This first post has been updated to list all the information related to this install. To read the orginal post and responses, scroll down.

Flowmaster® 70 Series Big Block II Muffler Install

I wanted to give my Titan a little more aggressive sound, but not so much to be annoying. I wanted an exhaust sound that had a signature V8 rumble, but with a civil highway ride in the cabin. I had good experiences with other Flowmaster mufflers in the past and like their signature tone. I also wanted the look of dual straight back tips. After researching on the Internet (including this site), talking to various shops, and getting quotes, I decided to go with the Flowmaster 70 series Dual In/Out.

All the factory pipes would be removed just aft of the flanges behind the cats. From there 2.25″ aluminized steel pipe would be run to a stainless steel X-pipe. Then from the X-Pipe to the dual inlets of the muffler. The dual exits then snake over the rear axle. The left side squeezes around the spare tire, and is a pretty tight fit. The tips are mounted directly next to the sides of the trailor hitch and just past the edge of the bumper.

Below is a simple layout of the exhaust:

Flowmaster 70 Series: The 70 Series Big Block® II is designed around a large Flowmaster case for maximum volume and efficiency. The case is two-inches narrower than Flowmasterâs original Big Block® muffler, making for easier installation in tight applications. The 70 Series offers a mild mellow exhaust tone and incorporates a Resonant Tuning Chamber for reduced interior sound levels. It is great for tow vehicles and RVs and trucks with dual exhaust.-Taken from Flowmaster’s Website

Flowmaster’s 70 Series Information Page
Muffler Specifications (PDF)


X-Pipe: The X-pipe is an alternative to an H-pipe, both can be called crossover pipes. They are used to help balance the exhaust pulses coming from the left and right banks of the engine and to improve the scavenging effect. Therefore increasing low end torque that may be lost by increasing pipe diameter and/or removing the factory Y-pipe. Flowmaster strongly recommends the use of an H-pipe for dual exhaust set ups. I started a seperate topic on the subject here. I bought my X-pipe online from Husker High Performance. They were out of aluminized at the time, so I went with stainless, which will be better in the long run.

Tips: 3.5″x17″ rolled edge slant cut tips were used for the outlets. I think the rolled edge gives it a better look than the plain thin tips you commonly see. The tips were chromed steel, stainless is available but a good deal more expensive.

Pipes: All 2.25″ aluminized steel was provided by the install shop. At the time of install, Flowmaster didn’t offer a complete system for the Titan, so a custom install was required.

The original price of the system was $330, including everything except for the X-pipe. I had the X-pipe installed later, which cost $45 for the part and another $45 for install. An H-pipe would be far less expensive, especially if it were installed at the same time as the muffler. The 70 Series muffler goes for about $100 from online vendors, and my installer matched prices.

Sound: I’m very pleased with the overall results of this exhaust modification. The sound is definately much more aggressive at WOT and has a more recognizable idle rumble. At the same time, it is not overly loud in the cabin at cruise speeds. I can still listen to the radio at low volume settings or carry on a conversation. The exhaust is loudest (other than WOT) when travelling at low speeds (<40) under a load (ie. up steep hills) in the 1600-1900rpm range. The 70 series is by far the most tame of the Flowmasters, but still has the signature sound. After clocking several hundred more miles I feel the system is sounding even better.
Performance: Immediately I could tell a slight improvement in the upper RPM range. During full throttle accelerations the power band seems extended upwards. The low end seems to have improved slightly, but nothing to write home about. A future dyno is planned and results will be posted.
Mileage: After installing the exhaust I have improved from 16mpg highway to 18mpg. I have gone from 13 to 15mpg in city driving. Better results could probably be had, but I drive an average of 85mph highway.

Sound Clips:(mp3 format)

Sorry, but the mp3’s got deleted, I do have the original AVI video files still. You can watch/listen to them here[/url].

This one is accelerating from a right turn to about 40mph. The recorder was placed on the center console storage box.
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This one is a hard accerleration from about 10mph to 65mph, then cruise at 65 for a few seconds then punch it to 80mph. The recorder was on top of the steering wheel. The engine makes alot more noise then what you are hearing from the exhaust.
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And of course, some more high revs from outside the truck. The recorder was placed on the ground about 5 feet behind the rear. Turn up the speakers for this one!
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:gunz: :gunz: :gunz:

::::::::::::::ORIGINAL POST BELOW:::::::::::::::::

I got a few questions for those of you who have installed dual outlet exhaust systems, specifically those who have used flowmaster mufflers. My plan is a single muffler (probably 70 series) with dual outlets.

Flowmaster offers a muffler with dual 2.25″ inlets and outlets as well as one with a single 3″ inlet and dual 2.5″ outlets. Would it be better to remove the Y-pipe and run pipe directly from the cats to a dual inlet muffler or to leave the Y-pipe and run it into a 3″ single inlet?

I noticed the factory Y-pipe looks kind of restrictive and might have too much back pressure, if need be an aftermarket Y-pipe could be welded in and still run a single inlet muffler. Any suggestions?

Just for reference here’s the link to the 70 series muffler:
And a link to the data sheet (PDF) on the 70 series:

The two mufflers in question can be found on the data sheet (part #’s 524704 and 530712) So far I’ve been given one quote of around $200 for install and $100 for the muffler.


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