fasteddy

I'm in the process of planning an 1800cc diy turbo system.

I don't like air-air i/c's becasue of the space requirements and plumbing complexities. I want to use a chilled water/air i/c, and the only practical way I can see to do so is to use an a/c compressor system with a loop thru the water reservoir tank, as iced water is only good for such a short period of time. AND, I live in the hot zone (GA). I've looked at Spearco air/water cores, and seen to have found the one I want.

Now comes the engineering.

Anybody out there (ME types) who can tell me if the system will have enough cooling capacity to be effective in spirited street use? You don't have to make the heat loading constant, as I won't be in mucho boost mode all the time.

Basic plan is to have a temp switch in the water half of the i/c, hooked to the circulation pump. Another temp switch in the reservoir cycles the compressor (and a branch refrigerant circuit valve) to chill the reservoir water back down to the target temp. I'm shooting for a reservoir temp somewhere around 20*F, since as I understand thermogodamics, the greater the temp diff, the more efficient the cooling of the charge air. I'm also shooting for sub-ambient outlet temps from the i/c.

Puzzle loving ME out there? Can't afford a consultation fee...

Joe Perez

iTrader: (8)

cardriverx

iTrader: (12)

while your idea sounds cool, joe is right, it will end up being more complex than a air/air lol. Ill get back to you in 3 years when I have my ME degree =)

levnubhin

iTrader: (30)

Geesh, Installing an air to air intercooler is by far less complex than all that. Not to mention there's PLENTY of space for intercoolers.
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gospeed81

iTrader: (51)

So this would need to be a saline solution? Or just gonna run antifreeze? Either way...doesn't sound fun


Umm, I can design it for you, but the system will cost more to build than any consultation fee. If you really really want to get serious, look at the ZR1's design. Chevrolet got something like a 140*F drop out of their "block style" intercoolers, and are seeing below ambient.

For an "1800cc motor" any air-to-air intercooler is going to be plenty efficient. And what can be simpler than hooking up two silicone hoses?

fasteddy

Dead serious. It's a lot easier to plumb 1" diameter flexible lines than it is to plumb 2.5" hard tube. AND you don't have to go under/around/through the radiator core support, thereby reducing the strength of the monocoque chassis. AND the reservoir tank can go anywhere there's room for it, like the trunk. AND you don't have to seperate the air flows in the front between the i/c and the radiator.

There are other obvious (to me, at least) advantages. The best air/air i/c you can buy won't get the charge air temp close to ambient. You don't have consumables (i.e, water injection, ice). You aren't running the chance (unless you breach the i/c water barrier) of hydrolock that you run with meth/water injection.

gospeed81

iTrader: (51)

Ok, you seem to have some understanding of thermo, so I'll play.

Would the power benefit of being below ambient outweigh the power loss of driving the compressor?

It would basically be like driving with the A/C on. And in that case, you might as well just use the existing evaporator instead of going all the way out to the trunk, with all the extra plumbing and parts sourcing.

fasteddy

Re expensive, not all that bad.

Used water/air Spearco core about $500, sheet stock for reservoir about $10. Custom a/c hoses about $50. A/c valves from the boneyard, $5 or so. Circulation pump from RV JY $20. $100 worth of hoses and fittings. Thermoswitches maybe another $100 for Hobbs from any industrial supply.

Re air/air efficiency, not near good enough for me. I first thought of this about 15yrs ago, while jamming a Starion turbo motor into a Mitsu 4wd pickup, which has neglible room for an air/air i/c. Better after I transplanted that motor into a Mitsu Montero, but still had to hack the core support, causing excess body flex offroad. This system (in an a/c car) is no more complex than a mommy van with rear air...

fasteddy

Yes, I proudly failed thermo in 1968 at Jawja Tech, but I 'membered some of it.

I figured on running the a/c intermittently with an accumulator. Pressure switch on the accumulator to cycle the compressor. Just some wiring...

I don't have any calcs (yet) to support this argument, but I figure I can get the charge temp down to where I don't have to retard the timing or fuel dump to prevent det. Just the increased charge density may be enough, and should be enough with no spark retard.

gospeed81

iTrader: (51)

My sentiments exactly, but...

I still don't see a compressor in that list...planning to use the stock one?

Which brings us back to square one: Is it worth doing?

Square two: Is there a better way to make that much more power for the cost ($1K+)?

Square three: Surely someone's done it before, somewhere. Can that existing system be fitted to what you want to do?

EDIT: Where are you? What year car, mods?

levnubhin

iTrader: (30)

Why not? You said earlier that the car will be used for "spirited street use". Plenty of people do just fine with air to air intercoolers on open track events.

Good luck though.
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Joe Perez

iTrader: (8)

Ok, you pass the retard test.

This is a very interesting idea. You're correct of course that chilling the water will increase delta-T and thus improve the efficiency of the intercooler. Bathing the IC in ice is a common drag-racer trick, though of course those guys reduce an entire igloo cooler full of ice to warm water in a matter of seconds.

Doing the math would be relatively easy were it not for one problem- I have utterly no idea what the capacity of the stock A/C system is. It's not printed in the service manual, and I know sufficiently little about refrigeration that I wouldn't know how to estimate it even if I knew the displacement per revolution of the compressor.

My gut feeling is that if you have a sufficiently large reservoir, you'd probably have enough make-up capacity to deal with sporadic periods of boost, such as drag-racing. For sustained duty, such as a trackday, I can't imagine that the A/C system could even come close to preventing the coolant from boiling after a minute or so.

I don't think I've ever heard of anyone proposing such an idea, but it intrigues me.

