Recovery is also an indication of radiator performance, so a faster recovery time would indicate better cooling performance, indicating that it's truly an upgrade over stock.

If you still want better cooling, try adding airflow by opening up the stock grille. How I did mine was to take a dremel plastic cutting bit and epoxy a length of metal brake tubing onto it as a guide. Then I just had to cut through the middle of the blanked grille section and run it along the ribs, cutting out the blanked area. It makes for quite a clean cut and you can then do more cleanup with a sharp knife. New grilles are pretty cheap, so any mistakes aren't going to cost you much. I'd recommend doing it on the car though, then you'll see which sections are worth cutting and which will be blocked from behind anyway.

Yes, the grill makes a notable difference aka Mazdaspeed bumper cover that has the whole thing open. Cut mine out over the off-season several years back and the sanctioning body changed the rule disallowing it that next race season :crying:

I'd cut most of the lower section out with a 2 or 3 vertical sections remaining as it is intended/designed to provide support across the flexible bumper opening

but again my recommendation is not to foam the whole front end closed. Either run the fans or build a forward enclosure to trap air for the radiator, but still allow some air to pass into and cool the engine bay. IMO closing it off completely will increase drag at high speed because the air can't get through fast enough despite the pressure buildup in front of the radiator.



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I didn't leave any vertical strips of solid and it didn't seem to be an issue at 130mph. If you're worried about it, maybe some metal supports could be added from behind that block less airflow. I started out cutting only what would be hidden behind the license plate, but needed more, so I then did everything that didn't have something else immediately behind it that would then block the air and that you would be able to then see through the grille.

I figured the extra airflow helps offset the extra sealing, as the job did is far from perfect, so there's still some air getting around.

I did consider the drag penalty, but since I was having to do cool down laps before, this is definitely faster overall.

I didn't think so either until it cracked/broke ... that was maybe 8 years ago or so

This is me. I have no gauges, and was just at the track in 90-95* weather. No gauge, ignorance was bliss... then I started thinking about it... and then I started worrying about it, haha.

I got back, ordered an OBD2 sensor, and will have something ELSE suction cupped to my windshield.

I guess I'll need to start looking at reinforcing that area with something lower profile then.

well I was slapping cones, but for you it might be smacking curbs or going off ...

Just wanted to add something here regarding fit with the racing beat revi intake. I did not notice an issue with the stock intake, but since decided to switch to the RB intake and it was tight. I have not looked from under the car after wedging in the RB airbox, but I expect the top of the radiator is pressing into the underside of it. Hopefully this does not cause an issue for me down the road.

Well I got the car back on track last weekend and it does seem to run cooler.

Before: completely stock engine & cooling w/midpipe.
After: BHR rad, left and right side foam thicker than oem. foam around 3 sides of each oil cooler. Engine rebuilt.

After seems to be at least 5 degrees cooler on track.

Thanks for the update. I ended up removing the foam from the passenger's side completely. My engine compartment temps were universally higher than OEM--even as my coolant temps were lower after I swapped the radiator and went crazy with the foam. Removing that foam allows air to reach the exhaust manifold, and the negative pressure created by that flow pulls air in from other openings to create air flow throughout the engine bay.

who'd a thunk it?


oh yeah, that guy ...

Yes, yes, you told me so.

Not you specifically, but have stated it on the forum for quite a while now and you were one of the first to break the monkey-see, monkey-do mold to find out for yourself

Congratulations and good job

Since s2 radiator fits the s1, would the hh series koyo radiator also fit an s1 without issue?

In theory, it should.

The reality is, no one has done it yet, so no one can say for sure.

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Well, I purchased this radiator along with fal 420 fans and both will be going in with the turbo setup. Once complete I'll report back for those s1's that are curious.

A few final notes about radiator foam after tracking the car in the Texas heat for a year with the new radiator:

1. The radiator has a maximum flow rate. Trapping more air in front of it than it can flow does nothing beneficial.

2. Cooling the engine bay is important. Going crazy with the foam like I did at first is not the ideal configuration. My ECTs increased by about 50F with full foam. Some air needs to flow into the engine compartment to keep ECTs down.

3. The best way I found to accomplish both goals is to foam the top, bottom, and driver's sides of the radiator and let air pass unimpeded on the passenger's side. The air passing by the radiator on the passenger's side draws heat away from the exhaust manifold and pulls air into the engine bay from other openings to create a cooling effect throughout the engine bay. It also cools the transmission tunnel.

4. Removing the foam on from the passenger's side reduced ECTs to OEM levels without having any impact on coolant temps.

thanks for the update - I've been debating what to do on mine too - I'm also going to end up venting the hood as well to try to reduce the pressure behind the radiator as well. I don't track data the way you do, so my results won't be as helpful, but at least it will give you a "yes this setup worked in 100+* temps or no, this setup didn't"...

I spent some time prepping my car for a July 11 track day this evening. Here are a couple of photos of how I approached the undertray foam last year. I drilled a hole next to an existing opening in the undertray just to the side of each lower radiator mount and used a heavy duty zip tie over each mount to cinch the undertray up against the bottom of the radiator, which trapped the foam just forward of the radiator under its mounts. Upon taking the photo, I realized I could have gone wider than OEM with the bottom foam, so I decided to cut another piece to 27" to replace the 24" piece I have in there now. I'm changing all fluids tomorrow, and I will swap the longer piece in then.

https://cimg7.ibsrv.net/gimg/www.rx8...0562b22ec6.jpg

https://cimg5.ibsrv.net/gimg/www.rx8...7c6d284a55.jpg

I find it a real pain to remove the undertray and the uprights... a ton of things to disconnect and tabs to pop out... is there a trick to this? do I not have to remove the uprights to remove the undertray?

Since I'm a masochist and a data guy, here is a chart of my coolant temps during a 30 minute track session in 100F heat with the Koyo radiator and 3-sided foam treatment described in post 92.

https://cimg8.ibsrv.net/gimg/www.rx8...d38f8f8b0a.png

Data dispels all myths.

Here is a chart from earlier in the day, when we had some cloud cover at 93F, before the ambient temperature spiked.

https://cimg5.ibsrv.net/gimg/www.rx8...d82543ab74.png

Data.

Yep. Love it. Much better than listening to guys try and makes excuses as to why they still have coolant temps of 230F after buying $500.00 radiators.

My buddy has had good results with his Koyo as well on his S2, it has changed my opinion of Koyo honestly from the early days when guys had fitment issues and not great results on the track.

Interesting data. Was the earlier data with all sides of the radiator sealed?

I'm not seeing a huge difference, possibly a slight improvement:

2016 data:

IAT ECT Delta T
100 216 116
93 214 121

Prior data:
IAT ECT Delta T
91 216 125
90 212 122

Some data of my own:

Track Laptime Radiator IAT ECT Delta T
TH 02:13.2 Koyo 106 234 128
TH 02:11.5 Koyo 93 223 130
LS 01:51.2 Koyo 84 216 132
TH 02:09.5 Koyo 97 230 133
TH 02:10.4 Koyo 84 221 137
TH 02:13.9 Stock 84 221 137
LS 01:51.3 Koyo 61 199 138
LS 01:52.2 Koyo 77 216 139
TH 02:15.6 Koyo 59 198 139
TH 02:07.0 Koyo 86 225 139
LS 01:50.3 Stock 72 212 140
LS 01:51.2 Stock 70 212 142
TH 02:14.1 Stock 70 214 144
TH 02:12.3 Stock 70 217 147
TH 02:12.0 Stock 61 214 153

I have foam on all 4 sides of the radiator, and around 3 sides of each oil cooler. More recently I also zip tied my undertray.