It's all about airflow and air pressure differentials.

I'm going to simplify this greatly, and ignore a few other aspects for the sake of clarity of the basics here, so I imagine there will be a few people that want to point out other things too.

Radiators function by transfering heat from the coolant to the air passing through the radiator. The air passing through the radiator isn't just wandering through though. Air always moves from zones of high pressure to zones of low pressure, through any route it possible can. The greater the pressure differential between the two zones, the more airflow will occur. On the track, the car's forward speed builds up a high pressure zone in front of the radiator, and the resulting high pressure there moves the air through the radiator. The engine bay is also getting pressurized however, because that air doesn't just disappear. There are escape routes for the air along the transmission tunnel, or off the trailing edge of the splash pan, etc... where there is lower pressure than in the engine bay, so this pressure in the engine bay doesn't become excessive, and the pressure in front of the radiator is always higher.


However, if you can do anything to increase the difference in pressure between the front of the radiator and the back of the radiator, you will directly increase the airflow through the radiator, and thus it's efficiency. There are two paths you can take to accomplish this, and neither excludes the other. Most race cars do both.

In front of the radiator you can increase the pressure by ensuring that every single bit of air that enters the mouth, has to go through the radiator. Ducting and sealing the radiator to everything around it, sealing off the alternate paths through cracks or gaps, or like behind the oil coolers, etc... Everything you do to ensure the air has to go through the radiator increase the frontal pressure. Even a front splitter helps, because it increases the amount of air that won't go under the car from the front lip, and has a measurable effect on how much air is jammed up in front of the radiator.

I don't know what all you have in front of, or beside the radiator, but if you don't have a sealed tray, or have any missing seals between the radiator and the frame around the radiator, that alone could be really hurting your temperatures on track. High pressure in front of the radiator won't mean much if that pressure can escape in ways that don't aid in cooling.

The other side of the actions you can take is to reduce the pressures behind the radiator. The most common method of doing this is through hood ducting. You can dump pressure under the car a whole lot more easily, but on track, dumping air under the car has other aerodynamic problems, so out the hood is a better option.

But not just anywhere out of the hood. Again, pressure differentials.

At speed, air builds pressure in front of the windshield. But it also has a pressure drop just behind the front bumper.

Here are some images to help visually describe what is happening. Every car is different, and I don't think anyone has published similar images for the RX-8 yet:






And pressure readings for an NC and then NB Miata:



There is always a pressure drop behind the leading edge of the bumper, that shifts back to a pressure increase by the time it gets to the windshield. Where the "ambient" pressure is stabilized shifts based on the physical shape of the car, the angles, etc...

So back to pressure differentials, if you want to get as much air out of the engine bay as possible to drop the pressure there, you want to use the lowest pressure area of the hood, to encourage as much extraction as possible. The angles of the louvers, leading edge lips, and the like are all things to try to encourage a sharp drop of pressure right above the vents, to improve the amount of air extracted. Location matters far far more however. A rear vent can actually cause the engine bay to increase in pressure, reducing the radiator efficiency. You want them as far forward as possible, while still being behind the radiator outlet, which is fairly easy with our angled radiator, other cars need to pay much more attention to this.

So the first observation I have about your vents is that they are too far back. They aren't in a point to actively hurt you, but farther forward would have a much improved result, because you would have a much greater low pressure zone to leverage. Where they are, you probably have almost half of the total area of them in the neutral pressure range, perhaps even slowly going to positive pressure.

The other observation is really mostly a guess without more pictures of the engine bay. Do you have a lot of stuff between the radiator outlet and the louvers? Battery box, battery, air box tray, and fans/shrouding all come to mind in a stock RX-8 as directly restricting the ability for air to flow between the radiator outlet and the hood. If you still have these there, remove them. Obviously, this is easier said than done, but an AEM/RB intake would allow you to remove the stock airbox and tray completely, and the battery is something that requires a more complicated relocation solution. But if you want maximum effectiveness, restricting the airflow out of the hood isn't going to be helping you any.



For an idea on how big of an impact it can make, take a look at race car radiator sizes where they can duct the entire mouth of the car to the radiator, and then the entire radiator out of the hood. They are smaller radiators than our street cars. And they can get away with it because of the highly managed airflow means they are hugely more efficient than street radiator setups.

