73Gremlin401 wrote: Note that some of the stuff, EGR, PCV, and TAC are all good things, and if in proper condition with no vacuum leaks and good valves, really do make your stock 6 run a lot smoother, and I'd recommend leaving them in place, or repairing as needed. In general, AMC did a better job with emission controls than the big 3 did on the 6 in the late 70s and 80s, with regard to general driveability.  Sometimes stock is better, and if your motor is as delivered from the factory, keeping the emissions stuff as close to OEM as possible is actually a good thing.

You'll get a big "amen" from me on that. GM did a pretty good job, too. My 1977 Buick runs really good with all its stock stuff. Of course, AMC used a lot of Rochester (GM) emission control parts. 

You won't notice any performance increase by using a straight-through glasspack muffler instead of the stock type chambered (also called turbo) muffler. With the correct size pipe (2" is plenty) just about any muffler will flow more than you need. All you'll do with the glasspack is make your early 80s luxury car sound like a rice burner, but without the performance to show for all the noise. 

Converters also help make the car quieter, and if they are properly sized and in good condition they have essentially zero impact on performance. That being said, a clogged old converter will murder your performance, and old carbureted engines are dirty enough that they tend to clog up their converter pretty quickly.

2" exhaust pipe, Thrush or Walker turbo muffler, downturned tip. It makes for quiet exhaust, but you get a nice low rumble at idle. It sounds respectable. 

^ Yep. If I had a car with a pellet cat, I'd pull the drain plug and let all the pellets out, then sell them for platinum. 

People do the same with monolith cats, though there isn't much reason to. A good monolith cat doesn't restrict unless the engine is out of tune and plugs it up...which a lot are. 

ps, love to see that 258 V6!:)

purple72Gremlin wrote: On certain cars, the EGR needs backpressure to open.  (some GM cars did)  AMC used Delco EGR valves, (althrough I have a AMC 360 with the Chrysler EGR valve)....   and usually if you keep everything working and hooked up correctly, it will run good.

Yeah, he almost certainly has a positive backpressure EGR valve. Most AMC engines got them from 1976 onwards. The more backpressure it has, the more exhaust it recirculates, so less backpressure due to a higher flowing exhaust would simply mean less EGR. That's not necessarily a bad thing. 

I wouldn't worry about throwing off the EGR with an exhaust change. I have two engines with positive backpressure EGR: one is a 1977 AMC 232 I6 and another is a 1977 Buick 231 V6. I drove both of them with their stock exhaust systems (both 2" systems with converters) then I drove them again with improved, higher flow exhaust systems (2" or 2.25" with no cat) and noticed zero change in performance or how the EGR operated. I've even driven them with no EGR what so ever and they didn't ping or have any ill effects. Some engines will ping without their EGR unless the timing and fuel mixture are changed, but mine never have. 

purple72Gremlin wrote: Ive noticed that the engines run smoother with the EGR working...I keep the EGR functional if I have all of the stuff that works with it.

I agree and do the same. The only time EGR has given me problems is if the carburetor is on the edge of being too lean. They'll run ok without the EGR, but lean bog like heck when the EGR kicks in. 

I like EGR. The idea of a cooler running engine that uses less fuel sounds like a win to me. It's just variable displacement. Take a 300 cubic inch engine, fill it with 100 cubic inches of inert gas, and you only have to give it 200 cubic inches worth of fuel and air. Open the throttle more, the EGR stops, and now you're back to a 300 cubic inch engine. I think that is really cool.

Wait, you and I agreed on something. Good on ya, mate.