This is a reading guide built from four forum threads between 2010 and 2016, and much of the argument was heated. Several of the people posting sold, fitted or tuned for one kind of cooler. The numbers below are what owners said they logged, with the conditions where they gave them. Most were not controlled tests, so don't compare one figure with another too closely.
The short version
- The standard intercooler is fine for road use at standard or mild power. On track, with a stage 2 map, owners recorded intake temperatures from the mid 80s to over 100 °C.
- An uprated air-to-air intercooler is cheaper, lighter and easier to fit than a charge cooler. Owners with one said it kept intake temperatures to about 40 °C in warm weather, including Le Mans traffic and sessions of 15 to 20 minutes on track. Others doubted the air supply through the side vent could keep that up.
- A charge cooler gave the lowest logged temperatures in the thread (40 °C or so at full throttle in two owners' logs), at the cost of price, weight, plumbing and fitting time.
- It matters because the ECU takes out ignition advance as the intake air heats up (see below).
- Nobody posted a proper like-for-like comparison. Several owners asked for one and the thread ends asking for data.
The arguments
For the air-to-air intercooler
- The heat goes air to metal to air, whereas a charge cooler goes air, metal, water, metal, air. The more steps, the less efficient it is for a given size.
- It is one component, whereas a charge cooler needs a pre-radiator, pump, reservoir and several litres of coolant. One owner put the Pro Alloy kit at 14.25 kg plus about 7 litres of coolant, against about 6 kg for a large aftermarket intercooler.
- On track, the water in a charge cooler can only hold so much heat. If the front radiator can't get rid of it, the system warms up.
For the charge cooler
- The engine is behind the driver, and the only fresh air is the small side vent. A water system lets the heat exchanger sit near the engine and the pre-radiator sit where there is airflow. Several owners said this was the main reason the tuners chose it.
- The water has a large thermal mass, so the intake temperature changes slowly when the car stops, while an intercooler in a hot engine bay will heat soak quickly at a standstill.
- An owner said an intercooler in the ear dumps its heat straight into the engine bay, while the charge cooler's pre-radiator vents ambient air over the top of the car. Owners said another car's heat problems (a melted crank sensor and gear cables) were probably made worse by keeping the standard intercooler in place.
- A charge cooler is the only choice on a supercharged car, because the manifold is water cooled. One owner said the standard Laminova cores are fine for about 200 bhp and a bottleneck above that. See the supercharged charge cooler notes.
The lag argument
One owner said a bigger or denser cooler on a standard turbo costs boost pressure and adds lag, and claimed a 4 to 7 psi loss across a charge cooler. A tuner relayed Pro Alloy's own figure of 2 to 3 psi. Another owner worked out that even four extra litres of volume at full flow takes under 0.02 seconds to fill, so the lag is not noticeable, and said lag mostly comes from the turbo itself. One owner running a stage 4 intercooler on a stage 2 map said any extra lag was too small to notice. The pressure loss figures were not measured in the thread.
What owners logged
| Set-up | What was reported |
|---|---|
| Standard intercooler, stage 2 (245 bhp) | Peak 106 °C over 9 laps of Combe in 20 to 25 °C ambient, on boost for about 70% of each lap. |
| Standard intercooler, stage 2 map | Another owner saw peaks in the mid 80s on track. |
| Standard intercooler, standard map (200 bhp) | 66 °C at the end of the straight at a French track day. |
| Uprated intercoolers, about 250 to 275 bhp | 74 to 94 °C at the end of the straight at the same event (about 5,500 rpm in 4th), depending on ear size, airflow guides, the cooler and the map. Another owner called 94 °C implausible. The owner who logged it said it came from the OBD port. |
| Large aftermarket intercooler vs Pro Alloy charge cooler | Over 12 seconds of hard acceleration in 22 °C: the intercooler went from 24 to 60 °C, the charge cooler from 28 to 43 °C. The owner said the charge cooler was three to four times as effective. |
| Pro Alloy charge cooler | A maximum of 40 °C in a full-throttle pull from 140 to 265 km/h, and the same on 8 minutes of hard autobahn driving. The owner also saw a richer mixture (lambda 0.77 against 0.69 with an intercooler) and a leaner, cleaner exhaust. Another owner said he had never seen more than 40 °C on a 300 bhp charge-cooled car. One said temperatures were close to ambient on the fast road and only a little higher on track. |
| An early Courtenay charge cooler kit | One owner logged his own data and was disappointed on track. Fast-road temperatures rarely went over 45 °C anyway. He took it off, and said he thought the later Pro Alloy design was a better product. He had not tested it. |
| Uprated MMG intercooler, stage 4 | Owners said intake temperatures stayed around 40 °C at Le Mans in 27 °C weather, in traffic and on track, with a friend's car doing the same. A tuner who sells them offered a bet on no more than 50 °C after an hour out. One owner whose car was logged at Le Mans did not post the results. Treat these as owner and seller claims. |
One charge cooler owner argued that intercooler cars described as "perfectly happy" might spend little time at full throttle, be winter cars, or have the ECU protection switched off. An intercooler owner replied that the car he meant had been driven hard to Le Mans and on track.