Here are some pics of completely ducted radiators:





(this last one i think is actually ducting an intercooler, but same concept)

 

The ONLY thing that eventually worked for me to keep track temperatures down was a very large DUAL PASS radiator. Not a larger radiator such as the one Mazda Competition sells but a huge DUAL PASS radiator that is made by Ron Davis Racing Radiators - Ron Davis aluminum radiators for racing, offroad, performance street car, and other custom applications

It will set you back about $800-900 and will take them about a month to custom make.

They have the specs on file - just ask for the "Mother's Wax Special" RX-8 radiator or you can have them look up my order history (I've had two built) under John Magnuson.

If you still have your air conditioning some extra work may be required as it's not designed to accommodate the air conditioning condenser.

Some other minor work is required such as modification of the radiator hoses and some clearancing on the fan shrouds

But it works really really well.

 

you need a better radiator, not a waterpump

the argument that reducing pressure behind the radiator increases flow makes the assumption that there is a restriction there already. You are not going to create a vacuum area behind the radiator discharge face with completely redesigning the car from an aero perspective. For practical purposes you can only ensure that there is no pressure backup at the radiator discharge, which IMO your kit does. Regardless of how much pressure you build up in front of a radiator the laws of physics/fluid dynamics still apply. The radiator design has a lot of influence as to how much air passes through before the law of diminishing pressure/flow returns kicks in, same for heat transfer duties.

Bottom line, the OE radiator is not up to full boogie track conditions for this engine and never will be



.

 

Is there nothing to be said for replacing the 2004 water pump with a later version? Also the thermostat at the same time since that may not be fully opening now if it is 11 years old?

Another simple (cheap) thing to check is that the oem black foam is in place top, bottom and sides of the radiator.

In comparison to my experience your temps seem a little high, so I would start by making sure the stock cooling system is running as well as possible - my data running Laguna Seca at a 1:50.xx pace shows an ECT of 210F while air temp was 70F. Car was stock except wheels/tires/suspension/decat and mild tune. I have an s2 though, which does have a thicker radiator.

There's some info on radiators in this thread: https://www.rx8club.com/series-ii-af...r-48mm-245281/
Summary of that is: s1 radiator is 27mm thick, s2 is 36mm (and will fit), koyo s2 is 48mm (not sure that would fit). The one result posted there does not show much gain from the oem s2 to the koyo, however, that may not be representative of what you would see going from an s1 rad.

I would approach this as follows:

1. foam
2. latest oem pump & t-stat (I don't think the mazmart ones are worth the extra over the later oem ones)
3. radiator: either s2 oem replacement, koyo racing rad, or that ron davis one depending on budget.
(I'd probably try the oem one first for your application)

The other idea is to open up the slots behind the oil coolers, and add some foam around the oil coolers. There is another thread on opening up the slots somewhere.

EDIT: btw, I don't disagree that the oem s1 rad is inadequate. My oem s2 is barely adequate and it is much thicker. Team, did you notice any improvement yet going from the s1 (27mm) to s2 (36mm) radiator?

 

Thanks RIWWP for another great post. Some great info there for us noobs.

 

if you want to try and create additional flow IMO it would be better to rig a switch and run the fans on high continuously while on the track than to block off off the front nose completely. First, only so much flow can go through the radiator regardless. If you block it off and the flow into the bumper chokes regardless then you're causing more harm than good. Second, some cool air into the engine bay is beneficial. It's a too much or too little situation though. IWith the vents I doubt you can get too much. A shroud on the radiator front-side that allows some air to pass by but traps most of it is the best solution IMO.

 

Team,

Any thoughts or design input for a drip tray to use with these vents?

Should it get caught in the rain parked or even driving that's a lot of water

IMO the vents are pleasing to the eye and shouldn't be restricted to just track cars if your catching my drift.

Travis

 

WOW!!! Huge thanks to all of you for the replies, especially huge thanks to RIWWP!!. I have been racing (spec miata), autocrossing, and/or HPDE driving for 20+ years and have never really explored cooling systems in this level of detail but am very excited to put these suggestions into practice, albeit one at a time so I can measure the difference of each one.

