Mark in Baltimore

Greg,

Thank you! Your old car sounds great.

Did you ditch your cats for weight distribution reasons? Besides the aural assault, what were the downsides in terms of power, torque and, most importantly, lap times?

Flying Finn

Bill,

I agree, cost must be an issue. i.e. those 997 headers are very simple to make and you need quite a bit less material than i.e. those 964 eq. lenth headers. And also in some cases, since stock cars didn't have eq. length header, some race cars are forced to use those because of the rules.

I was also thinking maybe weight could be one of the reasons since eq. legths usually end up a lot longer but I don't think that can be the reason for not doing eq. length.

pcar964

Here's a question in the spirit of the thread - I have old cats and I'm hearing a rattling sound in my exhaust. I have a suspicion it's the cat core that's partially broken apart, possibly from track use and age. Are there any disadvantages to removing the cores from the stock cats and using them as a de facto bypass? Is there anything else I should know about?

Greg Fishman

I don't think it made a big difference either way in the hp. If i had to guess it did decrease some low end torque but made a bit more hp at the top end. I don't know that this made much a difference in lap time, my laps time were much more affected by me and my learning curve regarding other set up issues. I think the main benefit is that you lost that weight on the wrong end of the car. Also it is nice to be able to hear your car over others at the start so you don't miss a shift.

Mark in Baltimore

Thanks, Greg. That's what I keep on hearing, no pun intended. Some say that more HP at the top end is better for a track car that is spending much of its time in the upper rev range. Possibly this can equate to better lap times?? I know what you mean about the driver learning curve and car set-up; I chased my Motons for a dozen events and feel that I am now learning to really trust my car and myself again.

Greg Fishman

I know several that have done just that. No issues.

nbooth660

I removed the cat cores from the standard cat (as mentioned earlier in the thread). No problems, great sound and costs you the price of a few new bolts......not $700.

Nick.

993MAN

How much noisier was the system by removing the insides of the cat?

nbooth660

On tick over it's only slightly louder than standard. On acceleration it has a nice rasp to it and at WOT it gets louder again. No resonance problems. Even sounds good from inside.

Nick.

Caveman

Someone else on the forum has converted their standard cast to 100 cell cats by changing the cores; I would second Nick's comments on the effect on sound.

pcar964

Thanks, that sounds like a good option - does anyone know where to find 100 cell cat cores that will fit in the stock pipes? Also, assuming you wanted to just remove the cores altogether, what is the easiest way to do this? Do you have to cut the pipes and re-weld them, or can you use the old broomstick method?

Caveman

Search is your friend; in this case Google. There are quite a few companies selling standard cores. I think FVD in Germany is one of them if memory serves me correctly.

Cheers,

David

nbooth660

There's no chance to get the std cores out without cutting and rewelding. I took an educated guess where to cut and knocked out the remaining core. They are just pressed in so no problem when cut open. I'll dig out a picture of mine re-welded if it's of interest.

I kept my old cat and cut another one from a breakers so I could put the old one back when it's time for emissions testing... . If you want a 'one shot' conversion, get the 100 cell cores. I still have an old core so could check the diameter if needed.

Nick.

pcar964

Interesting. I guess I should add that the core already sounds like it's coming apart, so maybe that would make the 'broomstick' method more viable?

nbooth660

If I did it again I could probably avoid damging the old core and cut it in a different place. There are compressions in the casing to hold the core in place at either end. Knocking it from either direction pushes the core up to the compression if you know what I mean and will not budge.

I tried to get it out with a broom handle, but the bend on the outlet makes it vertually impossible. Also, the core is very dense with cells so would need drilling out.

Maybe the picture makes it clearer.

Nick.