Aero, air flow, and oil cooler efficiency - thinking time....

[Chepsk8]

A question on airflow, aerodynamic pressure differential, and oil cooler efficiency.

When racing, my oil temp gets very hot, 120-130 degrees C, which equates to over 240 degrees F. Hot oil. The water temp stays good, between 180 to 210 degrees F. I run an oil cooler, but am wondering if it’s location and the car’s extra areo are causing a reduction in airflow. As many have seen, I run a lot of body mods to try to both push/suck the front of the car down at high speed, as well as try to get the air out from under the car and evac the engine compartment. I run a large front spoiler, hood, fender side and top vents, and a sealed cowl intake. Out back, I have the diffuser, though I do not know if it actually works. I have noticed with the new front spoiler that at high speeds, (130+), the interior panels on either side of the footbox next to the motor/trans actually now shake/vibrate, which they did not do with the older standard FFR front spoiler. I also notice the trans tunnel a little warmer. The oil cooler is located under the front “X” member, but fed by a 6” duct directly from the oil cooler opening.

In theory, this set up creates some sort of high pressure at the front, and then the air is pushed over the car, through the nose openings, and vented out through the body openings. Is my thinking seemingly correct? Based on this, am I indeed getting airflow to the oil cooler through the traditional opening? The rear of the oil cooler is open to the engine compartment under the radiator, and unobstructed. I checked the oil cooler lines, hot, so oil is flowing. So, is there an areo issue preventing the airflow to the oil cooler, or is just running the motor in a 20-30 minute sprint, usually at 4k – 6K revs, just pushing the oil too fast through the cooler so it cannot really work? I run a 7QT road racing pan, lot of oil, and changed twice a year. I will add that the suspension was complety revamped, and now the car is much faster on every track, in some cases MUCH faster. During cool-off laps at much lower RPM’s, the oil temps comes down fairly fast. On the street, everything is normal.

So, in your opinion or based on any aerodynamic knowledge, what do you think is happening with the airflow through my car? Put your thinking caps on……

[dallas_]

I'm having a hard time visualizing where your oil cooler is. Do you have a photo?

[Chepsk8]

Will try to post some pics tonight at home!

[ROADRACER83]

Chepsk8:

What's the size of your cooler and what's the air pressure differential delta from the front of the duct to the rear air outlet from the cooler? If the air pressure inside the engine compartment is close to the pressure at the front of the duct, not much air will pass. Not easy to measure except with two sensitive manometers either electronic or tube type.

7 quart pans are great for racing because they keep oil at the pickup, but they don't conduct heat out worth doo doo. The oil in the pan just sucks up heat and it stays there until it gets passed through the cooler which may not give it much time to cool if the cooler is too small. Aluminum heads add a lot more heat to the oil than cast iron. The type of cooler has an effect on efficiency also. Just for comparison purposes, on my American Sedan 305 motor I had to go to an Earl's 19 row, wider cooler from a 10 row to get the oil temps where I wanted them at about 210-215 for a whole 30-40 minute race. It took 4 laps to get the oil temp up and one lap to cool to 180 or so. On a cold day I had to put a piece of cardboard on half the cooler to get the temps up to 210. I didn't like the oil thermostat idea as it seemed like one more thing to go wrong.

Ron

[Sanford]

delete

[Sanford]

Originally Posted by Sanford

I trimmed my air dam behind the oil cooler to let air flow thru. Actually its a Power Steering cooler in the usual oil cooler spot. Using that conveyor belt air dam from ....I'm drawing a blank.

never mind, reread you post. Maybe there is not enough of a pressure differential from your air source to the air outlet of the cooler for sufficient air flow.

Just throwing something out there, if you put a large cooler above the radiator where you would add a block off to force all air thru the radiator in the nose.

[trevor]

mine runs at 250-255 F on the track. I think it is working. I have a side pod in my radiator that has an oil cooler built in. I think you are fine as long as you run full synthetic. I use redline racing oil.

[CraigS]

trying to measure airflow might be kind of expensive. I wonder if some yarn and a relatively cheap video cam might be able to give you some hints. My first thought would be yarn and a cam looking at the outlet side of the oil cooler. you mention that the cooler is fed by a duct so I wonder why it isn't right up at the traditional oil cooler location just below the radiator. Thinking avoiding crash damage to the cooler? There have been a lot of posts about air ducts in the trans tunnel sides so we know that the underside of the car has pressure. What we don't know, but could be affecting your cooler, is how far forward that pressure exists. just a few thoughts for you!

