just spoke to my mate who is a scooby expert and he said uk engine and heads are the same as the sti v4 , all you will need to swap is the camshafts , thats the only difference mate


We were discussing a my97 uk wrx engine.

 

he talking Sh*t, STI's have forged internals and the heads are also different.

 

Not strictly true.

Basically the heads are identical its the Valves, springs, retainers, buckets, shims and cams that are different.

With The UK spec the buckets sit over the valves and a shim goes ontop of the bucket and lies in between the bucket and the cam.

The Jap STI spec is the opposite in that there is a little shim that sits in the retainer ontop of the valve and the bucket or "lifter" goes over that. The bucket is then in direct contact with the cam and not the bucket. Hence the names over bucket shims and under bucket shims respectively.

The cams on the Jap spec are slightly bigger(lift) with a longer duration.

The springs are also bigger and stronger on the Jap spec hence the higher rev limit. Here are a few pictures comparing the two:

UK spec starting from top left. Valve, spring underneath those are the two retaining collets then you have from the left, the retainer itself a shim and a bucket or lifter.



Jap Spec notice the small shim (bottom middle)



Now comparing the two:

Retainers, Jap STI spec on the left and UK spec on the right



Shims, again Jap STI spec on the left UK on the right



Retainers Jap on left showing shim inserted.



UK spec bucket the UK shim sits ontop these



STI Version 5 Bucket notice its flatness compared to the UK one



Finally a comparison of the springs the thicker and stronger STI spring is on the left.

 

MY97 UK WRX?

 

Good post Daz thankyou
What about block and internals?

 

Good reply daz, didn't know the actual difference with the heads/valvetrain, knew there were differences and that the cams were definatly different.

Block is the same AFAIK, but the internals are forged

 

Some early STI's have forged pistons not all of them do.

The cranks are the same, the bearings are the same and the rods are the same.

 

Would the cams out of the STI fit straight into the WRX heads then?

 

Not 100% sure on that one but i would say yes. But you'll need to make sure first.