Want cooler engine bay without changing hood
 

Everybody wants a cooler temp engine bay, but some of us dont like changing the factory hood, it's already light and its FACTORY! I like most of my parts factory especially the body of the rx7. I've been trying to find a solution to keep my engine cooler but i really dont want the aftermarket hoods and hood scoops, it ruins the smooth flow of the FD, well I finally found the best thing to do if you also like the factory hood, on top off the hood (firewall side) there is a weatherstrip that seals the hood around the cowl area (top of firewall) simply remove it, but becareful and dont just yank it out if you dont want to damage the rubber weatherstrip just in case you want to keep it,there is plastic fasteners that holds it so pry that off first. Now... you probably wondering and know that it's there for a reason, true, but it's worth it and it really doesn't matter because water will most likely enter the cowl hole first before entering inside the engine bay, besides aftemarket hoods are worst at this because of the big opening that could damage your electrical like your alternator, it's just more worries. After you remove it, you will only have about little bit less than an inch of opening across the whole hood, doesn't look much? trust me it's actually alot of ventilation if you do your math, cosidering it runs across the hood, also when the car is moving it creates a high pressure area on the base of the windshield therefore low pressure inside the engine bay, what will happen is outside air will actually pull out and create vaccum out whatever is in the low pressure area therefore removing heat from under the hood, its called the scavenging affect, pretty much the same theory on exhaust headers. I wouldnt even worry about the rain especially when the car is moving, only maybe when your washing your car.. just dont point the hose directly behind the hood, again aftermarket hoods are worst at this. Think about it there is nothing that vents the FD engine bay on a stock hood, under the car maybe, but heat rises, this will help it alot and best of all it's free and takes less than a minute to do.

I like the Idea. I have been pondering the same problem and I was thinking of geting a couple up machined blocks to put under the hinges. This would have raised the edges of the hood of course and made it look strange at best. I never take out the seven in the rain so washing the car is the only way water is going in there. I will have to take a look at the car when I get home to see if I want to go that route.

Terry7

This is flawed thinking. The windshield does cause a high pressure zone at its base at speed. By removing the weatherstripping, you're actually pressurizing the engine compartment causing less airflow through the radiator and intercooler and higher engine and intake temps. This has already been tested. There may be some small benefit to removing the weatherstripping if you're not moving. Not worth it in my book; mine is staying on.

Edited: I see Mahjik beat me to it. :-)

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It doesn't work. I've actually tried the test where you put a couple strings of yarn and at speeds they get sucked into the engine bay. This is where the idea of "cowl induction" came from and why alot of the older muscle cars sucked in air this way. While stopped the air might escape, but another downside to this is I noticed on hot humid days it fogs up the outside of the windsheild.

I agree, that solution next to the windshield does not work. I also used "cowl induction" on my very fast and auto-X champ 83 Mustang with great success. At low speeds you can expell air from the engine compartment but, at higher speeds the high pressure area if front of the windshield actually will press air into that opening.

A much better solution is to cut out the plastic fender liner openings that are visible from the inside of the engine compartment. Way back in 1995 when I did a lot of testing on my first FD, I had found that cutting both of those wheel well areas out and replacing the plastic with an open wire screen, actually reduced my 60 - 160 MPH acceleration times a full 1.5 seconds. That is a HUGE gain in anyones book. It was tested 4 times and results were consistent.

Thus, my conlusion is that removing those liners drop pressure build up inside of your engine compartment which, also should allows for a much better exchange of air as it is allowed to flow thorugh instead of being trapped underhood.

BTW - I just did that very mod on my 2nd FD a few weeks ago.

If you want your engine bay to be cooler after shutdown, install a fan controller. With a fan controller, you can turn on the fans a few minutes before shutdown. This will get your coolant temps down around 180 when you turn the car off. This is much better than shutting it down at 210 ............ or higher :).

This is another example of if enough people do it, it must be true. Not fact based, just copied over & over.

Unless you plan on occupying the engine compartment, what make you think it's too hot?

Is it because you measure it by feel when the car is not in motion?

Have you seen documented evidence that components are failing due to "excessive" heat?

The only thing I have heard is that the engine wire harness gets brittle over time, but it's routed 1/2" away from the block. Unless you direct a blast of airflow directly over the block, the wire harness will still get heat soaked.

I understand the need to tinker. Free thinking is good, but your just rehashing a thread that has been beat to death.



Hey, you might want to drill a row of 4" holes in your rear bumper to release all that trapped air that is slowing you down. I've heard that works Civic's.

The real puropose of a deep chin spoiler (air dam) and side skirts IS to reduce high pressure build up under the car, so that you do not need to drill those holes in the bumper. I'm not sure how many people actually separate that function of the spoiler or air dam from the "cool racer look" function.

