Exhaust Help

EBFoxbat · 04-04-2005, 09:24 PM

I don't know much about exhaust so I'm throwing this out to the wealth of car knowledge here.

I want to add a switchable exhaust cutout before my catalytic converter. I want to run a pipe from the cut out down the length of my truck to merge with the tip. That way there would be no outward appearance of anyhting being different other than a thunderous roar when I flip the switch,

If the cutout goes before the catalytica converter, will the sensor that controls fuel flow (that's in the exhaust isn't it) trip an engine warning light? Is it bad for the engine... I mean will it end up flooding itself with gas or is it just a light?

Because running with the cutout open is illegal on-raod, I won't be doing it much. Mostly just for show, maybe a flame system later. Would the check engine light reset itself once I closed the cutoff and the exhaust ran through the stock cat and muff?

Please offer input here. Google didn't help me much with a "exhaust cutout" search. Thanks.

Dudes99 · 04-05-2005, 02:36 PM

Good question. No way to know unless you test it. If you just get under the car and disconnect it the ECU should put the car into a cold start situation (it will run rich) 0 volts sensed)shouldn't hurt anything though. Being a GM product it will probably throw a code though..........

Google'd exhaust oxygen sensor bypass

dodgetimes2 · 04-05-2005, 06:47 PM

My Ram has no exhaust and I get a Check Engine every once in a while. To get rid of it I just disconnect the truck's computer or the battery for a few minutes.

EBFoxbat · 04-07-2005, 06:21 AM

Running rich will just kill my mileage right, not my engine?

Scouse Monkey · 04-07-2005, 06:27 AM

Quote: Originally Posted by EBFoxbat

Running rich will just kill my mileage right, not my engine?

I think so. it will also kill the cat if you are running one but as youa re doing the bypass that won't matter. A rich engine will run cooler (one reason, apart fromt he obvious waste of fuel) why it will not be as efficent as the hotter you can run any engine the more energy you are extracting from the fuel.

I think the new Ferrari has some kind of exahsut bypass system so when you are really gunning it it misses out part of the exhaust to give more power but when driving in town gently the extra section is used tokeep it quiet.

I doubt you will be able to find one of those mechanisms on ebay just yet though!

EBFoxbat · 04-07-2005, 10:15 AM

I just got out from a while under my truck.

The O2 (i think its O2) sensor is right after the cat. There's no room to put a cutout in before the cat, so I'm going to do it after. That will just bypass my muffler. The cutoff exhaust and stock exhaust will meet up before the tip so it will only look like one exhaust.

Anyone know what a straight-5 roar is like w/o a muffler? I'm the only one I know with the new 3.5L inline 5-cylinder engine. I decided it was foolish to have dual exhaust (I wanted split rear) with out a V-engine... something about having only one header and making a fake dual exhaust makes me feel silly.

Hmm... I may do this on my own... known need to pay a shop what I can screw up on my own...

maxxell · 04-07-2005, 11:15 AM

I'm not claiming to be an expert in this, but if you start changing the way your exhaust works, your ECU is going to get all confused. Any major exhaust changes usually require an ECU reflash to learn how to efficiently utilize the new system. If you're changing on the fly, your ECU wont have a chance to learn, and you may end up actually losing performance when you switch to bypass the cat.
Again, I may be very wrong, but until you discuss this with someone who knows more about mods, I would be hesitant to start cutting parts.

red green · 04-07-2005, 12:32 PM

Quote: Originally Posted by EBFoxbat

...Anyone know what a straight-5 roar is like w/o a muffler?...

First, let me say that you might want to check with an inspection station first, as I'm pretty sure Taxachusetts has a couple of rules regarding modification of exhaust systems.

I'd say the sound has less to do with the cylinder configuration and a lot more to do with cam profile and displacement, so you might want to ask other folks who have 3.5L engines. In fact, a good comparison might be the old 4.0L Jeep inline 6. I'm sure there are several off-roaders out there (at Off-Road.com) with headers and no mufflers.

Also, I question your need for the cutout. You might be much better off with a carefully planned system that includes a high-flow cat and an appropriate muffler for your setup. In fact, you might want to visit a GMC forum like GM-Trucks to get more expert advice on your particular setup.

HTH

RPI Geek · 04-07-2005, 12:39 PM

Quote: Originally Posted by EBFoxbat

Running rich will just kill my mileage right, not my engine?

Yes, but it can also foul your spark plugs. IIRC, Running rich leaves excess carbon in the exhaust gases, which will end up all over your cylinders, valves, and spark plugs - fouling them.

WebDog · 04-07-2005, 12:53 PM

Quote: Originally Posted by EBFoxbat

I just got out from a while under my truck.

The O2 (i think its O2) sensor is right after the cat. There's no room to put a cutout in before the cat, so I'm going to do it after. That will just bypass my muffler. The cutoff exhaust and stock exhaust will meet up before the tip so it will only look like one exhaust.

Anyone know what a straight-5 roar is like w/o a muffler? I'm the only one I know with the new 3.5L inline 5-cylinder engine. I decided it was foolish to have dual exhaust (I wanted split rear) with out a V-engine... something about having only one header and making a fake dual exhaust makes me feel silly.

Hmm... I may do this on my own... known need to pay a shop what I can screw up on my own...

I did that in my old jeep and can you SAY LOUD! It sounded a bit like a big *** diesel truck. so much more power.

pyros · 04-12-2005, 01:07 AM

do a search on electronic exhaust cutouts.... there are a lot of systems out there.. and i've heard nothing but bad things about them mostly relating to the motors burning out due to the high exhaust heat.

you might throw an engine light since the o2 sensors wont sense much, but i'm not too sure on this. i know if i want to run without cats on my '04 i need MIL eliminators which simulate o2 sensors.

yes, what you're talking about is illegal everywhere in north america. you are bypassing an emissions control system which is a big no no regardless if you use it or not.

i'm not sure if you'll run rich or lean, but better rich then lean. run lean and you'll end up blowing your engine.

Tidder · 04-12-2005, 01:48 AM

Yeah, I agree with ol' red, just get a better exhaust system, hi flow cat and such.

Dudes99 · 04-12-2005, 08:48 AM

EB, do they check under the vehicle in MA? Down here in VA they do not, so as stated if they see the bypass you will most likely get cited for it.

I think a good cat-back system (if offered) would sound great, just don't put a fart can on the back end. Nothing worse than a truck trying to sound like a ricer!