85 GLH 3" TU system Muffler choice

[PunKid]

I hate to throw another muffler thread on the pile but I could not get the answer I wanted while searching.

I am running a full 3" TU system, and Have limited my choices to a Magna Flow 3" straight through Oval design.

My goal is to be as quiet as possible with a straight through muffler design in the stock location (no cat either)

So I have come down to 4 oval choices

The two Variables are

A 5"x8" oval or a 4"x9" oval

And the Case length of 14" or 18"


So obviously the 18" case length would be better but because the overall length is 24" its going to be next to impossible to fit (I measured and in a perfect world it would barely fit)

Next is the oval. Both will fit but I am at a loss to which one would be quieter. I am thinking the 5"x8" might be cause it adds distance to the case on the short width. with out know the min and max radii I can't calculate cross section area. But if I dumb it down to rectangles the 5x5 is bigger. Yea I know stupid logic.

So two questions

1) has anyone run the 18" muffler case in the rear position of an Omni with a 3" exhaust
2) can anyone confirm which would be quieter a 5x8 or 4x9 case

[GLHNSLHT2]

a round won't fit? My 6" round is quieter than my buddies oval. I'd say the 5x8 is going to be quieter than a 4x9.

[PunKid]

Really, I was thinking the exact opposite, that the rounds would be louder.

[The Pope]

a round won't fit? My 6" round is quieter than my buddies oval. I'd say the 5x8 is going to be quieter than a 4x9.

I don't know I think it is a little more quiet, but not for TWICE AS MUCH....

[GLHNSLHT2]

????? Your oval was more expensive than my round was.

[Ondonti]

I would assume the shape is for fitment and not for some huge difference in sound.

[PunKid]

I emailed Magna flow, and the tech guy did say that the ovals are quieter then the rounds, but he thinks there is no real difference between the two ovals.

So anyone ever run an 18" case length behind the axle in an omni?

[4 l-bodies]

I emailed Magna flow, and the tech guy did say that the ovals are quieter then the rounds, but he thinks there is no real difference between the two ovals.

So anyone ever run an 18" case length behind the axle in an omni?
16" round Dynomax ultraflow fit perfect. Not real loud either. Not sure about TU's kits, but the JRB/FWD kits are designed for a center in center out muffler configuration. Stray from that and you'll need to do additional fabrication.
Todd

[trannybuster]

Borla..ftw

[PunKid]

I ended up with a Magna flow 3" offset oval 4X9 with an 18" case length. After looking at it more I decieded to put the muffler in the cat position because there is more room. I think a 5X8 might have been a better choice, right now I have plenty of clearence if I were to remove all the heat sheilds, currently the heat sheilds are still in place and it looking very close.

I welded up most of it, I still need to adjust the over the axle pipe, and then add an extension to get he pipe past the bumper. I will try to get some photos, and maybe a video clip of the sound.

[PunKid]

All welded, clamped and hung. Over all the install is pretty good, I do have a slight rub on the gas tank (hopefully shifting the tank will fix that) and a slight hit on the reverse lockout which I should be able to solve with a clamp adjustment and or a strategic dent.

New problem is how loud it is. Obviously I expected it but its got a couple drone point that are pretty bad, I only drove it around the block so next time I take it out I will figure out what rpm and throttle it happens. I think part of the problem is the tail pipe only sticks out past the body, not the bumper. I read that any exhaust that does not terminate past the body usually gets drone, is this also true on the omni with the open bumper?

Other then that I only did a couple half throttle runs so I will let you know how the power increase feels after some more miles.

[trannybuster]

I put a Borla at the end, where the muffler normally is located and my exhaust sounds perfect. I even got pulled over for not dimming my H4 headlights (oops) and he said nothing about my exhaust (3" no cat, straight through borla lbody charger)

[PunKid]

Well after driving it around a couple hundred miles it did quiet down a bunch.

At idle its pretty normal for a performance muffler. You can tell its louder then stock but its not so loud as to get me in trouble.

cruising at low speed it can drone especially between 30mph and 40mph. once you get above that speed it improves. On the highway there is almost zero drone, and the wind noise and a radio (if I had one) would eliminate it.

1/3 to 1/2 throttle is VERY loud. I actually think its louder then WOT haha.

All of this is from inside the car I will have one of my buddies drive it at some point to give me an idea of how it sounds from the outside.

[Vader85]

I would assume the shape is for fitment and not for some huge difference in sound.
I would suggest you try Dynomax's VT, Magnaflow's 3" inlet, 4" round glasspack x 18" body (18129), 3" inlet, 6" round x 18" body (12649), or my choice for my 3" exhaust a 3" inlet, 7" round x 24" body with dual 2.5" outlets.......:eyebrows: