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Recently went on a 800km trip over easter. I noticed that the cab floor and engine bay was getting quite warm. Engine temp stays OK but the cab gets a bit uncomfortable. It's the first real run since I fitted the turbo and intercooler. I was expecting a little more heat in the engine bay because of it, but I need to do something about it before the next trip.
I am trying to decide on a bonnet scoop to go on the patrol. I am thinking that the draft that the scoop will generate will help to cool the engine bay.
Question is, do I face the scoop forward to create a positive pressure in the engine bay and force the hot air under the car keeping in mind that this will compete with the radiator fan and so may reduce the amount of air moving through the radiator? Or do I reverse the scoop to create a negative pressure in the engine bay and suck the hot air out the top of the engine bay and over the windscreen, increasing the air flow through the radiator but eliminating the "bubble effect" in the engine bay during water crossings and effectively allowing the engine bay to flood because of the unsealed bonnet?
Please tell me your thoughts. Input from people who have done either of these setups would be helpful.
Thanks.
1997 GQ 4.2 Diesel Wagon
Aftermarket turbo & intercooler, 3" Exhaust,
4" susp Lift, 3" body lift, 35" Muddies
Spotties that start bushfires at 100m
Pleasure in life : Towing Toyotas
My vote is for backwards, ultimately you need to maximise both intake and outlet of air, and if you have the scoop facing forward as well as the normal rad intake, you are all "in" and no "out".... unless you really feel the rear/underside of the engine bay is letting heaps of air flow out.
You've got a diesel there, you don't need no air pocket!
When you cut your hole, maybe you can cut it in such a way that you can re-do the scoop later if you change your mind.
Have you got air con? I dunno if it would be good having a scoop facing backwards if the windows were open.
(have not done this on a fourby but on V12 jags we used to be able to reduce engine bay temps an amazing amount by spacing the bonnet opening up a tiny bit. Not even a lot. This was a front-hinged bonnet ie opening near the windscreen.)
before you do anything, space the rear of the bonnet up about half an inch.
that way you will know if removing teh air from the enginebay will help you much.
My bet is that it will reduce temps dramatically.
BUT.
if you every blow something in your enginebay, its going to be all over your windscreen. Even just a heater hose will mean you have bugger all visibility.
cheers,
Jes
ATTACH BROKEN TOYOTA HERE--->
DUCATI <-----Worlds best warning label
Air won't come out of a rear facing scoop.
Have a look at a Torana bonnet scoop. It is facing backwards for a reason.
There is a high pressure area at the back of the scoop that forces air into the car.
Yeah if you want air to come out of the engine bay then the vent will need to be in the front half (ish) of the bonnet. I've seen a few that work (Patrols) where there are vents either side at the fron to suck ait out and a vent in the centre in the middle to get air in. This means the air through the radiator is sucked (to a point) out of the front vents and then new colder air is sucked in the centre vents and that goes out under the truck.
93 Nissan Pathfinder / Terrano Turboed VH45, GQ Trans and T-case, coil overs, hydraulic winch and fair bit of other stuff. (Currently a pile of parts in the workshop)
The same happen to me over easter.....I have a v8 in my truck and I found the heat coming from the gear stick cover....It had come away under the carpet and when drivnig It pushed the the heat out into the cab...I dont know what to at the moment..(not really thought about it) Maybe look at that.....
There was a bloke on Patrol forum that tape bits of string/wool in 4inch lengths all over his bonnet. Went for a drive and keep an eye on which ones move and which ones dont.
still lookin for the thread, but he was doing it for the bonnet scoop gig too.
I have a WRX STI scoop, it was fitted for clearance more than anything as my top mount WA IC sticks out of the bonnet by 1".
I have done alot of big km's ie Darwin to Vic 3800km's and back via QLD 4800km's durring some of the hottest days this summer 47 deg C.
Between Alice springs and Cober Pedy a bird flu up and went straight through my scoop at 110km/hr, at the next stop I did the usual checks under bonnet and could not find a trace of the bird so I guess it's a bird catcher not bug catcher, so obviously getting enough flow through engine bay, cabin temp and engine temps all good. Also helps to open up front grill with 4" grinder on excess plastic and replace with perferated mesh. My advice is to check the laws in your state before you go to big a scoop though. I also made stainless heat shields for my manifold, turbo, and clutch slave cylinder. You may also be able to get some self adhesive heat shielding from clark rubber to put on your fire wall. Happy wheeling.
Lots to think about and this is looking to be a bit more difficult than just slapping on a scoop.
I have a few days off from tomorrow so I will try blue-tacking some wool to the bonnet and have a look at the air flows first.
If I am reading correctly, am I to expect the top front of the bonnet and the top of the windscreen to be high pressure, while the bottom of the windscreen to be low presuure?
If the area inside the engine bay just in front of the fire wall is a high pressure zone and the area on top of the bonnet directly above it is a low pressure zone, would this be a likley place to start looking at an extraction type scoop?
Had another thought meanwhile. If I fit a thermofan to the underside of the bonnet directly below the scoop to force the air from or into the engine bay, it won't matter so much about placment. My body lift gives me enough room to do it. The fans are fairly cheap but am I just getting carried away or what?
