2 1/2" or 3" Exhaust?

[ROCKthe68]

I have a 396 in a 68 SWB and I am trying to decide what to do for exhaust. Planning on putting 40 series FM. Any suggestions would be appreciated.

[Solego]

Try posting in the engine section. Those experts should be able to give you a more technical answer for your set up.

[LockDoc]

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I don't know about the 396 but I read somewhere on the 350 you can actually go too big and it hurts performance.

LockDoc

[clos69]

Those 40 series FM are way too loud for my taste....I would go with a bigger series like 50 especially if your putting them under the cab.... my .02

['70_402]

2 1/2" pipe is fine unless you're pushing 500 or more horse... if it's a daily driver with street manners then go with 2 1/2" it'll be cheaper and you won't gain anything going bigger.

[Quickshift-Perf]

I'd say if you're pushing much over 500hp at the crank you should probably go with the dual 3".

Originally Posted by '70_402

2 1/2" pipe is fine unless you're pushing 500 or more horse... if it's a daily driver with street manners then go with 2 1/2" it'll be cheaper and you won't gain anything going bigger.

Edit: Ooops, sorry. Missed your post but said the exact same thing lol.... My bad.

Mike

[cjohnson6772]

This may or may not be true, but I've heard that the bigger pipe is better for more horsepower on the top end, but that a slightly smaller pipe would be better for torque on the bottom end. From a back pressure standpoint I think this makes sense.

Also 3 inch pipes will be unbearable unless you're 17 yr old or have 7 layers of dynamat.

Once again though this is just one man's humble opinion.

[Zoomin]

Is your 396 modified, larger cams, head work, headers? If so, the 3" would work ok. Otherwise, go with the 2.5". The smaller exhaust will, in most cases, yield better torque, and will be easier to route.

If you like the look of a bigger pipe, just do the tail pipe in the 3".
Posted via Mobile Device

[Ole Greenie]

I have a LS6 454 and just installed 2.5" piping and 40 series Flowmasters....but I also installed an "X" pipe under the cab. (Not an "H" pipe) Mufflers were attached under the bed. I'll post pictures when I get home.

[tubbedII]

I had a mild 454 in my camaro with 2 1/2 at first, and switching to 3" just made it louder. It never really made much low end torque so it was hard to say it lost any by the bigger pipes.

[piecesparts]

Originally Posted by '70_402

2 1/2" pipe is fine unless you're pushing 500 or more horse... if it's a daily driver with street manners then go with 2 1/2" it'll be cheaper and you won't gain anything going bigger.

Totally agree with this thought path. There is a breaking point for performance and it all hinges off of the collapse of exhaust gases from the engine and the resulting reversionary pressures that are resultant of the early collapse. Unless you are going to run the engine hard, then the 2 1/2" will support your needs.

[kwmech]

3'' single. Plenty of flow. Less 'stuff' under the truck. Decent sound. Got a 3'' single on my 68 with a semi-built 454, more than enough. Pipe runs hotter....less rust

[Ole Greenie]

OK....Here are a couple pictures of the 2.5" pipe I installed a couple weeks ago:




Again 2.5" pipe with a "X" pipe and flowmaster 40's.

[lakeroadster]

Here is a helpfull chart. Pick your estimated horsepower and find the appropriate exhaust diameter:

[ROCKthe68]

Originally Posted by Ole Greenie

OK....Here are a couple pictures of the 2.5" pipe I installed a couple weeks ago:




Again 2.5" pipe with a "X" pipe and flowmaster 40's.

How much was this setup if you don't mind sharing?
Posted via Mobile Device

[Ole Greenie]

This install cost $400 not including the polished stainless magnaflow tips I bought that dump right behind the rear tires. Add $104 for the tips. All materials and labor was $502.00. (Pics of tips and rest of truck coming after I get it back from the paint shop.)

I would like to say however about eliminating drone.. Eliminating loudness and/or drone can be accomplished many ways:

1) For true dual...Add a section of tube perpendicular to each of the exhaust tubes prior to mufflers. This will remove sound waves to a great extent as they would reverb throughout the length of the added tube. Tube will have to be cut to a certain length to minimize sound dependent on the frequency and amplitude of the sound wave.
2) Decrease the diameter of the exhaust tube.
3) Install an "H" or "X" pipe. "X" pipe is better at this than the "H" pipe.
4) Install a resonator before the muffler.

Hope this helps...

[dznucks]

Not sure if your truck is lowered or if you are thinking about lowering it. And not sure about how you want it routed.

But the 3" pipe will be more difficult to hang "high and tight" and get over the back axle if you keep it between the frame rails.

I put 2.5" under mine with an x-pipe and love it. 3" is too big unless you running some type of forced injection or huge heads and cam on a large displacment engine.

You should expect to spend around $300-400 in labor for a decent exhaust job.

[Ole Greenie]

agreed... the lower the more difficult. 3" piping is difficult to work with period. Mine is lowered 3.5"/4" and it was a bear fitting it up and over the axle and then up and down again inside the fender well to get the desired look I wanted. Bends also decrease the loudness associated with larger diameter pipe.

[llowlife]

If your plan is to not lose HP due to the exhaust then plan on 2.2 cfm of flow per hp. 1 sq. inch will flow 115 cfm on a short straight pipe with no bends. Frankly the FM's will be the restriction even with 2.5" pipes.

[lakeroadster]

Originally Posted by llowlife

If your plan is to not lose HP due to the exhaust then plan on 2.2 cfm of flow per hp. 1 sq. inch will flow 115 cfm on a short straight pipe with no bends. Frankly the FM's will be the restriction even with 2.5" pipes.

Ironic that "Flow - Masters" aren't "Masters of Flow"

I am assuming Cherry Bombs (glass packs) are less restrictive than Flow Masters. Anybody know of any flow testing that verifies this?

[Ole Greenie]

Originally Posted by lakeroadster

Ironic that "Flow - Masters" aren't "Masters of Flow"

I am assuming Cherry Bombs (glass packs) are less restrictive than Flow Masters. Anybody know of any flow testing that verifies this?

Shoot...along this line of thinking just run straight pipes!

The chamber design of any muffler interrupts the flow of gases through them. This interupts the frequency and amplitude of the "signal" through the tube. Since Glass Packs silence this effect through holes in the side of the pipe into the fiberglass surround I would imagine that they do flow better. I just cant get to appreciate their sound.

[lakeroadster]

Originally Posted by Ole Greenie

Shoot...along this line of thinking just run straight pipes!

The chamber design of any muffler interrupts the flow of gases through them. This interupts the frequency and amplitude of the "signal" through the tube. Since Glass Packs silence this effect through holes in the side of the pipe into the fiberglass surround I would imagine that they do flow better. I just cant get to appreciate their sound.

With full length tail pipes glasspacks sound great, IMO. To me Flowmasters sound like a motor running under water.

[jakeblues652]

Originally Posted by lakeroadster

With full length tail pipes glasspacks sound great, IMO. To me Flowmasters sound like a motor running under water.

couldnt agree more.

[todd99]

I have a 350 and was running ceramic flowtech headers and 3" pipes with flowmaster 40's. It was seriously lacking torque so I added an x-pipe and heat wrap and now it runs like a raped ape.