Why intake temperature costs you power
- One owner with a copy of a tuner's metrics sheet said the stage 4 map starts pulling ignition advance from 50 °C intake temperature, and that he lost about 15 bhp at 55 °C. A French owner saw the advance fall after 50 °C and become a retard at around 85 °C.
- Another owner said anything under 75 °C would show no power loss. The first owner corrected him. The sources agree that it depends on the map, and a supercharged map may use a different threshold.
- An owner said the Turbo cuts power for a few seconds at about 85 °C even with a standard intercooler.
- So fitting a charge cooler without a good front radiator, or a bigger intercooler without airflow, may protect the engine but not give the power back. Check with your tuner how the map reacts to intake temperature.
Getting more from the cooler you have
- One owner said improving airflow through the standard intercooler was worth more than replacing it with a slightly larger one. Ideas in the threads were a ram-air scoop with the gaps sealed with foam, venting the arch liner behind it, an intercooler water spray with a controller, and ducting.
- An owner with a stage 2 car asked for a half-way step between stage 2 and stage 4 without paying four figures. The replies were to buy the smaller MMG unit (rated for standard up to stage 3), or go straight to a stage 4 cooler and a proper remap so the car is ready for it. One owner said a bigger generic intercooler is hard to fit, because there is very little room in the ear, and a cheaper but bigger core is unlikely to match the more expensive one.
- An owner with a stage 4 intercooler said they had run it on a stage 2 map with no trouble. Another said a big cooler works less well on a low-power car because of reduced flow, so ask the supplier.
- If you take the route of a generic cooler plus a remap, one owner suggested fitting it, getting a stage 4 map loaded, watching intake temperature (OP-Com, or a gauge that logs), and upgrading the cooling if it gets too hot.
Logging your own temperatures
- Check where the intake temperature sensor sits. One owner asked whether it reads after the cooler. A ScanGauge shows the current and maximum values but doesn't log them, so it only helps if you watch it.
- Owners suggested a Bluetooth OBD adapter with a phone app, or a DashDAQ-type logger. The data from an OBD logger can also show ignition timing and the air mass reading, which tell you what the ECU is doing about the heat.
- One owner said a proper test would need ambient temperature, plus temperatures before and after the cooler, and boost.
- Compare like with like: the same track, the same weather and the same amount of full throttle.
Driving with no cooler
In 2014 an owner whose charge cooler had failed connected the turbo outlet pipe straight to the throttle body top hat to move the car. It ran, with the intake temperatures getting a bit hot. The advice he got was to stay out of boost, because uncooled air risks detonation. One owner suggested unplugging the MAF to stop it boosting, but another said it would still boost on a fixed map, and that the safe way is to disconnect the rubber hose at the top of the wastegate actuator and seal it. For getting the old cooler out, see Intercooler replacement and hoses (Turbo).
Boost pipes and routing
A 2016 thread by an owner fitting a charge cooler to an engine-swap car (with a custom manifold) added the following.
- Pipe sizes. One owner who measured said the standard rubber pipes are two different sizes: 2 inches from the turbo to the intercooler inlet, and 2.25 inches from the intercooler outlet to the throttle body top hat. Another said from memory that it is all 63 mm (2.5 inches). The numbers disagree, so measure yours before ordering anything.
- Route. The lower pipe from the turbo goes over the lower wishbone mount and under the chassis, then a 90 degree bend runs up into the cooler. The same pipe is used on the Pro Alloy charge cooler.
- Spares. Standard pipes come up on eBay and from breakers, and are rarely needed. One burst at 25 psi.
- Custom pipework. The owner advised against chaining many silicone bends and joiners because they tend to leak. He had a local welder make a hard pipe in the garage for £70, with short silicone joiners at the ends to allow for engine movement, and doubled up the clamps on it.
- Sizing. The usual practice is to increase the pipe bore steadily from the turbo to the engine. A large inlet fans the air out across the core and cuts the pressure loss. One owner asked the supplier to increase the Pro Alloy inlet and outlet to 76 mm because he thought they were small.
- For the factory steps see Intercooler replacement and hoses (Turbo), and for fitting the charge cooler see Pro Alloy charge cooler: fitting to a Turbo and Turbo charge cooler kit. For the stages see Turbo stage 2.5, exhaust and power limits.
Help wanted
Logged intake temperatures for the same car and the same use (track and fast road, with the ambient temperature) with the standard intercooler, an uprated intercooler and a charge cooler would settle most of this. If you have such a log, please send it.