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First-Gen Cooling

Old 04-02-16, 03:30 PM
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CA First-Gen Cooling

Tired of running hot at the track so upgrading my cooling system. Looking for aluminum radiator recommendations. Have a eBay unit that's no better than stock so looking for larger model that will fit in the available space. Brand, size, type and SN would be great. Does not need to be 'drop-in', just something that has been successful for racing in a first-gen.

Thanks in advance.
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Old 04-02-16, 04:06 PM
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TII radiator fits. Its bigger, maximises the space between undertray and hood. I'm using a koyo "n flow". It works really well. There are probably other options but at least the TII rad has the outlets where you want them and fits with some mods to the outlet angles and mounts. Had a stock tII rad for 12 years before switching to the koyo, that was more than capable for my purposes too.
I'm also running a tII oil cooler mounted to the front cross bar. Again very effective.
Hav'nt done any track work with this set up yet but running an efr8374, giant front mount intercooler and 400rwhp and the water doesnt get above 86c. The oil, inexplicably, stays even cooler than that, even when stuck in traffic. Seen a few 40c days and zero problems.
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Old 04-03-16, 02:18 AM
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What do you have for a bumper? Airflow management is absolutely critical. If you have a front mount oil cooler and no A/C condenser, you should also have some sort of ducting to prevent air from bypassing the oil cooler. (I just ziptied a length of mudflap to the crossbar over the oil cooler, works fine for me, but admittedly I'm more concerned about fan-based flow rather than forward speed flow) I found that having the under bumper panel/lip missing was worth 40-50 degrees at highway cruise. You can bet that I put that sucker right back on again

What kid of revs are you seeing on the track? If you have stock pulleys, the water pump essentially does nothing at over 6000rpm and overheating is the result. Get a smaller crank pulley so the water pump doesn't go so fast that it cavitates. That all but eliminated my bulk overheating issues - I could go from 180 to 220+ degrees in forty seconds before the pulley change.

I use an eBay aluminum radiator. I was going to try an FC radiator but the core size is almost identical to the '83-85 radiator so I did not bother.

Last edited by peejay; 04-03-16 at 02:23 AM.
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Old 04-03-16, 04:12 AM
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I'm pretty certain the fc rad is bigger in both dimensions than fb, at least back when i was measuring up and deciding what rad to get they were.
In this link there is a pic of my oil cooler, the front spoiler acts as a funnel and a fourth wall for the small aluminium shroud that i bent and pop-riveted on. The shroud, by the way is always exactly the same temp as the cooler so thats food for thought that a bigger one would add to the cooling area even more as well as simply ducting air.
I think the secret to the Mazda oil coolers is the "turbulators". Mine works great, but a lot of the fb race cars over here use two of them welded together.
http://ausrotary.com/download/file.php?id=48469
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Old 04-03-16, 04:20 AM
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FC and "tall" 1st-gen radiator are both 19" tall cores and 22 (maybe 24) inches wide. I thought the FC would have been larger, too.

Ducting questions were to OP.
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Old 04-03-16, 04:27 AM
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Yeah ok, could have sworn they were different. Maybe i was comparing Aus spec s3 rad or whatever was on ebay at the time here, thanks for clarifying.
as to the ducting question, i know, just trying to contribute.
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Old 04-03-16, 04:32 AM
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As to water pump cavitation at high rpm, this has always worried me - im wondering if the certain amount of inherent belt slip is ok on your average twin v belt arangement, or if an underdrive pulley will really be that big of a no-no on a car that see's street use?
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Old 04-03-16, 04:32 AM
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The '79-82 12A radiator WAS a lot smaller. It's only 16" high, the oil cooler sits underneath it.

'83-85 12A had a full height radiator and no air/oil cooler, while GSL-SE had a front mounted air/oil cooler and similar full height radiator (not the same: it had a bevel at the bottom left for oil line clearance).

Regarding underdrive pullies. I drive a 3" crank pulley on the street. The only problem is that the alternator doesn't do much of anything below around 1100-1200rpm. Since this only happens at stop lights, I simply don't worry about it, and turn the idle up to 1500-1800 or so for competition when I need the car to idle for extended periods with the fans on.

I do not use a mechanical fan. They suck power, eat belts, and are worthless for trying to cool a 230 degree engine down in grid. A nice electric setup gives max cooling any time you turn them on. You just need a GOOD fan solution, the little crappy 1600cfm or whatever fans are worthless. Need something in the 3000-4000cfm range, and something that flows with a pressure drop across the radiator. A lot of the aftermarket fans that are rated high are rated with no pressure drop. Stick them on a radiator and they don't do anything useful. Need curved directional blades and a powerful motor. If you can run the fan on a single 20a fuse then it is insufficient. It's not enough power to be able to pull mass quantities of air through 2-3" thick of radiator and oil cooler.

