Cat Bypass 78 SC suggestions/advice
 

I just acquired a 78 SC. 35,000 miles and it appears to be equipped just as it came from the factory. I figure the CAT is plugged/useless and will impact performance. I see no reason to keep it, so the plan is to take it off.

However, I may want to upgrade my muffler at some point with something that sounds a bit deeper and throatier. Perhaps a winter project along with upgrading the chain tensioners while the muffler is off. But, in the meantime, I want to put on a CAT Bypass. I see a number of CAT Bypass options -- both OEM type and "performance" type. Big price difference.

So --- can I put on the OEM CAT Bypass and later put on a performance muffler or will the OEM CAT Bypass restrict me to an OEM muffler?

I would look up RarlyL8.com (fellow pelican) he makes great products. I dont see a problem in installing a bypass pipe first and muffler later.

My guess is that you won't notice any difference, except for a little more noise. I'd imagine all of these are designed to be used with stock heat exchangers and a stock muffler, so the attachment points will be suited to those. Having said that, most single inlet mufflers have the same inlet mounting dimensions as the stock muffler, so they can be installed on otherwise-stock vehicles.

SO, my guess would be the mounting details will all be the same. I'd pick the one you think might be the best quality, or the least damaging to performance. ;)

I'd also make sure you order all of the gaskets you need and a plug for the O2 sensor bung that is in most of these.

JR

I've got a euro pre muffler I just took off my 79SC when I put SSI's on. If it's anything you'd be interested in let me know. It's slightly louder than the CAT that was on it but not by much.

Any single inlet muffler will work with a bypass pipe.

I just gutted mine out with a piece of rebar. Just a little louder

I like that idea -- gutting it -- for the short term. Thanks.

Why do you figure the CAT is "plugged/useless"? They rarely get plugged unless you've had a fairly long term full time miss in one or more cylinders. This one's (conservatively) under a third of it's minimum life expectancy. I've had customers with 300K+ miles on theirs, and they still work fine. If you have that, you have more serious issues than just replacing the catalyst. The car will be noisier than with the CAT, and I seriously doubt you will truly be able to notice any actual HP increase.

As for the chain tensioner "upgrade", it's not. It's a major wallet emptying when a hundred bucks and a couple of hours of your time spent rebuilding your old tensioners will do the job just as well. You may not know it, but the pressure fed variety fail, too.

The Cap'n

agreed with the cap'n -- my cat is @ 160k and 25 years old and still works like new. Unless you have a clear indication that the cat's plugged, I really doubt you'll obtain a perceptible performance increase adding a bypass and you'd be better off leaving your exhaust system as-is until you can perform a significant upgrade -- many folks look at a ssi header / exhaust system as providing a noticeable performance (and sound) improvement. If your stock exhaust is in good shape, it could well be of interest to somebody trying to smog their sc and could help finance a significant portion of the ssi/dual in muffler setup

fabspeed and M&K both make well-known pre-mufflers (cat replacements) and costs are reasonable - $400 or so. a pre-muffler will hook up in the same position as the cat and attach to any muffler in the stock position, leaving your options wide open.

rarlyl8.com seems to sell M&K mufflers, but some of his products could be proprietary. i'd like to see someone make a single or dual resonator option for a muffler besides fabspeed. no complaints on their piece, but it would be nice to have options without resorting to dynomax/magnaflow products and a muffler shop. i'd also like to see another vendor producing a muffler bypass pipe.

I'd like to see somebody dyno test these things, to see if any of them actually do any good. "Pretty" does not always equal "well designed" or "a measureable improvement:

JR

Brad; be sure to check your state's smog laws, in CA removing the cat would be illegal.