I have a relatively stock 4.9L engine with the original catalytic converters and stock type round muffler. I would like to help the engine to breath a little easier, without changing to later EFI manifolds or the HD exhaust, until the engine requires rebuilding. It runs quite well, now!

What I envision is a new headpipe with a 3-way catalytic convertor mounted where the original pre-convertor currently is and then a pipe to a turbo type muffler and then tailpipe to the rear.

I believe the original headpipe is 2.250" in diameter. It may be smaller? This pipe is the later design which is flared on the end and does not use a doughnut gasket. Can a replacement pipe be made which is larger in diameter? It would have to properly mate to the exhaust manifold and be able to fit inside the locking ring, which holds the pipe and manifold together.

Thank you!

 

Sounds to me that if you wanted to go to a bigger diameter (2.5'' would be a nice improvement for a stock 4.9, but no bigger) it would be easier if you told the shop to start with the pipe size you want, then to neck it down on the end where it bolts to the manifold to the factory size.

Say start out with 2 1/4'' at the manifold with factory style hookup, then flare "out" back to the original 2.5'' pipe size that you want to upgrade to, then run the pipe with a new convertor and muffler out the back.

If you have to have inspections where you're at, check out Summit Racing's universal converters. I got mine in 2 1/4'' for ~$100. They have a great selection of mufflers for cheap as well. I wouldn't buy a muffler or converter from an exhaust place or from the auto store unless it could be had for a really good deal.

 

I would probably stick with the original exhaust size. If you increase the pipe size, it will increase the amount of exhaust gases that need to be pushed out. A nice universal cat and turbo muffler will decrease the back pressure a little and allow it to flow a bit better. Also, using the original size pipe will allow you to mate the new parts with the old.

 

It won't necessarily increase the amount of gases that need to be pushed out, but going too large can make it to where it's too hard to push out what's in there. Exhaust scavenging and all that. The stock 2 1/4'' pipe is just fine for a stock 300.

I agree with sticking with the stock 2 1/4'' pipe size and just changing the muffler and replacing the stock cat(s) with a high-flow model. It's easier, cheaper, and will work just fine.

 

Thank you, knowledgeable gentlemen!