My fans have two dedicated 40a fuses and they move enough air to cool the engine DOWN when on a chassis dyno.


With no mechanical fan, and an underdrive setup that keeps the water pump from cavitating, you'll find that you do not need two belts. A single belt is more than sufficient. Heck, I've had the same belt on my engine since 2011! I was going through a belt every month or two with the stock pulleys and no mechanical fan. Running a minibelt from the crank pulley to the water pump seemed to make the life of both belts get even worse, incdientally. Most of the increase in belt life is from the water pump no longer cavitating (which puts a lot of shock loads on the belt interface) and the rest is because you do get a slight amount of more belt wrap on the water pump. But 2 degrees more wrap is like double what it is with stock pullies

Last edited by peejay; 04-03-16 at 04:48 AM.
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Old 04-03-16, 04:48 AM
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Thanks for the insight on that. My idle is set at around 11-1200 anyway due to crappy (non-existing) cold map and whatnot. Will double check my e-fan specs and capabilities. I'm pretty sure its ok.

I think you were right about the sizing too, at least koyo-rad seems to agree Koyorad Racing - Products : High Performance Racing Radiators although it seems they dont list the N flow anymore.

Ok. i'll stop thread-jacking now. Sorry op!

Last edited by WANKfactor; 04-03-16 at 04:52 AM.
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Old 04-03-16, 11:48 AM
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Thanks for the comments. Have the comp pulley & ducting. Been racing with my current set up for over 10 years with no issues. Towards the end of last year my factory sized three row radiator seem to finally give up. Replaced with the eBay aluminum radiator but my temps are higher than with my older set up. So I am looking for an improved set up and was hoping to get examples of what others are using for their race-only applications. I do not use a fan.

Ron Davis, Howe and Koyo are some brands that I've seen while searching. What Actual rad dim are people using? Double pass? I was hoping some other road racers could let me know what rad has worked well for them. The current short rad eBay model doesn't work as well as my older unit. I figure now is a good time to get a larger quality unit especially as I have a freshly rebuilt motor. Im okay with relocating my oil cooler and although my oil temps are okay, may also set up dual coolers since I will be reconfiguring that space anyway.

I am also going to take this time to delete the thermostat/ plug bypass. Any recommendations for reduced diameter opening would be appreciated.
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Old 04-06-16, 01:20 PM
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"I am also going to take this time to delete the thermostat/ plug bypass. Any recommendations for reduced diameter opening would be appreciated."

Are you talking about the water thermostat or the oil cooler thermostat?
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Old 04-07-16, 07:47 PM
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Water. Oil temps/pressure have been fine. BTW, I did not mention but this is a NASA PTE car.
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Old 04-09-16, 07:30 PM
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I'm using the ebay rad with a T stat that the center was removed, crank under drive pulley and water wetter.
I was having some troubles on very hot days. Was getting up to 200deg. Then I sealed all the openings on the ducts with tape. That helped like 10deg. Then cleaned out the dirt and rubber out of the fins. That got me back to 180deg.

Are you going to make NASA's BW next weekend?
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Old 04-10-16, 10:39 AM
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Gian, thanks for the advise. Just running NorCal events but will be out of the country for thill event. Trying to have everything in order for the May Laguna event.
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Old 03-25-17, 10:56 AM
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Originally Posted by kurtf View Post
Gian, thanks for the advise. Just running NorCal events but will be out of the country for thill event. Trying to have everything in order for the May Laguna event.
. I run a R31 skyline or pintara alloy radiator. Factory Calsonic unit . Inlet and outlets are on the correct side and it fits the factory RX7 shrouds perfectly. Also cheap I was buying them for around $120 aud. They are only thin single core but huge surface area. Dropped engine temp buy around 20-25c.also helped the oil temp. Because the radiator is so tall when mounted to the top of standard RX7 shroud it lined up perfectly for where I have the oil cooler mounted. It's mounted directly under the round cross bar there for I placed a peice of 1/8 alloy sheet from the front spoiler all the way back to the bottom of the radiator and with a 90 degree edge and a couple of holes the rubber bushes are perfect to mount the bottom of the radiator. With that done all the air that comes through the lower grille has to go through the oil cooler and the radiator. And it also protects the hole lot. I haven't got the part number on hand now but If you would like I can go to the workshop and get it for you. Genuine Nissan part very cheap so I purchased 2 of the 1 for a spare. Cheers Mark.
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Old 03-30-17, 12:36 PM
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My car has a double pass radiator - 19 x 21 - that I think is from Ron Davis. I bought it from an ITS racer when she up graded to a larger rad. I have a pusher E-fan that I run pretty much all of the time. The T-stat bypass is blocked and I run a 3/4" restrictor in place of the T-stat. I have the Racing Beat single belt under drive pulleys for the water pump and crank.

