Project MR2 Turbo: New, Efficient Mishimoto Fans for Our SW20 MR2

J.G.
Update by J.G. Pasterjak to the Toyota MR2 Turbo project car
Nov 2, 2020

For those of you playing along at home, you may remember the poor state of the original fans in our 1991 Toyota MR2 Turbo that we discovered when installing a Mishimoto radiator

While we reinstalled those old fans at the moment in order to get the car back in service, we also placed an order for the matching Mishimoto fan shroud kit designed for our new radiator.

Fan installation in an SW20-chassis MR2 is a quick and easy job that can be completed inside an hour. Here are a few tips to cut down that time even more.

As with radiator removal, you’ll need to pull a few brackets in order to access the fasteners securing the fans. We used this opportunity to clean up some rusty fasteners. 

Sure, we could just replace them with common hardware, but there wasn’t much structural damage, and we like the captive washers found on the OEM bolts. Typically we use something like CRC Rust Converter for these small hardware jobs but it was the weekend and we were out of CRC magic sauce. So, we threw our hardware in a dish of white vinegar overnight, followed by a quick trip to the media blast cabinet, then a quick soak in oil. Good as new.

You’ll need to do some simple wiring to install these fans, so clip off the connectors from the old fans and leave a bit of wire to work with. You’ll also need to confirm which of the wires heading to the fans is hot and which is the ground so the new fans run in the proper direction. Disconnecting the temp sensor on the radiator defaults the fans to the on position, and you can use a test light to confirm polarity.

We made our splices using some cold-melt, heat-shrink solder connectors we got from a Facebook ad. They’re awesome for stuff like this. Way better than the at-home surgery kit or the imitation Flowbee we also got from Facebook ads.

The Mishimoto fans are twin units housed in their own custom shroud which pull up to 2300cfm of air across the radiator. The shroud covers the entire surface of the radiator, and weatherstrip tape provides a positive seal. This ensures that the radiator sees the maximum volume of forced air across its core for the most efficient heat exchange.

The fan occupies a lot of lateral and vertical space in the radiator area, but not as much depth as the OEM units. It’s a very space-efficient fit.

The fans bolt neatly up to the Mishimoto radiator with zero stress. It’s a perfect fit all around.

Like the radiator, the fans occupy the maximum amount of lateral space available in the car. We even had to flip around our hose clamps so the screw part was out of the way of the fan shroud.

And that’s a wrap on the front-of-the-car cooling upgrades. As we mentioned before, we’re going to put a lot of effort into max chill for this car. Between the pressurized air coming from the turbo and the mid-mounted engine position limiting airflow, dealing with the resultant hot air and coolant in and around the engine is a big priority before we put real effort into more mower.

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Comments
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Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
11/2/20 8:49 a.m.

Pretty skinny fans on a shroud that's very close to the core. How do they do pulling through multiple heat exchangers? That's the usual downfall of slim fans with no torque.

Jerry From LA
Jerry From LA SuperDork
11/3/20 1:04 p.m.

In reply to Keith Tanner :

Lots more aluminum involved with this setup aiding heat exchange.  These new fans have to be better than the OEMs, especially with the extra sealing.  Maybe we look at the overall system rather than one segment of it.

Tyler H (Forum Supporter)
Tyler H (Forum Supporter) GRM+ Memberand UberDork
11/3/20 1:40 p.m.

That Corbin clamp on your upper hose is hurting, but I don't blame you for leaving it alone.  There's a hundred ways to lose knuckle skin on this job.  

When I have to remove that clamp, I typically disconnect the hard pipe brackets and pull it back into the frunk to work on it.  I once bought an MR2 Turbo that someone had installed silicone hoses on, which I replaced with durable, reliable OE hoses.

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
11/5/20 9:15 a.m.
Jerry From LA said:

In reply to Keith Tanner :

Lots more aluminum involved with this setup aiding heat exchange.  These new fans have to be better than the OEMs, especially with the extra sealing.  Maybe we look at the overall system rather than one segment of it.

