I have an 84 Firebird, 305. I’m doing the exhaust this spring I need some advise, months ago I had another topic on this, but I’m not looking for specifics this time more specs. I had intended to go 1 5\8 headers with a 3 inch collector, and a 3 inch pipe, dual exhaust all the way back, dual mufflers and do not have to pass emissions. Recently I was told that going to big will actually do more damage than good is this true or is it a myth, I’m not too experienced with exhaust and backpressure. I intend later to put a 350 in but I can’t afford it right now and still want to make power. So basically I need advise on pipe size.

I live in Alberta, Canada and do not have to pass emissions.

Also I’m interested in advise on anything else you would recommend, brand specific or not, to make power, and or improve overall performance, intake etc anything that you would do. I also intend to replace my intake manifold at the same time I need advise clearance/performance wise.

Oh and I might as well throw this in here to, Tires, recommendations...

 

nothing?

 

sorry I plan to the same but I got PRO-FLO exhaust which I think sounds good

 

3" true duals would be too big for even a 350. A 3" catcack exhaust, though, would be great. If you really want true duals (like if you get long tubes) 2.5" would be more than enough. 2.25" would probably be fine too, but I am not so sure.

You are either gonna spend alot of time / work / money bending true duals to get over the axle, or you can dump them before the axle like alot of people do. Also, you could run them out right in front of the rear tires, but that is a little more work, and will decrease ground clearence a little.



If you decide to go with true duals, you are going to want to make an H-pipe to equalize the pressure. Some people run this over the driveshaft, almost contouring the tranny tunnel. Some choose to run it under the driveshaft. Some choose to do without.



For mufflers, that is up to you. Any typical muffler can be made to work, however if you really want to preserve ground clearence, you will want some kind of round muffler. Some of the most popular small mufflers are:

-The classic Cherrybomb Glassplack, for that hillbilly, white trash sound


-The Dynomax Bullet, for that very loud, performance roar


-The chambered tube (by classicchambered or stainlessworks) for that old school 1960's muscle sound