oil cooler / condensor idea...need open minded, engineer inputs!!

[konish]

Just free thinking here.
Oil cooler. Since some guys have already eliminated their spare tire (a point of contention and possible PIA, I know), I thought the void left would make the perfect location for an oil cooler...out of the way of road debis, and a larger one could be fitted than in the fender. I figure a small opening in the front bulkhead, and a very small NACA duct on the hood to evacuate the hot air from the trunk would allow it to cool as well as a fender mounted rig. Oil lines from the trombone could be plumbed through the right hand fender into the cooler. The cooler I had in mind would be off an old oil-cooled GSX-R...big, yet compact and integrated pull fan with t-stat for the fan unit. Obviously, the ducting would have to incorporate some sort of louvered covers and drain plumbing so the trunk doesn't fill with water during a rain storm. Obviously this seems similar to the thru-hood design, but seems easier to mount and requires only a small NACA duct instead of a huge, molded vent for the hood mounted cooler.

Condensor:
I've examined 4 different condensor housings, and it seems that most of the motors had corrosion on the bearing surfaces of the rotor at both ends. I'm going to drill the motor housing in order to be able to quickly shot a shot of lube on either end of the motor, and plug with rubber covers...should be easier to maintain the motors. Also, now this is a stretch. I'm probably never going to use the headlight washers, but I thought it would be interesting to plumb two windshield washer nozzles at the bottom of the plastic condensor housing with plumbing to the headlight washer pump. When I really want the A/C to perform better, I'd just flip the switch on the dash and soak the condensor heat exchanger...along with the air flow from the fan cage, I'd think it would help out quite a bit. This is along the same lines of the Subuaru WRX intercooler that taps into the windshield washer for a performance boost...I've also seen a water mister like this on a Toyota MR-2 Turbo mounted on the left side intake. I know most folks have a love/hate relationship with their A/C's, but in this part of the country its really required. Instead of spending potentially hundreds of dollars to extract more performance from the A/C unit that is only used int he summer anyway, I figure a few bucks worth of parts is worth the experiement.

Could any engineers types comment on potential problems with heat exchange rates, NACA performance for venting the trunk, water cooling rates for the condensor...etc. Thanks!

R/
Dustin

[widebody911]

Originally posted by konish

Oil cooler. Since some guys have already eliminated their spare tire

I haven't yet, but if I can get myself to the gym more often and cut down on the carbs...
I thought the void left would make the perfect location for an oil cooler...

Yup. This is quite common on track cars.
I figure a small opening in the front bulkhead, and a very small NACA duct on the hood to evacuate the hot air from the trunk would allow it to cool as well as a fender mounted rig.

I don't have the time to write out the CFD math here (and I'd have to go to school for it first ) but you need an exit path that's a certain percentage of the intake path, or you won't get maximum cooling.

Oil lines from the trombone could be plumbed through the right hand fender into the cooler.

Yup. And I recommned AN-16 lines when you do it. Elephant Racing sells the adapters for this.

The cooler I had in mind would be off an old oil-cooled GSX-R...big, yet compact and integrated pull fan with t-stat for the fan unit.

Others on here have used various Mazda coolers. You have to deal with the fittings, however.

Obviously this seems similar to the thru-hood design, but seems easier to mount and requires only a small NACA duct instead of a huge, molded vent for the hood mounted cooler.

Once again,you need to make sure you have enough exit volume.

Condensor:
I've examined 4 different condensor housings, and it seems that most of the motors had corrosion on the bearing surfaces of the rotor at both ends. I'm

So you threw out the spare, you're going to go thru the trunk for your oil cooler, but you're keeping the A/C?

Also, now this is a stretch. I'm probably never going to use the headlight washers, but I thought it would be interesting to plumb two windshield washer nozzles at the bottom of the plastic condensor housing with plumbing to the headlight washer pump.

Seine Systems sells a system like this; the headlight washer system will chew thru your water supply too quickly.

[Chuck Moreland]

See this thread:
RFC - front oil cooler venter thru trunk on a street car...