What aluminum? In the shroud? That doesn't help. Note that I've been involved in actual instrumented dyno testing under controlled conditions, so I have a bit of insight into what makes fans work.

These new fans do NOT have to be better than the OEMs. I don't bash non-FM products as a rule, but I make an exception for the Mishimoto fans for the Miata because they are terrible. The slimline motors have no torque to pull through multiple heat exchangers and the shrouds are far too close to the core, which means the fans really only pull through about 50% of the core surface area. Looking at this application, I see the same.

The fan manufacturer should be able to tell you how the fans perform not just in free air, but also when there's a pressure gradient involved. Slim, low torque motors will fail in the latter application, but unfortunately it's where fans actually really come in to play. You need big beefy motors that suck a lot of juice. Coincidentally, that's what most OEM fan motors look like.

The shroud has to be far enough away from the core to allow air to move sideways. The closer it is, the less airflow you have through the core that's not directly under the fan. We want to see at least an inch and preferably more. GRM states that these fans don't use all the space available. I would be willing to wager that proper testing would show that adding spacers under the shroud stand-offs to move the shroud further away from the core and use up some of that unused space would improve the cooling ability of the car. Again, you'll notice that OEMs do this. They also have the abililty to shape the shroud to direct airflow, which is not possible with the folded sheet metal shrouds usually found on aftermarket setups.

Sealing to the core - I've mentioned that. But again, look at the OEMs. They're pretty well sealed.

What part of the overall system did I miss here?

Maybe when this car's cooling system is struggling next summer GRM will try to space that shroud off the core. It's the easiest fix to try. Swapping in some stronger fans would be a second choice. Since these fans were most likely donated to GRM by Mishimoto in exchange for editorial (hey, it's what makes project cars possible), the former experiment would likely be more palatable to all involved.

 

JG Pasterjak
JG Pasterjak Production/Art Director
11/5/20 9:29 a.m.

Long term testing I guess will be the decider. We have some space at the bottom to offset the shroud, but almost none at the top. But worst case, should we find that the flowthrough isn't sufficient, it's conceivable we could offset teh lower part of the shroud and create a higher volume low pressure area between the core and the fans.

 

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
11/5/20 9:42 a.m.

Cool. It may make for some interesting articles, honestly. Like radiator design, there's a lot of bad assumptions out there about fans. If you want, I could probably dig up some numbers from our testing. We had an engine that could run under a set load as a heat generator and a radiator in a box with multiple fan setups tested. We tested time-to-temperature and drop across the core. Not easy to do in the car, but it's pretty useful data.

If you're constrained at the top, that is going to make things more challenging. Going with a wedge will probably help. Where does the air go afterwards, do you have any aerodynamic assist to help out?

Here's an example of the effects of motor torque. The only difference between the orange and grey traces is the size of the motor on one of the fans. Obviously both of them are dwarfed by the two blue traces, but you can see how the grey setup consistently outperforms the orange. It would be a lot more obvious if we scaled the graph from 0-1800 CFM :)

The blue traces? Massive brushless motors that are a pain to package and have huge power feeds. These are the ratings from the manufacturer, shroud design is not taken into account.

JG Pasterjak
JG Pasterjak Production/Art Director
11/5/20 10:11 p.m.
Tyler H (Forum Supporter) said:

That Corbin clamp on your upper hose is hurting, but I don't blame you for leaving it alone.  There's a hundred ways to lose knuckle skin on this job.  

When I have to remove that clamp, I typically disconnect the hard pipe brackets and pull it back into the frunk to work on it.  I once bought an MR2 Turbo that someone had installed silicone hoses on, which I replaced with durable, reliable OE hoses.

When I did the rad, one of my plans was to replace them wth the proper OEM spring clamps, which I have a big box of that I've collected over the years. 

Except... I couldn't find ones that fit. And as I was working—as I frequently am—at like 1am, I just put the old clamps back on because they had nice grooves already and I know they worked. 

Of course, when I was putting tools away I found—wait for it—the OTHER box of Toyota clamps with the proper size. They sit. Waiting. Just in case.

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