ABC'S of 80's Cooling Part IV - Hood Vents

[SUMOTOY]

The saga continues... In Part I, II, and III, I identified the need for aux cooling, the options in terms of fan hookup, and the relay install using the A/C pressure switch. In Part IV, I will put in hood vents to relieve the higher underhood heat created by a supercharger and the Aux Fan install.

In Part III I posted some data regarding underhood temps with the Aux Fan installation. My main concern is the Airbox heat soaking, as I measured 200F airbox temps at 95F at idle with the A/C and Aux fan on. As intake Air Temp increase is effectively the same as driving the truck at higher altitudes, it is now apparent that the convective heat release under the hood at low speeds is not at all optimal. To get rid of that trapped heat, my target is to now use hood venting. This should help with both running (active/forced) convectiive heat, and shut down (passive/free) convective heat.

Originally, I chose the Z34 Hood Vents because they have a huge surface area, and they are metal, and look aweswome on just about any hood. The problem I ran into right away was the Hood Frame dictated that the placement of these vents would be in line with the HVAC intake. Previous experience has taught me that engine fragrances into the HVAC system can cause trouble with peace in the cabin. And it's a safety concern IMO. Smoking engines will fill a cabin quickly. These concerns caused me to ditch the Z34 in deference to another set of vents I had on the shelf (working on the app, but see pics.

After testing low pressure zones on the hood with yarn taped to the hood, I determined that the brick-like 80 has a lot of low pressure zone on the outside of the hood bump. This allowed me to put the vents outboard of the diagnal hood brace, below the hump, and quite a bit forward (15in to back of vent) of the rear hood line.

Ok, for the install. I used painters tape doubled up to protect the paint from scratches. Then I measured forward of the rear hood line 15in and inbound of the hood edge 4in to clear the hood frame. I traced the vent template onto the tape, drilled a couple holes to insert the scroll saw, and started cutting. The first one took about 1.5 hours (measure 6 times cut once), the second one was under 30 minutes. I still have to figure out what I'm doing with the hood insulation, but I'll put some sort of high temp edging on it to keep it from getting water soaked.

I installed the DS first, then waited a day and installed the passengers side. IMO and measures, the PS is the key, but the vent temps equalized during measures today. At 81 degrees ambient, A/C on, Aux fan running, parked and at idle, I got peak temps from both vents (identical max temps) of 153F (+72F over ambient!!).

The supercharger has a noticeable reduction in tip in throttle response, and reastarts result in a much smoother idle immediately. I'll data log some high speed runs when I can, but this appears to be a good modification to the 80. Attached are the install pics

Scott Justusson
QSHIPQ Performance Tuning
Chicago IL
FZJ 80 Supercharged and vented hood

 

[SUMOTOY]

More Hood Vent Pics

Final product.

Scott Justusson
FZJ80 Supercharged and vented

 

[Cattledog]

Nice cutting. So what are the temps inside the engine compartment DS and PS? What is the total reduction in temp after cutting the hood.

 

[Moby]

Could elaborate on the yarn technique for identifying low pressure spots? What does the yarn look like in a low pressure area as opposed to a high pressure area?

Excellent set of write ups, I really appreciate the effort to document your work on this!

 

[re_guderian]

Do your vents have any kind of drip tray? Jusk askin', cause it rains like 5-6 times a year here...

 

[SUMOTOY]

Could elaborate on the yarn technique for identifying low pressure spots? What does the yarn look like in a low pressure area as opposed to a high pressure area?

Excellent set of write ups, I really appreciate the effort to document your work on this!

I used the same technique described here, and have done so for years
http://www.oman4x4.com/hoodvents.htm

And I'd bet the same hood vents he used would work pretty well too
http://www.oman4x4.com/hoodventinstall.htm

HTH

Scott Justusson

 

[alia176]

Scott,

Nice job! Are those LR vents by any chance? If not, they look very similar! What about a drip tray and a pic from underneath?

Thanks.

Ali

 

[SUMOTOY]

Nice cutting. So what are the temps inside the engine compartment DS and PS? What is the total reduction in temp after cutting the hood.

