Bob Y

So I have I replaced the factory driveshaft with a straight aluminum shaft. The mufflers have always rubbed on the shaft. I replaced the rear coil springs because the rear end was an inch lower than factory height. The new coils helped, but when going over a big enough bump, the mufflers would still bump on the shaft. I finally had enough, and just had the mufflers deleted. Car has a nice sound, even with four cats, I still get a tremendous amount of de cell pop. I've read of several fixes for this including dyno tuning. That seems a little pricey for added component. Wondering if anyone has deleted thier mufflers and found a more economical sure fire solution. Sometimes I actually like it, but probably would be best to tone it down a bit.

Jontall

Only a tune will help with the popping when decelerating. DFCO (deceleration fuel cut off) is what does it and it saves a lot of fuel. You can probably fit 2 Spintech 9000 mufflers without rubbing the driveshaft. They sound great, are low cost and should help with the popping, but a muffler will need to install them.

Bob Y

Thanks for the feed back. I will take a look at the mufflers.

blackbyrd

iTrader: (14)

Since the GTO is a IRS car the center chunk doesn't travel when going over bumps like the rest of the suspension. Maybe a poly diff insert would stiffen that up as well, but id say your exhaust is moving more than your DS and rear diff. Doesnt matter now since you removed them. Likely experiencing decel pop due to lack of restriction/backpressure with the mufflers gone especially since you still have CATS. Unless you have some other significant performance mods I dont think a tune will clear up the pop. Now if you have longtubes no cats and the pop thats a different story.

Bob Y

Thanks for the info. It sounds pretty straightforward. Someone else mentioned putting Spintech 9000 mufflers on the car. I've listened to a couple of YouTube videos of 04,s with those mufflers on. For as good as the quality of sound from a smartphone recording is, which in the best by any means, it still sounded pretty good, and no de-cel popping. I've looked the mufflers up online, and found out they measure 4x6x9 inches. It's a case of having to order them, and seeing if the muffler shop can fit them in. Still trying to decide what to do. I can get the Spintechs online for $134. If they don't fit, I would have to ship them back.

dw456post

Get a cardboard box and cut it up to make a 4x6x9 box and see if it fits where you need it.

AnotherWs6

iTrader: (17)

You mean a muffler would actually install another muffler? I've never had a muffler work on my car before. Never even seen one move on it's own.

Bob Y

I actually thought that. Spintech 9000 mufflers are 4x6x9 inches. The oem mufflers that I had removed were, I believe something like 4.5x7.75x18 inches. The spintechs should fit. They're $134 for a pair. I've listened to an LS1 with Spintechs on YouTube, and even though the sound quality is not professional, I think they sound pretty good.
Thanks

Jontall

They sound great!!!! I use them myself.

Bob Y

Thanks for the feedback!

gametech

iTrader: (1)

The best way to reduce decel pop is to quit being a ***** and never decel.

Bob Y

I'll take that under advisement. Thankyou

dreadpirateroberts

iTrader: (1)

if you have the stock midpipes, you only have two catalytic converters.

unless you meant actual cats. i would take them to an animal shelter.

Bob Y

No, there are four catalytic converters on the car with o2 sensors. I did, however get stuck with two cats that my daughter left when she moved out that I would love to get rid of. My Daughter and Wife will not let me. I have pulled the exhaust out twice two replace the clutch, slave cylinder and the rediculus two piece driveshaft with solid one. I had a muffler shop delete the mufflers and the owner confirmed that there are indeed 4 catalytic converters.

gametech

iTrader: (1)

Interesting. I read an early magazine article about the GTO that stated it had 4 cats, but I know with absolute certainty that mine only has the normal 2 cats, 2 resonators, and 2 mufflers.
edit-- Oddly enough, the PCMs do have a provision for a sensor 3 heater circuit error code in GM vehicles, but I don't recall seeing any with more than 2 oxygen sensors per bank.

Bob Y

Please read the pasted article. I will not argue any points, as I want to remain on good terms with all the members of this forum. In case the copying and pasting does not work, I will explain what I just read. The 2004 GTO was supposed to come from the factory with four catylitic converters, two per side, two resonators, one per side and two mufflers, one per side. I bought my car when it came back in from a two year lease. I,m assuming that the exhaust was one. That having been said, I hope you will trust me when I say that mine had two catylitic converters per side, one muffler per side and no resonators. If I had the resonators, I don't believe I would have the de-cel pop after removing the mufflers. Perhaps somewhere along the way GM made a change and we are both right.
However, there’s one nagging glitch that some diehards can’t seem to get their heads around. It’s that goofy exhaust system. Even though Pontiac went to great lengths to reconfigure the original Holden Monaro pipes to create a true dual-path system with four catalytic converters (two per bank), two resonators, two mufflers, and two chrome outlets, it’s the way they poke out from beneath the driver-side of the car that gives many observers flashbacks to the Smog ’70s and the bad old days when single exhaust systems were as good as it got

gametech

iTrader: (1)

I have no interest in arguing with you. I am merely stating that the info from a respected magazine article that I have read is completely wrong based on my personal 2004 GTO. Your statements have led me to believe that your GTO conforms to what the magazine article stated. As a person who is in the industry of making car parts, I can easily see how this could happen. As a person who dislikes middle management, I can be utterly pissed at why this happens.

Bob Y

Point taken. I wish my car had resonators on it. I had the mufflers removed because when I installed the 4 inch solid aluminum driveshaft, the back ends of the mufflers rubbed on the driveshaft. I read that the rear coil springs were inherently weak. I purchased and installed aftermarket rear coils that had thicker coils to return rear of car to original ride height, it had dropped an inch. That helped to a point. I still had a bit of a problem going over speed bumps. Eliminating the mufflers and replacing with straight pipe totally eliminated the problem. I love the way the car sounds now with the exception of the de cel pop. I am considering 'Spintech' mufflers which only measure 4x6x9 inches. That will be next year. I live in Mi and the car goes in storage at the end of the month. As I said, I bought the car when it was returned from a two year lease with 24000 miles on it and assumed it was factory exhaust. How it ended up with the exhaust that was on it, I don't have a clue. I have a manufacturers shop manual. It's from Holden but has a section for the LS1 GTO and shows one cat per side, one muffler per side and one resonator at the rear of car with both exhaust pipes running through it. I simply don't have that configuration and have no clue as to why.
Regards, Bob Yeomans

Rob

iTrader: (6)

Please take pictures of these 4 cats. Where are the O2 sensors? The car came from the factory with two cats, two resonators, and two mufflers. The resonators look like cats but they are just resonators.

2ToeRacing

iTrader: (5)

Here I can fix this....take all of it off. install a set of headers, no cats, and a decent muffler. Then have it tuned, you'll pick up some power and the decel pop will be gone