I am very committed to the RX8 (and Mazda in general) and intend to keep this chassis for track use for a long time to come. As such, I will also be exploring further upgrades such as aero but I'm not planning on adding much in the way of power adders, such as forced induction. My time in Spec Miatas taught me you don't "need" massive HP to be fast or have a kick-*** time on the track.

To answer a few questions:

1) The battery, air box, etc, is all still there. I'm open to removing the air box and replacing with an intake, but my earlier research on this forum led me to believe the stock air box is the preferred intake for the car and better than any of the aftermarket intakes. So, to replace for better cooling or leave for better airflow to the intake??

2) The chassis is a 2004, but the engine was replaced by Mazda at 99k miles and only has ~25k miles, so it's fairly "new". I'm not sure if Mazda replaces the water pump when they do the engine replacement (warranty version).

3) I have not checked all the seals around the radiator, but will certain ensure that is up to par. Getting as much air as possible into the radiator makes a ton of sense and ensuring it has a way to get out makes sense as well.

4) I may not be moving the louvers forward for a while as I would need to get another hood. But great advice for anyone considering using these. The instructions specify the mounting location to be 11.5 inches above the bottom of the hood.

 

There is in a stock setup. Quite a lot of restriction. Even the radiator fans and shrouding can impose a restriction at high flow rates (unknown at what point that is, or the actual metrics around it).


A sharp pressure drop behind it is indeed possible, and measured, but it has to be designed correctly, I agree with you on that.


This is certainly true too. One of those other points I didn't get into. I agree that he needs a better radiator, but since the topic was about the vents, the vents is what I was answering.

Running the fans on high only presumes that the fans can provide a flow increase? Do you know how much flow goes through the radiator at X speed with fans on vs off? Most track cars get rid of the fan shrouding and even the fans to maximize flow at speed, as they are designed for maximum efficiency at low speed, which isn't what you see on track. This is why you usually see a smaller fan set to the side, just something to use in pits/paddock to prevent overheating with minimal restriction at speed.

I don't understand the "than to block of the front nose completely", since I don't think anyone is suggesting that.

Don't forget the airflow from other sources other than the mouth, like the oil cooler area.

That's a bit humorous, as I learned more about this from the Miata community than the RX-8 community

There are still other solutions for cooling that you can explore, so I can't really make a specific recommendation here for you. The stock airbox really is very good, so if you opt for another intake for other reasons, there are really only 2 that are options to avoid power loss or problems.

Yes, the remans come with a new water pump from the reman facility.

I'd be curious as to why they make that recommendation, specifically if they did testing for the ideal spot.

 

Not block the nose openings off completely, blocking the flow so it can only go through the radiator. With an OE radiator and probably some aftermarket radiators it all won't be forced through. It will instead stall and back up at the front of the car. In the mean time the amount of cool air getting into the engine bay has been significantly reduced.

The oil coolers are small in regard to the main nose opening and cavity. Otherwise they are separated into the wheel well/fender area, not the main nose cavity. I agree with blocking them in, but not the radiator which was the main focus of my comment.

Do you understand the concept of compounding, meaning using two pumps, fans, turbos, etc. in series? It may be that the fans and shroud create a restriction. It will be a significantly less restriction with the fans running on high. A rotary engine without a fan can't idle long when warmed up before overheating. If you can accept and deal with that more power to you.

Some of my suggestions are counter-intuitive, just because everyone does it a certain way doesn't mean they are doing it right. As you've been at this a while you well understand the monkey-see, monkey-do racing mentality. Not going to argue about it though. Do whatever you want.


.

 

BTW, RX8Performance sells a dual-pass radiator too. Only other one I've seen for the RX8. Maybe the same one even, not sure.

http://www.rx8performance.com/produc...mance-radiator



.

 

Yes, I think that's the same Ron Davis radiator.

 

Great discussion. Good info. Here is my setup...I'm running the re-amemiya FRP D1 hood. The design of the hood comes with rain ducts. There are 3 large vents...each about ~5cm gap, with the first opening in the front, directly above the battery & the intake... the design of the hood and the duct were design for and tested in the super GT300 series in Japan (Based on information from the re-amemiya site).

