I have two 3" catalytic converters I want to put on my car. I'm building the exhaust myself since theres not much to buy for v8 turbo f-bodies. I'm not using any mufflers(the turbos keep it quiet enough), so I was wondering if I could put the cats behind the rear axle so I don't have to fit them under the passenger seat. That would save me a ton of work. The only problem is that they might not get hot enough to work properly and get clogged. I'm doing a 3" y-pipe into a single 4" pipe over the rear.

Does anyone think it would be fine to put the cats there

 

Exactly, thats why the are placed as close to the engine as possible.

 

I think you answerd your own question.They need the heat to work properly

 

I thought so, but I was just wishing it would still be hot enough in the back.

 

I live in smog **** territory but it might be illegal in your area as well.

It might.

 

It probably is illegal... its just that no one enforcing it could ever tell the difference! Baltimore is a copycat city of CA emmisions/inspection standards, but the "inspectors" are too ignorant to enforce it properly.

 

yep, like everyone said, they need to be as close to the engine as possible.

 

The exhaust temp. on a turbo car is higher than on a naturally aspirated car so you might be able to get away with it. Get a temp gun and compare the temp. of the exhaust pipe in the rear of your car with the temp of the exhaust on your bro's car under the seat.

 

thats a good idea. I'm going to do it the hard way to be sure. I fabricated the 3" pipes (from the downpipes to where the cats are supposed to go) today... so i'll just put the cats on the ends of those under the passenger seat, and then merge the cats together into a 4" pipe.

One of my brother's tailpipes melted the dyno strap when he was on the dyno, so its probably pretty hot back there...he doesn't have any cats.

 

I finished the exhaust system and put the cats undr the passenger seat. It was a tight fit! now those converters turned out to be a huge restriction on my exhaust! I only see 5 psi of boost when before I had 8psi.

 

actually quite the opposite unless maybe you consider before the turbo inside the manifolds. but after that the turbo cools the exhaust down a little bit plus with the generally richer mixture that even further helps to cool the egt's down.