I have a 72 340 Demon est 450 horse motor. tti headers. What size exhaust like the tubing size would be the best. Would like to put an x pipe in also. Thanks

You're on the border there, I think 2.5 would be sufficient with good mufflers though.

What is the collector diameter?

I too agree with 2.5" and good flowing mufflers. 2.5" is good for apx 463hp (521cfm).

What about 3" x-pipe/mufflers, then 2.5" over axle/tail pipes since you are close to the 463hp mark?

I would suggest 3". Std hooker BB headers have 1&7/8 pri tubes (TTI's might be 1&3/4 iirc) but to me, pushing 1&7/8 times (4) into 2&1/2 is restricting the flow. A 3" setup is gonna require regular muffs plus in addition glasspacks along side the rear leafs to get the noise down to an acceptable level & yes X pipes do work to quiet it. Make sure the glasspacks you pick do not neck down where the end nipples are welded to the case. The BEST killer setup (IMNHO) is an electronic (cable might suffice but I like the touch of a button/switch) is 3" open cutouts right at the collectors (no reduction) plus a restricted system rearward (even if 2&1/2) for noise compliance then when the time comes open em up & before they figure out what hit em the 10 second race will be over & the money will be in your (or a third parties') hands . No need for constant racous noise until needed (we ain't in high school).

All you need is 2.5" mandrel bent....if you go with compression bent exhaust you may want to use 3" to make up for the restriction. The best pipe in the world won't help much if you use crappy mufflers so chose wisely...


Dave

I would put a three inch system on it now, you may want to add HP later so why do the exhaust system twice Some parts of hot rods should be built bigger than needed, fuel supply, exhaust, suspension and so on for future growth BTW, Summit has a real nice collector back three inch systems for Mopar A bodys It is not a X pipe system but it would be easy to add a H pipe to it or a X pipe also

I think the TTis are 1-3/4. I like the idea of open cutouts. Where is a good place to buy them with the electronics. You talk about good mufflers also. What are some of the good mufflers you would recommend. I understand that too small would be choking the flow. what are the cons with going 3 inch if it is a little big. Thanks for all the great help and replies ,much appreciated.

I agree with both of Dave's posts. Those are 3" collector exits and with that Hp, keeping the 3" collector to the next interuption makes some sense. I'd take it back to an H pipe. From the H to mufflers could be 2.5. Getting good flowing mufflers will be the critical item. If this is an issue, and high rpm is important, then an X could be better than an H. In theory it allows more sharing. In theory 'cause the best way to know is test on your engine. Even with a program like Pipemax it is recommended to test. The easiest way to test is bolt on open collectors of different lenght. When that is established, the H pipe can be placed there or an X at the next harmonic.

The exhaust gas is cooling and therefore takes up less volume as it moves along. So even if a 3" is needed at the collector, it won't be needed for the entire system.

My vote on mufflers is Dynomax Ultra Flows or the Hooker Max Flows!

As far as as volume goes, its pretty straightforward physics.
As a given amount of gas molecules are cooled, density increases.
Wherever there is a temperature differential, there is heat energy flow. So as soon as the combustion is done, heat starts flowing out to the cooler surrounding environment - the heads - then the exhaust system it passes through etc.

The sound reduction adds a level of complexity, but as far as heat goes the principle is straightforward. Sound is also energy and in reducing sound amplitude some portion is converted to heat.

The real complexity comes in with the sound versus pressure waves and how that impacts the gas flow. Calvin Elston has been posting his thoughts (and questions!) on headers. One of his conclusions has been that the most important thing is to get the gases far enough away from the exhaust valve so they don't get sucked back in. The OP's TTI step headers will do that as well as anything non-custom on the market. So I think everything else is about not stuffing it up with a major restriction in the mufflers, and how every much time and effort he wants to invest in tuning the placement of the first major change in pipe flow after the primaries. The latter is gravy unless ringing out max performance is the goal.

ok sounds like maybe 3s back to the muffler then step back to 2 and 1/2 from mufflers back or from h or x pipe back. Dyno ultraflows or the droneless dynos being muffler of choice. I like the exhaust to sound real good just not getting pulled over good. Does this sound like a pretty good recipe. Really appreciate the help guys, thanks.

This is my 63 with the 3" TTI system with an X-pipe and Dyno-Max Ultra-Flows. It is not super loud unless you nail it then it gets louder. I like it because I can listen to my radio when driving around. I went with the X-pipe because I race through the pipes and wanted a good flowing system. Ron

https://www.youtube.com/watch?v=bYIM2HLaOI4

2.5" syatem & good-flowing mufflers. What's the downside if you go with 3" system? I think it's too large a diameter for that HP range, & you'll lose flow velocity which will affect bottom-end & midrange performance that you could probably feel. Also, a 3" system will be a LOT louder than a 2.5". 3" is simply overkill unless you are going to be running the car at the dragstrip all the time & never seeing RPM's under 4,000.