I'm not thinking of the holes and louvers that we see on FC/FD builds. I'm thinking of putting the hood latch on a cut metal plate. One could adjust the latch up or down by an inch or so manual with wing nuts or something. Im fleshing this out.

If the hood was cracked open slightly would the under hood air be sucked out? Or is there too much exterior pressure that would negate this?

Hope I'm making sense.

 

This mod was a trend among drift cars in the 2000s.
I think it's too close to the windshield to be a vent and pressure will force air inside, but I'm no aerodynamicist.

 

This is what I am afraid of and why I'm here asking. Perhaps I could tape some ribbon on the car and see if the ribbons get sucked into the engine bay or are blown out.

 

Richard, I do this every Summer when the temps get into the 90's (since 2018). You can unbolt the hood latch and just re-mount it an inch higher using 2 of the 4 bolts. It still locks/latches securely and hasn't flown off up to 120mph. No significant wiggle or wobble. Takes 10 minutes with a 10mm wrench and is easily reversible if you don't like it.

 

This drawing would imply that it is not likely that air will be sucked out. Your idea of taping yarn to the hood with it propped open makes sense though to try it.

Carl

 

@Carl that's a great diagram of the pos & neg pressures over a stock-bodied car with the hood shut. It shows why automakers put the cowl vents at the base of the windshield to force air through the cabin. And shows why hood vents right after the radiator work so well. But it doesn't necessarily show what the high-pressure air under the hood would do if you popped the hood.

Obviously there is air being forced into the engine bay by the fan at low speed, and much more as the car speeds up. This air blows out under the car providing some small degree of lift as you drive. I think with the hood open an inch, that the hot air would rather leave at the highest point at the rear of the engine bay, rather than go down and under with increased flow from the cowl pressure.. BUT this is just an assumption. As mentioned, I have driven at 120 down the TurnPike with the hood propped like this and the car showed no negative handling, and at low speeds I can see the hot air waves exiting the hood.

I think Richard's idea of air ribbons is the way to figure this out. If ribbons taped to the hood and cowl blow up, then it works. But if they suck in, then I'll know I've been foolish. Kind of like the pickup truck tailgate thing - Everybody thinks that dropping your tailgate (or using a net) increases your fuel economy. But wind tunnel testing shows the complete opposite (leave your tailgate closed for best aerodynamics).

I was just looking for a simple and reversible way to vent all that power-robbing, wire frying, vac-line cracking, oil-line drying, paint peeling 250* air that our cars are famous for. But I am not an engineer or racer... just a hobbyist.

Now, who's got some ribbon and scotch tape?

 

I installed a vent in my hood a couple of years ago. I finally did the yarn and tape test a few months ago and it showed that the venting was working. Unfortunately the video camera of the test was incorrectly located so no video just my eyes and memory.

I agree that trying both lifting the hood and testing with yarn and doing the same for vents in the corners of the hood (check mustanghammer's venting location) makes sense. Simple, quick and definitive I think.

Carl

 

If the goal is to lower underhood temps, air forcing its way in may not be a bad thing.
Try Maxwedge's mod and use one of those remote oven thermometers to check engine bay temperatures before and after.

If more air flow through the radiator is the goal get a digital coolant gauge to check.

 

Looking back at racing, didn't see hood venting just front opening. But I don'

t think they ran turbos much back then...

 

This may be a moot point but I remember a time when my hood did not latch and I drove away before I noticed it, so just for ***** and giggles I kept going and after I reached a certain speed the hood raised itself a couple of inches and hovered there. Not sure what that means.

 

plus its festive!

 

That's normal.......the pressure will make it to open and hover a little but it won't open completely because or the wind pressure against it .....

 

Correct, but does this just go to show how strong the push of air is trying to escape from under the hood? With the hood closed like the pic Carl attached, the air pressure pushes down on the hood and cowl. but given the chance, it seems from our shared experiences that all that hot air wants to blast right out. This is what Richard was wondering about in the first post.

 

yeah i did that once at highway speeds. It would raise several inches, more like a foot before it equalised and stayed there, regardless of additional speed.

 

Now I’m thinking of an actuator controlling raising the hood . Maybe based on temp and boost.

Maybe a button reading “pursuit mode”

 

90s is a refreshing day where I’m at. We hit 115 once, peaks to 112 not to uncommon. I’m really not messing around to thermal management. At least within my budget.

 

Not exactly the prettiest option, but with the addition of a Gurney Flap at the leading edge, this is how a V-Mount is supposed to be ducted for peak efficiency while simultaneously reducing drag. Great post, Carl.

