exhaust pipe diameter for a mildly modified 340

[Icetech]

ALso a 340 under the hood now.

340 is just too many cubes... no idea why people get greedy

 

[toolmanmike]

I believe it's actually a resonator and no muffler.. i'm too lazy to go look though

The stock HP single system is pretty quiet inside.

 

[1971 CY Dodge Dart]

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.

Mine got louder when I went with a full 2.5” system vs my previous 2-2.25” exhaust. Same mufflers.

 

[Dale Davies]

I thought a street engine needed some back pressure to keep lo rpm exhaust velocity up for low speed power?
Isn't that why street driven engines benefit from a small cfm carb and why the factory reduced the tail pipes
to 1 7/8" from 2 1/4"? This wouldn't apply for an open header race engine at 6000 rpm.
....but the question is how much power might be lost going from 2 1/4" to 2" exhaust? I'm wondering if there
may even be an improvement below 3500 rpm?

You need to search and watch David Vizard Powertec 10 videos. One is about zero loss street legal exhaust. Another delves into equal length headers.
Ben Alamida also has a video wherein he states backpressure requirement is a big lie.
Get a copy of Vizard's How to Build Power book, that will clear up a bunch of issues.

 

[RustyRatRod]

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.

View attachment 1716144483

Don't you still have his wagon, Tom?

 

[MoparMike1974]

Yes, bigger pipe = louder exhaust. The biggest factor on how loud a car is would be compression ratio.
I have two 340 cars with the same TTI exhaust system. One is 10.5:1 and the other is 8.5 or whatever a stock 73 340 was. The 10.5 car is easily 3x louder.

 

[1MeanA]

2.25" minimum. I always run 2.5" on my street 340's.

I've always run 2 1/2" with manifolds or headers (street cars). I just received my TTI 2 1/2 system for my 340 Swinger. When I look at the size of the pipes (except where they smashed it to fit around the starter) I can't believe this wouldn't be more than adequate for any small block up to 6000rpm.

 

[ir3333]

i wonder how often most guys drive their cars past 4000 rpm?
90 mph with 3.23 gears and a 26.5" tire is only 3685 rpm.
90 mph with 3.55 gears and a 27" tire is 3976 rpm.

 

[Mattax]

i wonder how often most guys drive their cars past 4000 rpm?
90 mph with 3.23 gears and a 26.5" tire is only 3685 rpm.
90 mph with 3.55 gears and a 27" tire is 3976 rpm.

Now you're getting into facts. Why would you let facts get in the way of a good story?

using factory option E70-14 would have diameter around a 205 70r14, which is 25.3"
with a 3.23 gear, 4000 rpm is still 93 mph, and 3000 rpm is 70 mph.

The place where its most important for exhaust pipes to handle a large volume of flow with minimal resistance is the race track. Read enough here and anyone paying attention has a pretty good sesnse of who brings their car to a track now and then, frequently, and not at all.
Even for those who want maximum horsepower, IMO too many miss that power throughout the gear is often more important than the peak. More so for those of us with gearing that results in hitting the finish line before the hp peak. IMO maintaining flow away from the exhaust port in the low to mid range is going to bring the most gains. If we can do this without stuffing up the top, even better.

 

[ir3333]

i agree. Most responses are for 1/4 mile or max peak HP, and max hp is not the most important
part of the build for racing or street driving....

 

[Mattax]

Calvin Elston touches on this in many of his posts.
Here's one Tri-Y Headers vs. 4:1 at part throttle... - Don Terrill’s Speed-Talk

He's also posted about advantages of using a single exhaust in many situations.

 

[ir3333]

I know it's like "beating a dead horse" but did any of you guys notice on the engine masters video that below 3500 rpm the 2.5" made more power?
... 3500 rpm and under is where everyone drives 99% of the time. And when you launch or break the tires
loose it's always from idle or lo rpm.

 

[Mattax]

maintaining flow away from the exhaust port in the low to mid range is going to bring the most gains. If we can do this without stuffing up the top, even better.

Calvin Elston explains how he views the mass of exhaust gas leaving the cylinder.
Better way of thinking about exhaust than flow and backpressure, or even worse simply maximum flow and resistance at maximum flow.

Novice exhaust question: What is "blowdown length"? - Page 2 - Don Terrill’s Speed-Talk

 

[ir3333]

i think this thread is finally dead so i'll just throw this out there. The last info i read (that was way over my head) said at lo rpm 1lb. back pressure kept the cylinder filling, overlap and scavenging events uniform.
I can hear those murmurs!

 

[Mattax]

i think this thread is finally dead so i'll just throw this out there. The last info i read (that was way over my head) said at lo rpm 1lb. back pressure kept the cylinder filling, overlap and scavenging events uniform.
I can hear those murmurs!

Makes no sense. At least no sense without context. What's the pressure in the intake? Where was the pressure in the exhaust measured? Are they measured on the same scale? Modern cars use absolute pressure. Atmosmopheric pressure is 14.7 psia. 1 psia is very low pressure.
This is why I recommend Calvin's way of looking at exhaust flow. Its focused on the most important job of the exhaust system, not on a limited rpm range.