smshirk

Before I get flamed for not searching, I have spent over an hour reviewing various threads for bypass pipe installation. My question is related more to the outcome of having completed the mod. I am having some issues that could be a blocked CAT, but there I am going through the car a little at a time, and as you can imagine it is starting to get expensive. I could take it to my independent shop, but I would really like to get the car running acceptably before going to the shop, where more major items may need to be addressed.

I have a 1980 911SC that has been sitting up for quite a while prior to my purchase. In GA, where I live, cars more than 25 years old are exempt from emisions testing, so that is not an issue, at least from a legal perspective.

If I do decide to take this route, there seems to be a fairly wide disparity in the cost depending on the vendor. Does anyone have suggestions as to which bypass pipe is of the highest quality, relative to cost? Or am I wasting my time? The car runs great at idle, especially during the day when the ambient temperature is warm. Just after sunset the car starts backfiring with hard throttle inputs, although I can maintain satisfactory, if not spirited performance, bu applying throttle input slowly and holding each gear up to 4 to 5k RPM without ever really getting on it.

I have slowly and somewhat methodically been addressing fuel and electrical issues, with some degree of success, but I'm not there yet. As usual, any and all suggestions are greatly appreciated.

psalt

How old are your ignition parts ?

84_Carrera

If the car runs well ANYTIME, it's probably not a blocked cat. I've had a couple myself, and it's a case of allowing just enough air to pass through at low throttle / idle, but give it gas & it starts to choke off.

As for the cat-bypass question, I have the Fabspeed one for my 3.2L, and I love it - performs, looks good (until it heat-discolors, then polish it again), quality welds. The copper gaskets are a little off on the bolt-pattern, but fairly easy to open up the holes with a drill.

theiceman

If you think what a bypass pipe is it may help, jus a piece of tubing to replace the cat. As long as it has quality welds they all pretty much do the same thing.

Diamond Blue

The cat by-pass is just a tube to by pass the cat. And there are the euro-premufflers from Fabspeed and Dansk, Dansk is the oem manufacturer of the pre-mufflers Porsche used on the euro cars. Pre-muffler have been dyno'd and have a 5-7 hp increase. If you are going with the bypass and the cat is history just punch out the inside of the cat and try it with that before you decide which way to go.

Loaded

PLEASE PLEASE PLEASE addres your FI problems AFTER two 1/4-1/5 tanks of Techron filled fuel. Coking and carbon fouling and gunk are problems with lightly run/periodically run Porsches.
After that then chase down your issues.....

Jay H

I have a Dansk cat bypass (euro pre muffler) and it's a quality piece. It fits very well too.

JV911

+1 on the fabspeed euro pre-muff

i'd try removing the cat's guts first before forking out the $

gunlover05

I put a Bursch cat-bypass on my 85 carrera...fit perfectly with a M&K 1 in 1 out.

spence88mph

I gutted mine and it did make a little difference but think a straight pipe would be better as the gases would expand in the cat then bottleneck as they leave.