[92sho16]

Originally Posted by Chepsk8

A question on airflow, aerodynamic pressure differential, and oil cooler efficiency.

When racing, my oil temp gets very hot, 120-130 degrees C, which equates to over 240 degrees F. Hot oil. The water temp stays good, between 180 to 210 degrees F. I run an oil cooler, but am wondering if it’s location and the car’s extra areo are causing a reduction in airflow. As many have seen, I run a lot of body mods to try to both push/suck the front of the car down at high speed, as well as try to get the air out from under the car and evac the engine compartment. I run a large front spoiler, hood, fender side and top vents, and a sealed cowl intake. Out back, I have the diffuser, though I do not know if it actually works. I have noticed with the new front spoiler that at high speeds, (130+), the interior panels on either side of the footbox next to the motor/trans actually now shake/vibrate, which they did not do with the older standard FFR front spoiler. I also notice the trans tunnel a little warmer. The oil cooler is located under the front “X” member, but fed by a 6” duct directly from the oil cooler opening.

In theory, this set up creates some sort of high pressure at the front, and then the air is pushed over the car, through the nose openings, and vented out through the body openings. Is my thinking seemingly correct? Based on this, am I indeed getting airflow to the oil cooler through the traditional opening? The rear of the oil cooler is open to the engine compartment under the radiator, and unobstructed. I checked the oil cooler lines, hot, so oil is flowing. So, is there an areo issue preventing the airflow to the oil cooler, or is just running the motor in a 20-30 minute sprint, usually at 4k – 6K revs, just pushing the oil too fast through the cooler so it cannot really work? I run a 7QT road racing pan, lot of oil, and changed twice a year. I will add that the suspension was complety revamped, and now the car is much faster on every track, in some cases MUCH faster. During cool-off laps at much lower RPM’s, the oil temps comes down fairly fast. On the street, everything is normal.

So, in your opinion or based on any aerodynamic knowledge, what do you think is happening with the airflow through my car? Put your thinking caps on……

What kind of oil do you use? Check manufacturer website and see if its within the recommended range, 266ºF doesn't seem excessively high.

[Chepsk8]

Some good thoughts up so far, and I'll hit on a few:

Yes, my oil cooler is smaller, maybe I should step up in size.

it is located further back, as I lost my first via rock damage when it was up in the body. Protective move, and shorter hoses.

Running traditional oil, 10w40

Good thoughts on the oil pan!

Yes, aluminum heads

[Chepsk8]

New spoiler:



Old spoiler:



Roughly twice the surface area of the old FFR piece without the plastic wicker, and damn is the car stable at high speed!




Don't have a handy oil cooler pic, will get one

[Chepsk8]

Blurry pics from a few years back, but hope you can see the system...

[Avalanche325]

I wonder if the chin of the oil cooler opening sticking out past the spoiler hasn't got the opening in a turbulance area.

The cooler also looks to be pretty small.

Of cource aerodynamics are not a visual thing. What it looks like may not be how air is flowing.

[rich grsc]

You may not believe what I say, but 240* oil temp on the track is in NO WAY too hot. Most high quality oils will handle 300* for short periods of time. Why would you want your oil temp the same as your water temp?

[tirod]

Agreed - 240F is normal, not hot, as a relative expression of working temperature. It's sprayed under the piston to grab heat and get it off the underside so it won't melt.

Shroud your cooler so that there is no way for air to bypass it. If necessary, get a Magnahelic gauge and plumb it to prove the system actually delivers higher air pressure in from of the cooler to force air thru it (not around it.) There could very well be an inrush of air from behind the tires delivering higher pressure under the crank nose than from the grille.

A Magnahelic is like an IR temp gun, everybody "knows" how hot something is getting until you actually check. When the hard numbers are actually recorded, then you can measure changes and choose them.

The guys in Land Speed Record and doing aero improvements use them: Series 2000 | Magnehelic® Differential Pressure Gage | Dwyer Instruments

[Bob Cowan]

A couple of years ago I installed a full width air dam. My oil temp went to 240-260*.

The problem is that the full width dam creates a dead space behind it, and didn't let air flow through. The answer would be to place ducting behind the oil cooler, and direct the air out of the engine compartment.

