Exhaust system diameter

ZenArcher · Postby **ZenArcher** » Sat Oct 20, 2007 11:33 pm

OK, maybe this is a can of worms topic, but I would be interested in comments on this.

First thing is - what is the diameter of the standard exhaust system on the 1.6 and 1.8 MX5's ?

I know many of us believe that 2.25inch system is the way to go. But I've been doing some research and found some websites which actually recommend a 2 inch system instead - this is for non-modified, naturally aspirated 4 cylinder engines. They wrote that anything wider in diameter does very little in the way of extra power and torque (though they recognise that there is a small gain), but mostly when you go larger thatn 2 inch, you get more noise and drone in the system.

What do you all think?

I know my 2.25 inch system doesn't drone at highway cruising speed on the flat, but when uphill or under power there is a growl.

I'd be interested to know the diameter of a standard 1.8 exhaust as I've been for a drive in a standard NB ( no exhaust mods - no intake mods std airbox too) and it was so quiet inside it was like being in the family Astra. Even when I was up the loud pedal going up a steep hill, I could barely hear anything in regards to exhaust noise.

Also what are opinions on say a 2.25inch system with dual mufflers. Proper mufflers - not those cannon things. Quieter or louder than a single muffler?

fastfreddygassit · Postby **fastfreddygassit** » Sun Oct 21, 2007 3:55 am

You'd have to dig up my muffler thread from a while ago but you will have difficulties fitting 2 mufflers in the rear.
I have 2.25 from extractors back (2.5 hiflow cat though) with one loooong resonator.
At the bifurcation the system steps down to 2 1 3/4 inch with 2 resonators (largest diameter that can fit-no room for \"mufflers\").
I think it i still a bit loud

adamjp · Postby **adamjp** » Sun Oct 21, 2007 10:43 am

If you desire very quiet, buy a very large muffler.

If you wanted one muffer, I would buy something like a Magnaflow. The quality is very high, the sound reduction is great, and the flow is very good.

You could fit two smaller mufflers in series under the rear. This arrangement will knock the noise down alot, but it will be very tight.

I always wanted to try the following.....

1 x large straight through muffler (I suspect this would drone too much).
2 x small mufflers in series.
2 x hotdogs in series (I know this would be too loud, but sound very nice)
1 x 24\" hotdog split into 2 small mufflers going to 2 tips (much like many modern Jap cars).

Ajay · Postby **Ajay** » Sun Oct 21, 2007 11:14 am

drive to sydney and you can come for a drive and hear my magnaflow ...

i have 2 1/4 from Xforce headers back to a 4\" tip..

Boags · Postby **Boags** » Sun Oct 21, 2007 11:16 am

mx5_boy wrote:back to a 4" tip..

Sheeeeesh. Got tip?

Pics or ban.

fastfreddygassit · Postby **fastfreddygassit** » Sun Oct 21, 2007 12:13 pm

lads, there is SFA room under there
This is an earlier pic of mine with the first version of the exhaust.
These resonators/hotdiddlydogs have since been replaced with the largest oval resonators that can fit.
Still a bit loud though.
And there is a loooong resonator b/w the cat and the diff.
If you do find something that fits AND does twin tips, I am all ears (well ringing ears :mrgreen:

)

Matty · Postby **Matty** » Sun Oct 21, 2007 12:27 pm

Much of the noise level comes from the diameter of the last section of pipe. Step it down here and you'll keep the noise in check, without upsetting flow significantly.

They're right, 2\" is probably adequate (for a 1.6 anyway).

adamjp · Postby **adamjp** » Sun Oct 21, 2007 1:54 pm

The setups that FastFreddy has tried are two of the ones I was thinking of.

I'll bet the 3 x hotdogs sounded VERY nice, almost Alfa, but was disliked by the neighbours (and the constabulary).

I'd be interested to know what the hotdog & 2 small mufflers sounds like.

As for a twin tip - have a gander at the Magnaflow catalogue. They list a couple of twin tip mufflers for domestic US heavy metal (camaro, etc.).
http://www.magnaflow.com/02product/shopexd.asp?zone=main&id=637

And take a gander at these kits for the MX5
http://www.magnaflow.com/02product/shopdisplayproducts.asp?SID=4Mazda&zone=Sport&id=173&cat=Miata

meanmx · Postby **meanmx** » Sun Oct 21, 2007 7:21 pm

Would the twin exhaust from the NC fit up to an NA6? I would think that a sports NC exhaust would be about 2 1/2 inch which would be perfect for my car

Ben

ZenArcher · Postby **ZenArcher** » Sun Oct 21, 2007 8:03 pm

Does anyone know what the standard diameter is on the 1.8 or 1.6 MX5's

4sfed5 · Postby **4sfed5** » Mon Oct 22, 2007 9:21 am

standard on the 1600 is 1 7/8\" from memory...

my turbo system is mandrel bent 2.5\" with a 18\" \"hotdog\" straight through style resonator and a custom made rear can based on a design for rotary engined cars...large diameter semi-straight through design.

Matty · Postby **Matty** » Mon Oct 22, 2007 10:39 am

I thought it was 1.75\" OEM?

ZenArcher · Postby **ZenArcher** » Mon Oct 22, 2007 8:42 pm

Matty,

that's what I thought as well, that both the 1.6 and 1.8 were 1.75 inch. But was hoping that someone here could have definately confirmed that for me.

adamjp · Postby **adamjp** » Mon Oct 22, 2007 9:47 pm

I thought my stock system was 1 7/8\" when I binned it, but I also recall that it was double walled in places. Probably means it was 1.5\" effective dia.

The double wall also reduces noise alot.