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vent holes for high speed cooling

7K views 42 replies 11 participants last post by  pedal2themetal45 
#1 ·
Tomorrow I was planing on putting some holes in the firewall into the wiper mechinism area for some higher speed cooling vents. That is where I am heating up a little.
has anyone else done this with any success?

the car is a 89 mustang LX
 
#8 ·
All my vehicles have the rear of the hood vented in some manor. Most just rasied some at the back. I spent a lot of time studying under hood air flow as well as weel wells and such. Made some real big gains in performance.
The cowl hood on my 84 Stang was open in the rear many of the new ones I have seen dont. I wouldnt want one of the closed off ones.
 
#10 ·
Using aero flow to cool

I wouldn't think the back of the hood is the place to try to vent heat. It will work when sitting still but will make the car unstable when at high speed. Starting around 55mph the car will want wander due to the air being pushed under the car from the windshield base.
Cowel induction is designed to use the HIGH Pressure air at the base of the windshield to force feed the intake system. If you open the back of the hood or cut holes in wiper box you will lose power, increase aero drag and lose downforce. Go to circletrack.com and do a search for aerodynamics.

Two good places to "vent", or better yet, "draw" air, are both in the wheel wells on a street car.
First, look at the mid 1980's Trans Am or Z28. The gills (aka NACA Ducts) in the fenders behind the front tires were easily made functional but worked better if moved back a few inches.
High speed air rolling off where the fenders meet the windshield will create a vacuum on the side of fenders near the gills. This opening located in the low pressure area will pull air from under the car through the engine compartment increasing downforce and pulling hot air out. *Note, This opening is located behind the inner fender on a T/A so air flow had direct access to engine compartment. Your Mustangs inner fender would need (1) 3" or (2) 2" holes on each side, located as high and as far back as can.

So you don't want to cut holes in your outer fenders? The the second location is ready for you to take advantage of. In front of the front tires, air is being pulled out from under car when in motion. The next time you are on the highway on wet roads, watch the cars around you and how the mist flows around the side of the cars. You will see mist smoothly flowing out from infront of the front tires and mixing or rolling down the sides. Semi trucks are a good example of this also.
If you hole saw through the side panel of inner fender, in front of shock tower, the vacuum should increase down force and under hood circulation.
I'm not sure how much good theese fix's will help when sitting still but should help when crusing around town.
 
#25 ·
OK

I wouldn't think the back of the hood is the place to try to vent heat. It will work when sitting still but will make the car unstable when at high speed. Starting around 55mph the car will want wander due to the air being pushed under the car from the windshield base.
Cowel induction is designed to use the HIGH Pressure air at the base of the windshield to force feed the intake system. If you open the back of the hood or cut holes in wiper box you will lose power, increase aero drag and lose downforce. Go to circletrack.com and do a search for aerodynamics.

Two good places to "vent", or better yet, "draw" air, are both in the wheel wells on a street car.
First, look at the mid 1980's Trans Am or Z28. The gills (aka NACA Ducts) in the fenders behind the front tires were easily made functional but worked better if moved back a few inches.
High speed air rolling off where the fenders meet the windshield will create a vacuum on the side of fenders near the gills. This opening located in the low pressure area will pull air from under the car through the engine compartment increasing downforce and pulling hot air out. *Note, This opening is located behind the inner fender on a T/A so air flow had direct access to engine compartment. Your Mustangs inner fender would need (1) 3" or (2) 2" holes on each side, located as high and as far back as can.

So you don't want to cut holes in your outer fenders? The the second location is ready for you to take advantage of. In front of the front tires, air is being pulled out from under car when in motion. The next time you are on the highway on wet roads, watch the cars around you and how the mist flows around the side of the cars. You will see mist smoothly flowing out from infront of the front tires and mixing or rolling down the sides. Semi trucks are a good example of this also.
If you hole saw through the side panel of inner fender, in front of shock tower, the vacuum should increase down force and under hood circulation.
I'm not sure how much good theese fix's will help when sitting still but should help when crusing around town.
Just to make sure you say in the wheel well in front of the tires down low
i would like to vent as much heat as possible out and colder air in
 
#12 ·
bowsher21
Thank you for your write up here
I have a question

"Your Mustangs inner fender would need (1) 3" or (2) 2" holes on each side, located as high and as far back as can"

are you talking about IN the plastic wheel well just behind the tire?

or somewhere else

I dont want to put vents no the fenders but the steel inner fenders I can modify and the plastic inner fenders are game also.
 