Richard is trying to do "Cowl Induction" type aerodynamics which can either 1) create turbulators that suck down towards the rear of the engine or 2) extract underhood pressure to the vent region towards the windshield. I'll let him test with yarn to see what happens, but I don't think it's the effect he's after.

What will likely happen with the rear hood riser strategy is an increase in coolant temperature due to stagnation of the engine bay air. Air will likely come in at the top, not exit, and it's already being forced in through the heat exchangers at the front of the vehicle, now with the only place to go is down and out... Heat rises.

 

Then there's the Le Mans RX-7, but they also stuck the oil cooler up in a T-configuration.

 

Yep. That's the way it should be if you're not using that space for an intercooler.

 

what about the bottom pan under the engine? I left mine off thinking some air could escape there.

anyone know if thats a good idea or if I should put it back on?

 

You would be creating a huge issue with airflow in the engine bay and increasing drag substantially with the underpanel taken off.

 

One of the things I've been thinking about was getting a headlight cover with the NACA duct in it and building some kind of air path down across the header and out under the car. The theory is to try and push as much heat from the exhaust out of the engine bay as possible. Anybody thought of or tried that kind of thing yet?

 

The under panel is what keeps air from bypassing around the radiator, so I think it is pretty widely accepted that removing it is a bad idea if you are trying to keep coolant (and subsequently engine compartment) temperatures down.

 

Well, here is some practical experience to offset the theoretical thoughts on a few things;

I live in the desert. It gets hot. It's not unusual for me to drive my 84SE (FMOC, A/C, et al) in 115-118F temps with the A/C on full blast adding heat from the condenser to the air going into the radiator, and it's never run hot. I don't have hood vents, but on hot days, when I get home, I immediately open the hood and leave it open for an hour or so to let all the heat out and not soak in. This has made a noticeable difference on every car I've driven. Harnesses last longer, electronics last longer, and everything just works better when you let the heat out when it sits. When you're driving, you have a constant flow of high-speed air carrying away the heat, but when you stop, it just cooks in place. I now run an Aluminum KOYORAD radiator and have never seen lower engine temps - it consistently runs at 1/4 gauge and never higher. I've also bypassed my heater core - because you don't want anything fighting your A/C when it's that hot outside. I also have the Mariah Mode4 airdam which directs TONS of air in the front, into the radiator and oil cooler, and I don't run the undertray. Air has mass, and that mass wants to keep going straight instead of getting pushed down the face of the condensor or radiator, plus there's a fan on the other side sucking fresh air through it. Notice on your shroud that there's a rubber flap door to let more air OUT of the shroud and fan at speed - because otherwise, the airflow inside the shroud would be slower than forced air in the front.

All of this to say; I don't think there's much you really NEED to do to keep your engine cool. Change your oil, add quality oil when needed. Change your coolant, and fill with 50/50 mix with antifreeze, maybe add some water wetter (* I don't), and go from there.

Hood vents are only cool until its raining and something important gets wet, leaving you stranded somewhere.

 

I agree with LongDuck. If the engine and cooling systems are maintained properly you should not have problems with sufficient cooling. I raced my completely stock (except for minor suspension upgrades) 1984 RX7 (Spec7 class) in Phoenix for 5 or 6 years and never had an overheating problem. That included days at over 100 degF.

I added hood vents to my race car (the only RX7 I own) when I was having some other cooling problems (ended up being related to a replacement radiator and relocated oil cooler). Experience has not really convinced me that the vents really make much difference when all is said and done, but running essentially WOT for 7 hours at a time in temps sometimes well over 100degF, I figure it is cheap insurance. I would not install them on a street car, unless you really like the look (and there is nothing wrong with that).

Yes air has mass. It's mass is not sufficient to prevent a significant amount of it from flowing around a cooler (water radiator or oil cooler) if there is not ducting "encouraging it" to go through the core. I don't recommend removing the undertray. .

For what it is worth, the Mariah Mode 4 airdam does a good job of directing air to the radiator, and not too bad a job even with the undertray removed. I had one until a couple of months ago, when a co-driver went off course and ripped the airdam off. My track testing however, did not show much difference in cooling with or without the airdam at Willow Springs with 102-108 degF ambient temps.

The Koyo aluminum radiator, assuming it is the full height for 84-85, has 65% (i.e. 1.65 times) more heat transfer surface than the stock tall radiator. That can definitely make up for some amount of reduced air flow through the radiator core. I have one of these too and it definitely keeps the water cool.

Richard, I assume your car is a 1980. If so, have you checked whether or not your short radiator has 2 or 3 rows of tubes. I believe that the automatic had the 3-row stock? In any case, 3 rows vs 2 rows is 50% more cooling surface.

Carl