anyone knows why subaru offers complete different engine power for the uk and jap models?

 

European emissions laws are more stringent, meaning that Subaru have to strangle the car's exhaust to comply with the Euro regulations.

Also, the latest JDM STI car has a higher spec engine including equal length manifold and twin scroll turbo which help extract more power over the Euro spec cars.

A decat zorst soon releases the horses though!

LC

 

Any company will make products which it's marketing department thinks suitable for the market concerned. However there is one big difference between the UK and Japan, the availability of high octane fuel.

The octane rating indicates the resistance to exploding. You want the fuel to burn in a controlled way to generate maximum cylinder pressures (and hence more power) without detonation (explosion) which causes damage. The higher the octane rating then the greater resistance to detonation and therefore the greater timing advance you can run. The more you can advance ignition timing without provoking detonation, the closer you come to liberating the theoretical maximum amount of energy from the fuel and the more power you generate.

So the only reason for the difference is the availability of higher octane fuel.

In the UK the highest octane fuel you can buy is Shell Optimax which I saw in another post recently is quoted as having an octane rating (RON) of 98.6 (correct?). Ordinary super unleaded in the UK will is 97 RON, regular unleaded 95 RON. In Japan we have high octane fuel of at least 100 RON (with popular opinion that some distributors sell 100+ RON fuel).

In many parts of Europe you can get 100 RON fuel, so the UK is the poor neighbour in comparison. However consider the pool old US who have to make do with even lower octane fuel. It's one of the main reasons why US cars have such large engines, they have poor fuel.

Edited to add: the same car will develop different power outputs in the UK and Japan simply because of the octane rating of the fuel. There are different emissions regs too which affects what Subaru can take to the UK. For example the 2.5 litre twin turbo engine cannot meet Euro IV regulations. However Japan is planning to adopt new emissions regs which will be as tight as if not tighter than Euro regs. When that happens anything made for Japan could be taken to Europe. But who knows what engines they'll be?

 

if the above is true how come my JDM STI passed the sva and UK emmisions tests? The car must be ok to run over here or it would not have passed

 

I think it's more to do with European Type Approval than the availability of high quality fuels. JDM cars can be remapped to run on UK fuels without damage, they just develop a bit less power - though still more than their UK counterparts.

However, getting an engine through the Type Approval process is expensive and time consuming, and Japanese emissions regs would appear to be easier to meet (though they're more just 'different' than necessarily more relaxed). This means that new engine developments tend to come to the Japanese market alone, because it's simply not worth the cost and R&D to get the latest engines type approved.

 

SVA rules are not the same as the rules required for a manufacturer to generally import vehicles for sale (i.e. quantities >50? ). Look at Mitsubishi and all their limited edition Evo's. Similarly the twin scroll Subaru engines found in domestic cars here. Look at all the hoops that Subaru had to jump through to sell WR1's, register them first and then have additional kit fitted by the dealer etc.