The problem with having a supercharger that is spinning much faster than it is designed to is that a lot of heat is generated, particularly so as the efficiency drops. The supercharger on the MR2 is a Roots type which is very good for mid-range torque and makes a very driveable car, but the problem is as the revs rise that the blower starts to turn into something of a hairdryer. 

Obviously the MR2 is intercooled as standard, though being a mid-engined car the intercooler is in fact in the engine bay. The idea being that air is drawn up through the engine bay, through the intercooler and out the top of the engine lid where there is a low pressure area due to airflow from the roof over the engine lid. 

With standard boost (around 8psi) this is generally fine, but when you are running around 12-13psi the air coming through the intercooler is not sufficient to cool it. 

The design of the original air-to-air intercooler location and size makes it marginal even on stock cars when running on track. One of the main problems is the reliance on air being sucked through the intercooler as well as that air already being a fair few degrees above ambient due to it already having flowed up and over the exhaust manifold, over the engine or around the gearbox.

The first option I tried was having a fan underneath the intercooler which certainly helped provide a higher rate of airflow, although the air was effectively warm. Heat soak when road driving wasn't too much of an issue unless you had the supercharger on for long periods of time. But on the track it was all too noticeable and effectively resulted in raised boost pressure (due to the expansion of the heated air) and far less power. I have to guesstimate at power losses, but they must be in the region of 30Bhp or so.

Intercooler immediately post conversion. Please note that the intercooler here is from a MR2 MK2 Turbo or Celica GT4. This intercooler has fewer cores that are more tightly packed in comparison with an original MR2 Supercharger. This is because it is designed for a high airflow mounting position such as in the side engine vent in a MK2 MR2 Turbo. The MR2 Supercharger intercooler has more channels spaced further apart indicating it's design for a relatively low air flow.

My first step in improving the intercooling centred on finding an original Supercharger engine lid which is fibreglass and has two raised vents (you can see it in the above picture). One of these vents is basically a dummy, but the other one seals to the top of the intercooler. I also sourced an original SC intercooler, but the problem was that as I had an AE92 spec engine which came from a front-wheel drive Levin the outlet pipe from the supercharger was different, so I didn't have any of the corresponding pipework to plumb the intercooler in. Realising that it'd be very difficult indeed to source these I elected to have the necessary parts made by a local exhaust specialist in stainless steel. Richard at JP Exhausts  was very helpful and as Mark has two original MR2 Superchargers and an engine in bits I was able to lend Richard at JP the original bends to copy. 

Low res. This is the lower pipe that connects to the supercharger outlet to the intercooler. The black pipe is the plastic original used as a template.

This is the intercooler to inlet manifold pipe. Again the black plastic pipe is the original which was used as a template.

I had to get a supercharger outlet pipe made up as well which involved having a flange to mount to the supercharger laser cut

Really nice bit of work by Richard at JP. This is the supercharger outlet pipe. On the original outlet pipe which is in alloy, there is a branch that comes off to go to the ABV valve. As I am running above standard boost pressures there is no need for this, so effectively an outlet of this design ensures that all boost goes to the engine!

Another view of the supercharger outlet pipe.

Another problem I encountered once I had the intercooler in place was that it was fouling my induction piping which is in Samco hose that goes to the air filter in the boot. Back to JP again this time with Mark's OEM induction pipe to be copied to give enough room for the intercooler.

Very sexy pipe work though because the original Toyota induction pipe has a very sharp bend onto the throttle body in rubbery plastic, this can't be recreated in stainless so cutting back the throttle body was the only option.

Another view of the induction pipe work clearly showing the reducer from 70mm to around 65mm.

Original supercharger intercooler with cover in place

With all the shiny pipe work and intercooler in place, intercooling was improved but still nowhere near good enough for track work. My plan all along had been to fabricate ducting from aluminium in an effort to seal the intercooler from ambient heat within the engine bay. The plan was to duct air from the engine side vent over the cam covers then down and up through the intercooler. The intercooler would be sealed to the engine lid, so as to help increase the effect by air being  'sucked' out through the intercooler by the low pressure area above the engine lid. To further aid airflow through the intercooler I also manufactured a side scoop which would help force more air into the ducting. The engine bay fan is permanently on which should provide a nice cooling effect on the intercooler when not moving. Flexi-hose was used to pick up air from behind the fan and to connect to the ducting, thus allowing engine movement.

This is the engine bay fan. You can see the flex-hose immediately behind it .This does not cover the entire area behind the fan as I wanted to allow some air to still get to the engine bay for cooling.

Intercooler ducting is in fact finished in this picture. At the top of the pic, the flexi-hose can be seen. The ducting goes over the exhaust cam cover and then down and underneath the intercooler to which it is sealed. Aluminium is riveted together and sealed with industrial double sided tape that forms a sandwich between the joints of aluminium and is then pop riveted through where it is under structural stress. The intercooler when removed has the ducting attached to it, but will slide out from the ducting over the cam covers.

A clearer pic of the flexi-hose which is tie wrapped to the rear of the fan. Intercooler stainless outlet pipe can be seen immediately in front of the duct.

Foam is used on top of the intercooler to seal it to the engine lid. Really the intercooler should be higher but I had problems raising it enough and elected to use the foam as a temporary measure for test purposes. Induction piping from shortened throttle body can be seen to the left. 

Yes I know, what beautiful pipework. Sometimes functional things really can look the part. A good advert for JP Exhausts I think! Bottom pipework is induction from air filter in boot to shortened throttle body. Position of temperature probe can be seen at top right of intercooler (white disc)

So does it work? Well previously on-track at Spa and on cruising at 90mph  the temperature went off the scale which is limited to 70C after a lap or so of the circuit or around 10minutes of cruising on the motorway. With the ducting on temperatures were stabilised at just under 50C. This could literally be a halving of the intercooler temperature! The car felt much, much better on track as with the heatsoak under control power didn't noticeably drop off. See Beard pt 3 for the Side Scoop. Furthermore temperature was reduced to near ambient when just idling with the engine vent fan running within a few minutes. I actually experimented running on the M62 at around 90mph. The M62 is the highest motorway in England and has some steep inclines. Temperature never rose above 32C. On the M1 I tried cruising at around 70mph without the supercharger running. Temperature came down to within 2 degrees of ambient after 15minutes and could be seen to drop a degree or every minute.

Mark has just received a proper temperature module that is faster reading and more accurate as well as allowing two probes to be inserted into the intercooler inlet and outlet. This will give us a much better idea of intercooler efficiency and the effect of the ducting than the cheap Halfords special which is simply placed on top of the intercooler outlet.