Hi guys, I have an original rear box which is fitted to a '97 non-turbo MR2 which carries the number 17478. I now have an excellent second hand rear box but this has the part number 17447 which I think was from a 'K' reg. The boxes themselves look the same but I'm not sure about the flange fixing. Are these two boxes interchangeable ? Anyone know ?

The only difference throughout the production run on the MK2 was due to the size of the Cat.

See

http://www.jap-spec-performance.co.uk/mr2/...na/cat-con.html

Get your tape measure out - just to be sure.

Thanks Gazza1286, I take it from that if the distance from the exhaust flange to the fixing bracket at the centre of the box is approx 420mm then it had a cat fitted & would fit my '97 MR2. Wonder why the difference in part number ?

The back-box dimensions are the same throughout (I should have said that on my first post really..)

It's not unusual for Toyota parts to be re-numbered. AFAIK only some of the digits of the part number actually identify the part. The others may indicate minor revisions/improvements etc. This is certainly true of parts like the oil filter which has had any number of different part numbers over the years for the same item.
That said, it may be worth a call to Mr T to clarify this.