CD:
Haven't taken the 'after' temps yet. The before temps were 200F at the airbox, and 175F peak on both sides of the motor at the firewall. 95F ambient, aux fan, A/C running. I'll try to get up some underhood data today, but were forcasted for upper 70's weather, probably not ideal for this.

I will note, IME, the temps on both sides of the motor were measured the same, and the release temps I measured at the vents were also the same.

SJ

 

[SUMOTOY]

Do your vents have any kind of drip tray? Jusk askin', cause it rains like 5-6 times a year here...

I put the vents as far back as I could on the hood, no drip trays yet. Below The PS is part of the air can. Below the DS are the ABS line/box. I really see no use for drip trays as installed, maybe some strategically placed rubber sheeting, btdt on other installs. Part of all my hood vent application testing, is to use a garden hose and a car wash "operations check".

SJ

 

[SUMOTOY]

Scott,

Nice job! Are those LR vents by any chance? If not, they look very similar! What about a drip tray and a pic from underneath?

Thanks.

Ali

Thanks Ali... Could be LR vents, not sure. I accumulate a wide assorment of vents since I do this operation quite often in my shop.

Again, no drip tray, I have mild concerns on the DS regarding the coil, but it can't rain directly on it, so I doubt I'll have to install any. Assuming it passes the water tests today.

I'm trying to figure out how to seal up the hood insulation hole. I tried duct tape, and it didn't work.

SJ

 

[re_guderian]

I'm trying to figure out how to seal up the hood insulation hole. I tried duct tape, and it didn't work.

SJ

Exhaust repair tape?

 

[SUMOTOY]

Here is a pic from underneath the hood. I see no reason to put a drip tray on the PS as it sits over the airbox. On the DS it's over the ABS lines, which I'll probably just spray with undercoating to keep corrosion at bay.

Rob G thanks for the exhaust tape idea, I'll probably try that with some sealant, since sticking to that insulation is the tough part.


Scott Justusson

 

[Walking Eagle]

Or you could cut a piece of sheetmetal to use as a big, vent shaped washer, and just sandwich the insulation between it and the hood.

 

[SUMOTOY]

Or you could cut a piece of sheetmetal to use as a big, vent shaped washer, and just sandwich the insulation between it and the hood.

Good suggestion, and if the exhaust tape doesn't work, most likely my plan B.

Thanks

SJ

 

[slowpoke]

If you have a couple more of those vents laying around, I'd like to buy a pair from you.



(They do look like Land Rover Defender vents)

 

[citadel]

SUMTOY,

what is the problem with cutting into the hood bracing? What issues will this cause?

 

[LandCruiserPhil]

SUMTOY,

what is the problem with cutting into the hood bracing? What issues will this cause?

What are those vents off of?

SJ - Photoman also cut the braces on his 80 hood IIRC

 

[citadel]

z34

 

[airlaird]

You know, LX-Extreme caught a lot s*** from the list for having his turbo vent in the EXACT SAME place Sumotoy put his PS vent. LX-Extreme.... you were right all along. Nice install Sumo!!
airlaird

 

[SUMOTOY]

SUMTOY,

what is the problem with cutting into the hood bracing? What issues will this cause?

One word: Safety

In my shop, I do it on race cars and actually cut out the bracing for the additional weight savings. For street cars it compromises the front end crash engineering characteristics. Hoods are designed to fold up, not guillatine the occupants of the vehicle. My concern with cutting braces is in a front end impact, the hood will most likely sever at the cut brace and potentially do bad things afterwords. More specifically, it just won't do what it was designed to do, whatever that means...

Make another visit to IDougs writeup of his brothers front end collision. I believe that cutting braces in that truck would have yielded a quite different front end picture, and possibly a more tragic chilling story.

Z34 vents are some of the best production vents to be had, and color matched, they look awesome on just about any vehicle. I use them whenever I can. The hood bracing on the 80 is extensive, and dictates a lot of modification to add z34 vents to the outside of the hood bump. You will cut a lot of bracing to make that z34 vent work in the 80. So much so, I'd wonder if the hood could support itself without adding bracing.

Citidel, I just accepted the compromise that another set of vents would do the job, and could be installed in an hour without even removing the hood insulation. I'll find another hood home for the Z34's, I always do.

Cheers

Scott Justusson