Feeding a 911 for a while

I have a californian spec. 180BHP SC here in the UK. I am trying to make the car breathe a little more easily by carrying out sensible modifications to the exhaust system. I have already removed the air pump and all the sad paraphenalia that goes with it - the question is what should I do next. is it possible/advisable to remove the EGR system and what could I hope to gain by removing the cat and fitting a euro pre-muffler. Which is the best muffler to use?

I am not looking for a massive increase in power - I just want to lose that 'strangled' feel that afflicts engines fitted with early emmission control systems

Should I just bin the whole system and go for SSI's (the cost puts me off a little)

By the way, the existing exhaust system is the original - including the heat exchangers!

Any other ideas to improve the car would be welcome.

Tom F

I would not remove the air injection, because it increases exhaust gas temperature, thereby keeping the insides of the exhaust system cleaner for longer. The power to drive the air pump is negligible. Chances are good that the catalytic converter has broken down inside, and is inhibiting exhaust gas flow. Since you're in Europe, why not just fit the factory primary muffler, which fits where the converter is now? You'll almost certainly notice a difference. The SSI's are the way to go, IMHO, but it's big bucks (or Euros, pounds or what have you). Going with SSI's means new muffler and new oil lines, plus it's tough to get some of the old stuff off, especially with the engine in the car.

Feeding a 911 for a while

Thanks for the reply. I think I will try the euro primary muffler idea as it is much cheaper than SSI's. The main reason I removed the air pump was improve engine bay access - I have also removed the entire air conditioning system ( a really nasty aftermarket DPD setup). As for removal of the exhaust system, I have already been through that painful experience as I recently replaced all the head studs.

Is there any way of telling if the cat is blocked by looking at it? When I had the exhaust system off the car, the cat honeycomb looked very clean.

I have heard people talking about modified induction kits - is any experience of this out there

Bill Gregory

Although not cheap, I'd go with SSI's. The hp gain is real and you retain heat/defrost. If heat/defrost isn't needed, you could put on Bursch headers, which are considerably less expensive than the SSI's, although they aren't stainless steel. If you want to see what's involved, I wrote up the SSI procedure and it's on tech.rennlist.com under 911 engines. If you don't want to go with different headers (SSI/Bursch/Other) then bypassing the cat will at least help the engine breath easier.

With the a/c out, you're almost there to seeing the whole engine. You can backdate the hot air source to the pre-mid 70's. Another article on tech.rennlist.com under 911 engines tells you how. After that, the engine compartment would look like (this happens to be an 81SC):

Tom F

I would second what Bill says. The only issue is cost, because the SSI's are unquestionably an improvement.

I don't know a surefire way to tell a bad cat. The couple of times it's happened to me, the internals of the cat were rattling, though you couldn't tell anything by a look into either the inlet or the outlet. You sure could feel the difference once a new cat or a "test pipe" was installed.