Because there is no clear, concise answer, I'd like to gather some REAL-WORLD information on what is needed to cool a 20B.

In my search for answers, I've come up with nothing but "Custom" when it comes to a proper radiator on a 20B FC. What I've found so far is nothing but brand names and "as big as you can" but no actual dimensions for the core or end tanks

Now, I'm well aware that it has to be of sufficient size and thickness to do the job, but I've yet to see any actual numbers on this. And the same goes for ducting, we all know that you have to get air passing through it, not around it.

To put things in perspective, a S4's radiator is 24" wide x 23" tall x 1.5" thick including the end tanks, that is 828 cubic inches total volume. According to Summit Racing, the core is 21.625" Wide x 16.75" Tall x 1" thick, for a volume of 362.22 cubic inches

Based on 30% greater heat output, a sufficiently sized core would be 470.88 cubic inches. Is this correct?

 

shouldn't it be 50% more heat....

 

Yes... plus the water flow through the engine needs to be changed.

-J

 

Japan2LA, I agree 110% that the commonly believed figure of 30% greater heat makes no logical sense. That figure came from FC3Spro's 20b articles. As for changing the coolant flow through the engine, why would that need to be done on a stock 20B-REW? Every rotary has always had a front-to-back coolant flow from the factory and it'd worked quite well so far. Of course, "better safe than sorry" is always in my mind so it's going to be supplemented with some Redline Water Wetter as an added precaution.

So based on 50% greater heating capability, 543.33 cubic inches is the appropriate volume. For reference, a Be Cool 35023 Dual Pass radiator (26x19x3") has 832.5 cubic inches of core volume (22.5" wide x 18.5" Tall x 2" thick). The Be Cool 35024 (28"x19"x3")'s core volume (24.5"x18.5"x2") is 906.5 cubic inches. Would either of these be an appropriate choice for this application?

 

If you wanna cool a 20b, you need flow and capacity. Plain and simple. I'm not gonna talk radiators but I will talk about water pumps. I've been back and forward with my 20b project with various experiments and I can say that the 20b water pump is what you wanna run on this engine. It's the highest flowing water pump Mazda makes for rotarys (2nd gens being the second). My engine has been on a test stand for some time. With the Fd's set-up, temps would quickly rise and I would need to engage my fans. If I engage the fans too late, it would take a while before the temps would start to come down. When I modified my set-up to accept the 20b water pump with Fd pulleys, I was amazed at the differences. The sheer flow of the 20b's pump, kept the engine much cooler and longer before I had to turn the fans on. Even when I let the engine get hot, as soon as the fans kicked in the temps started dropping. I really couldn't believe how much of a difference that water pump made. You also get the advantage of moving more water through TWO T-stats. I simply cut the upper housing off and attatched an aluminum radiator cap and base to it that I bought off of ebay. Both of my T-stats are just regular Fd T-stats. If you think about it, there's only so much water you can flow though a single thermostat.

Now there is a down side to the 20b pump. Though the pump moves more water, it will also hurt Hp some. It's swirl impeller is designed to really move the fluid so it will cost you some pony's. How much??? I don't know but I could tell that my engine didn't rev as fast with it on. The housing and pump will also add some weight to the front. Lastly not having them readily available in rebuilt form is also an issue. Mine started pissing out water out of the bottom weep hole. There may be light at the end of the tunnel. I've contacted a specialty water pump rebuilding company who claims they can rebuild my unit for a round $100.00. I'm getting ready to send it off so I will report back on the quality of the rebuild. I can't wait to get this water pump back on my engine.

 

I am thinking about buying an electric water pump but unsure if it would be suitable as I don't know the flow rates of the standard 20b water pump.
EWP capable of flowing 55 gallons per minute but inlet to the front plate is a -16 fitting.
So i'll be keeping an eye on this thread...

 

I run an AFCO double pass, the core is 20x18x3=1080 in^3. fits in almost stock location no problem, and has no problem keeping it cool. Costs around $200, but you have to make mounts.

I am also using a TII water pump, and it is not adequate. I kicked around the idea of modifying the 20B one to fit under the hood, but I decided to use a more commonly available pump instead. I havent had time lately, but I was researching flow rates to try and find a performance v8 one that was roughly the right size and flowrate, then just adapt it to mount in place of the stock one. If anyone knows the flowrates of the FC and 20B pumps that would be a good piece of info...

 

Personally I run a series 4 waterpump, which measures larger than the 20b unit. This combined with a 5" mazdacomp pulley has worked great even during extended 10k rpm on track.

 

Really the series 4 has a larger impeller? Series 4 Rx7 is one Rx7 I haven't played with yet. That and a GSL-SE! Don't you have some other special cooling mods?

 

Yeah the series 5 and 20b look identical to me in size, series 4 is larger. GSL-se I believe is one of the largest, that and the 12a which are the same? Idk been too many years since I played with 12a's in high technical regard. The cast iron housing kept me away from the SE and 12a stuff though, series 4 seems to have best of both worlds. You are right, there are some other cooling mods I've done To this day I CANT get water temps above 185 degrees.

 

Are we talking about cooling on the street or track use? On the Street my FD water pump and koyo rad setup cools very efficiently I found the key was intercooler placement. We have around 5-20b guys up here running a custom v-mount setup which lays the intercooler flat allowing direct flow to the rad with no cooling issues.....

 

Being down in the south is a WHOLE different storey. We have 100+ degree days on a regular basis. So what works up their wont necessarily work down here.

