Thanks for chiming in, Al. I should have known the crack staff at the X-Factory would have calculated relative grill opening vs. stock.

The photo doesn't really do Al's grill justice. It looks much more restrictive than it actually is. If, next summer at my first hot and humid track day, I am still having issues, I'll simply remove it and run without for a session. I have a hunch it won't make any difference. I'm hoping it won't - I really, really like this grill. On top of that, not many can say theirs is "factory installed," by the President of the company himself... :D

I do have the louvered covers on the back sides of both coolers. I would not run without them - they do, in fact, materially improve air flow through the coolers. And they keep hot sticky slicks from pummeling them with rocks.

Verified so far:

Both thermostats open, and both open at the same temp. Not surprising, since the '72 is unique in that the second thermostat is, in fact, just like the engine mounted thermostat.

The gauge and sender are working to give me accurate temperature readings.

Both front coolers run at nominally the same temperature, as verified by an infrared heat gun.

The plan going forward:

Plan A: Properly block off and seal the driver's side cooler as I have done on the passenger side.

Plan B: If still too hot, go back to using the headlight ring with the screen on the passenger side.

Plan C: If still too hot, make another headlight screen for the driver's side.

Plan D: If still too hot, try running with the grill removed.

Plan E: (Now I'm starting to sound like a Ferrari F1 race strategist...) Learn to live with 250 as more or less acceptable on the rare days that are hot and humid enough to drive the temps that high.

The only real frustration here is now I will have to wait until it gets hot and humid up here again, which means some time next summer.

Jeff, do you have closing panels below the coolers to direct all the air thru coolers. In this “R” pix, you can see the coolers before the lower closing panel is installed. The triangular piece fits between bumper, inner fender and louvered fender well piece. http://forums.pelicanparts.com/uploa...1662424983.jpg

I have one on the passenger side only right now, Gordon. It's kind of a quarter pie shape, with the front rounded to fit inside the bumper. I have it all sealed with round foam pipe insulation, exactly like Roy showed us. I just need to make another one for the driver's side.

Maybe I missed it, but do you have a wideband to verify you are not going lean on high humidity days?

MFI is rather unique in this respect. It's what I like to call a "double blind" fuel and air delivery system, wherein neither the incoming air nor the fuel has any way of gauging, or responding to, how much of the other is going into the motor.

Carbs are actually the original "smart" fuel/air delivery system. Fuel delivery is dependent upon air flow creating a low pressure zone in the venturi, where we locate the various jets. As such, it does respond, within its range of capability, to weather changes such as temp and humidity.

"Modern" injection systems utilize various means to mimic this behavior. The mass airflow sensor on CIS is a good example. More modern systems utilize various other means.

Well, MFI has none of that (outside a mechanical "barometric sensor"). So, on hot and humid days, with less air "available", it "has no idea", and only responds to the position of the throttle arm on the side of the pump and the rpm's at which the internal flyweights are being driven. There could be no air going in, and it would still pump as much fuel. So, long story short, MFI will go rich on hot and humid days for a lack of air density. The barometric cell is supposed to help with this, and it does sort of, but not like modern systems.

And, well, beyond that, yes - I do have a wideband O2 sensor, in the form of an Innovate Motorsports LM-1. While it does not stay on the car, it has certainly spent plenty of time on it. I would venture to guess that mine is one of the more fussed over, fiddled with, and checked MFI systems out there today. So, no, there is no possibility that it's leaning out.

I think I have solved this issue to my satisfaction, at least as well as I can for the time being. Like I mentioned earlier, with the weather cooling and no more track days (with the clubs I run with) for the year, I was afraid I might have to wait until next year to test any solution. Fortunately, however, we have been blessed with unseasonably warm and humid weather up here, so I made a plan to try to take advantage of that.

I wound up taking a couple of trips to the east side of our state, and to the east side of Oregon as well. Central Washington and Oregon, believe it or not, have some pretty hot and arid desert regions, in spite of our reputations for rainfall. I was "lucky" enough to find 90-100 degree temperatures, with high humidity to boot.

There are some very lonely roads in those regions, and many of them descend down into and climb back out of some seriously deep river canyons and valleys. The plan was to drop into those bottoms, and do some rather "spirited" hill climbs back up and out of them. With a clear run, this allows for some ten to fifteen minutes at pretty much full throttle, going up and down through the gears. Probably even a more severe test that a track day, really.

And that is exactly what it proved to be. Starting at the bottom on several of these hill climbs, with the car already at 210-ish degrees, it was no problem getting it up over 250. That was with the X-Factory grille in place on my first trip.

A week later, with the weather conditions unchanged, I made a second trip with the stock grille installed. Driving the same roads, under pretty much identical conditions, the first thing I noticed was the "starting" temp at the bottoms of my makeshift hill climbs. It was running right down "on the thermostat" - fluctuating between 180-190 as it opened and closed, fully 20 degrees cooler than one week prior. The really big difference, however, was the temps at the top of these little runs - I could not get it to go above 210 degrees. What a huge difference. All the difference, really.

The final "data point", as informal as it was, was that I could actually grab the engine mount cross bar and comfortably keep my hand wrapped around it. With the X-Factory grille in place, it would burn my finger to even lightly touch it. So, yes, I have no doubt that it was really running as hot as indicated.

So, where do I go from here? I have to say, I really like the look of the X-Factory grille. I may continue to run it during the "off season", with no track days on the calendar. And through our typically wet, rainy winters, it will never pose a problem. It takes all of ten minutes to swap them out. Maybe I'll just have a "street" grille and a "track" grille. That wouldn't be so bad. But at least I'm pretty sure I've figured out what's going on.

That was my guess, the rest of your system seemed up to the task just like it apparently is. Nice to have an answer.

