PheonixLS1

iTrader: (4)

I have been driving around for about 5 months on them ( only like 1000 miles) and I have not had a single code on my front o2's. My question is, if I gut my cats and lose that back pressure will I start throwing codes on my front o2's or will I have absolutely no problems at all. Thanks

Zlow28

iTrader: (11)

You will get a code for the rear O2s. But the car will have no problem due to removing cats. The computer read the front o2 sensor, which should be changing constantly. Then it compares that reading to the rear o2 sensors, which should be more stable due to the cat. If the cat is removed, the rear sensors will read similar to front ones. Thats how the computer knows if the cat is working or not. The front o2s wouldnt be affected and you can always tune out the code later on.

However, i heard if you have a v6 camaro and gut the cat, you will smoke vipers and have no traction under 80mph jk your title reminded me of that story

KevinR

The rear O2 sensor acts kinda like a "monitor" for a lack of a better term. Just get it tuned out.

RezinTexas

yep, it won't affect your front o2's at all.

PheonixLS1

iTrader: (4)

So if I gut them how much louder will it make my exhaust

Zlow28

iTrader: (11)

not much louder. You should be able to hear a small difference if you listen carefully, but your neighbors wont hear a difference at all from a distance. At least on a stock exhaust.

LS6427

iTrader: (2)

I did after my 427CI went in, maybe 6 months later. Made a definite and clear change in the tone while at part throttle cruising.....I can't really say it got louder though. WOT it sounded great and pretty much the same. Had zero FEEL in any performance gain. I had my rear 02's tuned out when it got dyno tuned.

.

PheonixLS1

iTrader: (4)

Exhaust is anything but stock. LT, true duals, x pipe, lm1's, under axle and out the back. So that being known, will it make it noticably louder.

Element

iTrader: (5)

Maybe a bit louder; definitely raspier, with those mufflers.

To clear something up from the initial post, a car neither "wants" nor needs backpressure. It's a bad thing.

crainholio

iTrader: (2)

What is the source of this information? Published engineering document, something you read on Teh Intarwebz, or personal intuition?

Element

iTrader: (5)

Basic physics, multiple threads to be found on this site, and the Advanced Tech forum.

Choking the exhaust doesn't increase performance at all (actually, it can be actively controlled via exhaust or jake brakes on larger trucks to provide increased engine braking to reduce wear on brake pads and rotors). Backpressure myths probably come mostly from backyard mechanics deciding they need the largest exhaust diameter possible (from the head flange to the tailpipe) who don't understand scavenging and gas velocity flow basics.

I'd also note that something that's commonly done - increasing the exhaust pipe diameter further back from the engine - is actually counter-intuitively a bad thing. By increasing the pipe diameter, you slow the exhaust gas velocity, which in turn creates a greater restriction further back, as the faster-moving exhaust gases in the smaller pipe collide with the now slowing-down exhaust gases in the larger pipe. By decreasing the exhaust pipe size further from the engine - where the exhaust gases are naturally slowing down some due to wall turbulence, gas compression, and that sort of thing - those exhaust gases can actually be forced to pick up velocity without offering a negative increase in backpressure closer to the engine, resulting in a better-performing exhaust.

Now, that ignores a lot of the more advanced tech stuff, which belongs in the Advanced Tech forum to be described by people more intelligent about this subject than I am.

But, as far as longer and better worded arguments against backpressure go, here are a few links to check out:

http://www.thumpertalk.com/forum/sho....php?p=6554557
http://www.thrashercharged.com/tech_htm/exhaust.shtm
http://www.aa1car.com/library/exhaust_backpressure.htm
http://my.prostreetonline.com/forums...php?t-1639.htm

crainholio

iTrader: (2)

Figured.

There have been threads on this site that say engine oil gets thicker as it gets hotter, by way of explaining the notion of 5W-30 multi-viscosity specs.

I'll stick with published engineering info when making my decisions about exhaust system design, and focus on the right amount of backpressure instead of aiming for zero.

Element

iTrader: (5)

Well, if you want to believe backpressure is a good thing, you go right on ahead. Your engine, your loss of power, not mine. If you can come up with even a remotely reasonable explanation of how backpressure helps make power, you'd be the first one to ever do so.

Funny that it seems you didn't even bother reading any of the links and probably don't understand exhaust velocity in the first place...but...whatever. That's what the interwebs is for.

crainholio

iTrader: (2)

If I understand what you're saying, your point is that an engine exhaust system needs velocity but not backpressure. Accurate point and I can see your logic.

However...we're talking about the entire engine, not just the exhaust system and this is where I think you've gone off track with your statement that "cars don't need backpressure." We likely agree more than you think, but that statement is misleading. Read on if you like.


I don't have to eat a turd to know it tastes bad, either. I just checked the articles for any evidence of engineering credentials on the part of the authors.

You would really enjoy taking a crack at reading "Scientific Design of Exhaust and Intake Systems" which will move your focus from the exhaust pipe to the combustion chamber and cylinder where the magic really happens. Learn about cylinder filling, harmonics, and the effect of the fuel/air charge being partially blown out the still-open exhaust valve in an improperly-designed zero-backpressure system, and you'll have a ball.

PheonixLS1

iTrader: (4)

Ok,,can we get back to the actual questions of my thread please. Thanks

RezinTexas

I've never done it to an LS1, but I gutted the cats on my old 540i (4.4 V8) and the sound was somewhat rhaspy. It sounded just ok, not great.

PheonixLS1

iTrader: (4)

I guess after the feedback my question is will it get NOTICABLY louder. I want louder, like alot louder......