LS1GTO Forums banner
1 - 20 of 46 Posts

GR-RRR!
Joined
8,524 Posts
Discussion Starter · #1 · (Edited)
For those who aren't keeping up with my 04 mods and to recap what I have here is a mostly stock 04 GTO with a basically stock LS1. Exhaust consists of JBA shorty headers, custom made 2.5 inch midpipes with Magnaflow cats and O2 sensors retained all feeding into an SLP catback. This catback was on the car when I got it. Best I can tell it is what SLP used to call their LM1 (Loud Mouth) system which uses bullet shaped resonators instead of mufflers. So effectively other than the cats the system is pretty much straight piped. And that's the issue and while it sounds great it is now very loud. With the stock mids it sounded great but wasn't horribly loud. Of course the new mids don't include resonators like the stockers did and that seems to be the reason for the loudness and of course the piping is now 2.5 inch as opposed to 2.25 for the stock stuff.

Here's a short video of a cold start and gentle revs (since it was stone cold).


For reference, here is how it sounded with the stock mids. Skip to about 3:00 to hear the start up. This was a warm start. Sounds pretty much the same but a little smoother and a whole lot less loud.


So, my challenge is to find a way to not only get rid of the horrible drone between 2500 and 3000 RPMs but to also lower the overall volume quite a bit. An additional challenge is given the build of the new mids and their placement I'm kind of restricted in how large of a new unit I can install. I'll be pretty much limited to using a bullet shaped resonator or muffler and the overall length can't be more than 13 inches. This could be a problem but it is the environment with which I have to work within. The stock resonators were pretty small, only about 10 inches long.

So, should I be looking at a resonator or a smaller race muffler? What brands would be best? I've read that resonators tend to cut the drone sounds within certain RPM ranges but don't often really reduce the over all volume of sound. How can I determine what size or style will do what I want (remove drone, reduce overall volume)?
 

GR-RRR!
Joined
8,524 Posts
Discussion Starter · #3 ·
To me it is almost deafening. Bordering on obnoxious. I want this car to be a cruiser, don't want it to sound stupid loud. This is about 3 times louder than the long tube, high flow cats, Magnaflow catback system on the 06. That system has no resonators but does have big straight through mufflers out back.
 

Seriously?
2004 Pontiac GTO, LS1, 6 speed, Quicksilver/Black
Joined
2,439 Posts
If I remember correctly, there were lots of people commenting how loud and how bad the drone was with the SLP catbacks. In any event, it is what you like and what your tolerance is. Resonators will help loudness, but I don鈥檛 believe they will effect drone much. I have SLP long tubes with cats, no resonators and the Corsa sport and there is zero drone. It is loud when I want it to be and quiet at cruise.

You have a couple of choices鈥 try a pair of resonators and see what happens. Skip the resonators, replace the muffler(s) and see what happens. Or, just replace the catback outright with one that you know that won鈥檛 drone and have a sound output to your liking.

Very shameless plug - my 2004 Corsa sport will be up for sale soon. I plan to swap my JBA on this weekend. When you see the for sale thread, all of the details, pics and a start up/idle video will be there.
 

Registered
Joined
904 Posts
To me it is almost deafening. Bordering on obnoxious. I want this car to be a cruiser, don't want it to sound stupid loud. This is about 3 times louder than the long tube, high flow cats, Magnaflow catback system on the 06. That system has no resonators but does have big straight through mufflers out back.
No I get you, i just like rumbly loud cars. Can you get lets say get some quieter mufflers and make up the difference if they are short with welding a piece of exhaust piping on the existing pipes? I mean its worth a shot if nothing else can be done.
 

GR-RRR!
Joined
8,524 Posts
Discussion Starter · #9 ·
You know, LM2 mufflers might make more sense.
Doubt the size effects any of it when it鈥檚 still that small and no long tubes. Get rid of the resonators and swap them for lm2 mufflers. Made mine much quieter.
i swapped LM II glasspacks on and sold my resonators. much quieter.
And are they a straight through muffler? What's the difference between LM1 and LM2 in construction? Any quick way to know for sure which I have already? Pretty sure they are LM1 because they are frickin' loud. No real muffling going on.
 

GR-RRR!
Joined
8,524 Posts
Discussion Starter · #10 · (Edited)
I just took a look at the existing mufflers and one bonus that I found is that the mufflers are bolted in with slip fit joints. Assuming I could get them apart, all I'd have to do is buy the mufflers and I could do the swap myself, no cutting or welding. Yay!

I love Mangnaflow mufflers and catbacks but they are going for $1200+ and I don't really want to change it out anyway.
 

Registered
Joined
1,521 Posts
You know, LM2 mufflers might make more sense.


And are they a straight through muffler? What's the difference between LM1 and LM2 in construction? Any quick way to know for sure which I have already? Pretty sure they are LM1 because they are frickin' loud. No real muffling going on.
Still a straight through. LM1 is just hallow, while the lm2 actually has muffling chambers. If you can look in and see the inner sides is 1. If you see perforated metal, its 2.
 

GR-RRR!
Joined
8,524 Posts
Discussion Starter · #14 ·
I bet it would sound fantastic with the factory catback with those shorties an mids.
I keep hearing that but I didn't get the stock catback with the car. The SLP was already on it. If I could find a low mile used set local to me for a reasonable price I'd probably buy it.
 

|G|et |T|urned |O|n
05 GTO, PBM, M6, SAP, 18s
Joined
1,796 Posts
As I undertook my own project to finish the conversion to full SAP, including exhaust, I too wasn鈥檛 certain whether pulling off my Pypes Hbox and Bassani cat-back and switching back to my OEM mids, resonator and stock SAP mufflers/tips behind my Kooks headers/cats would be too quiet.

Before I had even finished installing the SAP bumper and mufflers, just in case, I found a stock 05 midsection on eBay, chopped off the 05 resonator and spliced in my Pypes Hbox, just in case I wanted more volume, or more H-pipe grunt.

But thus far, I鈥檓 quite happy with how things turned out. The volume isn鈥檛 too loud or too quiet. The SAP note is deeper than the stock 05/06鈥攂ut probably not quite as deep as the 04 note. It鈥檚 rather subtle at idle, and has great sound under throttle or WOT. No drone鈥ero鈥.if it had any, I would have to change things.

Yes I鈥檓 quite curious how it would sound if I swapped my OEM midsection out for the modified one I have sitting in my basement鈥. but like you, I do not want it to be too loud, and no drone allowed. Hearing what you鈥檙e describing, now I doubt more than even that I鈥檒l ever climb back under the car to swap out the midsection. Full OEM behind headers seems the way to go for many folks lately.

My Kooks/Spintech days are behind me, as amazing as it sounded with a cam, at the end of the day it was just so obnoxiously loud and had some drone. For that matter, my Bassani days are likely also behind me.
 

GR-RRR!
Joined
8,524 Posts
Discussion Starter · #17 ·
Which magnaflow cats did you go with?
Not sure I recall the number. They were universal fit spun converters, 2.5 inch in/out and 4 inch diameter body.

Nothubert: I bought them from you, do you remember the part number? Were they 59956?
 

Have Bar, Will Travel
Joined
12,977 Posts
off the cuff I think you'd be happy or near it if you dropped the LM1 out and put a basic magnaflow muffler in it's place. clamp down on the drone and the tone shift - and make it tollerable if not sound smooth and clean.

I never liked the sound of any of the LM stuff and my favorites where magnafow and corsa.
 
1 - 20 of 46 Posts
Top