NA6C-Guy

iTrader: (1)

Seems like alot of trouble and money to get the same results as an air to air intercooler. Like already said, intercoolers are already doing just fine for street and track use on pretty much all forced induction Miatas, I dont see the need. But, its your car, dare to be different. Post up some pictures of the build when and if you do it.

matttheniceguy

This sort of design is somewhat possable at least, but you are going to over run the capacity of your AC system very quickly if you get into much boost with any frequency.

All the heat your removing from your intake air charge has to go to the outside air eventually, and with an AC system like this, the condensor is the only thing that removes heat. The compressor, any required water pumps etc will all just add heat, and trying to get your charge below ambient will mean a constant heat load.

I would say it is possable to make an AC system that will keep the intake air right around ambinat temps when you are out of boost and cruising, but even getting a degree or two below ambiant is going to be nearly impossable. Just look at the mass air flow rate and how much heat energy your AC system will have to deal with. You would need a seriously large compressor, one that would cause a huge power drain on your engine. As soon as you actually get into boost the ambiant temperature coolant will work for a while just like any other air/water intercooler, but you will very quickly overrun the AC system and have high intake temps again.

Just use a standard Air/Air, or if you must a standard Air/Water... Mixing in an Engine powered AC system to try and reduce intake temps into that engine is a thermodynamics nightmare. It is possable to make it sorta work under very low loads, but forget it when you put your foot down at all.

(If you still want to do something to get sub ambiant intake temps, but don't want to run actual water injection, look into spraying water or some other fluid into the air infront of your intercooler)

JayL

iTrader: (12)

Check out these guys for some ideas. This isn't a new concept.
Killer Chiller

RotorNutFD3S

iTrader: (33)

I ran an air/water setup in my turbo Saturn. It was a good setup, never had any issues out of it whatsoever from a mechanical standpoint. I actually still have the intercooler and marine pump, considered using it again on the Miata, but did not. Main reason being is that while a very efficient setup, it did heatsoak, which it seems that you are looking to overcome, albeit in a method that seems to add some complication to a mostly simple system. However, if you work it out, props to you. I agree with the sentiments above though, you're going to be making the engine do a lot of work to make your system work.

I toyed with a similar idea while using the A/W IC to overcome heat soak and to lower IATs. I looked into using an electrical a/c compressor from a hybrid car. However, the power required to make it run and the weight required to have power for it was also the killer of my idea. I really didn't want to add weight and complexity to a system when it's not necessary.

Good luck however, this would be very interesting to see done!
And since you're in GA, check out www.mx5atlanta.com.

matttheniceguy

Also note that in those systems they are adding the AC chiller in line with an existing Air/Water system, and they are keeping the existing Air/Water heat exchanger to disipate the bulk of the heat energy, and then using the AC cooled chiller to lower the water temps further prior to the water going to the intercooler. They certianly aren't relying on the condensor to remove all of the heat energy.

sixshooter

iTrader: (12)

Joe,
I'm estimating that stock system to be about a 17,000 BTU setup from what I've seen.

Eddy,
For saying at first you didn't like complexity, welcome to reinventing the wheel.
Are you going to 1. Leave the stock A/C and split the lines like the rear air vehicles do? 2. Or run it instead of the stock A/C?
3. Or run a second A/C compressor? If so, where and how would you mount it?

Option 2 is easiest, obviously. You could even remove the evaporator from the passenger compartment and reuse it in your tank.

On second thought, none of this is easy. Have you thought about air to air with a cooling nitrous spray bar on the intercooler? That is easier and cheaper than what you are doing.

If it is just an engineering exercise to see what you can come up with. Go for it. If it is to get the best performance you can, you are making this more difficult than it needs to be.

patsmx5

iTrader: (16)

Haha, I love this. Ok- you will have to relize this will be the heaviest, most complex, IC stystem ever fitted to a miata. So your ideas of avioding complexities is out the window.

And cost will be high. You will have more failure points.

To really make this work and work well it would be complex and heavy. Neither are good. You'd need a large efficient water/air heat exchanger. I have one actually. It's rated at like 80kBTUs or so. Copper/brass unit with a cast iron encasing. Weighs about 400 pounds, but should be up to the task. I know it will dump 150HP worth of heat continuously with a 5/8 Jabsco feeding it, so however many BTUs that is.

Cool water enters the Air/Water exchanger that the engine's boost runs through. Water exits and it's now hot. Hot water goes to a heat exchanger that's maybe 60% efficient. Then it goes to your reservoir where the remaining 40% of the heat will have to be pumped out by your compressor. That's just to get you to ambient. If you want supercooled, you're gonna need one badass compressor/condenser/evaporator and a brine, which will eat away at the components.

Or, another take. Put a huge Air/Air IC up front that's say, 95% efficient. (my temps recorded after intercooling suggest my 20x12x3 core is ~95% efficient). Then send the charge to an air/water heat exchanger where your compressor system sends cold water to cool the charge further.

For that matter, you could get creative and ditch water all together. Build a box and enclose an evaporator in it and push the air through the evaporator to cool the charge, and pump freon through the evaporator like normal. But this takes away your ability to "store" cold water, but it reduces the number of systems and reduces weight.

Or sit back, think about all this for a while, and realize that no matter how "cool" is sounds/would be, it's utterly not necessary. A good 18x12x3 core IC will fit in your car and can be plumbed up in an afternoon, and offer 90%+ efficiency at all times, without any maintenance or failure points that your proposed system would have.

dynokiller90

a simpler although much less effective way (without adding any strain on the car) would be to simply put the heat exchanger from your air/water intercooler in the plenum of your a/c system. cool yourself and the heat exchanger at the same time.

of course that wouldn't help in the winter when you use you heater, but that could easily be fixed by using a second exchanger for winter use with some simple valves for choosing between the two.