There have been a number of threads lately about hoods and cold air supply and such so I thought I'd start one of my own as the two topics are somewhat related. Actually I was inspired by a recent repost of a thread by REELAV8R (thanks).

https://www.corvetteforum.com/forums...g-results.html

My car is a 69 with ample room between the high rise hood and the radiator surround. Not the best picture, but here's what it looks like under my hood.




Back when I was putting the car together, I debated whether I wanted to seal that space or not. It's about 3". I decided with the slanted radiator the way it is, that was an ideal situation to direct air over the top and into the engine compartment. I never did get around till making any measurements until yesterday.

I'd bought a couple of the temp monitors mentioned (available on eBay super cheap). See above thread for instance or picture below. You guys that are actively pursuing some air ducting would be well advised to pick up a couple of these.

I had in mind putting one in front of the radiator and one somewhere near the air filter. The lead wire wasn't long enough for the former so I decided the heck with it. For the latter I taped the sensor to the air filter cover which is a nice metal piece very responsive to air temps. I taped the display to the wiper cowl where it was easy to read and went out for a drive.




The air temp was 25C and I figured all I really needed additional was the temp differential. The multiplier is 9/5 C to F.

Results: Quite nice at 55 on the expressway. The top of the air filter went up about 4 degrees C, which is about 7 degrees F. This suggests that the air over the top is getting to the right place when the car is moving at a reasonable speed. I really should have gotten on the freeway and collected some more data but it seems to me it would only get better.

Back home and idling in the garage until temps settle out again is a different story. The monitor settled out at 55 degrees C. That difference is another 54 degrees F over ambient. Actual underhood temp is 131F idling. But ... that cools off very quickly when under way again.

So .. a very nice benefit to not doing a darn thing.

I have to wonder though if a 68/69 is a bit of special case as the open gills probably help keep the engine compartment back pressure down.



Maybe somebody will get inspired and install some ribbons and a camera to see what's going on under their hood. I have in mind using my two sensors to check the air exhaust temps out of the gills and out under the car.

Take this all for what it's worth in that my circumstances also somewhat special (hood and year of car). Also I have a deWitt's and the fans never come on when the car is moving, even in 100 degree heat.

 

You have the 9/5 multiplier right...but you forgot the 32 degree offset that also needs to be factored in to the F* to C* conversion. 32*F is equivalent to 0*C, if you remember. Check the internet for the conversion formulae.

 

I'm only looking at the temperature differential above ambient so don't care about the offset. Mostly just interested in how much hotter over ambient was the air at the air filter.

In case you didn't know there is a real easy way to go back and forth

add 40
multiply by 9/5 or 5/9
subtract 40

thus starting with 32F

40 + 32 =72
72 x 5 / 9 = 360 / 9 = 40
40 - 40 = 0C

voila 32F -> 0C

pretty easy to remember this math "trick" for temp conversions

 

ignatz.......thanks for the tests......and let us know the results of more testing at the gill area.
Because my '68 project was/is a basketcase I was able to try several different mods under the hood (lonnnng story) to reduce the temp. .
I finally got several mods to "work together" with good results.

 

C* x 2

Then minus 10%

Then add 32.

Example:

15C x 2 = 30.

Minus 3 = 27

Add 32 = 59F

I do this everyday to convert C* to F*

Great info!