Which exhaust would flow better?

[markrinker]

Here is one for the mechanical engineers out there:

My local shop just got a new exhaust tube bender for up to 3" tube. The owner suggested he bend 3" tube from the Heath downtube, through a Flowmaster type muffler that splits into two 2.5" output tubes. I am interested, but undecided.

Would this approach flow better or worse than 3.5" tube to the rear?

[ 06-09-2004, 05:05 AM: Message edited by: Mark Rinker ]

[DmaxMaverick]

Wouldn't this be similar to a single 4" pipe? No. A two inch pipe has an area just over 3". A four inch pipe has an area over 12". The two 2" pipes will have nearly half the area of a single 4" pipe.

A single 3" pipe will have an area similar to two 2" pipes.

You also have to consider the restrictive surface area. The more surface area you have for a given cross sectional area (multiple pipes to achieve the desired area), the more turbulant restriction you will have.

Kinda' confusing, huh?

The advice you got doesn't sound right to me. Dual exhaust is fine, it just needs to be of sufficient flow. A one-into-two muffler is a restriction without any help. Not a big deal on a N/A gasser, big deal on a turbo Diesel. Best bet, for sound and performance on a turbo Diesel, is a single pipe of sufficient size. If you insist the dual setup, it would be better to split off at the downpipe with 3", and install 2 mufflers (if any). Elsewise, just run a single 3" pipe all the way, with a non restrictive muffler/resonator of at least that size. You won't get much performance over a stock exhaust w/o the cat. Also, forget about a balance pipe. They only work on N/A true dual exhaust systems, in case you didn't know.

If all this doesn't make sense, I'll give it another shot.

[DmaxMaverick]

I guess you were editing while I was typing. Same thing applies. The area of a 3.5" pipe is about 9.5". Still better than two 2" pipes, with less restrictive surface area.

A 2.5" pipe has an area of about 4.9".

Two 2.5" pipes would theoretically flow similar to a single 3.5" pipe. The 3.5" pipe would take up a lot less space under there, than two 2.5" pipes.

OK. Try it again....

[Cowracer]

For a quick visual confirmation of this;

Draw a 4 inch circle on a sheet of paper. Cut out two 2-inch circles out of posterboard and lay them side by side on the 4 inch circle. All the area inside the 4 inch circle that is NOT covered by the two inch ones is the extra volume that a 4 inch has.

I had to do this same thing with an engine builder that tried to tell my buddy that 2 small pipes are better than one. The jerk coulndt even understand the math involved when I showed him the figures. :rolleyes:

Tim

[Kennedy]

3.5 mandrel bent is best size IMHO.

3" mandrel bent is marginal...

[markrinker]

Thanks for the quick and educated replies. It didn't seem right to me. I'll be going with a 3.5" system and a straight 'flow-through' muffler designed for diesels and not gassers.

One more question: Why is the max diameter tube diameter bent by muffler shops 3" ??? Does the equipment get mondo expensive after that ??? All the exhaust 'pros' around here max out at 3"...

[Cowracer]

Originally posted by Mark Rinker:
One more question: Why is the max diameter tube diameter bent by muffler shops 3" ??? Does the equipment get mondo expensive after that ??? All the exhaust 'pros' around here max out at 3"... Supply and demand. For 99.9% of the automotive market, 3" is more than enough (or outright overkill). They have to draw the line somewhere so the machine manufactures chose 3" It would take more power and bigger dies for 3.5" up, and with little or no market for pipes that big (automotive-ly speaking) the muffler shops can't justify the additional cash outlay.

Now, go to a place that works on over-the-road big rigs. They usually can bend up to 6". 3.5 and 4 inch is right in their wheelhouse...

Tim

[Spindrift]

Maybe it's a case of supply and demand. Here on the right coast you won't have too much trouble finding a custom shop that will do 4" work. Maybe there are some advantages to over population. New Jersey has the highest population density in the U.S. An average 1,030 people per sq. mi., which is 13 times the national average! Believe me, sometimes you just want to go and hide. I prefer to sit in my truck.

It might be worth a ride to Minneapolis/St. Paul to see what the Twin Cities has to offer.

[Kennedy]

I find it hard to find someone to even EXPAND 3.5"or 4" pipe.

I always thought most truck shops just bought pre bent bolt on stuff and added a little flex where needed...

[CleviteKid]

Once you choose your pipe size, you have to choose a muffler or mufflers. If you are going over 3", buy something diesel-specific from the vendors on TheDieselPage.com.

For 3" or less, you can learn a lot from the DynoMax website. Just as an example the DYNOMAX SUPERTURBO (http://www.dynomax.com/documents/super_turbo_specs.pdf) catalog section list the noise level ("Sport" or "Street") and the CFM flow rating, then two horsepower numbers, as a single and as duals.

The horsepower is what DynoMax calls the "Free flow" horsepower - in other words a particular muffler will not noticeably choke off an engine up to that power level, with the corresponding pipes, off course. I am running a pair of 17770 mufflers, each of which can flow 563 CFM, and the pair will handle up to 512 horsepower. That will be enough even with all the new bottles in the bed feeding mystery fluids ;) to the intake manifold.

Dr. Lee :cool:

[moondoggie]

Good Day!

The math is pretty simple. Area = π r^2. From this you can see that area increases as the square of the radius. So, if we double the radius, we quadruple the area. This is why a single large pipe (say, 3.5

[CareyWeber]

Originally posted by CleviteKid:
That will be enough even with all the new bottles in the bed feeding mystery fluids ;) to the intake manifold.

Dr. Lee :cool: Hey now DOC don't be so stingy with the details. smile.gif smile.gif

Carey ;)

[DmaxMaverick]

[quote] Wait a minute

[moondoggie]

Good Day!

[DmaxMaverick]

They have a forum for that?? Wow! Ain't America great?!!

Guess a muffler wouldn't hurt there, either.

[ees]

At least in my area anything over 2.5 is hard to find mufflers for. On a gas turbo project I was working on I ended up with racing mufflers from Summit. The only choices for 3" my local shops had was flowma$ter.

I wish I could find a local shop with a mandrel bender. I guess until then I am under there with the welder.