exhaust pipe diameter for a mildly modified 340

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furyus2 said:
An episode of Engine Masters shows that an engine does not need backpressure. Check it out on YouTube.
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People at the drag strip have known it before those engine master guys were even a glint in their daddy's eyes. lol
 
Back pressure = power loss in most anything we tested. The higher it was, the more power we lost. When none was there, the engine made the most power and the cars ran the quickest, almost 100% of the time.

My 320 HP 340 knew it had restriction but realistically, it only hurt about a tenth and 1 MPH when running 104mph and shifting at 6100.
 
Long day....just got in and see lots of chatter. Great stuff guys!
OK... the mufflers are the restriction and back pressure has no effect!
I have watched most of the Engine Masters videos but they are usually for hi hp builds through open headers for the quarter mile.t
I do like a quiet exhaust, Rumble. Ultradyne tech spec'd the cam and said headers would produce no real gain in my build. Engine was built to give good street performance and will never see high rpm.
So...how much gain or loss could you notice driving on the street from 800 to 5000 rpm. 15 hp...20 hp?
 
ir3333 said:
Long day....just got in and see lots of chatter. Great stuff guys!
OK... the mufflers are the restriction and back pressure has no effect!
I have watched most of the Engine Masters videos but they are usually for hi hp builds and more times than not
they are through open headers on high hp builds.
I do like a quiet exhaust, Rumble. Ultradyne tech spec'd the cam and said headers would produce no real gain in my build. Engine was built to give good street performance and will never see high rpm.
So...how much gain or loss could you notice driving on the street from 800 to 5000 rpm. 15 hp...20 hp?
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Back pressure loses power. I'd say that's an "effect".
 
ir3333 said:
So...how much gain or loss could you notice driving on the street from 800 to 5000 rpm. 15 hp...20 hp?
Click to expand...
A 600 hp is pushing out about twice the air as your 340 and has only a 13-20 hp difference between 2.5 vs 3. They said 3” was about par with open headers.

So how much you lose by going 2” ? Instead of 2.5” probably about the same. Unless you put some power killer mufflers on some are terrible and might kill twice that. Testing is the only way to know for sure, I wouldn’t go with 2” but it don’t seem like you overly care about power.
 
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In my mind....and I know that's gettin dangerous, the biggest need to do away with back pressure has to do with not contaminating the next intake charge with exhaust gasses. Which of course leads to a power loss. I think we can all agree that's a bad thing.
 
lotta people trying to pick pepper out of fly **** here.

600hp motor loses a few hp/tq, @VOETOM shows 1/10th & 1mph

if you're going from a single or a real crappy dual set up, then sure stepping it up to 2~2.5 with some good mufflers is going to be a marked improvement. but the difference between a 2" system and 2.5" system in a sub 400hp street car? what's the ROI on that? a nickel?
 
Correct, i've built a few cars and maximum power or racing is not important, but when i step on it
something has to happen.
I actually bought a complete inexpensive used 2" exhaust just to get me driving when i reach that
point with the current project.
So i thought i would see what some of the more knowledgeable guys on the site thought about how
much would be left on the table? Maybe it will be adequate
 
ir3333 said:
Correct, i've built a few cars and maximum power or racing is not important, but when i step on it
something has to happen.
I actually bought a complete inexpensive used 2" exhaust just to get me driving when i reach that
point with the current project.
So i thought i would see what some of the more knowledgeable guys on the site thought about how
much would be left on the table? Maybe it will be adequate
Click to expand...
When the time comes Run it and measure the back pressure if it's low then probably good enough if high then a possible upgrade in the future, if you do measure please share the results, also could do open vs the 2" see what difference it makes.

Testing/measuring is the best way.
 
My 340 runs stock manifolds and it likes good exhaust systems.The difference between the very best system and stock setups on mine might be .15 and 1.5 mph so it is not much to worry about unless you need very tenth.
What does matter is the driver's side exhaust pipe out of the manifold. There is some serious power loss and for sure, I'd fix it. Tom Swope at Accurate can bend you 2,5. pipe to get aorund the starter and torsion bar and that is worth doing. The stock set up is about a 2" pipe squashed in half. It has to hurt although I can't say how much since mine has always had a homemade big pipe on the drivers side.
 
I went with manifolds, and a TTI 2.5 inch exhaust. The fit on the driver's side is tight, but doesn't hit. I did need to cut a 5/8 wrench to tighten the bolts.
The other concern is sound. Smaller pipes IMO sound like pea shooters.
 
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273, this chart above was from testing on Dad's car long ag. Pretty easy to see. We made a single system so we could really see what mufflers did or didn't do.

Book cover.jpg
 
Yup, when the time comes i'll install them.The complete exhaust came off a 340 Dart with the same
...549, and ...553 manifolds that i will use. The previous owner/friend restored a show quality numbers
matching 69 340 4speed convertible. I think there may only have been about 50 of those cars made and
these replacement pipes had no business on that car but it won't matter on mine.
 
Icetech said:
View attachment 1716144240
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It's not just the diameter of the pipe but the bends also, as well as the type of muffler. I use 2.5 with Walker Turbo mufflers, tail pipes comes out in front of the rear tires (none over axle). This is my van set up with a 70' 340. Note: Being a van, the collector is 2.5". I welded flange to the pipe, then attached to collector, by bolts. I noticed a huge difference between 2" and 2.5".
 
I wonder if anyone has done a study on decibels of loudness between the different size exhaust using the same mufflers for the given size so you could get apples to apples comparison. That could also be a deciding factor for some of us older folks that don't like too much noise anymore but still like power.
 
nckennyb said:
I wonder if anyone has done a study on decibels of loudness between the different size exhaust using the same mufflers for the given size so you could get apples to apples comparison. That could also be a deciding factor for some of us older folks that don't like too much noise anymore but still like power.
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I think the bigger pipes are more mellow sounding. Think of a old pick up with skinny 2" tail pipes cackling up and down with rpm. What a stupid sound! :BangHead:
 
toolmanmike said:
I think the bigger pipes are more mellow sounding. Think of a old pick up with skinny 2" tail pipes cackling up and down with rpm. What a stupid sound! :BangHead:
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Stupid!? no way... This is the exhaust i want...
 
Icetech said:
Stupid!? no way... This is the exhaust i want...
Click to expand...

That doesn't sound like a old pickup though. I remember watching those videos. That's like a Commando single exhaust. But if I remember right, that's not the "Hemi style muffler" and no resonator. Sounds great and he really get's after it at about 28 min. Downshift and go. And then at 30 min.
 
toolmanmike said:
That doesn't sound like a old pickup though. I remember watching those videos. That's like a Commando single exhaust. But if I remember right, that's not the "Hemi style muffler" and no resonator. Sounds great and he really get's after it at about 28 min. Downshift and go.
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I believe it's actually a resonator and no muffler.. i'm too lazy to go look though :)
 
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