For air flow one might do well to look at successful race car constructions as the better ones have been through wind tunnel testing. Most often you will find some kind of a venting arrangements to release high pressure from under the hood that would have no other place to go than under the car where it would provide lift, instead of the desired donwforce.

Did you find it lowered temps as well? I'd like to see pictures of how this looks (size of the screen, etc). Do you find your engine bay gets more dirty/dusty?

diffusers...won't let the air get trapped in the bumper.

after I installed sideskirts and diffuser on my car, it seemed to accerate quicker.

Anyone care to illustrate these points using MSpaint or something? I'm having a hard time visualizing.

I truly have not noticed much additional dirt accumulation. After all, the air is supposed to be moving out of the compartment instead of IN. I assume that in rainy conditions you would get more wet inside than normally but, I do not drive this car much in the rains. The first FD, however, was a daily driver and I even raced it in the rain with no problems.

It helps to either relocate your battery for a clean air flow path from the radiator or, have on sit on its side (Odessay), like mine. On the pass. side the M2 box tends to be blocking air exit to a point but, altogether, I still think the opening there is beneficial as underhood pressures will find the way around a blocking element to exit.

Edit; To answer your question I never did underhood temperature tests in this car. My goals were primarily driven by high speed performance gains and cooling was never a problem for me.

Also, diffusers are designed not so much to block air from getting under the bumper but, to provide a low pressure area under the back of the car. When you gradually expend a restricted high pressure air flow (as diffusers do) the air pressure will drop to the point where instead of positive pressure it can create negative pressure or vacum.

Formula and other racing cars that use that simple technology by creating diffused air tunnels under their sidepods can develp huge downforces. As an example, when I raced Formula Mazda with front and back wings but no diffusers, my downforce was adjustable probably between 200-400 lbs at high speeds. On the other hand, a Formula Atlantic car with much smaller wings BUT, underpod diffusers had developed 2400 lbs of downforce at 140 MPH. Plenty enough for that car to be driven on a ceiling, upside down and be sucked to that ceiling.

That is why it was impossible for my FM to keep up with a well driven FA in corners.

Hey, simpletons............

Ever heard of Sarcasm????

I put removing the weather seal from your hood (to cool your motor) in the same catagory as the drilled bumper.

Hey

I believe that around these forums we're looking for real solutions, instead of negativity, trolls and sarcasm.

Good try, though...

How long have you been "around here"?

I must have missed the No trolls/negitivity/sarcasm rule. MY BAD

If the post subject had ANY merit I might have been more helpful.

Good read about your racing resume. Almost make me think you know what your talking about............. Almost.

FYI - you have not seen my racing resume. I just deeply suspect that the number of my racing years may very well exceed your whole life time.

BTW - I used to do all my work on all my racing cars, including chassis repairs, mods, engine work and the rest.

As to how long I've been around here? You already know that by looking at my user profile. On the other hand, how long have I been around Mazda rotary tech? I was amongst the very first FD owners to start modifying my FD in early 1994 and raced it with pretty impressive results until I crashed it hard at Sears Point, while swapping fastest lap with a 400+ hp, highly modded Vette driven by an ex-Trans Am pro and backed by his team of mechanics. That was the last time I took a street car onto a race track.

I am sure, from the looks of your post, that your knowledge of general automotive and racing technology is superior to mine. That is great, particularly if you express it in positive ways!

this is very interesting. I am definitely going to try this. I can't believe you gained that much acceleration simply from removing those pieces!
https://www.rx7club.com/attachment.p...hmentid=169194

Who pissed in your cheerios? lol ;) The topic has merit, he (f150rx7) just went about achieving cooler engine bay temps in the wrong way.

On-topic: Someone on this forum did the same mod (cutting the fender liners) and placed fans there to blow hot engine air out. It looked fairly ghetto, but I'm sure it worked just fine. I'll see if I can find the pic...

*edit*

It was "airborne" on this forum that posted the pic in this thread, but unfortunately the pic is gone now.

https://www.rx7club.com/showthread.p...&highlight=fan

Maybe he will show up and comment.

To place it in perspective my 1.5 second gain was off of a time of approximately 25 seconds, (60-160) without pulling out my old records. If I remember correctly that was one of the last mods I did before the crash.

BTW- not that extreme gain when compared to an other test that I ran with both headlights up and down. The air resistance introduced by the raised headlights increased the same 60-160 acceleration times by over 1 second. So, we're taking about roughly the same amount of reduction in drag in both cases.

good info, thanks :).

back when I was making a little less power I timed myself at 40-140 mph in 14 secs. If this mod can decrease that time by even half a second it is worthwhile.

I've always hated the sleek headlight kits, I suppose that is one good reason to run them. I guess no more racing at night for me, lol.

Rich

Rich,

don't you think you could achieve the same affect by getting a vented hood?

Hmmm, so instead, you became a hindrance. How about if you don't have anything of MERIT to add, don't add anything at all :rolleyes:

That's not the same guy who used a pair of vise-grips to roll his front fenders, is it?

I don't doubt you sir...but just for the sake of thoroughness, was everything else left exactly as is? Seeing that air resistance increases exponentially at higher speeds, I think it's very plausible to have a considerable gain by modifying the car in such a way that it decreases the amount of drag (I'm guessing that's what this is doing...by allowing air to flow through).

I'd love to see what temp changes (if any) would be recorded via this mod, and if there would be any noticeable difference if combined w/ a vented hood. Paging Scrub! :stickpoke :D

~Ramy

thanks for the pictures...this is something I'm interested in trying. I do AutoX in the rain, but like to keep a some what clean bay...Battery is in the cabin and I run an open intake, so blocking objects are no issue. Looks like I'll need some some of shield for my intake if things look like they can get too wet.

not if you like the stock hood ;)

I rather get a vented hood. IMO

If I find some time this week to complete this mod, I should have some before and after datalogs. Same conditions to my best ability.

That would rock :D And do you have a stock or vented hood?

stock

Hi Bob,

Right before I had my car painted back in 2004 I put a lot of thought into whether i wanted a vented hood, what front bumper i wanted, should i change the rear wing, etc.

I came to the conclusion that I really like the stock look (with 99 spec front bumper). I wanted something classy and flowing, basically an FD where I can pull into a Ferrari meet and not feel out of place. The scoot hood, whale tail wing, etc look definitely isnt for me. Plus, having to deal with rainwater inside the engine bay seems like a pain in the ass :).

Rich

The test, every single time I made a modification, was performed on a 2.1 mile flat section of the freeway with 4 runs each time and averaging the results. 2 runs in each direction to account for any wind differences.

If you wonder, at the time, that section of freeway was fairly abandoned at daybreak, when I did those runs. The only variables were the air temperatures but, I used to record them as well, and since most of my tests were done during one CA winter, those temps were probably easily within 10 F degree.

As I look at today's far higher degree of knowledge and modifications, the results of my testing seem to very nicely correlate with posted dyno results. At that time those few of us who were doing these things were kind of stumbing in the dark, taking chances with our mods... still made some incredible changes...

Your right...I'm not a fan either of gaudy hoods and still love the stock/99 spec look.

I was thinking for of the FEED hood since it doesn't change the look much.

You probably will not notice much differences at AutoX speeds which are usually way below 100 mph. On my timing sheet the difference in acceleration times really showed up over 140 MPH where the exponentially increasing air drag and resistance must be overcome by either exponentially increasing horsepower or reducing drag.

That's a good idea for a number of reasons. So dirt, mud and debris wasn't an issue with the screen in place? I'd think water might be a threat to the fuse blocks etc. coming from underneath.

No, I never personally experienced any problem with dirt or water. Regading mud, that could be ugly but, you know how ugly it is when you run off a racetrack into the mud and pack it into every possible opening in your chassis and engine compartment. In such case the screen would be the smallest of your mud problem source. I remember spending long hours scraping, hosing and cleaning mud from my racecars following those off road incursions. So, I suggest stay away from mud any time, any car.

As to water problems. It may be a good idea to either move the fuse block or wrap it. Having said that, I did not worry about it as shorts in electrical circuits tend to happen when high voltage arcs across contaminated water. Clear water has very high resistance to electrical current flows. (for instance, in the Bay Area, utilities use Hetch Hetchy tap water to wash their dirty insulators on energized lines up to 500,000 Volts). The low voltage levels (12 volts) represent very little dangers for arc to develop. There is simply very little PUSH behind the electrons to start moving across any resistance. It is the level of voltage that initiates an electrical arc, followed by the appropriate amount of current (that does the damage), according to Ohm's law.

And which reasons are those? :)

So did you ditch the whole fender lining and use the mesh or just cut out part of the lining?

Just cut out the lining inside of the openings and slipped and riveted the wire screen between the steel fender and the rest of the plastic lining.

doesn't this affect air flow for the wheel well?

I am not sure what your asking here as far as wheel well aiflow being effected? Certainly you will be expelling a certain amount of extra air through the wheel wells but, what is it that worries you about it?

Let's put it this way; I have not found any handling or braking problems as the result.