Through-hood venting is a proven effective solution. It's best used on dedicated track cars since storage is seriously compromised and water sealing can be difficult.

I'll agree with Thom, seems a contradiction to have AC on a car with a through-hood vented oil cooler. But the effectiveness of water spray will depend on flow volume. You'll also want to atomize the spray. Then you'll need distilled water or mineral deposits will soon ruin your day.

[SC-targa]

"I figure a small opening in the front bulkhead, and a very small NACA duct on the hood to evacuate the hot air from the trunk would allow it to cool as well as a fender mounted rig."

Aren't NACA duct just low drag air inlets, not outlets?

Jerry Kroeger

[911pcars]

"Aren't NACA duct just low drag air inlets, not outlets?"

Yeah, that's my understanding too.

For an outlet, you'll need a big vent with some thought to create negative pressure to aid in venting. There are other threads showing what has been done before to vent from the hood.

Low volume, small particle, high pressure water spray can lower air temps approx. 18-20 deg. F., but water consumption is always an issue; best used for specific cooling purposes.

Sherwood
http://members.rennlist.org/911pcars
www.seinesystems.com

[Jack Olsen]

I'm no engineer, but it seems there's a lot of air movement (even) in the front fender, compared to the trunk (which is like a thermos). To match the effectiveness of the external placement, I think you'd need a bigger inlet and outlet than you're imagining.

[konish]

Thanks fellas. Not sure why there seems to be a contradiction in removing the spare for an oil cooler while retaining the A/C. The spare removal isn't necessarily for weight savings / performance, but more for the extra mounting space for an oil cooler. Both issues deal with heat management...hot oil and a hot driver. I remember vents/ducts on the aircraft in my squadron that would vent a space (or provide air flow) flush mounted to the skin using the low pressure of the air travelling over the vent (they looked like small, backwards intakes...I thought they were called NACA ducts). I figure a small vent/duct on the hood would make full use of the low pressure caused by the airflow over the hood...thereby pulling hot air out of the trunk.

R/
Dustin

[RickM]

I'd be concerned with how one may affect the aerodynamics of the car. If people (and Porsche) insist that you have to use a matched front and rear spoiler OR ELSE then imagine what you could do by venting air under your hood and out...wherever. Not saying it's not doable but should be done with some good research.

[widebody911]

Honestly, most of us are not in the game at the level where we're seriously concerned about airflow over/under the car. Sure, air under the car isn't as desirable, but the people to whom this is very critical aren't driving flat bottomed cars with A/C, windshield trim, rain gutters, CD players, etc.

Ducting over thru the hood is best, but it's not the end of the world if you don't do it on a street/weekend warrior car. Since you're already talking about ditching the spare, I'd say go for it. I thought about it, but didn't want to ditch the spare.

I recently revamped my front cooler setup when I installed my 965 front bumper. I'd had a little booboo and destroyed my oil cooler, so re-cut my trunk 2 1/2" higher. Previously, I was ducting all of the air under the car. I tracked the car a lot and didn't come anywhere near having an incident like the GT-1 @ Road Atlanta.

When I modified the box, I installed 2 2 1/2" ID "shunts" on either side of the air box, which dumps a portion of the incoming air into the fender wells. I plan to add a small section of sheet metal on each side to help guide the air into the shunts. It's a compromise. I'm hoping I'll get a bit of a venturi effect from the air going thru the brake ducts, which I hope would pull air thru the shunts. It is what it is, I won't be doing any quantitive testing, and I'm not changing it unless I absolutely have to.

More pix @ http://66.34.72.138/howto/965-bumper/index.html

[911pcars]

Dustin,
For a street-driven car, creating a hole in your hood (vent) creates some compromises with rain water, leaves, etc. not to mention the visual effect it will have. If the car is otherwise modified (like Jack's), your planned modifications might look right at home. On a stock-bodied 911, a vented hood is really unnecessary; aesthetically, I think it'd be a little much. Do you really want to install NACA or other ducting/vents on your hood?

FWIW, I have a smaller-than-an-RX7 cooler in the front of my RS bumper. Temperature wise, it's fine; never gets above 210 deg. F, even with limited/no space behind the cooler for exit air (no A/C however). It's right in the air path versus the fender location where a fan, high vehicle speed or added air vents are needed for adequate airflow.