[ROADRACER83]

Chepsk8:

240 is a little hot for conventional oil, but for a good synthetic that is not a problem. Red Line, Royal Purple, etc. full synthetic race oils will be fine with that temp but conventional oils will start to break down and should be changed every race. Synthetics also are slipperier and cut friction loses and the oil will run cooler because of that.

You can tell it's time to change oil that has been overheated. It will look very dark and smell like sh*t. Full synthetics are more bucks, but you will get 2-3 or more races on an oil change so it works out about the same bucks per race. Plus you will pick up some horsepower. Change out the filter every race or two and and cut them open with a filter cutter and you can diagnose a lot of problems before they become a hole in the block.

Your cooler is a little small but too large a cooler and you can over cool the oil on a cool day. Tirod has come up with an incredible tool that I had not heard of before. That Magnahelic gauge would be tool #1 to have if you are doing aero testing on a race car. Inexpensive and accurate. What's not to love? Find out if all those holes are really doing what they are supposed to.

Ron

[rich grsc]

Ron sorry but 240* is not too hot, just do a little research.
"A key new test for GF-4, which is also required for API SM, is the Sequence IIIG, which involves running a 3.8 L (232 in3), GM 3.8 L V-6 at 125 hp (93 kW), 3,600 rpm, and 150 °C (300 °F) oil temperature for 100 hours."

[CraigS]

I would go to a bigger oil cooler and have a sealed shroud connecting that big hose to the front of it. I also think the spoiler is causing your problem. I say this cause my oil only gets hot when the car isn't moving fast enough. The temp will rise in traffic and drop quite quickly once back up to speed. I don't have a spoiler so the airflow under the car and across the 9 qt. pan cools it off.Your spoiler kills that normal airflow so you need to carefully duct air to the cooler.

[G-Pete]

240 degree oil temperature, with the right oil, is just right to assure the oils get everywhere.

Your worry is not warranted.

I say it again, under race conditions and constant high load, that temperature is NORMAL.
Nothing is wrong with your setup!

[narve00]

Originally Posted by tirod

Shroud your cooler so that there is no way for air to bypass it.

+1

The cooler is a resistance to flow. The air needs to be forced through it.

[ROADRACER83]

Originally Posted by rich grsc

Ron sorry but 240* is not too hot, just do a little research.
"A key new test for GF-4, which is also required for API SM, is the Sequence IIIG, which involves running a 3.8 L (232 in3), GM 3.8 L V-6 at 125 hp (93 kW), 3,600 rpm, and 150 °C (300 °F) oil temperature for 100 hours."

Rich:

I agree 240F is not that hot for the newer conventional oils, but there is a difference between a fuel injected 125HP test engine at a steady 3,600 RPM's in a bench test and a carbed race motor making according to chepsk8's signature, 345 HP at maybe 6,000 RPM's. As you know, in a road race the engine RPM is varying between maybe 2,500 and maybe 6,000 with periods of very high cylinder vacuum under braking, and very high cylinder pressure under acceleration depending on the compression ratio. On a typical weekend of racing the engine may see 2 to 2-1/2 hours of these conditions. Under braking with high vacuum the engine oil gets sucked past the rings and under high cylinder pressures VERY hot scorched oil gets scraped off the cylinder walls and along with unburned fuel and carbon gets pushed past the rings and goes into the pan. All that junk dilutes the oil pretty fast and the viscosity goes to hell. 240F is no reason to panic, but there's more to the equation than just temperature.

Ron

[Dan Babb]

Not sure if the size is right, but if you got another scoop like the one you have in the oil cooler opening and ran it at the end of the hose (round end on hose...big end in front of the cooler), that should be a simple way to shroud the oil cooler.

[DealsGapCobra]

Originally Posted by narve00

+1

The cooler is a resistance to flow. The air needs to be forced through it.

No doubt that this is the first thing to do.

Also put me in the camp of you temps are just fine.

Lastly, the air dam is not reducing the airflow into your scoop. I don't really know what is going on behind the cooler but would be shocked if the spoiler was doing anything other than improving the cooler flow.

Now, if your oil temps are bothering you, get the duct installed.

PS - the original design where the cooler exit is in front of the radiator is a pretty poor design, I ducted mine to exit below the radiator in a lower pressure area.

[Someday I Suppose]

Dan, FWIW I would also suggest the temps aren't that high, from when I thought I was having a oil temp issue I read every post I could find, it seems pretty normal for oil to run 30-40 degree higher then the water temp which is right where you are. I would switch to a true full synthetic and not worry anymore about it.

