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Mats · Post by **Mats** » Mon May 21, 2007 3:15 am

From a technical standpoint you can punch holes anywhere in the hood and the flow will always be in the out/up direction. The pressure under the hood will be roughly the same as the static pressure in front of the nose which is much higher then the pressure at the base of the windscreen. Venting at the front will yield a larger pressure differential which will draw more flow.

However I must ask; why do you want to vent air? What problem are you trying to rectify? Lower under hood temp is not something to chase after unless you have a problem with it.
Cutting holes in the hood means more mass flow through the engine bay and that equals higher wind resistance -> slower/thirstier car.
If you need more cooling you should make an air tight ducting from behind the radiator up and out through the hood, note that this does not vent any air from the engine bay. If you feel you need to be quicker you can then add some kind of obstruction (duct tape!) in front of the radiator to lower the mass flow of cooling air through the radiator -> faster car.

So the interesting question remains, why do you want to add vents?

x-rad · Post by **x-rad** » Mon May 21, 2007 9:24 am

Short: you cant make a 5 inch louver longer because the punch will tear the metal, i want the louver to almost cross the hood opening. I don't want 2 five inch louvers next to each other either..As for the Summit scoop, it is plastic and you have to cut holes in it...i was just buying it for a mold...but i appreciate your input!! you are right about the scoop look, it would have been modified to fit the Alfa looks!

Mats: some sites say pressure is highest just in front of windshield and at leading edge of hood (but the windscreen pressure is less than leading edge so flow is up and out as you say)... but I am going for some cooling(especially when sitting still) and better looks. I am not a fan of the plastic hood piece!

I just located a Jag E type hood vent all metal one piece, vents measure 8 x 14 inches which is perfect.. I will run a bead around surround edge and drop it in the recessed margin of the hood hole, hold it in place with a few alu rivets and some poly for a real smart look (I think!)
will paint it to match hood..

Alfettish: not my style, but thanks for the help...

car never sees rain so not worried about water drain

sh0rtlife · Post by **sh0rtlife** » Mon May 21, 2007 12:58 pm

die stamped lovers your right cannot be lengthened but a "rolling die" can be as long as you want..ive seen trunk lids of 32 fords and some 60's PU's where they litteraly had 4 foot long single louvers...one of the 32 ford trunk lids i saw basicaly went up the drivers side across the top and down the passenger side as a single louver with more inside of it shrinking tward the center...thats why i said a shop with a rolling die

ill be curious to see how the jag piece looks even mocked up and unfinished..soon as you can post a pic :p

Greg Gordon · Post by **Greg Gordon** » Mon May 21, 2007 1:46 pm

In spite of the fact that he lives in an area where cooling is rarely a big issue Mats is right. I doubt there is anyplace on the hood where air would not flow out of the engine bay due to the relatively higher pressure under the hood.

x-rad · Post by **x-rad** » Mon May 21, 2007 3:05 pm

shortl: read your post too fast....you are right about rolling dies , of course.....but I managed to find the only E type hood in USA (probably) which the owner was willing to cannabilize to cut out the vents for me...

Greg G: you are right, but there is already ahole in the middle....

They measure ~8.5 x 14" and the Alfa hole is ~11.5 x 15 so it should be a good fit and a good look..........will post pics upon arrival

The Jag louvers have a nice low profile and will be flexible enough to follow the hood contour....

x-rad · Post by **x-rad** » Mon May 21, 2007 3:14 pm

photo shop preview...

I think it compliments the vents in the rear as well...

I will bet that Alfa was going to do something similar but it turned out to be cheaper to put plastic in there !!

anybody want to buy a Summit hood scoop???? or a chicken???

Mats · Post by **Mats** » Mon May 21, 2007 10:26 pm

How will you solve the rain issue?

Maurizio · Post by **Maurizio** » Mon May 21, 2007 10:38 pm

How will you solve the rain issue?

Just drive fast enough

sh0rtlife · Post by **sh0rtlife** » Mon May 21, 2007 10:40 pm

soooooo ya got a second louver set to sell(hint hint nudge nudge)...i must say i like the way that looks....well minus the crude/quick slap together but the "finished" effect image in my head says that works VERY nice

solveing the rain issue is actualy alot easyer than you would belive if you make a slightly angled pan for it with a set of holes in the ends like the way a sunroof drains it can be done.....take a look at some of the 80's cars that had open air hood stuff and you can see how easy it is

Mats · Post by **Mats** » Mon May 21, 2007 10:43 pm

Maurizio wrote:
How will you solve the rain issue?
Just drive fast enough

Does Pinocchio have a roof over their drive-in window?

Alfettish · Post by **Alfettish** » Tue May 22, 2007 1:32 am

It's no good speculating about where you think the pressure is going to be lowest on top of the bonnet (which is where you'd put a vent ideally); it needs to be tested. But as Mats says it's most likely going to be really far up the front.

x-rad · Post by **x-rad** » Tue May 22, 2007 1:10 pm

yeah...getting two Jag vents...supposedly already blasted and primed...condition unknown at this point...

Alfettish: I agree with you...and since there is already a hole in the middle........

Got the Summit scoop...vacuformed plastic but pretty nice piece..about 1/16th thick...pics below

scoop is almost perfect for the hole...just a little too tall

As for the rain issue...there is no issue...its always sunny when I drive my Alfa

GarthW · Post by **GarthW** » Tue May 22, 2007 3:46 pm

How about using the same plastic panel you have now and cut louvers into that..? You retain original look, and you wouldnt notice the louvers till you got right up close..? Thats something that i will be doing if i dont come up with anything else, but i definatley dont want a scoop.

x-rad · Post by **x-rad** » Tue May 22, 2007 4:30 pm

It would be hard to cut louvers into the plastic..too brittle...and if I cut out a hole in the panel for the louvers, I might as well just use the metal margin already on the metal louver and just trim it to fit in the original hole....use the same mounting holes, etc...

actually, scoop doesn't look that bad in person and better if painted...

right now, the hood looks like a giant squinting Snoopy

Scott: read your post and did think about that...looked all over but nothing was right size or look

sh0rtlife · Post by **sh0rtlife** » Tue May 22, 2007 4:46 pm

cant say i could ever like that scoop..too tall and gives the car a modern rice trashy look to it

hood preview