Discussion: Intercooling - which is best?
When a car is running forced induction - be it turbo or supercharged, the air passing
through it will rise in temperature due to compression. The higher the boost, the
greater the rise in inlet temperature. Also, with turbos (at least in my case) there
is a baseline temperature rise even when off-boost.
This can be attributed to the fact the compressor housing is attached to the turbine
and therefore soaks up heat from the "hot" side of the turbo. On a 20'c day, off
-boost i will typically an outlet temperature of 50'c - therefore a temperature delta
of about 30'c as a penalty for running the air through the turbo. Running the water
lines to the turbos didn't make any difference to this figure.
Many people say that for low boost applications (6-8psi / .5 bar) that there is no
need to run intercooling. I did indeed run the car for quite a while with no intercooling
and it performed fine. Although on a hot day, i would see inlet temperatures peak
at 90'c (194'f) - which I considered to be too high for making best power. So i decided
some form of cooling was required (and i like researching this sort of thing)
Two methods of cooling your charge temperatures exist:
Front Mount Intercooler (FMIC) or also known Air to Air
and
Chargecooling or sometimes called Air to Water cooling. (but probably more accurately
Air to Water to Air)
The debate over which type is best continues to roll on, I think its less about which
is best, but which is more suitable. The quick answer in my opinion is:
Air / Air Intercooling is the best form of cooling.
Air / Water is the second best.
Benefits of intercoolers: Simple
Effective
Lightweight Cons: Requires quite high air flow to be effective
Requires long and bulky charge pipes to be plumbed round engine bay
Boost lag because of volume (i wouldn't get too hung-up on this factor unless running
very long and large pipes)
Benefits of chargecoolers:
Compact
Good heatsink ability
Can be placed very close to engine (if not ON the engine)
Flexible - can increase water capacity, pre-rad size to improve effectivness Cons:
Not as efficient as intercoolers - The water is just a conduit of heat, you still
need to cool the water back down
More plumbing
Requires a pump
Heavier
One of the only times a chargecooler can outperform an intercooler on a significant
scale is by pumping COLD water through the core. An ice compartment is placed in
the boot, where the water is pumped over it, this can achieve inlet temperatures
LESS than ambient. This is only of use on the drag strip or on dyno shoot-outs -
but a useful benefit none the less.
All coolers whether a air/air or air/water are also heatsinks, Chargecoolers provide
the best heatsink capability due to the fact that they contain water - in fact adding
more water is easy on increases the ability of the cooler to absorb heat without
having to (immediately) dump that heat - which I will go onto demonstrate here.
Chargecooling usually eases packaging constraints. The chargecooler can be placed
close to the turbo or manifold. The pre-radiators can be placed anywhere they will
recieve a flow. There's no need route large 2 or 3 inch pipes through to your front
bumper. The decision to chose an intercooler or chargecooler comes down to a few
factors. I would say, explore the possibilities of fitting an intercooler first and
if you cant find a good or easy solution - then look at chargecooling.
- Street use with speeds that provide constant air-flow over your cooler would steer
towards intercooling.
- For Drag Strip, Dyno queen or packaging constraints - then a chargecooler provides
good benefits.
So if intercooling is the best - why did i decide to build a chargecooler then?
I have opted to go for chargecooling because I'm a cautious person who always likes
to leave a reverse path to remove something if it doesn't work or I don’t like it.
I know an intercooler would provide good results on my car, but I didn't want to
route pipes out to the front of the car, possibly cutting the bodywork - which isn't
easily repaired. I was also worried that a large intercooler on the front of the
car may block cooling air going into the radiator - whereas with the chargecooler
placement, size and design of the pre-radiators is very flexible - if the car overheated
due to lack of air flow, i could easily move them into the wings or even to the back
or underneath of the car with a scoop to direct air-flow. This flexibility appealed,
so that's the route I choose.