Well guys I just had a Flowmaster 50 SUV installed. DI/SO (2.25/3.00) on my 5.7 DC

It really sounds great, but I'm almost certain I lost some low end torque. It doesn't feel like it gets up and goes quite as fast as it used to, feels somewhat sluggish off the line now.

Is this typical for an exhaust modification on these engines? I assumed that if I stuck with stock piping and just replaced the muffler I would be OK. I guess not.

Any ideas?

And.. which exhaust mods/systems are DYNO PROVEN to not reduce low range power? I really don't want to waste any more money modding if I'm just going to lose power.

Thanks guys! :)

Sounds strange. I found when changing the stock piping I seemed to lose low end but when returning the stock pipe I got it back. Butt dyno's are far from accurate, but if you really did lose a little low end perhaps the muffler you chose doesn't flow as well as the oem. Flowmasters have chambers with flat walls and straight 90 degree turns, which do hurt flow capability, funny they have a name like flowmaster. I have seen charts before in magazines that prove they're not the masters of high flow. I myself didn't like my flowmaster, changed it for a spintech and never looked back. Good luck.

Probably going over to some TRD duals soon, should be better off with the OEM TRD exhaust.

My opinion is that Toyota isn't putting very restrictive exhaust systems on Tundra's, so it's tough to get power changing it. Aside from the manifolds, and on 1st gens the y-pipe, there just isn't much to improve. I did a muffler swap keeping the stock pipe, didn't gain power or lose any but did lose at least 5 pounds of muffler!

The best way to quiet down an exhaust is to restrict it. If you look at the entire design of the exhaust system (Toyota designed the entire system to work together) you will see that it is designed to be restrictive. From the wheezy manifolds, to the crimped 'y' pipe and the humongo muffler. Some models even have huge weights welded to the outside of the tubing to reduce resonance.

When we start changing their design you can lose power, and in some cases you gain it. The only benefit, besides quietness, to restrictive exhaust is off the line throttle response. It actually makes the truck feel like it has power. The back pressure acts like scavenging.

Scavenging is what you really need, not back pressure. If you put any type of a bend or obstruction in an exhaust system (a tube that goes from stock to bigger than stock is an obstruction) you 'put on the brakes' . A lot of guys have an exhaust shop 'throw on' a Flowmaster and tubing thinking it will give power.

2 3/8" tubing is difficult to find so shops typically use 2.5" (I have tried 2.5" and 2.25" on my truck, both lost power) I have searched and searched, trying all sorts of mufflers and tubing. The thing that works the best is the stock tubing and a flow thru muffler with stock inner diameter.

Sound, power, mileage is best achieved with flow and scavenging, not back pressure. A friend of mine has helped me dramatically with my truck! He has done extensive research on his truck. He has built a website dirtydeedsindustries.com (http://www.dirtydeedsindustries.com/Custom_Exhaust_PN98.html) He actually hand builds his own mufflers!

Here's a dyno video
http://www.youtube.com/watch?v=KlUOaYUpPxc

His truck is a non VVTI 4.7L with drop in K&N, electric fan, coolant bypass, S&S LongTubes, custom hand built H Pipe, custom hand built mufflers, and Old Skool Nascar side exit tail pipes.

The truck laid down 242HP TO THE WHEELS! That converts to 300 HP to the flywheel.

Throw in a cia. It should help balance it out. Exhaust and cai on these trucks are pretty much for sound since the originals do a pretty good job on their own.

again . . . . . .
More references to "Exhaust Scavenging"
Has "anyone" taken the time to understand what"Dual Variable Valve Timing" is?

Hows does an exhaust system "scavenge" what isn't there to "scavenge" ?
You can not pull exhaust gas that hasn't been released by the ECM.
There are no magic elves in your tubing
On these OHC 5.7 motors your burn cycle is completed once exhaust gas's reach the
flange,be it stock manifold,shorty header or LT Headers.
That old school stuff doesn't jive with current Gen II technology,much less the aftermarket hype there of . . . . . ;)

Throw in a cia. It should help balance it out. Exhaust and cai on these trucks are pretty much for sound since the originals do a pretty good job on their own.

Induction and exduction from an engine is a very complex process.

Let's start with the CAI. More air in is basically useless unless you can do something with it. If you paid attention in your High School science class you'll know that for combustion you need fuel and oxygen. More oxygen does not make for a bigger burn in the cylinder. It may cause the burn to occur at a faster rate, much the same way a campfire burns faster when you fan the flames, but the net amount of energy released remains the same. Adding more air won't do squat unless you can add a proportionate amount for fuel to make for a bigger bang. So unless you go with a turbo/supercharger that forces a higher volume of fuel as well as air into the cylinders, you are just sucking wind (pun intended).

A well-tuned engine like in a Tundra is designed to precisely provide just the right amount of air for combustion; you don't need to add air.

Exhaust is another matter. Cool air is denser than hot air, and therefore, cooler exhaust gases require more force from the engine to expel them. If your pipes are too big (or to be more precise, if the volume in your pipes is too big), the exhaust gases cool down faster, thus becoming more dense, which will then require more work from the engine to push them out. Next time it is a real hot day, try blowing up a balloon outdoors. Then go inside to an air-conditioned room and try blowing it up again. It will be more difficult to blow up when indoors, because your lungs are pushing cooler air.

Again, Toyota has just the right amount of exhaust size to facilitate an efficient exduction of exhaust gases.

A poorly tuned engine might squeeze out a horse or two by opening up the induction and exduction, but if that is true, the problem is most likely that then engine itself has problems. A well-designed engine doesn't need it.

As for "a nice sound", it's what I call "audible bling." A nice sound and a dollar will get you a cup of coffee at 7-Eleven. It doesn't really contribute to anything.

P o i n t s !! Sd ;)