With my car I have learned over the years that oil temps have a direct bearing in water temps. Meaning that by getting oil temps close to 200-210 also keeps water temps happy. So that is why I run two Mazda coolers plumbed in parallel. The coolers are mounted ahead of the radiator in a stair-step mount and have had their T-stats removed/replaced by machined dowels that seal their bypass circuits.

The next piece of the puzzle is ducting. You want your grill opening to be approximately 30% of the area of the radiator. The expansion of the air mass on radiator side of the grill creaks a low pressure area. This improves air flow. You also want all of the air that enters the grill to be forced to exit through
the radiator. So this means the duct work ahead of the radiator/oil coolers cannot have any air leaks.

On a hot-humid day my street ported 13B runs at 210 water and oil no matter how hard I run it.
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Old 03-31-17, 12:54 PM
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I've had good luck in my FC with the Fluidyne radiator. It's a little pricey compared to Koyo but it's a quality piece that keeps my temps around 200F.

I also have custom ducting I made that is about 1/3rd the radiator height at the bumper and forces the air through the oil cooler and radiator.

I have a heat extractor in my hood right behind the radiator fan outlet and I'm using a Mercury Villager e-fan and shroud mounted to the back of the radiator. It fits really well, actually. I just cut the shroud a bit closer and used a couple L brackets to mount it to the Fluidyne. It fried the 30-amp fuse once so now it's running a 40 amp and works well to pull the temps down in stop-go traffic.
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Old 03-31-17, 08:48 PM
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My build log has a few good ideas and starting points. Ducting is everything.
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Old 05-09-17, 03:48 PM
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My ITA (now mostly endurance races) FB (1982) has a stock short radiator and oil cooler below. The engine is stock 12a with slowed down water pump and nearly stock Nikki jetting (for fuel mileage in endurance racing). I originally had the thermostat removed and bypass plugged, but there were too many days when the water temp would not get over 150degF without sticking some cardboard in front of the radiator. I put the thermostat back in and consistently runs 190degF. That is in 100 degF weather at Willow Springs and +95degF at TWS, in both cases running wide open for 8 hours at a time (with of course quick stops for driver change and fuel).

The short radiator is 3 row while the tall radiator is 2 row. As such, there should really not be much difference in cooling capability between the two. I think the short radiator actually has a little more heat transfer area. It definitely has less resistance to flow on the water side, because of the third row.

In my mind, the key is to have a clean radiator in good condition. If you are pumping out significantly more horsepower than a stock port 12a, I am sure you might not have the same experience.
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Old 05-14-17, 05:51 PM
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Originally Posted by Carl View Post
The short radiator is 3 row while the tall radiator is 2 row.
the tall radiator is basically the same size as the competition radiator, but the short radiator is the same size as the FD radiator! the FD is just a 2 row too.
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Old 05-14-17, 07:07 PM
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I am a little confused now. I was positive that my short radiator is 3-row, but I just checked my used spare and it is only 2 row. Looking at RockAuto the "short" radiator core dimensions are 11-7/16 x 21-5/8 x 1-1/6. The "tall" dimensions are the same for all 84-85 and NA/Turbo second gens at 16-3/4 x 22-3/8 x 1-1/4. RockAuto reports that all are 2-row. When I get a chance I will re-check the radiator in my race car and see if it is 2- or 3-row.

In any case, whatever thickness short radiator I have installed has worked quite well along with the FMOC.
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Old 05-17-17, 12:16 PM
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I just checked the radiator in my race car and it is a 3-row short radiator. Not sure how I got that compared to the old one that was only 2-row. Weird. The tubes in the 3-row are a little bit smaller than those in the 2-row, but it definitely has a lot more heat transfer surface than the 2-row.


Originally Posted by Carl View Post
I am a little confused now. I was positive that my short radiator is 3-row, but I just checked my used spare and it is only 2 row. Looking at RockAuto the "short" radiator core dimensions are 11-7/16 x 21-5/8 x 1-1/6. The "tall" dimensions are the same for all 84-85 and NA/Turbo second gens at 16-3/4 x 22-3/8 x 1-1/4. RockAuto reports that all are 2-row. When I get a chance I will re-check the radiator in my race car and see if it is 2- or 3-row.

In any case, whatever thickness short radiator I have installed has worked quite well along with the FMOC.
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Old 05-18-17, 07:04 PM
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I installed a short ebay aluminum radiator and taped up all the gaps around the shroud. Will be running at Sonoma this weekend and hopefully all is well.
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