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Exhaust 5.7 HEMI Exhaust Discussion

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Old 05-05-2010, 11:23 AM
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Default Exhaust Info from Dynatech

Some of you may have read that Dynatech has headers for our truck but they have only been installed on a 4x4 and they need a test truck to see if there are any differences with a 2wd.

I have been in contact with them for a few weeks not and my last email to them was with the intentions of running true duals with an xpipe and 2 mufflers. Eliminating the restrictive Y-pipe.

I wanted to share with you their response to me and the explanation as to why NOT to go with true duals.

Interesting read.

I would run the Y-Pipe.
The Y-Pipe is designed to give you torque. Many people just look at the horsepower number. With a truck or any vehicle for that matter, that is the worst mistake you could make.
Let me explain.
If you had the ideal header for an application and decided to make changes, one change you could make is to go smaller on the tube size. This would result in more low end torque and less high end horsepower.
The opposite would produce the opposite. Larger tube would result in less low end torque but more high end horsepower.
If you take two 2-1/2” tubes and direct them into and X-pipe with two 2-1/2’ outlets, you would be sending this exhaust through an opening equal to 9.8 sq inches.
Sending the two 2-1/2” tubes through a Y-pipe with one 3.00” outlet you would end up with a single opening of 7.07 sq inches.
The formula is below.
The Y-Pipe will obviously give you the low end torque this truck demands. If you must run duals, get the best of both worlds. Run the exhaust through the Y-Pipe. This gets both sides of the exhaust balanced for added power. You would also get the torque needed. Then run two outlets off of the Y-pipe outlet to get your duals.
You may ask, How is this different than an X-Pipe. The answer: It’s all in what diameter opening you run it through. An X-pipe that had a center section that necked down to a 2-1/2” center section would act very similar to a Y-pipe with a 2-1/2” opening.

(The formula: Area equals 3.14 x the radius squared. In this case:
Radius = 1.25
Area = 3.14 x (1.25 X 1.25)
Area = 3.14 X 1.56
Area = 4.9 sq inches (per 2-1/2” outlet)

We have two 2-1/2” outlets so the opening would be 4.9 x 2 = 9.8 square inches.

With one 3.00” outlet (Y-pipe) you would have
3.14 X (1.5 X 1.5)
3.14 X 2.25 = 7.07 sq inches.

The cats we use are a high flow ceramic cat. They provide the best balance between durability and cleaning the exhaust enough to not throw a check engine light.

Be careful when selecting cats. There are some great flowing cats out there, however typically with the higher flow, you get less cleaning of the exhaust.

I have included a link that shows the flow of our cats. The one on your system, would be the middle one @ 349 CFM

Pricing would be a little more involved. If you leave out the Y-Pipe, you would be required to buy the components individually instead of in a package.
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Old 05-11-2010, 03:59 AM
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Valldar Valldar is offline
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Very informative thanks for posting this.

If anyone here could answer me this, if lowering the diameter gives more low end torque and increasing the diameter will give more horsepower this means that bigger is not necessarily better? I would like to get some more horsepower outa my rig but not t the sacrifice of a lot of torque, maybe just a 1/2" bigger, lemme know what you guys think.

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