Yes, I know they're a cork in the exhaust , but it's illegal to run without them here, and car has to pass an inspection every 2 years. This includes something like your smog test, and the car won't pass without cats.

Cheers,
Erling

 

lol, you mean it wont pass visual,

and why not just stick the factory cats back in for 2-3 days every 2 years

 

Thats an idea of course - would also make the cats last longer...

Seriously though; isn't the computer etc. tuned to run with inputs from the lambda sensor ? Can you just take it out of the loop without any repercussions - or adjustments to be made ?

Cheers,
Erling

 

Erling, if you look at the pics I put up, look at the middle of the X portion and you will see that I have the O2 sensor sitting in pretty much the factory location, and it reads before the cats regardless.

So yes it can be put in with no ill effect.

 

If I was a betting man I'd suspect that’s what a lot of us do. With the older Sharks like mine it's takes about 15 minutes (with a beer break in-between ) in my garage to swap-out the Y-Pipes.

In fact the PO replaced the Cat Y-Pipe a few years before I bought it from him and storing it for emissions testing every two years it looks almost new.

 

A little off topic but does anyone know if they make some kind of paste to put between the exhaust pieces where they join to prevent them from fusing together from the heat and rust? The big reason I hate doing exhaust work is trying to pull apart even a bolt on exhaust that has been fused together.

 

Here is some information I assembled. Might be a useful explanation.
http://www.performance928.com/cgi-bi...ss_parent=1128
Dave Lomas (Motorsports in Salt Lake) has a custom cat(s) that are both efficient and effective. He makes his own narrow agle inlet/outlet transitions that are way better than the short wide angle transitions on all other cats. He also has internals that are 100 cells per inch rather than the normal 400 cells per inch so flow a lot better. If you are going to do it, might as well do it right.

 

Thanks for the pictures John,

Does anyone have pictures of a Y-pipe?

 

Here is mine. It was made by Tom Cloutier to attach to MSDS headers and a mandrel bend 3" exhaust. He made it from mandrel bent tubing and even ground the welds inside.

 

Here in sunny Texas we did a comparison on a 91 GT on the dyno - with and without cats - no difference in HP - no loss no gain.

Both the X pipe and the Y pipe are available with cats.

Also in SS and aluminised steel.

 

Roger,
That was with an )( pipe and without/with Dave Lomas cats, right? I can't believe it would be no difference with the stock cats.

 

I was seeing 1 to 2 horsepower differences with these new 100cpi cats, not enough to call a reasonable amount knowing the variables of the dyno. I saw 7 to 8 hp loss with the 300cpi spiral wound metal matrix (Random Tech style) and 14+ loss with the 400cpi ceramic bricks sold as high performance by Magneflow and others.

Louie, I think Roger was comparing a crossover to crossover with cats.

 

Here are some pics of the Y-pipe I built for my racer. Nothing special, let me know if you have any questions.

 

RED that is a nice and simple looking exhaust. Excellent work. Jason

 

Thanks, I had to add a Borla XR1 3.5" muffler where the stock cats were located... just too loud as it was.