 

Interesting! When I compared my 20b impeller to my NA S5 water pump, the 20b's was bigger. I thought all S5 water pumps (NA and turbo) were the same? Guess not! I do however need to find a way to get a larger pulley for the 20b water pump to reduce cavitation. I think mine is flowing too much at idle.

 

way back in the 20th century, ReTed bought a 3 rotor engine, and brought it home. he and paul ripped apart a white 1988 Turbo 2, and measured the radiator opening. they then proceeded to order an AFCO radiator which is double pass, and has a core size that is exactly the same size as the opening in the car. or in other words its the biggest thing that will fit.

i had one, HIGGI has one, patman has one, etc etc.

because of the frame rails you really can't go much larger than 20x18x3 (don't forget 20x18x3 is the CORE size)

paul and ted ran an s4 FC water pump, i ran the cosmo, they both seemed ok.

i think running at least 2 stock FC oil coolers is a good idea too.

 

^ damn, I thought I was the first one with the AFCO.

good call on the oil coolers, I use a small intercooler as an oil cooler, and it did make a big difference when I switched from the single FC unit I was running before.

 

must be pretty close, but remember Pko and Ted had a 3 rotor Fc running in the 90's!

 

Thank you to everybody that has contributed to this thread. I'm sure it is well worth a sticky and provides some REAL answers on one of the the biggest concerns when going 20B.

What I've chosen to do on my build is to get a 26x19 double pass radiator from Jegs (Part#555-52037). The core on it is 20x17.5, but is 2.25" thick so it has over double the cooling capacity of the stock FC radiator.

Had to remove the crossmember, cut out the old condenser/radiator mounts from the top to where the Passenger Side A/C hardline goes through and flatten the sheet metal a bit by where the crossmember was, but it fits like a bloody glove on OJ Simpson

 

that radiator looks good, price is right too

 

bump this thread up

 

i think its pretty cool

 

Now that we've established the water cooling system's needs, we can do the same for oil cooling. There's no need to discuss oil pumps as the 20B and FD both use the exact same NF01 oil pump and dry sump questions are most likely covered elsewhere.

The purpose of this thread is to be the starting point for any and all questions regarding all aspects of keeping a 20B cool, in order to aid newcomers to the 20B ranks get a foothold among all the options available. In retrospect, a 20B cooling FAQ

From what I've read, the FC's oil cooler is more than adequate for a stock 20B since it's a nice, long double pass cooler from the very start. In regard to FDs, what I've seen is that the proper approach is to use the R1/R2's dual oil coolers. For those with deeper pockets, a similar setup from Mazdatrix uses dual Mocal coolers is available too.

On a related subject, I've run into a small snag regarding my build. Since it has to do with cooling, I thought it would be appropriate to post here.

When doing a 20B conversion, AC is taken out of the car, or at least that is the conventional reasoning. But if someone wants to keep their AC, it presents a few challenges.

First off, the suction hose for the A/C compressor needs to be lengthened by maybe 12" to reach the proper location. This applies to both the FC and FD if you're using all of the stock components.

Now, because the radiator is an aftermarket one, it had to be moved, and that means relocating the condenser too. Assuming the compressor discharge hose can reach, that leaves the lines between the condenser, receiver/drier and ultimately the evaporator inside the dashboard. on my Series 4 car (with the Sanden Compressor), there is a hardline containing the pressure switch that joins the Receiver/drier and condenser. After the Receiver/Drier, there are two more hardlines, one attached to the firewall that has the High Pressure Service Port on it, and an extension hardline to mate to the Receiver/Drier.

Because the Condenser has been moved, these hardlines aren't useable anymore and brings up the question of the A/C systems' fitting thread pitches. In addition to the thread pitch of each fitting, it begs the question of using proper hoses in place of the no-longer-useable hardlines as well.

As we all know the FC has a total of four different A/C systems, those being the S4 Sanden (the most common AFAIK), S4 NipponDenso, S5 Sanden and S5 NipponDenso. To further complicate matters, the FD has 4 different systems as well, those being the 1993 R12 MANA, 1993 R12 NipponDenso, 94-95 R134a MANA and 94-95 R134a NipponDenso. In my research, I've found that Nippondenso systems are factory-installed, while the Sanden and MANA are installed by the Dealership or at the Port of Entry.

If you've followed me this far, you'll see that misinformation runs wild when it comes to the A/C fittings for our cars. I've seen that they use SAE, NPT, Metric, ACME and AN, but with no actual identifying notes. By that reasoning, I've determined that no one apparently knows because they've never approached it logically by measuring.

When it comes to 20B conversions, there simply is a DIRE need for clarity with these fittings, so each line/hose can be replaced or extended to suit the owner's build.

So with this in mind, I am requesting assistance from the entire 20B community to help solve the last piece of the puzzle when making a 20B RX-7. If you're planning on recharging your A/C, please do everyone a favor by measuring the thread pitch of each connection and posting that info along with the details for your car.

 

AFIK, Only 95 FD's had R-134a systems the 93 and 94 used R-12

Otherwise great info.


John

 

Since a few people mentioned the AFCO radiators and such.
https://www.rx7club.com/race-car-tech-103/big-radiator-fc3s-916420/

 

What oil cooler you use now?

 

i think if you are building a street car the FC cooler is ok, but it won't be if it sees track use. especially with the twin turbos, 2 turbos put a lot of heat into the oil.

my friend keeps the AC, and he just cuts the rubber hoses, mocks everything up, and has new rubber hoses recrimped on the stock lines, its cheap, and very simple. its also the way to go if you're not doing a mazda/mazda swap, or if your car/truck has a sanden system, and the you wanna use the 20B's ac compressor.

it also works for PS hoses too.