MazdaManiac: can you just give a summary of the conditions you are referring to?

my position is that this mod is effective where driving is at a speed where the pressure at the base of the windscreen is not higher than that under the hood (or a significant portion of it is like that, e.g. stop-go traffic, cool down laps at track).

As for people discounting the Volvo pressure/streamline picture because it isn't of an RX8, I've seen enough similar pictures to know it would be approximately the same for the volvo, for an Rx8, for a Supra and for a NASCAR.

The pressure at the base of the windscreen is NEVER as high as the pressure at the nose!
Why doesn't anyone get that?

On an airplane wing, which force is a greater contributor of lift:
1) The low pressure area above the wing
2) The high pressure area below the wing

If you do not have at least 40 hours in your log book, consider that a rhetorical question.

Its amazing that the only 4 people in this thread to actually take the time to see which way the air flows found different results... :rolleyes:

who cares because the pressure under the hood is not as great as the pressure in front of the nose - and the pressure difference between the base of the windshield and under the hood near the windshield will determine which way the flow goes :Eyecrazy:

the real answer would be

3) airflow circulation around the wing

If you don't have 3 credit hours from a 300 level advanced Fluid Dynamics class and studied and tested the design of airplane wings - consider youself pwn3d

heres some edjumacation for you

http://en.wikipedia.org/wiki/Lift_(force)

Sure it could work, if the new hood opening is eliminating some under hood action (air flow or pressure) that was limiting the flow through the radiator.

That is why you go with what works. Air flow and turbulence is funny. Look at the years of arguing about truck tailgates and the drag associated with them being up or down (and that would seem to be clear cut!).

I would be concerned additional lift or drag after this change. But knowing MM, that has been tested and found to be minimal.

He didn't test the airflow before the mod. What makes you think he tested anything afterwards?:lol2:

I was suggesting a more practical test....

Aerodynamics is not a cut and dry science or wind tunnels would not exist.

Show me a link concerning aerodynamics and the internals of engine compartments and we might have more to talk about.

But I get MM's attitude towards this discussion.

I did. I performed a very thorough dynamics testing on my car before and after.
Here are the results:

I run 140MPH before the mod, and 140 MPH after the mod on a wide and open highway stretch. Car feels the same.

Nice, tight and solid.
The only difference, the first time I came out of boost and my temp gauge was blinking red with temps ovet 100C like out of it's mind.
The second time it was 98C and not even a blink.

How's that for a test?

He heh he he he :moon:


With that, I couldn't give a rats ass where that air comes in or comes out. it could be coming out of Bin Ladden's asshole for all I care, as long as the coolant temps stay at bay, and the car doesn't get airborne. :yelrotflm

and in neither case do you have any idea on the status of either of your radiator fans which activate at that exact temperature... great test indeed :Eyecrazy:

you might have found a great way at reducing cooling enough to kick on your fans more often :rolleyes:

Well saves me from paying for other expensive mods.


:banghead:

You are like my wife when she has PMS. Just can't STFU :rollingla

Are you suggesting that the cooling fans would increase airflow over the radiator at 140mph??

Now who's trying to be a rocket scientist and doesn't know what they're talking about. You bought a Turbonator didn't you.:icon_no2:

No I think it was just this:

MEGA-HYPER ELECTRO-TURBO SYSTEM®[/QUOTE]


:rollingla

are you suggesting a 1/4" gap in the hood will?

Actually it is a 1/2"
You are not paying attention :spank:


You betcha it will.
Just for kicks and giggles try to calculate the size of the opening based on the width of the hood. It is freaking big. How much air can be flown through that hole do you think?

Depends on how much lower the pressure under the hood is compared to the cowl.

intersteing thing about this whole discussion-

i read a quote from Jim Mederer recently about how Mazda has shown less and less ability(or has made more styling over substance decisions) over the years between rx-7s and rx-8s to get proper good airflow thru the radiator and that he/they at Racing Beat have found on the 3rd gen and the 8 that a splitter/diverter spoiler thing that created better flow to/thru the radiator/engine bay made a huge difference in cooling efficiency/keeping the temps down.

now to just find it again.

maybe ill just email jim.

If any of you all need me, PM me. This thread is clogging my box with useless notifications, so I'm un-subbing.

That and the average American would bring their car back bitching about dirt and water stains on their engine cover if the hood was vented.

Yup, I read that too.

I've logged hundreds of hours on a cell phone, it doesn't mean I could design the chips inside.

it is, its just complex and expensive ;) I shudder to think at the time and expense to model, mesh and run a CFD simulation on a FULLY modelled car including engine bay. Wind tunnels are just easy for some stuff, and a good way to verify what you've designed.

If OEMs designed cars to have vented hoods from the factory they could probably do a better job packaging components so everything was properly ducted out, rather than like aftermarket hoods that just have holes placed semi-randomly (and getting dirt/water on engine covers)

Yes I'd love to have a Lotus Elise like setup where the airflow out of the radiator was ducted directly up and out through a screen in the hood. No more engine compartment airflow discussions needed.

Talking about discussions: this thread went like HOLY SHIT!!!! LOL
people left and will be "sucking in" the air at high speeds inside their hoods and disrupting the radiator air flow, causing fans to come on more frequently. lots of fun... :lol2:

By the way, loved the idea. +5 for inventing a new angle to the argument. :xyxwave:

LOL - My favourite line from the whole thread .

This thread is like fights I have with my GF...they go on forever and nobody gives in...finally somebody walks out...haha

you'd think that given 4 out of the 4 people in this thread that actually took the 5 minutes to verify which way the air flows and found the air to be "sucking in"... you might consider it to be "real" :rolleyes:


so lets see the possibilities of how this mod works...

a) it doesn't and its a placebo effect... and you owe people $ for new hoods
b) your results are radiator fans on and not your hood
c) by packing MORE air under the hood, it increases flow past the radiators
d) the Renesis shows unheard of ability for a water cooled engine to be air cooled

You were correct MM, I think I'll just unsubscribe also - Some of that hot air just reached me.