Dave
1997 GQ 4.2 Diesel Wagon
Aftermarket turbo & intercooler, 3" Exhaust,
4" susp Lift, 3" body lift, 35" Muddies
Spotties that start bushfires at 100m
Pleasure in life : Towing Toyotas
MuddyTroll wrote:Had another thought meanwhile. If I fit a thermofan to the underside of the bonnet directly below the scoop to force the air from or into the engine bay, it won't matter so much about placment. My body lift gives me enough room to do it. The fans are fairly cheap but am I just getting carried away or what?
This won't work at all. No offence. But it won't do squat, and even if it has some microscopic effect at low speeds it will do nothing once you're over 20-30 kmh, when wind will completely overwhelm it.
I wonder if a scoop under the front bumper might actually help you, too.
MuddyTroll wrote:Thankyou all very much for the input.
Lots to think about and this is looking to be a bit more difficult than just slapping on a scoop.
I have a few days off from tomorrow so I will try blue-tacking some wool to the bonnet and have a look at the air flows first.
If I am reading correctly, am I to expect the top front of the bonnet and the top of the windscreen to be high pressure, while the bottom of the windscreen to be low presuure?
If the area inside the engine bay just in front of the fire wall is a high pressure zone and the area on top of the bonnet directly above it is a low pressure zone, would this be a likley place to start looking at an extraction type scoop?
Had another thought meanwhile. If I fit a thermofan to the underside of the bonnet directly below the scoop to force the air from or into the engine bay, it won't matter so much about placment. My body lift gives me enough room to do it. The fans are fairly cheap but am I just getting carried away or what?
Dave
The base of the windscreen is about the highest pressure there is. That is why you get clean air in the vents that are there for interior cooling etc.
The front of the bonnet 'should' be a low pressure zone.
String on your bonnet is going to show air flow not air pressure. For pressure you need to use a pressure gauge. A piece of clear tube with water in it will do. Fill the tube with water and have the ends in the area you want to see the difference but also at the same level. If you then go for a drive as the pressure changes between the 2 areas the water will flow to the low pressure area.
If you do this with a really long piece of tube then you can have the water level inside the car and the ends of the tube don't need to be level. You will be able to tell pressure difference bythe direction the water flows.
93 Nissan Pathfinder / Terrano Turboed VH45, GQ Trans and T-case, coil overs, hydraulic winch and fair bit of other stuff. (Currently a pile of parts in the workshop)
bogged wrote:There was a bloke on Patrol forum that tape bits of string/wool in 4inch lengths all over his bonnet. Went for a drive and keep an eye on which ones move and which ones dont.
still lookin for the thread, but he was doing it for the bonnet scoop gig too.
air flow isn't as important as pressure.
if you want air out you need to find the spot on the bonnet with the biggest pressure change from the underside to the top side with the underside being higher.
then do the wool test to face it the right way.
a simple water manometer can be made and mounted in the car with long test line to run to the bonnet.
bogged wrote:There was a bloke on Patrol forum that tape bits of string/wool in 4inch lengths all over his bonnet. Went for a drive and keep an eye on which ones move and which ones dont.
still lookin for the thread, but he was doing it for the bonnet scoop gig too.
Just to clarify a bit. I have a front mount water 2 air i/cooler, so I am not trying to push air through a top mount.
I just want to solely move the trapped hot air out of the engine bay somehow. The more, the better.
The scoop is taking longer than I hoped but is getting there. After a couple of tests using my boost guage as a manometer, I am now leaning toward the rear facing scoop close to the base of the windscreen.
Will this create enough draft to push the hot air out under the body & will removing the rubber skirts from where the body & chassis meet in the front wheel wells help create a draft.
Cheers
1997 GQ 4.2 Diesel Wagon
Aftermarket turbo & intercooler, 3" Exhaust,
4" susp Lift, 3" body lift, 35" Muddies
Spotties that start bushfires at 100m
Pleasure in life : Towing Toyotas
I also have an old MIG that has detachable side panels with louvres. I'm going to see if I can cut holes in the bonnet the same size as the louvred section of the panels and then mount the panels UNDER the bonnet. This will have the advantage of clamping the sound/heat proofing material to the bonnet and it won't be quite as obvious as having the panels mounted on the outside. Sadly, my welding skills aren't up to flush mounting the panels and welding them in.
Burra Boy. 1x 89 LWB wagon, turbo, frozenboost IC, lots of stuff. 1X 90 leafie ute, AXT turbo, tough as nails and about as comfie...
I would vote for forward facing. PM awil 4x4 he has done some research on this.
Look at all cars built for a long time has ANY of them had to vent a bonnett to get heat out. NO. they spend a lot of time ducting/guiding air through the engine bay and out under the car.
Rear facing scoops are air intake not heat release scoops. Even then if you look at drag cars all scoops face forward to ram charge N/A motors so forcing air into the motor if rear facing scoops were better they would run them in attempt to gain the last tenth
GU 42td wagon for touring
GU ute for the fun stuff
http://www.allterrain4wd.org.au/
hotrod4x4 wrote:alot of cars have had vents rather than scoops to release the heat.
they were normally located near the rear of the bonnets on the sides.
turbo eg. the old Ford Sierra's at Bathurst
I'm sure you will find that the Sierra had them down the front of the on the bonnett not the rear and it also forced air into the engine bay not out. Same as a WRX. they push the air in and down under the car
edit. just googled the Sierra and the vents are about 15cms back from the headlights and right to the side so the is not much heat to vent from there.
GU 42td wagon for touring
GU ute for the fun stuff
http://www.allterrain4wd.org.au/
