Muffler size

[Spchlss]

I have a 1984 Nissan 720 and am looking to buy a muffler.  Does anyone know if it’s better to go with 2” or 2.25” piping and muffler?

[Knugcab]

2" should be enough for all engines you could get in the 720 standard IMO.

[datzenmike]

I think the 720 Z24 uses 2" stock pipes. I kept the pipe the same size on my car but used expansion couplers to match it to a muffler that was 1/4" larger diameter. I also don't agree with running inanely large pipe size maybe 1/4" larger, but mufflers? I would run the largest I could fit.

[banzai510(hainz)]

Walker.com

Get a quiet one

[Charlie69]

Years ago I had a muffler shop do a complete exhaust system on my 70 521 which my brother Garret and I swapped  a Z20 5 speed out of a 200SX.  The shop used 2.5" pipe.  This system was real loud and I had the shop swap out mufflers trying to quiet it down.  Ended up the shop had to redo the entire system in 2" pipe and this quieted it down.

Edited August 2, 2018 by Charlie69

[datzenmike]

I don't remember my pipe size on the 710 1 7/8? It's in good shape but when replaced I'll go 2". It does have a factory resonator which trucks probably do not. They make a big difference and needed on a car. Resistance to flow, like a smaller pipe, will quiet the sound itself. But too much and performance is affected. It's a trade off by the factory. A small increase will gain some relief and a small increase in power/torque at the expense of loudness... but don't expect the world from this. I ran a brand new never used 2 1/8" inlet muffler  at a yard sale for $5. Nothing special. It exits down at 45 degree angle in front of the rear end. I should imagine a tail pipe would put the sound behind me and be quieter but it's just right as it is. I wouldn't want louder even though many would call it very quiet. Loud is ok to go to work or shopping but it get tedious on long trips. Loud on a long trip makes you tire sooner.... and I like to hear the car 'talk to me' when driving.

 

So OP, you have a cat and emissions testing to consider. You will need the cat to stay (it probably quiets the exhaust sound slightly anyway) and if using a larger pipe, reduce into and out of the cat. If the 720 has 2" pipe go maybe 1/4" larger and a 2 1/4" inlet muffler. Take a good look at the muffler... some are all 2" but use a necked down 2 1/4" inlet to fool you. Exiting before the rear of the vehicle is illegal so up to you if you want to use a tail pipe. Exiting to the side in front of the rear wheel is ok.  

[720inOlyWa]

I had a stock muffler replacement, early in the game. It sounded like shit- way tooo damn loud, like a ceesey 4 banger glass pack. Plus, the flange leaked and that added a little more to the noise, even with a new gasket. So I had them reface the flange and put a Honda Accord muffler on the Fudgecicle. FANTASTIC! Nice and quiet, with just a hint of those lovely jaqpanese trucky tones. The perfect choice for quiet neighborhood trundling.. This is the only muffler solution that this old coot is ever gonna use from now on. I am very satisfied wth it..

[bottomwatcher]

Usually if it is loud there is a leak somewhere. There are lots of bends and connections, even the stock is fairly quiet if well maintained. There are better options. I use a welded thrush and have been happy with it. The noise on long trips does suck the life out of you and I am not talking about the 720 but the duramax 2500 I drive from Florida to Maine. 

[datzenmike]

I've noticed this phenomenon also...

 

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