I am trying to get my 85 volvo 760 turbo to pass emissions, it failed with the old cat by just a little bit. When we bought a new cat it failed even worse, but with the old cat is almost passes. My question is, the cat we bought was about $150.00, the dealer has one for $350.00 and they say that the car needs a special 3 way cat, thats why the cheap ones are no good. Can anyone shed any light on this? Thanks.

As far as I know a cat is a cat.You might have another issue with the car.
Try changing the oil and dumping a little bit of denatured alchol in the tank before you go and you should be able to pass then.
Also make sure you have no vaccum leaks or anything like that.
When was the last time the car was tuned up?

Thanks, the motor has been rebuilt, I guess I will just try to buy the other cat and see if it passes.

How long ago was it rebuilt?
If all the adjustments are not set properly then it will be very hard to get it to pass.