289 Exhaust sizes. How big is too big?

tbunker · 05-20-2009

I am getting ready to replace the exhaust on my 289 65 Mustang and was wondering how big is too big of exhaust for the engine? I have shorty headers on it right now and the collectors are 2 1/2". The current exhaust is 1 7/8" and I am looking to increase to either 2 1/4" or 2 1/2" (leaning more towards 2 1/2").

My main question is how big is too big for a 289 (bored out during rebuild by one of the previous owners, is now ~298CID)? And if I go bigger will I lose that blatting sound?

I looked forward to any knowledge, opinions or suggestions.

Calponycarsmike · 05-20-2009

You can run a 2 1/2 inch on the car, what mufflers are you using?

66mustang86 · 05-20-2009

2 1/2 will work fine sound isn't so much about the size of the exhaust just run the right muffler to get the sound you want out of it

tbunker · 05-20-2009

I haven't been able to decide yet. I am stuck between glasspacks and flowmasters. I am looking for that blatty sound and not sure if flowmaster gives that kind of sound but then I am also torn because I kinda might want some civilness when on the highway but if I can't get the blatty sound when turning it up then the other issue would be put on the back burner because most of my driving is just around town.

Joel_L · 05-20-2009

I'm using Hooker Comps and Magnaflow 2 1/2" on my 67 289, no complaints.

Joel

mustang402 · 05-21-2009

I had 2.5" and flowmasters on my 67 coupe and took them off when I put my new 302 in, way to loud and it droned. Installed complete 2.5" magnaflow X-pipe system with JBL mid lengths and I'm very happy with my choice. Exhaust is a personal preference I must say though. I agree if you are looking for that blatty sound glass packs will be your choice.

The Greek · 05-21-2009

I also agree, the FlowMasters aren't going to give you the sound that you're looking for. Glasspacks for sure, especially after they had a chance to blow out (break in).

Don't go any bigger than 2 1/2", that's the extreme limit in diameter for the engine that you have. Actually the engine will probably build a bit more torque with 2 1/4", but they just don't have the look of the 2 1/2". Maybe it's just me.

tbunker · 05-21-2009

It's not just you. Big exhuast looks nice.

If I go to 2 1/2 will it give a horsepower gain? I am usually all about torque but I have a lot of that going on right now.

Also, I am not going with a X-pipe. I may do H-pipe but I am also not leaning towards that. I will probably just put a brace between the two pipes for strength.

jspagna1 · 05-22-2009

Go with the 2 1/2" exhaust, this way your set for any future mods down the road. You have to have an H-Pipe. You need to connect the 2 exhaust banks of the motor for more horsepower.
H-Pipe is the least expensive.
As for mufflers, I love may Flowmatsers, but if you want to go with a nice muffler, the Dynomax Super Turbos are also a nice muffler.

Calponycarsmike · 05-22-2009

dynomax makes a great muffler.

The Greek · 05-23-2009

You really should install some kind of balance tube between the two exhaust outlets. It will help in promoting exhaust scavenging, especially with a long duration camshaft with valve overlap. The exhaust pulses from one bank help to evacuate exhaust gasses from the other. The crossover pipe should be within 1/2" of the diameter of the pipes in your system and should be located in the area of the trans tailshaft. You will want to build the exhaust system so that you will be able to remove the transmission without cutting everything up.

tbunker · 05-23-2009

Yes. I did want to have it so I can remove gear if I have to. There's a local guy who is really good at doing custom mandrel bent exhaust. When I do my consultation I want to get up under the car with him to figure out what is best way to run it with what I want.

The H-pipe sounds better than the X. How will the H-pipe affect sound?

Also, I haven't heard a lot of good things about dynomax.