#13 · (Edited)

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#15 ·
Try this link,
http://www.circletrack.com/techarticles/ctrp_0707_stock_car_aero_downforce/index.html

I did a search for down force. I also attached a pic of a Mustang I used for racing. Forgive me, but I forgot street cars have plastic wheel well liners that we have to work around.

In my picture you see arrows. Red arrows show factory holes already in the structure that can be used for pathways. The hole in front of shock tower is perfect for pulling air from engine compartment. Right side is for factory air box inlet. I don't recall what left hole is for. Back red arrow points to upper structure box. If you poke a hole from engine side of this box, you will create a pathway for flow into fender well.

Now you have to poke a hole or two in the plastic inner fender to complete the "pathway of flow" to the source of low pressure (wheel well edge). The closer you get to the edge of the wheel opening, the better the effect. How about slots? 1-1/4" x 3-1/2" long spaced 3" apart starting @ 10 o-clock position to 1 o-clock position, as seen from looking at drivers side wheel?

Your pic's position #1 inner fender and #'s 5, 6, 7, maybe 8 if you seal the bottom opening to prevent short cutting flow (yellow arrows on my pic).

Now looking at my picture again you see yellow arrows. This yellow air flow reduces the effect of under hood venting. Best to seal the good path of flow (green arrows) from engine bay to fenders edge.

Keep in mind you will collect stuff that gets tossed into the holes.
 

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#16 ·
Green area is were I vented air and water from the road and tires eliminated hydroplaing. The red circle in the top of the fender is were I built duct work to seperate engine compatment air from wheel house. With the air exiting from under the hood at top of fender along with air from the wheel house this car went from loosing speed coasting down a hill to picking up 10 or better MPH. Side winds rain etc had little to no effect on it. It felt like the front of the car weighed 2000 lbs not like the 500 or less that was on the front wheels stock with the trapped air in the front of the car.
Sides of the mustang ended up lookjing more like the AMG pictured when I was done.

Air out the rear down flow at the firewall was directed with the use of a belly pan and out the sides using ground effects sometthing like a Stang GT had but a bit more thoughtout.

Never realy finished the car as I got 25K for it trading in for a offshore boat
 

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#18 ·
well I put 3 2x6 holes in each of the inner fender wells the car still heated up. driving 55-65-70 the outer fenders were warm after the ride but I think I still need more.

I cut from the #4-7 zone on my fender pic

I also fabed up a small air scoop under the radiator that hangs down and catches air like the stock cars use.
 
#21 ·
545, 2 core new stock style rad,160 t-stat. Its an air flow issue because it cools when I slow down or stop.

as for right now I'm just feeling the car after a ride
I have a heat imaging camera at work s Ill try and get some thermo imaging on here

Im also going to try and run the car with the hood off and see if that helps, just for a test
 
#23 ·
The bottom line its a factory 3 row rad small 1/2 or 5/8 tubes just wont cool the engine as the rpms increase and more power increases.

I suggest a rad with at least 2 or 3 rows with 1" to 1 1/2" tubes. Howe enterprises make some rads for a good price and work great and dicently priced. If they dont have one that fits they will make anything you want.
 
#28 ·
On a Stock car, Road race car or Pro Stock drag car you will find them all with the back center of the hood raised as high as rules will allow but they are sealed to cowel/fire wall. This bulge in the back of the hood helps displace the high pressure at windshield base and push it over the car. If you have a cowel inlet on your car, make sure to seal it to the air box or carb and prevent air from packing under hood. This will increase HP and help reduce the effect of high speed lift under the car.

In short, the air is most likely trying to go into the back of the hood when moving.
 
#31 · (Edited)
Depending on application and with enough air flow trough the radiator either could be a perfect fit. The 2 pass could cool better in an application where there is plenty of air. A 3 pass wont cool anything off if no air flows trough it. Some applications may only require a single pass.
 
#32 ·
Of the 12 bigblock Mustangs I have built the only one that ever had any cooling issues was an 89 GT and that was because the closed off front facia would not allow enough airflow to the radiator. Changed the front nose piece and viola cooling issues were gone.
 
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