The Definitive Exhaust Upgrade Pictorial

[slownrusty]

Hey guys - I am the king of dreaming-up projects, typically way faster than I can execute them! Continuing with that theme, I've been wanted to free the M30 of the restrictive exhaust noose and liberate that sweet straight six. I know many of you have already upgraded your exhausts, but wanted to share my journey.

Based on that, I decided to "design" a few options which I present to you below.

At first I was just going to install the Ireland Engineering cat-back system and be done. But the more I slept on it, I felt I could do better than their system, plus with their set-up you still have to decide to re-use your cat, install a new high flow cat or fabricate a new section if you're not going to run a cat . I would like to mention that IE's set-up has 1.75" O.D pipes, which I feel is on the small side for the M30, plus I did not like their heavy rear muffler, the caveat here is I do like their products and service and I am going to use their ceramic headers as pictured below to replace the stock cast manifolds. As an aside, the header downpipes are 2.0" O.D.

Side note - The stock exhaust with the cast iron manifolds weighs just over 100-lbs (!)

Another side note: I will be using stainless flex joints, all stainless pipe, and I will V-Band the exhaust no matter which setup I choose. I have $600 into this little science project..so not too bad.

Ok so onto the options I came up with, the stock exhaust is shown as a comparo below too, by the way I had lots of fun thinking about this and putting it together:

Option 1 Side Exit: Twin 2.0" O.D pipes into a single Magnaflow and exit in front of the rear right wheel.
Pros: Nice and short, fairly easy to fabricate, light, probably will sound cool, looks cool and good power.
Cons: Heat might damage the paint on the rocker and trim right above that.




Option 2 Full length: Twin 2.0" O.D pipes into a single Magnaflow and exit with a 2.5" pipe and twin tips in the stock location
Pros: Will sound cool, looks cool also and good power.
Cons: A bit more complicated to fabricate and heavier than the side exit option.



Option 3 Ireland Engineering Cat Back system: 1.75" O.D pipes into a resonator and long barrel muffler and exist with 2.0" tips in the stock location
Pros: Fairly easy to install and fabricate the section where the cat would normally be placed. Decently priced
Cons: Heaviest of the three options, maybe adds a little less power (smaller 1.75" pipes) than the above two?



What do y'all think?

Yasin

[Shawn D.]

Interesting project! Not "definitive," though -- those aren't all the possibilities.

You need to do cross-section calculations. Two 2" pipes are 5.52 square inches area (once you consider pipe wall thickness of 0.063") and a single 2-1/2" is 4.43 square inches area -- you're losing 20% area going from the downpipes to the tailpipe.

However, if you run two 1-7/8" pipes into a 2-1/2" tailpipe as I have done, you're only losing 8% area.

[slownrusty]

Thanks Shawn, great reply and I also sat down and did the exact cross sectional area analysis.

Some additional thoughts I have:
1) The efficiency of the muffler, i.e straight through design versus baffled - the Magnaflow I have is a straight through design

2) Also there are no mufflers available that are twin 2.0" inlets and a 2.75" outlet, and a 3.0" outlet would be way too big for this car.

3) The 2.5" that I plan to run will be for approx. 5-ft, from the outlet of the muffler to the tips.

4) Provide some backpressure

[Shawn D.]

2) Also there are no mufflers available that are twin 2.0" inlets and a 2.75" outlet, and a 3.0" outlet would be way too big for this car.

That's why I went 1-7/8" into 2-1/2" -- both are larger than stock, but not excessively mismatched to each other. In case you hadn't noted it, stock is 1-3/4".

4) Provide some backpressure

That rationale disappeared over a decade ago. You don't want to go too big because you'll lose tuning, not because it doesn't have enough backpressure.

I didn't mention it before, but I wouldn't go with side exhaust. You'll lose ground clearance and then you have a big unused space between the spare and gas tank.

[Ordnator]

Have a look at these guys,

http://www.fritzsbits.co.uk/services/exhaust-analysis

The UK pound being in the toilet during BREXIT may make this more attractive / obtainable.

I had one of their complete systems fitted to my Diamantschwartz Eta when it was back in the UK in 2014. Seems to breath more easily, move more urgently and the sound from the loud peddle is an improvement over stock, especially in tunnels

Twin 40 mm pipes replacing one 38 mm pipe may have something to do with that.

Regards,

Mick

[slownrusty]

Made some great progress last night after work, I should be finished up this afternoon. Its falling into place really nicely.





More pictures to come.

[slownrusty]

It is 100% complete now, total fab. time was 9.5 hours. I'm excited to hear the car sounds and runs, still need to button up a few things before I turn the key.

Here is the last section from the muffler to the tailpipe:

[SlickDizzy]

Should perform well but that is going to be LOUD with only a single muffler!

[slownrusty]

If its unbearable, I will go back in and drop a resonator to tame (tune?) the sound...but like anything else on these cars its a bit of R&D and trial and error.

[adam_poll]

I built a similar system using Schmeidman headers (which were harder to transition from then the IE ones you used) with a universal cat, this summit muffle - https://www.summitracing.com/int/parts/ ... /overview/, And this muffler at the back - https://www.summitracing.com/int/parts/ ... /overview/

If you find yours is too loud the Dynomax muffler fits at the back very nicely and you could pretty easily add it to your system (Although it isn't stainless, I painted my whole exhaust with BBQ paint, so far so good and the car is only summer driven so hopefully it holds up).

Nice job on the fabrication.

Adam

[slownrusty]

Follow-up, I really like the sound of the exhaust, it has that straight six low growl when the toodling around that is not intrusive but barks when you hit the "wow" pedal. I know this as my wife accompanied me on the maiden voyage and she is very sensitive to loud, drone-y exhausts. If I went with the side exit, the story would be certainly different.

The new exhaust is about 50lbs lighter than the old system too. In terms of performance its hard to tell how much additional power I picked up (I should have dyno'd the car before...grr!), but seat of the pants is in the 15-20hp range.

Here is a quick video, enjoy and tell me what you think!:
https://www.youtube.com/watch?v=ynI4Y-imtPQ

[Shawn D.]

Sounds great!