i have a 1980 300 with stock exhaust right im going to change it soon but dont know if it will have enugh back pressure to run right and not loose power. for now im going to leave the manifold their and remove the cat and go with either a flowmaster 50 or a glass pac turned down right behind the cab will it work???

please help thanks

 

any body.....

 

Someone else may know more but from what I know the issue isn't back preassure but velocity. Every pulse of your exhaust is made up of a packet of air that has a mass. As that moves through the exhaust tube it creates a vacuum behind it that helps to draw the next pulse out faster. Like a plunger in a syringe, it draws the exhaust behind it out. This way you don't loose so much power from your engine doing all the work trying to push the exhaust out.
If you stick with the stock manifold and a 2.5 pipe you should be fine. You might think of upgrading to some EFI manifolds while you're at it though.
To illustrate what you do not want. Thionk of that honda civic next to you at a stop light that some loser has put a 4" coffe can on. It sounds like butt and he has to rev it to 4k just to get moving because he now has a 1.5 inch plunger in a 4 inch tube. It just don't work.

 

thanks for now its going to stay pretty much stock all but the exhaust. and later ill build on the engine.

 

just in the defense of the civic, usually its just the tip that is 4 inch or so the actual exhaust is gonna be like 2- 2.5in and it works just great from my experience.im not a civic fan by any means but a fan of all the hopped up little compact cars its amazing what 4 cvlinders can do nowadays.

 

4 cylinders? I got one in my 97 Grand Am GT and I'm real impressed with it, great MPG and fast to, I'm pretty sure though that if u cram enough cams on any engine you'll be impressed, 4 cylinders just get better MPG. As for having to have back pressure, it's an urban legend, I run a pure straight pipe out the side of my truck in front of my rear tire (been like that for 4 years), if the cops would let me I'd run a 4 in. stack out the hood, just put a rain cap on it, the thing that warps valves and reeks havoc in an engine is temperture change, as long as u run your exhaust downwards (even open headers) heat still rises and your head will not cool extremly fast, now if you run it upwards the heat leaves and your screwed, that's why at truck pulls u will see them sometimes slip caps on right after they finish the pull. Mattri is right about the complimenting cylinders theory except the fact that you have a log manifold which is a restrictive funnel and does very little of any of that (got the same darn thing), anyway that's more of a header concept, that's why the tubes are all certain lengths so each cylinder is complimenting each other evenly all the way through the exhaust. Another factor is turbulence, people think it's fun to have big exhaust, but there's a limit, take a wrapping paper roll for instance and hold your hand over one end and blow on the other side, then find a giant straw and do the same, that wrapping paper roll is like a big air tank (sort off) and u don't have enough air capacity (exhaust) to blow as fast as you can through the straw, the trick is to find a nice size exhaust that's gonna work for ya, big exhaust is ok for about 20inches on the end cuz it's blowin into open air, and you get a deeper sound. But I am appling a lot to striaght pipes here cuz once u put a muffler on it kinda screws stuff up (excluding a glass pack)