Just been looking at a new intercooler for my car (Focus ST(. the Brand name intercoolers like forge and pro alloy are all retailing at around £500 but there are intercoolers on ebay from "reputable sellers" for around £100 that claim to do the same thing is this possible or are they just cheap imitations? .... whats your thoughts ?
YOU GET WHAT YOU PAY FOR!!!
They may claim to do the same thing, but they don't.
An intercooler has to remove as much heat as possible from the compressed air whilst keeping the pressure differential between the inlet and outlet as small as possible.
If the intercooler isn't efficient the air entering the engine will be too hot. If the pressure differential across the core is too great there will be an increase in turbo lag.
Increasing the size of the core will help to reduce temperatures but at the cost of having to move vast amounts of air, again resulting in increased turbo lag.
To remove a lot of heat from the air without excessive pressure drop or having to be huge, the intercooler core has to be well designed and this doesn't come cheap. For example, the bare core alone for my car cost £350 and it is only 600mm x 170mm! However, it is only one step down from F1 performance.
If you are only changing the intercooler for looks, then buy the cheapest. If you want it to actually work, then you will have to dig deep. A properly designed intercooler will give you more bhp than any combination of cone filter/decat pipe/etc/etc.