Flowmaster U-fit universal dual kit

[T45]

I searched but came up with nada. I am going to install flowmaster's u-fit dual exhaust kit with flowmaster mufflers when I am nearing completion of my swap. I was just looking for opinions.

If you don't know already, the vh is going into my frontier which rolls normally on 35" tires and occasionally I do some towing, hauling and of course off-roading. I want torque. Plain and simple. I am getting the NICO ecu tune and have done a bit of port matching to the intake and heads. I haven't enlarged the runners, just cleaned them up a bit to improve flow.

My question is, what size exhaust should I use? They make the kit in 2.25, 2.5 and 3" sizes. What is the stock size and what would be the best for my application? Should I run a 2-1-2 with one muffler or a 2-2-2 with an H-pipe and dual mufflers? I want some nice tips so I was thinking the borla intercooled tips coming through the body of the truck on the rear. Would these tips have any positive or negative affect on sound? Also, opinions on going without mufflers alltogether. I have heard the clips on youtube and they sound sick but I don't want to lose any bottom end torque just for sound.

Too many options...

[Mettler]

You'll find 3" is excessive/too big for most 2L NA engines, so the same could be said for what's effectively 2x 2.25L engines.

I don't think you need any more than dual 2.1/2" exhausts unless you start producing over 500HP.

[sijoko]

I'm running a 2.5" setup with an X pipe and Spintech mufflers. The sound is amazing. If your goal is torque then a 2.25" setup might be better. If you're interested in the X-pipe, get the universal X-pipe kit sold by Jegs and then add the muffler of your choice.

[maxnix]

I searched but came up with nada.

Q45tech has extensive posts on his previous setup. Went back to stock because of minimal gains and bad resonances.

[Q45tech]

We made some detailed backpressure measurements years ago and Flowmaster mufflers didn't fare to well not the worst but solidly in the middle.

Dynomax UltraFlow is the winner [by a significant margin] if you care about performance instead of loud sound.

You would surely think flowmaster was the master of flow .....what they want you to think.

Always make sure what ever muffler you buy that you can see clearly thru end to end.

[T45]

Always make sure what ever muffler you buy that you can see clearly thru end to end.

Would you care to elaborate a bit more on this? The only experience I have with exhausts is on my current 3.3. I bought the truck used and it had a flowmaster with 1 in and 2 out to dual tips. Over time one of the pipes rusted and fell off. I noticed only louder sound. I needed an inspection so I welded a plate over the pipeless hole. I noticed a decrease in high rpm power but also noticed that it didn't take as much pedal to sustain mph on the highway. Like a decrease in HP but an increase in TQ.

I understand that a straight thru muffler will have the most CFM flow but if I'm going for torque wouldn't I want a little backpressure from a muffler and 2.25 pipe? Or would 2.25 pipe without mufflers be enough backpressure for my goals?

[Q45tech]

Never understood how the MYTH of backpressure helping torque got started ........ another cruel joke created by engineers to separate the knowlegable from the less educated.

Any back pressure is bad, in that back pressure slows the expansion of used gases out the exhaust port and can increase reversion out and up intake.

However it is always a balance between exhaust expamsion speed vs total flow volume and finding a compromise which allows the most exhaust to flow out the valves.

At low rpms the valves are too large, as the ports are too large and the speed slows down with too much exhaust pipe area.

Just like intakes the best method is to measure the back pressure with instrumentation so accurate repeatable measurements can be trusted.

Few muffler manufacturers provide scientific measurements and fewer still owners know how to translate these flows to match their engines.

A 4.5 liter [274ci] V8 just doesn't flow much exhaust even at 7000 rpm. 400-450cfm DIVIDED between 2 pipes.

Rear mufflers [of decent design] have little effect on exhaust........the farther away from the exhaust valve the less restriction matters.

[T45]

Right on, thanks!