Mixing dimensions - exhaust

mhjo · Aug 4, 2011

We are mounting new exhaust now and we have threes sets of tubes:

1. H-pipe 2"
2. Tail pipes 2"
3. Pipes 2.5" between H-pipe and mufflers (before tail pipes)

Are there any problems mixing dimensions (sonically or performance wise) ?

JonK · Aug 4, 2011

Sonically I don't think you'll break the sound barrier, performance wise they won't perform any better than an entire 2" system as that is the smallest size in the entire system. Imagine putting a 1/4" pipe in the middle of a 5/8" garden hose and turning the water full blast, you will still only get 1/4" of water out of the end of the 5/8" hose. If the tailpipes are crush bend from a muffler shop the bends over the axle will actually be more like 1 1/2"-1 3/4" internal size. If they are mandrel bent from a supplier they should be 2" still (won't have those creases at the bends).
Jon

mhjo · Aug 5, 2011

Thanks. I thought maybe the path with wider dimension could create a chamber causing boom / drone effekt

JonK · Aug 5, 2011

I think drone comes more from mufflers and the frequency they emit, depending on how the muffler is designed and if both mufflers hit on the same freq. at the same RPM (say cruising at 40mph) it resonates through the muffler and metal floor boards, etc. I looked but there is not a lot of info. out there on mixing sizes.
Jon

mhjo · Aug 8, 2011

JONK - se my other post:

http://www.stangnet.com/mustang-forums/837027-time-upgrade-exhaust.html#post8486204

PoppyMod · Aug 8, 2011

Hi,

I read your "other" post. I agree with JonK thoughts. It's more likely, the "drone" is based on your total package with the choice of muffs being the main ingredient and not so much the 1/2" dia. pipe change.
It's typical, when adding new muffs, one would simply step-up or down "at the muffs" with appropriate adapters,if needed.
So why plumb-in different dia. pipe, if it weren't the same throughout?
Good Luck!

mhjo · Aug 8, 2011

The muff's are the same as befaore I chnged the rest.
The dealer only had 2.5" left that day..

Any recomendation for 'drone free' mufflers ?

PoppyMod · Aug 8, 2011

mhjo said:
The muff's are the same as befaore I chnged the rest.
The dealer only had 2.5" left that day..

Any recomendation for 'drone free' mufflers ?

OK. Because what one hears as annoying another person may like. Therefore, I would suggest you attend a few cruises, car shows etc. Talk to the guys and maybe ask for a demo. Check some of the muff web sites as they have sound clips. Also, YouTube is a perfect place to check.
Good Luck and Happy Motoring in beautiful Norway!

bacfire · Aug 12, 2011

JonK said:
performance wise they won't perform any better than an entire 2" system as that is the smallest size in the entire system. Imagine putting a 1/4" pipe in the middle of a 5/8" garden hose and turning the water full blast, you will still only get 1/4" of water out of the end of the 5/8" hose.
Jon

While I agree that there wouldn't be a lot of practical benefit to the 2.5" pipe in this situation, it's not accurate to say that a system will not flow any better than its smallest section. Losses/resistance/backpressure in an exhaust system is mostly from friction and turbulance along the pipe walls, and any reduction in that...even for just a part of the length...is a good thing. A 50' long 5/8" garden hose with a couple feet of 1/4" pipe in the middle will flow *much* better than 50' of 1/4" hose. Try it!

tx65coupe · Aug 13, 2011

I just find it odd that he has drone issues with Dynomax Super Turbo mufflers. They are some of the mildest and least droney mufflers available. I'm curious to know why he has this issue.

JonK · Aug 14, 2011

tx65coupe said:
I just find it odd that he has drone issues with Dynomax Super Turbo mufflers. They are some of the mildest and least droney mufflers available. I'm curious to know why he has this issue.

This was curious to me also, I was expecting to read that he had flowmasters with the inevitable drone, the turbo in most any brand is supposed to be mild tone/no drone.

bacfire
'A 50' long 5/8" garden hose with a couple feet of 1/4" pipe in the middle will flow *much* better than 50' of 1/4" hose. Try it!'

I think this is just completely wrong, if you have a piece of 1/4" in the line it won't matter if you have 3" hose after or it ends at the 1/4" piece, a 1/4" stream is going to squirt out after the 1/4" hose. Imagine breathing through a straw vs. a 1" hose, won't matter what you put on the end of a straw you'll only get as much air as the straw allows.
Jon

Rusty67 · Aug 15, 2011

JonK, all other things being equal I think you are right. Also, water going through a pipe is different then exhaust going through a pipe.

Remember that you are dealing with thermal dynamics here. Exhaust gasses cool significantly before they reach the tail pipe exit and as they cool they become more dense. Being more dense, they need less space to maintain the same pressure as when they intially exited the head. Theoretically, a larger pipe can be stepped down to a smaller pipe with no performance impact so long as it is done far enough back in the system that it doesn't cause a restriction.

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