To maximize condenser efficiency, make sure it's clean; you've got another under the engine lid? Water spray can help but you're limited by the water capacity; works better in dry climates. Windshield washer nozzles are too coarse. You'll run out of water in no time.

MHO,
Sherwood

[Neilk]

Thom,

You should mount some E-rams to the "shunts" so that you can pull more air through the oil coolers at low speed.

[JTO]

Not to be a wet blanket on this discussion but, here goes anyway; didn't Porsche already solve the oil cooling problem? We have a variety of factory engineered solutions to just about any oil cooling need, right?

Troy

[widebody911]

Originally posted by JTO
Not to be a wet blanket on this discussion but, here goes anyway; didn't Porsche already solve the oil cooling problem?

Not sure what you're suggesting; leave everything stock? Send the car to the dealer or Stuttgart for oil cooling upgrades?

When my '77 911 rolled off the drawing board, I don't think they imagined some schmoe installing a 3.6L (without an on-board cooler) and tracking it in NorCal in 100+ temps. Or sitting in "rush" hour traffic in 100+ temps.

[JTO]

No, no Thom,

What I mean is that Porsche put a 3.6 in a car already and have fender mounted coolers adequate for the job. No need to reinvent the oil cooler or its location. That's what I mean.

troy

[Jack Olsen]

Originally posted by JTO
No, no Thom,

What I mean is that Porsche put a 3.6 in a car already and have fender mounted coolers adequate for the job. No need to reinvent the oil cooler or its location. That's what I mean.

The only problem with this idea is that the front end of the 964 was totally different from the design they used for previous generations of the 911. The improved airflow they engineered meant they could ditch the engine-based cooler to fit a power steering pump. Anyone who's swapped a 3.6 into an earlier tub will tell you, the factory 964 cooler (or Carrera cooler, or any other fender-based solution) is not enough to keep a 3.6 cool.

[JTO]

I understand what your'e saying Jack. Porche also put oil coolers in the front valence (like the IROC cars). I guess I am just saying why cut holes in the hood, fender, etc when Porche has examples of ways to cool the oil that don't require all of the cutting, sacrificing spare tire and trunk. Jack, don't you have two fender mounted oil coolers?

Thanks,
Troy

[widebody911]

I tried the twin-cooler setup, and it worked "ok" but I like the center cooler idea better.

While I have tremendous respect for the engineering that went into the 911 - or any Porsche for that matter - I think it's foolish to think it can't be improved upon. If that were the case, we'd be driving hand built, VW-powered, mid-engined, link-pinned little jobbies.

Everything is a compromise. Production cars are a compromise that mixes cost, consumer appeal, ease of repair, longevity, convenience, etc. With cost fairly high up the laddder. Race cars are also a compromise, but one which places a higher value on efficiency and longevity.

You can't assume that the execution of any given technology that went into any 911 was or will be the be-all/end-all of that technology. It's not.

Simply put, having the oil cooler front and center is the most efficient in terms of oil cooling. Ducting thru the hood is even better, as it adds downforce and keeps air out from under the car. This wasn't done on street cars as a matter of convenience - the automotive press has consistently ragged on the 911 for lack of trunk space.

Yes, you can cool adequately with 2 fender coolers, or a single fender cooler if you have a 964. Great. But if you're starting from scratch, the cost difference between having the better cooling with a front cooler or a driver's side cooler is negligible. When you're building a car for the track, you happily suck up the extra cost for the improved cooling. Jack doesn't like the aestheics of the front cooler, so he didn't go that route, and I'll admit his car looks cleaner without it.

The trunk on the 911 holds the battery, spare tire, and some basic tools - that's all. I compromised a small amount of trunk space, although I really wanted to duct up thru the hood. When I go golfing, I take the VW bus and put the clubs in the back. Plenty of room for a cooler full of beer, too. If I'm going out of town for a romantic getaway, we'll take %CURRENT_GIRLFRIEND_NAME%'s car.