exhaust plans

[black95hoe]

I'm not too familiar with exhaust systems but as of now this is my plan. Right now I'm running stock cats with no mufflers, with y pipe and dual exits. I love the sound of the current setup and would like for it to sound similar after new mods. Planning on ordering the Thorley Tri-Y (ceramic) headers, cutting off the cats, leaving off the muffler and continue running 2.5'' pipe into the y pipe and leave the 3 1/2'' tips on. Would this yield performance or mileage or should I change it up a bit...(In my case, mostly lookin for mileage gains with a bit of hp gains.) Any suggestions would be appreciated.

[diadora516]

you will at least want mufflers. running straight pipes would probably hurt your mileage. an x-pipe will help with some power but will also mellow out the exhaust

[Gerald]

Straight pipes will give you the best mileage out of any muffled set up. On a gas motor, back pressure is evil, but velocity is good. Often times ppl use tubing that is WAY too big for their aplication and that will hurt the mileage. 2.25-2.5" in a dual set-up is the best dia. on a stock motor.

[black95hoe]

so don't bother with an x pipe and add some mufflers? still leave off cats?

[Gerald]

yes, an x-pipe is supposed to increase tourqe right off idle. They are good, but change the tone a little. Its all your preference.

[black95hoe]

ok then, so the final setup (no cats, aftermarket muffler, thorley tri-y's, 2.5'' pipe, y pipe and dual exits) wont decrease gas mileage any and will give better performance?

[Gerald]

What do you mean "aftermarket muffler"? A flow 40 or bullet or what?

[black95hoe]

a flowmaster probably unless you would do otherwise. originally I wasn't planning on doing a muffler though.

[Gerald]

I would deff. choose an x-pipe over a y-pipe on a lifted truck. So basicly, run true duals from each header, then to the x-pipe, then muffler,then dump it or add tips out the back. All with 2.5" tubing. That would be a near perfect setup, and sound great.

I havent heard many setups on a 350, so I dunno about the muffler. I feel that flowmasters are over-rated, and over priced. Pick up a copy of summitt or jegs and look for Dynomax Bullets. Its designed to be a full out race muffler, and out flows anything other than straight pipe. Really cheap too, my 18" 3"in/out where like 40ea. Overall, they just have a louder and deeper tone than the flow 40s I had. Really impressed.

Bullets are loud like straights, but have a better tone.

[black95hoe]

I know I don't know much about exhaust so this may sound like a dumb question.. on my year model the stock headers come together up under the front of the cab, then split again. would this make it a little hard to run an x pipe with true duals?

[Gerald]

Nah, you can "X" it right before the mufflers if you have more room there.

[black95hoe]

would taking off my catalytic converter hurt my gas mileage any? keep in mind the cat is 11 yrs old..

[Gerald]

Personally, i'm not a fan of "no cats". Id say just run hi-flows out of jegs.

[Silverback]

Anything that flows better will make more power and get better mileage… but be aware that you can go too big… if the pipes are too big and the engine doesn’t fill them you will get reversion which will hurt flow.

Cats do minimally hurt flow, but remember that the mid 90’s and up GM truck cats are sold as high flow cats by the aftermarket, so in our case that would be a very minimal improvement. Mufflers are a similar deal, it depends more on design then anything else. FWIW, Flowmasters tend to flow about the worst of the aftermarket performance mufflers. Past that I would choose by the sound you want.

Crossovers, X or H, both smooth out the sound somewhat by balancing any difference in pressure/flow between the sides and also have a tuning effect. Both make more power also. There is a distinct difference between the 2, probably the best way to describe it is that an X tends to sound more like a revvy import, and tends to show the power increase up top, where an H has a lower, more muscle car sound to it and tends to enhance the midrange and low end torque. Honestly, I’m not sure why anyone would run an X on a full size truck on the street.

[Gerald]

well put, except an X is proven to make more lower tourqe than an H. Thats why we use them.

[Gerald]

Here's some food for thought from magnaflow.



How And Why "X"-Pipes Work
By Bruce Wayne, MagnaFlow Performance

There has been an enormous amount of press about getting more out of performance exhaust systems. By incorporating "cross-over" or "X"- pipes in dual pipe systems, to balance out flow, many enthusiasts have found an extra edge. However, the perception is that this is new technology. Nothing could be further from the truth. But, why is an "X" pipe better than an "H"?

The reason an X-Pipe crossover works better than an H-pipe crossover isn't more flow because of volume, but more effective use of exhaust gas velocity. Exhaust gas (or air) has surface tension, and flows much like liquid would through the same pipe system. As the cylinders of each bank on a "V" style motor fire, they create a pulse in the system. The pulses will alternate back and forth from bank to bank as the motor runs. With multiple cylinders, such as a V-8, the eight cylinders alternately fire creates lots of pulses in the system.

If you put your hand behind the tailpipe, it would feel like a constant flow of air, but what it really is a lot of singular pulses giving the impression of constant flow. The idea behind the H and X style crossover is to unite the two banks of cylinders for better exhaust gas scavenging. Instead of two separate banks of four cylinders doing their own work, the crossover uses the pulse created by a firing cylinder of one bank to create a vacuum in the other bank because of surface tension. When a cylinder of the other bank is ready to fire, instead of the piston having to force the exhaust gas out of the cylinder, the vacuum that was created by the other cylinder bank helps suck the exhaust gas out of the cylinder, hence the term "scavenging."

Whenever you can reduce the load on an internal combustion engine, you are likely going to see performance and efficiency benefits. The difference between an H and X crossover is a smoother path for the exhaust gas to follow. Exhaust gas, like a liquid, will follow a path with the least amount of resistance. An H crossover has a path with two sharp 90-degree angles that are close together. An X crossover has a path with a much more gradual bend to allow the exhaust gases to continue their path back out to the ends of the tailpipes, rather then turning sideways for a short distance, then turn again to head out the tailpipes. Smooth flow with high velocity means more power by use of scavenging. Using an exhaust system with too large of piping diameter work against scavenging in the same way that running an exhaust with too small of tubing chokes the motor and forces it to work harder to expel the exhaust gases.

[Silverback]

well put, except an X is proven to make more lower tourqe than an H. Thats why we use them.

Who’s “we?”

You’ll find that where people fit and what they argue the reason for crossovers working depends on what they sell… Magnaflow is firmly in the x-pipe camp and that is what they sell, as well as that is what they manufacture for other companies also.

Although the magnaflow quote sounds reasonable, I don’t know that it agrees with what appears to be happening in the real world. I don’t believe that it’s a scavenging issue (since a crossover or X would only help one cylinder per bank and hurt the strength of the scavenging for the other 3), and I’m sure it’s not about smooth flow through the crossover since I’ve seen dyno tests that show that the tube size and even angle of the tube in an H-pipe doesn’t really matter, something like a 2” crossover I a 3” dual exhaust has no loss of power over a 3” crossover, EVEN if it’s angled forward (making less then a 90* angle with the front leg of the pipe on one or both sides).

I have never seen a dyno test that has shown an X beating out an H pipe below say 3000rpm… If you have one I’d love to see it and some details.

Companies that carry both (for example Mac and BBK) tend to recommend them for different applications.

[Gerald]

"we" meaning lifted trucks.

[black95hoe]

hey man, just wanted to say thanks for the advice on my exhaust. I'll let you know what I come up with as for a final plan before I get ready to complete it.