When I raced the car I had the large brake disks with Wildwood calipers and still ducted cold air to my calipers so, never had any brake problems, if that is what you suggest. I certainly would not expect any problems for cars that are not raced.

Hope I answered your question.

why is the engine bay low pressure...it has air being forced into it by the front air damn and that air is much hotter than the surrounding ambeint air...in what way would this be low pressure? i dont understand...it doesnt make sense...what teh fuck?

This is what the forum is about alot of info that can be shared and discussed ,correct me if im wrong, on a hot day i crack one window open about an inch you can tell air inside the cabin gets vacuumed out(especially for smokers). I open another window and air doesn't get sucked out anymore, instead it circulates around the cabin and cause a turbulance, I understand what you guys are saying but would you rather drive on a hot day with only one window open or feel the temp. actually go down with another window open. If you drive a truck with a window in the back glass, you crack the drivers window only does it get really windy? how bout opening the back glass... then you feel circulation of air ,OK if air doesnt get sucked out from top of the hood and actually reversed than it's very believeable and i now learned it from you guys but it does circulate (vent) under the hood. Now for the radiator actually not flowing correctly because air is trapped due to removing the weatherstrip then what affect does the opening of under the engine bay do when the wetherstrip is on. Theres also been a thread about the solenoid black box from the 96 and up FD's not being able to work on US spec 93-95 FD's, alot of people tried and failed and said it's either not worth it or wouldn't work, I agree that it's alot of work but what is this after tinkering with our cars already. Well I happen to get one of these black boxes anyway and it's currently working on my car right now with the correct boost pattern all you need is a wiring and vaccum diagram and carefully chase each one. I never forced anybody to perform this mod to begin with it's just ideas that might or might not work , everything begins with an idea it's up to you to follow. I will perform a test on coolant temps. with and without the weatherstrip numerously and try to get consistent results. If it really raises coolant temp. than of course I will drop this idea my self, but i do know one thing for sure it will help it when the car is not moving.

Tried to find a diagram showing the high pressure that builds at the bottom of the windscreen. Could only find this one, representing lift.

I do not think that the engine bay is LOW pressure at all. What our testing seem to consistently indicate is that at high driving speeds the pressure build-up in front of the windshield exceeds the underhood pressures, thus is the reverse air flow into the engine compartment from the base of the windshield.

I did the same test as othes in this thread where I taped little piece of yarns onto the hood opening below the windshield. It was not on my FD but on a 83 Mustang and I was looking for not air exit but, cowl induction. Still, the test was consistent with the findings of others. At low city speeds the yarns were being blown OUT from the engine compartment but, when a certain speed was exceeded (forgot the exact number but, probably around normal freeway speeds) the yard were solidly being pushed back under the hood opening beacuse of the pressure built up at the base of the windshield

So, don't think of this as low pressure under the hood. Rather, high pressure against higher pressure.

f150rx7:

You are wrong. It has been repeatedly proven. Brian Davies (Wargasm) even tested this with underhood thermosensors and discovered that, if anything, temps went up a degree or two with the weatherstripping removed. Unfortunately, his website is down at the moment.

I also have cut out the fender liners. I installed a wire mesh and a layer of charcoal screen. Also, I cut out aluminum pieces that I can slip in if I'm going out in the rain.

I did it to try and help out my hot air intake but I didn't notice a significant temp difference. But its been like that for a few years and things under the hood haven't gotten extra dirty.

I'm more interested in dumping engine bay heat, so if air is exiting the bay, heat must be going with it, no? I route fresh air up under my intake, and if it has a low resistance exit path, the more air will flow...acceleration would be an added bonus ;)

further :offtopic:
I pulled the liners last night, and it looks like one could improve air flow through the oil coolers as well with a screen section behind each cooler. I know the 300ZX TT guys do something similar with their IC's (same location as FD oil coolers)

homemade louvers on a 300Z board
http://twinturbo.net/net/viewmsg.asp...&msg_id=868066

Are you referring to the fender liners dubulup? If so thats kind of funny. I thought that the fender liners combined with the vent behind each wheel were meant to *help* flow through the oil coolers.

^LOL, I think you are right.

nm, found it


https://www.rx7club.com/attachment.p...chmentid=94245

my problem with this is the windshield washer reservoir is right behind it. If there were an opening in the liner, wouldn't that be a less resistive path and generate more flow.

I, for one don't like to hack Mazda's engineering with the car...but hell, at this point there's no turning back, haha! You know, the liner is two pieces and they are stapeled together :rolleyes:

look at the brake duct in that picture as well :hahaha:

I noticed that's an R1 diagram. I have a touring and didn't see any ducting at all while I was cutting out the fender well. I guess the poor 1 oil cooler cars have to soldier on with no airflow.