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

 

https://www.rx7club.com/3rd-generation-specific-1993-2002-16/removing-seal-b-w-firewall-hood-bad-engine-temp-330649/

 

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!

 

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

 

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!

~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