Exhaust Toooo Loud Need Help Please!

[Midnight-280Z]

okay heres the story. I got 2 1/2" piping on my 75 280Z all the way back to a magnaflow muffler also 2 1/2" in/outlet with no cats or resonator. sounds awesome at idle but way tooo loud at 2-3K. my question is should i put a 2 1/4" resonator or a 2 1/2" resonator? how much quiter wouild this be and are there any downside to using the smaller 2 1/4" resonator. i been hearing things like i need back pressure. so i was thinking of going with the smaller 2 1/4" resonator to get some back pressure. my only mods are CAI intake (cheapo ebay), and i am instally my NISMO headers sometimes next week

[beandip]

You are correct about the back pressure issue, however the slightly smaller glass pack wont do what you are thinking. If you install a Thrush glass pack of 2 1/2 '' as a resonator it will help a lot with the resonance ,'' droning '' sound that occurs at around 2K. The other brands of glass packs have louvered center pipes that actually restrict the flow of gasses. The Thrush brand , actually they are made by Dynomax , has perforated pipe that just absorbs sound and remains the size of the piping. 2 1/2'' systems are for a high revving engines that have a cam making it's HP up in the 4k to 6k area . For a street engine how much do you drive the car like this . What is involved is the pulses of burned gasses traveling down a exhaust pipe cause a scavenging effect drawing the burned gasses exiting the combustion chamber to exit that much faster and better. If too large of a pipe is used then this effect will happen at higher RPM . So on a stock engine or one running a cam that's power band is around 2K trough say 5K , you are loosing your low end power or torque . It's not to say that the 2 1/2 piping is bad , it's just not as efficient as the smaller setup. 2 1/4 would be a better choice. Also Quieter . Unless you are racing on a track or comparing on a dyno , I doubt vary much that you could tell by the seat of your pants dyno. You can tell where to install the glass pack by using masking tape . Start at the collector of your header and run a strip all the way down to the first bend . Then start the engine and run up the rpm to the place where the resonance occurs and hold it there for 30 sec or so then shut off the engine and see where the tape is scorched and this is where to mount the glass pack. I got this from Dynomax . Hope this helps you . Gary:)

[Midnight-280Z]

yes, i will be going with a magnaflow 4" round resonator with 2 1/2" in/out. i am trying to stay away from the glass pack because i hear they go bad and actually gets louder. i should of gone with a 2 1/4" pipe. oh well whats done is done, now i need a decent set-up to run my 2 1/2" properly. thanks for the help

[Mike]

A long time ago I ran the 2.5" pipe and loved it. I guess it all depends on the muffler choice. As far as your question, you probably don't want to reduce size and then go back up again. The 2.5" in/out is a good choice. Send some picts when you're done! I'll be doing exhaust again soon and would love to see how it worked out for you.

[Arne]

I'll be doing exhaust again soon and would love to see how it worked out for you.

Mike, are you finding time to work on your car again? I sure hope so, I'd love to see it back on the road.

[Mike]

Yep...

http://www.classiczcars.com/forums/showthread.php?p=186171#post186171

[Ksteve]

Gary, Mike,

I went with a 2 1/4 glasspack followed by 2 1/2 tubing to the back. I am pleased with the sound but from your comments I am wondering if the smaller glasspack is doing nothing for me and may be detrimental. Do you think its holding back high end flow?

Im running an L24 with SUs, a mildly ported N42, stock cam, 3 into 2 header. (bigger cam on the Christmas list)

Any advice is appreciated.

Steve

[240ZMan]

Keep in mind that if you change your cam, you're going to change the sound of your exhasut. When I first put my 2 1/2" system from MSA on my L28, I had the stock cam and I too felt it was too loud in the middle rpm range. So I put an 18" glass pack on and the result was very livable, and still let me hear the engine. When I went to a more agressive cam, I was dissappointed that the exhaust note seemed to be much flatter. Then I added triple webers and I could only hear them. So I took the glass pack out, and it sounds great. It's probably too loud above 4k, but at the track it sounds sweet.

Just something to keep in mind if you have a new cam in mind

[beandip]

Gary, Mike,

I went with a 2 1/4 glasspack followed by 2 1/2 tubing to the back. I am pleased with the sound but from your comments I am wondering if the smaller glasspack is doing nothing for me and may be detrimental. Do you think its holding back high end flow?

Im running an L24 with SUs, a mildly ported N42, stock cam, 3 into 2 header. (bigger cam on the Christmas list)

Any advice is appreciated.

Steve

Steve , no you will be OK . It is just if you used a glass p that has louvers in the inner tubing then you have restricted the opening by the size of the louvers. so a 2 1/4 is down to a 2'' in reality . this will negate the benefits of the header. This is why I recommended either a ''race'' glass p or a Thrush because they have perforated pipe and the size of the inlet and outlet is what it is all the way through. You must keep in mind the larger plumbing is a benefit at the higher RPM like on track use really. How many times do you keep your engine spooled up to 4 or 5k and keep it there. And then down to 3500 and up to the upper Rs . For the track this is important but on the street only if you drive the same. It's the flow while you are in the power band , that is dictated by cam . Gary

[240ZX]

Gary's info is sound advise! A while back someone raised a similar question about their newly installed 2 1/2" exhaust system and wanted some input on reducing the resonance at around 2K to 2.5K. I suggested installing, as Gary also mentioned, a glass pack type muffler shortly after the header collector. The muffler I suggested is the small and farely short race type muffler....available from Summit Racing. Basiclly no restiction but resulted in significantly reducing the resonance.