010-2014-s197-mustang-kit

Bristol did it.

Using an A/C evaporator as an intercooler is one of my pet awesome ideas. Automotive A/C systems move a LOT of BTUs. The older ones that you're going to be junkyard-engineering are oversized enough to cool 120 degree air down to 32 degrees at fairly high CFM.

Using the heat of evaporation, twice, as a means of transferring heat is a MUCH more efficient way to cool than mere water-air intercooling, which is already more efficient than air-air intercooling. And the small losses you get from driving an A/C compressor versus a water pump are more than offset by the gains you can get from getting charge air cooler than ambient.

dean1484 wrote: It probably would not work during a run but I could see it as a staging cooling device to keep the IC from heat soaking

If the rules allow, you're much better off just setting a bag of ice on the intercooler. :)

An intercooler is a heat exchanger that has enough flow for the needs of the engine, as well as enough heat transfer capacity to cool that air down by a meaningful amount. To use the AC system for that you'd need to reroute the intake through the box that houses the evaporator (or move the evaporator box to be next to the intake).

So HVAC systems seem to run a few hundred CFM of air, but at very little pressure above ambient. Since the evaporator box isn't designed to hold pressure, you'll probably need to reinforce it (or replace it with a metal one). Since it's designed to run at low pressure it should have plenty of flow for the engine, but I doubt it's got enough heat exchanger capacity. The engine is flowing 4-5 times as much air (by mass) as the heater core, and it's got a larger temperature drop required.

A/C systems are mainly limited by not being able to get the evaporator colder than 32 degrees F without the outside freezing up. H-blocks, low-side pressure switches, variable compressor drives, everything is geared towards not letting the low-side pressure get lower than the pressure that its particular refrigerant is at 32 degrees. This is why R-134A is such a nice drop in replacement for R-12 systems, its low side pressure is so close to what R12's is at relevant temperatures that it works just fine. (And of course systems that have a temperature switch in the evaporator just sense temp directly)

An older system would use this 32 degree evaporator to make air go from 90-100 degrees down to 33-34 degrees F as fast as the air could flow through it. Modern systems are downsized a lot because the new paradigm is "30 degrees cooler than ambient". But even so, if you used a large older style A/C evaporator, with a larger modern-style ultra efficient condensor, and a decent sized compressor, even if you were able to "only" cool the charge down to ambient, you're already way ahead of what you can do with an air-air or air-water intercooler.

And, bear in mind that if you know you will be feeding it lots of hot low humidity air (by definition, if you make air hotter without increasing its water load, you're reducing its humidity), you aren't necessarily limited by freezing anymore. You can get an adjustable low side pressure switch and turn that sucker down if necessary.

Looking forward to seeing this at the challenge. Good luck may the engineering gods smile upon your creation

Knurled wrote: ...even if you were able to "only" cool the charge down to ambient, you're already way ahead of what you can do with an air-air or air-water intercooler.

Compressor outlet temp on an older Eaton could be 200F. Getting this down to, say, 80F is a much larger temperature drop than going from 100F down to 32F.

Also, a 3.8L engine running 7 psi of boost at 6000 RPM is 1200 CFM. I dunno what a Riviera's HVAC system is designed to flow, but aftermarket generic heater core blower fans seem to be rated around 200-500 CFM.

Dusterbd13 wrote: Meth injection. Thats the answer you are looking for. Cheap, simple, and effective.

Go to the junkyard and buy a washer reservoir that has a pump built in. Put a garden mist sprayer fitting into the intake pipe. Put a hobbs switch in to turn the washer pump on at a certain psi. Your idea is sound but DIY methanol injection is way more cost effective on a challenge car IMO.

guys there is no free lunch in physics, you can not gain more energy than you put in. Now you can store it and use it later like the ford system linked above, but its will be much easier to use a container full of ice which you refill(instead of making ice/cold liquid on-board with the A/C system)

In reply to codrus:

I think I might not have made the idea quite clear- if I were to do this as I initially conceived of it, I would be moving the evaporator core to between the supercharged and the LIM- essentially just like a conventional a2m intercooler would except using the refrigerant instead of coolant, so I would be fabricating an enclosure that would hold the pressure.