-Scott

[cobraless]

I mounted my oil cooler behind the "X" brace but it could be mounted anywhere. I ducted it AND used a Bilge fan in front of the cooler. I also ducted from the rear of the cooler. This allows the cooler to be installed anywhere and you can control the temps better by turning on or off the fan.

Second. if you are concerned about aero WHY do you run the full windshield?

[edhunter]

In your second pic, the cooler looks like one of the cheaper "Long" oil coolers, the pressed plate design. These are one of the lesser efficient designs. I ran a 12x12" cooler on my engine, (road race mustang) and my oil temps still ran high. I swapped to a setrab cooler that was a bit smaller, and my cooling improved significantly. So I'd consider going to a better cooler, and ducting the air through it/boxing the cooler in. Also, where do you take your temp at? The pan or after the cooler? If after the cooler, then your temps are the coolest they'll ever be, so your bearings may be seeing oil a lot hotter than that. I've read that anything over 240 to the bearings and the bearing will start to suffer...
If that's your pan reading then the oil to the bearings are likely much cooler, so less to worry about. Also a heavier oil will not cool as well as a lighter weight oil. 10-30 will shed heat quicker than 15-50.

[trevor]

I think 240F with conv. oil is pushing it. I would run full synthetic. The oil change is good insurance, A new motor is a lot more than an extra $40-50 per oil change.

Car done yet Ed? Hurry up. I am not going to SP this weekend, Im in NY for a wedding

[Thumper135]

Just my 2 cents: I agree that your temps aren’t out of line here for track time. Just make sure you are using oil that will handle the higher temps. From the looks of your air opening “snorkel” you made for the oil cooler, it looks like you may be experiencing something we call Rebound Air Flow. In short, look at it like a jet fighter. You can only cram “X” amount of air down the intakes to feed the engines. Once the engines get all the air they can handle, they will try to get rid of anything extra. This causes a back flow of air in the intake causing a dead air space just in front of the engine that intern causes an engine stall. That is why you will always see some sort of air escape or intake closure on aircraft that will fly around Mach 2 or higher. I think you are most likely having an issue like that here, but the air is being slowed due to the opening in your scoop and or the cooler only being able to handle a portion of the air you are cramming into it when you drive at higher speeds at the track.
Now for the air dam on the front. I have seen these create a “dead air space” under cars before that can cause the air in the engine bay to become “stagnate” and not allowing that air to flow out as fast as needed. As we know, sucking a car to the ground is caused by making the air going under the car travel faster than the air going over the top. This creates an inverted wing affect that will create a vacuum under the car making the care want to “suck” down into the vacuum. If the air under the hood can’t merge with the air going under the car at an adequate rate, it will not exit the engine bay as fast as you are putting it in through the front opening. The same affect will result as before and you will get a dead air space that will cause a lack of cooling. First rule, get rid of air behind the scoops as fast as you cram it in and the air flow will keep up. Second rule, if you need 20 cubic feet of air a minute to move over the cooler so it will work properly, then you need an intake that will move at least that amount to the cooler and a way to move that amount out after the cooler. *Formula* If you are moving 80mph, your cooler will handle a max air flow of 20 cubic feet of air a minute, your scoop set up is delivering that amount of air through the scoop to the cooler at that speed, when you go faster, you will be trying to cram more air in than things will handle and the for mentioned will most likely result. You may just need an air escape opening to control the amount of air being fed to the cooler, or be able to figure out how to get more air out of the engine bay faster so the air coming in will have somewhere to go.

[Chepsk8]

Wow LOTS of good info here! A real brainic thread.

After digesting alot of what was posted, I'm going to follow the following steps, so I can attempt to solve it one thing at a time.

1 - Add some vertical "strakes" on the body on either side of the oil cooler opening. I do agree, possibly the larger spoiler has affected the airflow in front of the car, so by adding some channels/diverters, I can gain some extra airflow into the cooler opening.

2 - Improve the air ducting to the oil cooler, and possibly add some "exhaust" ducting in an effort to aid air flow through the cooler

3 - If it's still hot, upgrade the oil cooler size.

Sounds like a good starting point and plan?

As well, time to look at the airflow under the car and engine compartment more. Thumper, what is your opinion on larger air vents on the rear of the engine hood? Also, I have always been batting around the idea of reverse tilting the radiator, and adding an exit like the original GT-40's. Any thoughts on that?