I feel sorry for you.

Now I'll unsubscribe from from my own tread.

If you get that information, would be great if you posted it. Especially if it give clues or is direct as to where RB saw the most improvements...

lionzoo do you remember where you saw the quote?

It's in Racing Beat's catalog and tech manual. It says what we're all trying to say. That the engine compartment doesn't evacuate well so there is cooling improvement to be had by increasing the airflow out of the engine compartment.

out of the engine compartment would be a good thing... by everyones observation, thats not happening though with this mod

That's where we disagree...

I honestly don't follow. Setting thin plastic streamers on the hood at the windshield clearly shows at speed that the streamers are sucked into the engine compartment. I don't care what any of the airflow examples or graphs have shown otherwise. I've seen it with my own eyes, as apparently have others.

Have you done this to verify for yourself?

Or have you done this after you performed this mod on your own car and found it changed the airflow?

I have not performed this mod on my car, but I suspect this would cause more air to flow in from the top of the hood and down around the engine and through the underside of the car. And apparently, in this fashion it is helping cooling.

Just because the streamer, or tufts, or whatever, point into the hood at speed (I am taking your word on this) does not mean there is no improvement in the air flow through the engine compartment.

It may mean that some turbulence or other condition was removed under the hood that allows better air flow through the radiator. It would be my guess that the improved air flow is mostly through the normal exits.

We have experience that shows better cooling at idle and at speed. We need to explain that, not deny it.

I for one, have no way of explaining or observing what the airflow under the hood is before or after this change.

So it is all talk until we come up with some way to demonstrate this.

But I am a sucker for bench racing!

I never stated there was "no improvement". I think that based on the findings of those that have performed the modification that it is working - for whatever reason.

Right, I'm just clarifiying from my viewpoint/experience that the normal exits are perhaps not as some suspect. I think some of us have demonstrated how the air flows - at least to the extent of how it flows when in OEM form, by some very basic testing. My only point of contention is that it appears many assume with or without the modification that air is flowing from the engine bay and up and over the windshield/roof. But from my findings, and apparently others, this is not so and it is in fact the opposite.

I also think regardless of which way the air has flowed or is flowing after the modification that this appears to have some tangible benefit from the various accounts. If I had cooling issues, that I don't since I'm NA and don't live in a very hot climate, than I may be tempted to try this mod myself.


And damn, now I'm running in circles on this subject.:banghead: Whatever, if it's working for those that did it and they're happy than that's all the matters. I'm out.

Correct. If you're going to be here for Sevenstock, you might as well visit Racing Beat for another catalog. It's so fun to read through that thing!

I haven't read the Racing Beat catalogue, but I don't see how this quote props up the hood mod - I read it as using a splitter to tap the high pressure at the front and help drive more air through the radiator, but nothing about making the engine bay evacuate air better (or the location of the exit points). Is that right, or is there devil in the details that gets missed in the paraphrasing?

holy crap.

tl;dr

if removing a rubber molding works for the people that have done it. good. dont diss it till you try it.

No one is dissing anything.

From Racing beats Water Cooling Tech tips:

"...Starting in 1993 the capacity of the stock cooling system was designed by Mazda to barely meet the needs of the stock car with no excess capacity for very demanding situations or modifications that increase the heat load on the engine. Based on a number of tests, we believe the primary cause of this problem is aerodynamic. In both the 1993-1995 RX-7 and RX-8, the air path out of the radiator is convoluted and restricted - leading to high water and oil temperatures. We have tried larger radiators, and to date, they have not helped. We have seen some improvement from improved sealing and directing the air into the radiator (using a spoiler lip under the vehicle) to create a lower pressure area under the car, to remove hot air."

The point Racing Beat is making is that the problem with the cooling system is evacuation of air from the engine bay to allow for more airflow through the radiator. They looked at trying to move more air out under the car (which is relatively high pressure). This mod is moving more air out of the engine bay through the rear of hood.

you seem to always be digging up cool bits of info Shaun - great stuff

Thank you for the quote. But as far as the air moving out of the engine bay from the rear of the hood, it does not exit the rear of the hood - in stock form. I will be raising the rear of my hood and re-testing the airflow in the area in the next week to see if this mod changes that. Again, I would like to say I am not arguing the effectivness of this mod to stabilize and control temps. That has been proven by those with gauges. My only contention is the specific airflow, and it is really only due to my own curiosity.

^^That's what I was referring to by "this mod" The one described in this thread. I agree the air doesn't move out from the rear of the hood in stock form because it's sealed up. That's the point of the mod. To open up the rear of the hood and allow air to flow out.

This thread should be a sticky.

there is way too much crap in it for it to be sticky . Hmmm - that doesn't sound right ....

What are talking about this thread is the stickyest of the ickyest!

^Yup.
Having a steeply raked windshield to avoid pressure build up in front is good. The air pressure is high as the air rammed into the front grill of the car. What is really happening is that the air slows down as it approaches the front of the car, and as a result more molecules are packed into a smaller space. Once the air Stagnates at the point in front of the car, it seeks a lower pressure area, such as the sides, top and bottom of the car.

The lower pressure area above the hood of the car creates a small lifting force that acts upon the area of the hood (Sort of like trying to suck the hood off the car). The higher pressure area in front of the windscreen creates a small (or not so small) downforce. This is akin to pressing down on the windshield.

There is a weather seal but that is to keep LARGE volumes of water, leaves etc into the engine bay. It is not sleaded by any means.