An A / B / C test with no grille would have been an interesting data point too.

I'm surprised by the results. Not to the point that I dispute them but just surprised based on what I consider looks like would provide plenty of air flow.

That would mean that there is a negative pressure in your engine bay with the Xfactory grill.

Interesting. Though it appears to have the same or more open area, the aftermarket piece must be more affected by turbulent air flow at the rear, IMO.

Well, that is interesting. The open area of the x-faktory grille is slightly more than the stock grille, per my original calcs...and I originally just made this for my 911 and liked the clean look. Other liked it to and so it goes. That being the case airflow was not an apparent issue and keeping the open area close to the originals was to ensure that rain was kept out , at least as well as the stock grille would . This consideration seemed to be important in the PNW.

However, i wonder if the stock grilles horizontal ribs and top surface actually improve the airflow at high speeds (not that Jeff would exceed the posted speed limits)

sometimes it's hard to improve on the Porsche engineering......

The Factory grill is not just about the open area. The design promotes air flow into the grill. The "flat grill with holes" design does the opposite.

Like the difference between a NACA duct and a round hole flush with the body. Maybe the "fins" of the stock grill keep the air more turbulent so it's easier to draw in, and there's maybe a strange boundary layer forming with Al's grille? Interesting situation--wouldn't have expected it.

I bet you could flow test these in shop and both would be fine, but put a 90mph flow across the face and what comes through the open area changes radically.

This is 80% out of my butt. You're welcome everybody!

There is a very interesting metric mentioned by Al here, and that is there was a calculation that at around 6k rpm the 3.0l motor was drawing in 150l per sec. I say interesting because based on the published graphic below (doesnt mean it is actually correct - there are a number of errors in the volume with subsequent errata issued, but Porsche AG is cited as the source...) the 3.0l fan draws 1380l/s at 6k rpm, or about 9.2 times the volume calculated. It could be that the 150l/s was a typo and should have been 1500, but if the calculation really was 150, then the fundamental maths are incorrect, and that may help to explain the great difference in temperatures between the stock and the custom grill.


http://forums.pelicanparts.com/uploa...1665772067.jpg

I had overheating issues on my race car and was also wondering if the gauges were accurate. After trying a bunch of different things, I finally put in a set of temperature sensors with a display I could read in car while driving. This helped so much that I've kept it installed in the car.

I used this 4 channel gauge: https://www.amazon.com/gp/product/B07D9JF5SD/

And I used 4 of these sensors along with it: https://www.amazon.com/gp/product/B00CWA3WEC

I used some aluminum tape to secure the probe to the various points I wanted to measure. It is important to use the style of sensor I've linked above because they can react very fast to changing temperature.

The sensors I used have 3 meter wires which is more than long enough to connect to the input and output of your oil cooler, thermostat and whatever else you want to monitor while mounting the gauge in car so you can monitor while driving.

The gauge has a min/max/avg feature so you can see the max and avg temperatures after a track session.

These things are cheap, and after a few months they can start throwing temp errors. I've had to replace mine twice...but they are cheap enough and otherwise work great to monitor my car so I live with it.

One tip: you need to press the hold and power button at the same time to force it to stay on (otherwise it turns itself off after awhile).

Good luck!

This is all fun stuff for me, continually learning about these wonderful cars and sharing what we learn on forums such as this. I think in this case, Scott and David have hit upon what I believe to be a very important factor - the role the cross bars play in "turbulating" or breaking up what would otherwise be a laminar flow across the grill. Even the expanded metal screen that comprises the grill itself would serve to do a bit of this, with its twisted, square section "wire".

Al, did you include the entire surface of the wire mesh screen, or did you not include that area under the cross bars in your surface area calculation? I can see where your grill would match the open surface area exposed between the cross bars. However, if we include the entire grill, even that area under the cross bars, it's readily apparent that the stock grill has significantly more open surface area.

The cross bars are not in contact with the wire mesh grill. They are about a 1/4" above it. This offset allows for airflow around and under them, so that the entire surface area of the grill is open to airflow. And, I believe, therein lies the difference.

I’ll hypothesize out of my rear end as well:

The stock grille has slightly rounded horizontal bars which perhaps smooth the airflow into the engine bay and direct the air to the openings whereas on the perforated grille the air smashes into the surface and tumbles around before being drawn in. My guess is that the perforated grille is actually stopping the air from moving into the engine bay quickly and more importantly, smoothly.

Whooda thunk it…

Here is a visual comparison. I do kind of question its worth, as many of the factors you guys are discussing might play a bigger role than mere surface area of the "opening". Breaking up the laminar flow, etc.

Try to picture as well the expanded metal mesh without the cross bars. As I've mentioned, I feel (due to their distance from the mesh) that they do not hinder airflow. I believe the air flow goes around and under them. So, with those cross bars eliminated from consideration, it's pretty clear which presents the greater open surface area.

http://forums.pelicanparts.com/uploa...1665780290.jpg

There is still a mechanical fan pulling the air into to do the cooling so its not just what is getting thru the grill with respect to flow and turbulance. I'm still just very surprised and wonder if there was other factors at play. It seems a far cry from having everything else absolutely constant.
Can you get the historical weather data for the two days you did this drive?
I almost want to support a go fund me to do this testing with better controls to get to the bottom of it. Count me in for $3, maybe $5 towards this endeavor, in the name of science!

The only source of air for the fan is that which comes in through the grill, so yes, it is absolutely "just what is getting through the grill".

From post #46:

Temperatures were as near identical as to make no difference, as was humidity. Within just a few degrees and points. That is what I meant when I said "with the weather conditions unchanged", and "under pretty much identical conditions". I would not have wasted my time swapping grills and making a second trip had this not been the case.