About a month ago our 91 745T failed Ohio eCheck three times before I bit the bullet and purchased a new cat. The car immediately passed the eCheck.

I could have been happier with the fit of the new cat as it hangs a little lower than I would like. The big difference after the change is the turbo sound. You can definitely hear the turbo spooling now and at just the right load and rpm's it sounds like a siren in the distance. No other changes were made so I am sure it is the new cat that is responsible for the added noise. It is not something I appreciate but I am willing to live with it. At 185K it has never run better. I am sure the performance has improved.

On the road the car before the new cat I could count on 24 mpg. On a trip this last weekend I got 27 mpg. I am fairly sure that the before and after tank fill was to the same level but I would like to check it again soon to verify the increase in mileage.

Randy

you may want to check your state laws to see if it's legal to get rid of the cat all together from your car before dismantiling it. something i heard from other guys is that they punched out the inside of there cat,cleaned out the entire inside and then put it back on for looks. this may work for you and still keep the appearance of the cat on your volvo. i know I'll be replacing the cat on my volvo here soon as preventive maintanance. as for takig a cat f a volvo, I'm not for sure what that does to the engine as to any help. may want to check with other volvo wrench heads and find out more info.

respectfully,

Volve
salt lake city, Utah

I'm a little ignorant about cats. How does a cat converter affect mileage? It's in place AFTER the exhaust manifold - I thought all it did was keep pollutants out of the air. Also, if it improves performance, how come most racers delete the cat? What brand of cat did you go with and was the price resonable? Thanx

I will be the first to admit I know very little about cats other than they can be a problem as they get close to 200K on them.

I am sorry I do not remember the name of the after market cat I put on but I got it at my local auto supply store for $135.

Perhaps my old cat was beginning to get plugged? If this were true perhaps less restriction of the exhaust lead to the improvement of performance and mileage?

The new cat brought the NO level down from a 1695 ppm to 19 ppm.

Randy

Ah ha! Lower restriction with a new cat, makes sense. SO....Since I don't have emissions testing in my state - then not having a CAT is even better right? There's no sensors on my 240 cat. Any one have any thoughts on this My cat is also due for replacement but I would rather go without it if I can.

Just because your state doesn't have local emissions testing doesn't mean that you can remove your cat. The Catalytic converter is a FEDERAL mandate and the removal of it would be prosecuted in Federal court. Just think of it this way, if your local juridiction doesn't have a law against dumping antifreeze into the ground, you can still be fined/prosecuted by the Feds (EPA). Since we all share the same air, please, for the sake of the rest of us, keep the Cat on your car.

A functional Cat offers almost no restriction, and on your Volvo it is part of a "Tuned Exhaust" system from the factory. I don't doubt the increase in fuel mileage as previously observed after changing the cat, since the exhaust is now operating much closer to the original specifications, offers less restriction, and the pulses are properly ducted together. Assuming you keep your car properly tuned (not running rich or lean), the original Cat should last the life of the car. If I remember correctly, the feds mandate that the auto manufacturer must warranty the cat for 10 years from the purchase date of a new vehicle (even though it isn't mentioned in the new-car-warranty information).

Random side note about exhaust systems: A larger diameter exhaust system is usually more restrictive than the factory equipped exhaust which is tuned for the engine exhaust volume (and keeps the exhaust pulses ducted together much like Nascars going around a track). A large diameter exhaust allows the pulses to dissipate, slows their rate of travel, and leads to a larger mass of air to be pushed before exiting the tailpipe. On the flipside, an exhaust system that is of a smaller diameter than apropriate for the engine volume (or one with poor bends) will contribute to the restriction, just like a large diameter system. There was a really well written article in Rolling in the last few months on the subject of Tuned Exhaust systems and how the components and sizes play a factor in increasing horsepower. -I believe it was the Jan/Feb 2005 issue, but I could be wrong.

God bless,
Fitz Fitzgerald.
--
'87 Blue 240 Wagon, 255k miles.

Thanks Fitz, did'nt think about it that way. Maybe a freeflow cat from a comparable 4CYL car would be the way to go? (translated = inexpensive)

Maybe a freeflow cat from a comparable 4CYL car would be the way to go? (translated = inexpensive)

There have been several people on the board (200 and 700 owners) that have had a local exhaust shop weld in a cheap cat, rather than replace it with a factory fit cat & pipe. So far I haven't heard any complaints from them (and they did pass their emission tests).

God bless and drive safe.
Fitz Fitzgerald.
--
'87 Blue 240 Wagon, 255k miles.