I'll have to look into the methanol injection idea as well, I really don't know much about it at all.

The meth injection is the easiest route here. The best part is that you don't have to spend a bunch of money on the fancy meth injection jungle juice, you can simply use windshield washer fluid! It literally contains all the same ingredients at the same proportions! (Just make sure you don't run out...)

echoechoecho wrote: guys there is no free lunch in physics, you can not gain more energy than you put in. Now you can store it and use it later like the ford system linked above, but its will be much easier to use a container full of ice which you refill(instead of making ice/cold liquid on-board with the A/C system)

While it is true that conservation of energy means you won't get out more than you put in, that applies to a closed system. This is not a closed system because cooling the intake charge means you can burn more fuel with detonating, and that increases the amount of energy that you're putting in.

+1 in the bag of ice. The F1 guys used to do it for qualifying back in the 80's. A 1/4 mile pass or 50 second auto-x run would be a shorter amount of time than 4 or 5 qualifying laps.

I once had this idea that was similar to the Ford lightning system mentioned earlier.. the AC cools a tank of water, which cools the intake charge.. wire it thru a switch on the throttle, and you could "charge" the coldness of the water in braking zones and thru turns, then disengage the AC pump when you go back to WFO.. this gives you a little more engine braking when you want it while using almost no power when you want to go fast..

I mentioned it on the Chumpcar forum, and the general consensus was that you'd lose coldness over time in that situation to the point where it had almost no effect towards the end of a run.

Dusterbd13 wrote: Meth injection. Thats the answer you are looking for. Cheap, simple, and effective.

+1 on this idea ... and to build on it further ... this past weekend I added 40lbs of lightness to my car by removing the whole A/C system ... would your car perform better in autox with an A/C intercooler or by being lighter?

codrus wrote:

Knurled wrote: ...even if you were able to "only" cool the charge down to ambient, you're already way ahead of what you can do with an air-air or air-water intercooler.

Compressor outlet temp on an older Eaton could be 200F. Getting this down to, say, 80F is a much larger temperature drop than going from 100F down to 32F.

It appears that way on the surface, but 32F is an asymptote. A/C will never ever cool down below 32F no matter what, because of the freeze-over limit.

So it's not that A/C can only cool down to 33-34F from 100, it's that it's cooling from 100 down to a couple degrees above its absolute minimum.

And, at any rate, Bristol did it. On a turbocharged small block Mopar no less. I could have sworn that Ford did it on one of the generations of Lightning, too.

In reply to Knurled:

Eh, not quite. If the dew point is below 32, the A/C can cool below 32 as long as the evaporator surface temps remain above the dew point to avoid ice buildup. Of course, outside of winter, the dew point will typically be 32 or higher, so 32 remains a lower limit for evap surface temp.

echoechoecho wrote: guys there is no free lunch in physics, you can not gain more energy than you put in.

You're not gaining energy from cold air. You're gaining horsepower potential from the ability to run more boost and/or more timing and/or leaner fuel mixtures.

Sanity check: A/C compressors can be easily driven by a V-belt that can't transmit more than 5-10hp. There is far more than 5-10hp potential available from more effective charge cooling.

For that matter you could use the TNSTAAFL argument against turbochargers. Sure intake pressure goes up, but exhaust pressure goes up even more, therefore large pressure gradient across the engine, therefore less airflow and less power.

I have a couple questions.

1) These have roots type blowers bolted right to the intake, no plumbing post supercharger, so where and how would you install the evaporator in the system?

2) What about all the water constantly condensing on it? Wouldnt you be sucking the water through the engine at a pretty high amount? Which, i guess all that water was already in the air, maybe it doesnt matter.