Headers and SSI heat exchangers

[polizei]

I am wondering if someone can set me straight on whether or not headers/SSI heat exchangers require a catalytic converter. I've been searching thru the forums and reading the product descriptions, and I can't come to a conclusion. This is the photo of the SSI heat exchangers which Pelican displays:



I circled the section in which I would presume the catalytic converter would be. I also noted that some of the full exhaust systems sold on Pelican include catalytic converters and some do not. I'm sure this is an ignorant question to many of you, but if you could help an ignorant guy out he'd appreciate it. Thanks!

[81 911 SC]

They do not require a CAT unless of course your car still needs to meet smog. I am currently running SSI's and a M&K 2in/out muffler with no CAT.

[polizei]

Thanks Tyler! I know the amount of extra HP gained by going to various setups has been debated time and time again, but I'm wondering how much of the HP gained by SSI's can be attributed to the catalytic converter delete...

[81 911 SC]

Like you said the HP gains are varried depending upon setup. In my case I am running PMO carbs, SSI, 2in/out muffler with no CAT. I've never dyno'd the car but the "butt dyno" tells me the car is significantly quicker than it used to be with the CIS set up.

[klaucke]

On a 3.2, a "test-pipe" or cat by-pass is the much more economical way to go. The SSI primaries are a bit restrictive for a 3.2, and hence the power gains are not as substantial as they are with a late 2.7 or 3.0. The by-pass will net you almost as much power gain (or possibly as much, depending on the plethora of variables), without the need to switch heat exchangers or mufflers.

SSIs and early heat exchangers are not set-up to utilize cats, and although they could be modified for such, it would likely negate a lot of their benefits. Additionally, they would require two separate cats with any normal style muffler, or some fancy solution for a single cat and muffler. SSIs do have the added benefit of excellent heating for the cabin vs. the later heat exchangers. 993 exchangers with flipped flanges are also a trick set-up with some benefits over the above mentioned alternatives.

[polizei]

klaucke, I'm assuming that headers such as these are not set up to utilize CATs either:

http://www.pelicanparts.com/catalog/shopcart/911M/POR_911M_EXHprf_pg14.htm#item13

If I'm assuming correctly, what would yield the best performance (completely ignoring that such headers would preclude heat in the cabin) - 1. replacing the stock heat exchangers and CAT with headers like those mentioned above OR 2. keeping the stock heat exchangers and replacing the CAT with a bypass?

I realize that in the first option I would HAVE to buy a new muffler, but if I'm aiming solely for performance... what do you think?

[Dennis Kalma]

I have SSI's on my Kremer 3.2 (CIS, 9.8 compression, single ignition) and I love them. They made a noticeable difference in power compared to the factory original set up, which used the factory catastrophic perverter replacement aka pre-muffler, nice part by the way.

I know the SSI's are tight for the larger displacements, but don't kid yourself, they still flow quite nicely and my car performs quite well when compared to others out on the track.

Only thing that ticks me off is that no one makes a larger diameter version of the SSI, complete with the beauty and heat...I understand that SSI's tooling can't do it in a way that works.

I for one, would by a set for my 3.4 project engine....

Dennis

[rbuswell]

Originally Posted by 81 911 SC

They do not require a CAT unless of course your car still needs to meet smog. I am currently running SSI's and a M&K 2in/out muffler with no CAT.

I was wondering what the best/most popular choices are for mufflers for the SSI heat exchangers?

[Dennis Kalma]

I use the stock Porsche '74 muffler, in my mind it is a nice combination of sound and power, plus it fits.