Bill/Cory Exhaust Thoughts

[Jackpine]

Originally Posted by dplummer87

See, thats what i was thinking, i mean, IMO, by the time it gets to the muffler, the muffler is probably just being used as a "silencer" i mean, its already gone through the restricted headers and the restricted cats right?

So unless i put some headers and highflow cats, the muffler is probably just sound....? Logical thinking or no? Please correct me if its not. Im here to learn

Isn't a muffler simply for sound suppression? That's what I always learned. And the CAT is there to transform unburned hydrocarbons into something that's good for you like water vapor or carbon dioxide (as opposed to carbon monoxide).

But, the simple fact is, both these devices cause back pressure that prevents complete scavenging of the cylinders during the exhaust cycle. The introduction of Exhaust Gas Recirculation (EGR) sort of does the same thing, in the name of reducing Nitrous Oxide emissions I believe. So, for one reason or another, we're not going to get totally clear cylinders for the next intake cycle.

However, it IS possible, through a carefully tuned exhaust, to reduce the backpressure somewhat, which WILL increase the power available. You can even do it while staying within noise and emissions pollution limits. But, it takes a skillful exhaust specialist to make all this happen. I doubt it's any kind of simple "bolt-on" mod.

I think Lars and Cody posted a pretty good discussion of this a while back, but I'm too lazy to look for it.

What I took away from that discussion was that the results did not justify the expense, unless you're an absolute "purist" who doesn't mind throwing dollars in search of perfection!

One more thing that not everyone knows: You can't simply chop off the exhaust manifold and get a perfectly scavenging engine! This system is synergistic and needs to be TUNED to the engine to make things work properly!

- Jack

[88Racing]

Okay I know we are kinda blue oval fans here but I doug up a test we did in the mid 90's with two bowtie trucks.

1st subject was a 95 with a 5.7(350) obd1 system tbifi.
Cut out and removed muffler replaced with straight pipe. No loss in power gained .35 mpg. Definatly improved mid range and made towing boat seam easier.

2nd subject was a 96 5.7(350) with obd2 system tbifi.
Same thing was performed and the results to our suprise were this.
Lost 2.45 mpg. Passing became a chore even became more gutless
when pulling. Cooling system ran hotter. Also got numerous o2 cel lights. Put a aftermarket turbo muffler back on and everything was normal.

We figured out that obd2 systems were really sensetive to almost no backpressure situations and maybe that a higher rate of flow wasn't necessarily good for them.

Even some of the motors I built and put into cars, I found that straight exhaust wasn't the best for the motor. I got more power with backpressure and a x pipe.

So look at what you do and make sure it's the best and well tested product for your truck.

Lars

[Jackpine]

Good post, Lars!

I think you're right about the OBDII systems. I'm sure the PCMs are calibrated to "expect" the backpressure of a muffler and to work with it. When that backpressure is missing, I bet they try to compensate by reducing the outflow (which probably cuts the inflow of gas and air - so, less power).

- Jack

[Dixie Design]

I've talked quite a bit about my exhaust on these forums, there's a couple clips in my sig. I did a few things in steps rather than just going from stock to my current setup and would be happy to chat about it all again.

Here's the original post, and again check the clips in my sig they are the newest

http://dygytalworld.ehost-services13...p?t=209&page=1

[DarrenWS6]

For a cat-back swap only, I also would suggest the Roush Off-Road. I still wish I had gone with it. The best performing exhaust is a 3" single for these trucks, with a 3" single tailpipe or dual 2.5" tailpipes.

One of the absolute best set=ups would the the Dynatech LT setup with Magnaflow hi-flow cats and Y pipe ( avail. as kit for $1400 from Troyer ) to a 3" single exhaust with a straight through muffler.

I noticed a little loss when I had my 2.5" true duals done. I had to have the sound though. True duals is not a good performance exhaust unless theres a cam and supercharger to back them up, otherwise stick with 2.25" for better scavenging. I couldn't bark the tires from a WOT punch after I got my exhaust, was able to again when I removed my rear converters, and i'm able to leave a couple black dashes with the Gryphon lol.

In general terms, my suggestion would be run 3" from the Y to a straight through muffler of some type ( Magnaflow, Roush kits, Bassani, Borla.. )