Hood vents: Urban myth debunked, Highly scientific content ... Options

[SirAndy]

Every time i have a discussion with people about venting the hot air from the front oil cooler out the top through the hood there is at least one fellow who insists that that will turn the inside of the car into a sauna.
(IMG:style_emoticons/default/rolleyes.gif)


Well, today i decided to do a highly scientific experiment to see if there was any merit to that claim.

After a 20 minute spirited drive i verified that the thermostat had opened and the front oil cooler was getting hot oil.
The oil temp was up to around 200F (That is normal operating temp for my car) and the cooler was hot.

I then proceeded to drive with the top off at different speeds and used my well calibrated hands to look for any temperature difference of the air coming over the top of the windshield.

• At 80mph, there was absolutely no difference in temperature across the whole top of the windshield.

• At 50mph, there was absolutely no difference in temperature across the whole top of the windshield.

• At 35mph, there was a hint of a minute difference in temperature between the sides and the center.

• At 15mph, i got nothing.


And that was just the air going *over* the top of the windshield. Most of that never even makes it into the cabin.

Totally scientific result: Completely bogus, made up and not a problem at all!
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[walterolin]

Jamie and Adam would be impressed, especially with the high tech instrumentation used..

[pcar916]

(IMG:style_emoticons/default/agree.gif) I hadn't heard about the supposed heating problem, but can attest to the changing of the water spray pattern on the windshield when it's raining.

It's not even a small problem, just different from a standard car. The new pattern has as much or more to do with the height and width of the air dam at the leading edge of the vent as it does with the outflow from the cooler, but it's part of the whole system so... (IMG:style_emoticons/default/beerchug.gif)

[stugray]

Now if you had just done the test with little streamers tied to the vent in front of the windshield, we would have known (beyond the shadow of a doubt) if that area is high or low pressure at all speeds.

Stu

[timothy_nd28]

What car did you use as the control?

[ThePaintedMan]

What car did you use as the control?

(IMG:style_emoticons/default/av-943.gif) My thesis advisor would be asking the same question.

[damesandhotrods]

If you recall the wind tunnel experiments that were posted a while ago, you would have noticed that most of the air hits the windscreen and goes down along the doors and merges in back over the trunk, which is why the flat bottomed 914 doesn’t become light until around 100 mph.. Also with the roof removed the air that doesn’t go around the car moves up vertically.

[Andyrew]

That jives with what I found when running a hood vent for my radiator. Lower speeds with some air moving you can notice something but thats about it..

[damesandhotrods]

My 914 Autocross Project




It took a minute to find it.

[r_towle]

I then proceeded to drive with the top off at different speeds and used my well calibrated hands to look for any temperature difference of the air coming over the top of the windshield.

He is German, so the calibration should be perfect for the test and no baseline should be needed.

Rich

[maf914]

Andy,

Could you please extend the test parameters to 100 mph, 120 mph and 140 mph. Inquiring minds want to know. (IMG:style_emoticons/default/laugh.gif)

[Krieger]

Great. Lets see some pics of the hole ya made.

[SirAndy]

Great. Lets see some pics of the hole ya made.

I'll leave that to McMark ...
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[Valy]

I'm sorry Andy but you solved nothing since you didn't measure the wind speed so the hot air could be going disestablishment because of that.
Oh, those wannabe TUV scientists....

[SirAndy]

Could you please extend the test parameters to 100 mph, 120 mph and 140 mph. Inquiring minds want to know. (IMG:style_emoticons/default/laugh.gif)

Confirmed at 120mph, still no hot air in the cabin.

And as a added bonus, the car feels more stable and less light now with the air going out the top instead of dumping it under the car.
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[Elliot Cannon]

The only time your car is HOT is when Amoy is sitting in it. (IMG:style_emoticons/default/drooley.gif) (IMG:style_emoticons/default/wub.gif) (IMG:style_emoticons/default/laugh.gif)

[stugray]

My 914 Autocross Project

It took a minute to find it.

Who is the "Chris" that did the wind tunnel tests?
His car looks like Chris Foley's, but does not appear to be the same "chris"

Stu

[Elliot Cannon]

My 914 Autocross Project

It took a minute to find it.

Who is the "Chris" that did the wind tunnel tests?
His car looks like Chris Foley's, but does not appear to be the same "chris"

Stu

I don't think Chris Foley's car has quite that much body lean. (IMG:style_emoticons/default/lol-2.gif)

[DBCooper]

My 914 Autocross Project




It took a minute to find it.

Most excellent. I didn't know that was you. Periodially someone refers to your project, points to findings or something, settle an argument about 914 aerodynamics or configure a car. It's really become part of 914 lore, so thanks for your curiosity and all the time it took. It's been helpeull to a lot of people, and I hope it also helped your autocross results. I assume that you've figured out by now that for a low-speed autocross more tires and horsepower beat aerodynamics... or not?