C'est en anglais, mais ca explique bien:
(merci a
http://www.mkiv.co.nz/ )
FMIC=Front Mount InterCooler (echangeur frontal)
Citation:
Intercooler Upgrades
When should I upgrade my Intercooler?
The stock intercooler is very good as far as factory intercoolers go and if you are running the stock boost of 11psi then there is no reason to install a FMIC (Front Mount InterCooler) apart from looks. However once you turn the boost up above 16psi (which needs a Fuel Cut Defender) then there are benefits to be gained from installing a FMIC. These are:
More power (approx 10-15kw extra at the wheels)
Less thermal stress on the engine due to cooler intake and exhaust temperatures.
Increased boost levels (2-4psi) before detonation occurs.
What size and brand of FMIC should I install?
They say size doesn't matter but when it comes to intercoolers it usually does. A good size for a stock turbo'd mkiv supra running say 18-20psi would be 600mm Wide x 300mm High x 75mm Deep. This should give you all the benefits listed above and should handle up to 300kw at the wheels. If you are running aftermarket turbo(s) and you are making more HP then 300kw at the wheels then you should install a bigger FMIC. A good size for 400+kw at the wheels would be 700mm Wide x 300-400mm High x 100-125mm Deep or bigger if you can fit it in. The gap between the front rails on the Supra is around 790mm so taking account of the end tanks on the FMIC, it will need to fit into this gap.
Just one word of caution with FMIC's. They do reduce the amount of air reaching the radiator and that air will be heated as well, so you can cause overheating problems if the FMIC is too big or too deep. A possible option to help alleviate this problem would be to install twin 12" electric fans instead of the factory thermatic fan and tiny subsidiary electric fan(s).
There are a large number of aftermarket FMIC's available but unfortunately there is very little data available on flow rates, pressure drop and cooling efficiency available. Spearco who make alot of the cores used in these intercoolers do publish this information, but matching their cores to actual branded intercoolers in well nigh impossible. There are also alot of small companies that make intercoolers and again there is unlikely to be any data on them.
There are alot of people that will tell you fitting a large FMIC is going to result in a big increase in lag but to that I say Rubbish! Whatever lag increase there may be from the FMIC will be mainly attributable to using larger diameter intercooler pipework and having an intercooler with much larger end tanks then the factory intercooler. When I created my FMIC using 3 factory intercoolers welded end-to-end I ended up with an intercooler that has a core of 660mm Wide x 270mm High and 125mm Deep. This hybrid intercooler will flow enough air to support over 400kw at the wheels and there was absolutely no perceptable increase in lag. This is because I was using the factory end tanks which are very shallow and the intercooler piping I used was only 63mmID. which is what alot of the factory system is. This piping does flow alot better then the factory setup though as the factory pipework squeezes down to around 55mm as it goes through the side chassis wall down to the intercooler.
If you go for a brand name product such as HKS, Greddy or Blitz then expect to pay around NZ$3000 for one. However, a non-brand name intercooler that performs identically can be had from between NZ$1000 to NZ$1500.
There are two core types for air-to-air intercoolers and they both have their advantages and disadvantages. The BAR & PLATE type has more pressure drop and a lower flow rate but usually has a higher efficiency. The TUBE & FIN type has less pressure drop and a higher flow rate at the expense of a lower efficiency and will be the lower priced of the two. The factory mkiv intercooler is a TUBE & FIN design. Here are links to two intercooler upgrades done by NZ Supra group members. See Kevin's Tube & Fin FMIC Upgrade or Lindsay's Plate & Bar FMIC Upgrade
Intercooler Efficiency
The stock Japanese mkiv intercooler has to cool 280hp worth of air (same intercooler as Export mkiv) when the motor is at stock hp rating. However as soon as you start increasing the hp (extra boost, high flow inlet, exhaust upgrades, cams, etc) the efficiency of the stock intercooler begins to drop very quickly. You don't believe me? As an example. lets assume we are now getting 400hp out of our mkiv. This is getting near the limit of the Japanese mkiv turbos of about 450hp, so is a good example.
If we divide 400 by 280 we get a minimum increase in airflow of 42.86%, or 1.4286 times the airflow. As we havn't changed the intercooler, or the size of the pipes feeding the intercooler, then the air (remember there is 1.4286 more of it) has to flow 1.4286 times faster to get through the pipe in the same time. If we assume the total cooling power of the intercooler is fixed (a reasonable assumption, which I'll discuss later) then there is 1.4286 times the amount of air to cool in 1/1.4286 (or 0.7000) the amount of time. If we multiply these two factors together (1.4286 * 1.4286), you get 2.0409. This means the intercooler is now only 1/2.0409 (0.4900 or 49.0%) as efficient as it was at stock hp.
Also, if we are running the stock turbos at higher boost levels to achieve the 400hp, then they will be running at a lower efficiency level then stock, and hence producing more heat, per unit of boosted air produced. This means the intercooler will have hotter air entering then at stock boost, thus further increasing the temperature of the air exiting the intercooler. The intercooler will now be less then 49% as efficient as stock, perhaps about 45% or so. The benefits of an intercooler upgrade become immediatly apparent.
What does an efficiency of 45% of the stock intercooler actually mean? Without getting technical, it means you would need more then two stock intercoolers, if they were arranged in series. By series, I mean all the air flows through one and then flows through the second intercooler. However, if you take those same two stock intercoolers and arrange them in parallel (1/2 the air flows through each one) then you can increase hp from 400 to 560 (280 x 2) and still get the same air temperature into the engine. This is because you now have the same amount of air as stock flowing through each intercooler, and the air is flowing through the intercooler at the same speed as stock.
I plan to produce some hard data soon, on inlet/outlet temperatures at different boost levels with a stock intercooler, and then with an upgraded intercooler system , to support (or refute) these arguments. My upgraded intercooler system will consist of two stock intercoolers (one in each front brake air entry), with 50% of the airflow going through each intercooler. Theoretically, there will then be about 200hp of air flowing through each intercooler, which should make my system (280 / 200 = 1.40) 40% more efficient than the stock system, with a considerable increase in hp and a large reduction in intercooler exit air temperatures as a result.
