Air Water Intercooler conversion

Ever since the original rebuild and subsequent roadtest I had noticed that the new setup , while ultimately far more powerful than the 8v / non-intercooler version, lacked a certain amount of responsiveness.

This appeared to be caused by the long runs of 2.5" intercooler piping and the ( huge ) intercooler at the front. The long runs were necessary simply due to the distance to the front of the SS1, but the intercooler could have been smaller. It just turned out to be the only one I could find online with inlet/outlet pipes that pointed rearwards and which fitted neatly between the chassis rails. With hindsight it could probably have been cut down to just a few rows though.

Anyway, with the seeds of dissatisfaction sown, I began to investigate an alternative arrangement - a water cooled intercooler with an air cooled heat exchanger.

There are kits now available here for these things, but they cost a lot, so I sourced the necessary parts globally via our old friend e-bay.

The basic components are:

water cooled intercooler ( 6" core length )

heat exchanger ( 30 row oil / water cooler )

water pump & electrical connector ( Bosch )

cooling fan ( Spal 7.5" pull fan)

inline filler cap

miscellaneous hose & unions

2" intercooler silicone pipes

The actual swap was fairly straightforward, although the whole nosecone of the SS1 had to come off first. 

• The old intercooler was removed and the radiator farings extended to be flush with the front armature. Additionally an aluminium plate was installed between the front armature and the lower edge of the radiator mounting frame. This forms a nice duct to get the cool air directly to the radiator.
• The small Spal fan was attached to the heat exchanger with aluminium bracketry and pop rivets and the whole mounted within the new ducting on the mounting points on the front armature that originally held the FMIC.
• The circulating pump was fixed to existing  tapped holes in the front armature ( which originally held the crossmember to which the Reliant cooling fan was mounted ).
• The intercooler was fitted to the inlet manifold/turbo with the 2" silicone pipe ( 3x 90 deg bends , 1x 2"-2.75" reducer ) .
• Two new items needed fabricating, a new s/s pipe with tees for the recirculating air valve and air bypass, and a 45 deg s/s pipe with a tee for the wastegate actuator pipe.

Overall the new arrangement is smaller and neater than with the air cooled intercooler and the path between the turbo and the inlet manifold is as direct as possible.

So with the new intercooler plumbed in and the front end reassembled it was time to see if the conversion had been worth the effort.

There are quite a few comparisons on the internet between the efficiency of an air cooled intercooler vs water cooling. Unfortunately they mostly concentrate on the actual efficiency issue rather than real life performance. All things being equal the air cooled intercooler should be more efficient as there is only one heat exchanging interface and the input charge is cooled by an effectively infinite supply of air at ambient temperature, whereas the water cooled option has two interfaces and a finite body of water to transfer the heat to the air cooled interface, so it is always likely to be above ambient temperature, though the fan assisted cooling should minimise that.

The real factor in favour of the water cooled intercooler however is the minimising of the length of the pipe run between the turbo and the inlet manifold, with the consequent minimisation of the volume of air that must be compressed by the turbo. If there is a blow off valve or recirculating air valve, then this volume of air has to be recompressed every time the throttle is closed and reopened. There is a positive feedback loop at work here, as in an amplifier, and minimising the amount of air to be recompressed increases the efficiency of the system, not just linearly but to according to a power law (ie dramatically ) . So reducing the equivalent of 3m of 2.5" piping ( excuse the mixed units! ) to 0.6m of 2" piping ought to make a radical difference to the responsiveness, aka turbo lag.

Did the road test bear out my armchair science?

I had to wait a week of torrential Australian  Easter rain ( I don't drive her in the wet ) before conditions were nice & dry - plenty of other things to tweak in the meantime though.

If it wasn't my own SS1 then I might have assumed the engine had been swapped or it was a different car. The change in performance was incredible, every twitch of the "loud" pedal resulting in instant response. It really confirmed my suspicions regarding the way big FMICs and fat intercooler piping saps the performance from turbo aspirated engines. It might look impressive but the moral of the story is to keep the pipework as short as posssible. That might seem obvious anyway, but in reality the way to achieve that is by using a water cooled intercooler because the only other alternative is to mount the (air cooled) intercooler right over the engine , with an air scoop in the bonnet ( a la impreza or many turbo diesel powered 4WDs ).

The conclusion then is that it really is worthwhile to go for a water cooled intercooler - the performance is sparkling ( ehem ).