I found this setup works for me as a DD summer car & track weekend car.



With the the rain ducts, there is still an ~1cm opening to allow air to through in the first opening. The air ducts drains excess water via the OEM drainage between the hood and the fender. Drove the car in the pouring rain a couple times and the rain barely got into the ducts due to the forward motion of the car...the most water I see entering the ducts is when I wash the car...but it quickly drains away.

Amazing Product Functionality & Quality. Amemiya-san is a saint!

 

2hit6 - by chance did you get any temperature deltas with the hood?

 

Ron Davis makes more than one model for the RX-8.

 

I don't have a baseline. I will be at the track this Friday and will try to do some readings.

 

I just purchased this as the louvers didnt solve my cooling issues. Will post back the results after my 11/21 track day.

 

Any update on this? I'm in the process of building my track car over the winter & the Collins system is a high priority to get it right before taking the car on track.

 

There's a bunch of feedback in this thread: https://www.rx8club.com/rx8performan...tor-v2-259722/

 

BTW I have one of these singular motorsports hood louver kits for sale. Brand new (no wait time for construction). Decided not to use it because I went a different route with my racing classification which would penalize hood vents. PM me if interested. $199 from Good-Win-Racing. I'll sell for $150 plus shipping.

 

Thank you sir, beat me to it!

 

Just did this as well - install was not difficult at all - the hardest part was getting it lined up and centered (for me at least).

Used an angle grinder with an aluminum cut off wheel, and actually did this about 1.5" closer to the nose than what Singular Motorsports had recommended based on my interpretation of RIWWP's post and the Miata diagrams, I figured that being closer to the front would put the vents in more of a negative pressure zone, which could / should only be enhanced by the top edge of the louvers.

When moving it forward, I realized why Singular had it there though - moving it forward means you have to cut into some of the bracing for the hood - it seems sturdy enough, and I didn't remove the bracket - just a portion of the bracket between the under layer of the hood and the top layer of the hood.

Hoping that this, plus the radiator, plus better foam on the bottom and on top of the radiator will help. I'm also looking into opening up some of the stock honeycomb in the nose of bumper (the S2 honeycomb has a lot of those holes closed off).

Attached is the finished product, to be put on the car later today or tomorrow.



PCS

 

Nice! Looks all business.

Did you make it out last weekend, and how did the car do for temps?

 

update w/ the rx8performance radiator and the singular vented hood - it's mostly a copy and paste from an email to blu3dragon, but figured I'd post it here in case it helped anyone... Not as helpful as a typical SteveDallas or blu3dragon response since theirs is backed with data, and mine is backed by butt dyno's and general impressions, lol, but...

From the equivalent of a butt dyno effect, I feel like it was helpful between the vent and the radiator up until about 103-105* on Buttonwillow #13CW. There is a looooooong section that is almost all WOT or steady throttle then WOT from after cotton corners, through bus stop and riverside until you get to Phil Hill - that is where I've reached 225+ in 103* temps (in the past). This time, I didn't push the temps past 220* (versus letting them get up to 225+ previously), but in similar temps (103*), had no issues going for a full session (no issues going to a lower temperature threshold). Above that ambient though, it would creep over 220*, and I just didn't feel like it was worth hanging out over 220*, and so I started shifting at 7k instead of 9k, and spent most of my time working on different things on the track.

Scott from RX8Performance brought up a point about cavitation - not sure if that's an issue or not running at higher RPMs for an extended period of time (the S2 seems to have an upgraded water pump and is more underdriven than the S1 from the factory), but what he was saying about it makes sense, I suppose? I only have an issue on that west section of the track (i think it's the west section, but on the map, it's on the right), where i'm at high RPMs for an extended length of time - of course, that could also be where there is the most combustion for an extended period of time, sooooooooo the answer is unclear.

I think ultimately it requires another test with better data or another hot day with an underdrive pulley on my 8 to get another comparison, but I'm not sure I want to subject myself to another 110* day at the track, hahaha...

 

The S2 pump, S1 OEM pump, and Mazmart S1 pump.





If I were you, I would consider running an auxiliary radiator, that along with the Fal FANS makes the biggest difference.