My muffler shop is owned and run by a third generation exhaust guy. His family has been hanging exhaust on minis for me since 1968. This young owner has taken the Nascar exhaust school in Charlotte each time they offer something new. We have come up with a twin box custom system that I have installed on all 1275 based minis I do. We use a cherry bomb in the tunnel and a normal box in the rear with a chrome tip to extend a couple of inches past the bumper edge. If you don't get out past the bumper it will suck fumes back into the car. I buy and supply new OE hangers for the system and have yet to loose a system to speed bumps or pot holes. If I want loud I can always crank up a vintage racer on straight pipe. Steve (CTR)

Keeping in mind every engine will have its own sound 'signature' depending on cam profile and compression... On my sedan with a fairly hot 1293 I'm running a maniflow LCB and a big bore, single box side exit RC-40...with the silly rolled edge cut off - a little to ricer for me - LOVE the sound, no drone at the speeds I cruise at, not too obnoxious ....at least I've never had any negative comments, and many positive ones.

I also changed over to the late model hangers and very happy with them, less resonance and after a number of big road trips that would've eaten the early ones it's still in one piece.

On my 1380 moke I've got a center glass pac and a turbo muffler and it's still pretty obnoxious....

Used a straight through exhaust with single rear box on Pooh's 998 without any dirt on the back or exhaust into the cabin...but was far too noisy.

Since have used RC40 twin box, side exit and it is the goods for a Mini exhaust up to well over 100 hp output.  Interestingly, it is the delightful sound of the gearbox when the 1380 is wound up that turns peoples' heads not an irritating exhaust blast.

Have Mini Spares big bore LCB on 1380 and wonder if the gas speeds and engine output could be bumped up with smaller pipes.

My car has a 1275 high compression MG Metro type engine, similar to yours, Marcus550.

I have a single-box side exit RC40 in stainless. It has the tapered tail pipe with the rolled end. It works beautifully and sounds mellow but solidly powerful at idle and part throttle, but gets loud at higgher rpmas DRMINI describes. No hint of 'ricer in a bean can' - EVER. I love the sound. If I was doing it again, I'd go with twin-box side exit, non-tapered 1.75" exit. I am still plagued with cabin fumes above 60 kph (40mph) and i suspect part of the problem is that th e tapered tail pipe either generates its own turbulence or doesn't 'throw' the exhaust fumes clear of the back of the car.

 

The glass pac resonator I used on mine has `angle burst holes' in the pipe, these must face the rear of the car. If you fit it on backwards (I tried this!) it will not only fail to reduce the `bark', but will soak up HP by increasing backpressure.

Back in the olden days these holes were just punched or drilled straight in, so it didn't matter which way it went then.
So, check what sort you have...

I know this thread is old, but I'm wondering the same thing if you ever made progress on this.  I have a 1275 with a glass-pack for a center muffler and a stainless steel center-exit muffler with dual up-swept outlets.  It is still too loud!  I thought the glasspack would act as a resonator and it did quiet it down a bit vs. the straight pipe that was originally here.  I want to keep the cool rear box and improve the performance of the center muffler.  Is the usual (RC40?)  center resonator like a glass-pack or is there some other baffles in there?  Any recommendations other than replacing it all?  I have a Maniflow freeflow exh manifold. 

Just another source for you in aftermarket mufflers

 

 

//www.spintechmufflers.com/

 

 

I originally had a single box RC40 on the 115HP 1310 with a maniflow medium bore LCB, it wasn't really loud but gave an annoying drone at ~3000 rpm in the car when cruising.
When I rebuilt the motor as a 1360 I went up to a 2" system using a rear box only. Same story, same drone.
So, ~3 months ago I pulled the front pipe and welded a 2" x 18" `hot dog' resonator into it. No power loss, sounds good (slightly quiter) but the 3000 rpm cabin drone is almost gone. 

What others have said- a centre zorst will give crap all over the rear of the car, and if the boot seal or rear side windows have any leaks you will suck fumes into the car.. not nice.

There are only 2 choices:  The maniflow or RC-40 side exit systems.

They are loud enough.  

There are important aspects of a mini exhaust system that you aren't considering.  Center exit will draw fumes into a mini.  This sucks, causes the car, its occupants and their clothes to smell.  Ick.

It also mucks up the back of the car.  Ick.

A center exit will also sit lower to the ground, being more likely to get torn off.

Keeping a mini exhaust on means several things:  Great header, properly mounted to an engine with good mounts in a subframe with good mounts, taking great care to fit the lower end of the header to the differential.

Any exhaust clamp needs to be carefully placed to maximise ground clearance and stay far away from the main battery cable.

The main pipe to the back needs to clear whichever type of shifter assembly you have, and touch nothing on its way back.

Muffler, resonator and tailpipe need to be mounted as high as possible to maximize clearance. Correct, stock mini mounts allow you to do this.  Off the shelf North American auto parts store hangers don't work nearly as well.

Also, the long center branch header is what makes a mini sound good.

Hey everyone,

 

I'm looking to purchase an XT-13 rear box (center exit, dual 2.5inch rolled tip) for my '74 mini.

So I'm faced with this question:  Do I get the mid pipe with or without the integrated silencer?

 

I do like some noise... a "growl" if you will.... a "throaty-ness" that is loud (not TOO loud).. and sounds GOOD!

But I do not like the "teenager in a civic with a glass pac" or "harley with straight pipes" kind of ULTRA loud and backfire-ish kind of sound...

So, if YOU have experience with this exhaust connundrum, could you share our thoughts?  (or even better, share any audio/video clips you might have)?

Of course, I know this is totally subjective... who decides what "too loud" vs. "too quiet" vs. goldilock's "juuuust right"?!  But still, any personal experience, advice, etc is greatly appreciated!

 

As usual, thank you all in advance!

Cheers