18 replies to this topic

[Morgatron]

What exhaust would people suggest? from the manifold I have 2" I want a straight through single box twin centre exit. I can not for the life of me seem to find anything...side exits yes but not what I want help please

[Blumeanie]

I also noticed the lack of current options. I hope to gains some insight on sources as well as I'll be in the market in the future (I hope MANY years in the future!)

I have a Jannspeed twin pipe center exhaust (with rolled pipe tips) which I installed in The Netherlands back in the day. It is the best sounding and best looking (my biased opinion, of course!)

Jansspeed (under another incarnation apparently) is no longer making most mini items - (certainly no longer making this particular exhaust...)

[timmy850]

If you can’t buy one off the shelf, then get it made at an exhaust shop?

You can also try someone like Bagsport as he custom makes them

[Mini Manannán]

https://www.fusionfabs.co.uk/

Matty would be able to do something for you

[Shooter63]

I think KAD do a 2" system, give them a bell, they are a really good company to deal with, Gemma is very knowledgeable.

Shooter

[bpirie1000]

Really depends on your set up, engine size and what you want,,performance or noise... I would always recommend 1 3/4" to allow for engine breathing.

https://www.minispar...-exhaust-system

Or similar...

Gives a nice note but not to much in your face. Nor does it require ear defenders.

Just make sure your manifold is compatible with link pipes etc..

[mab01uk]

Below is useful for reference.

 

Exhausts – RC40, Millennium and others tested Keith Calver 20/08/2005:-

https://www.minispar...ver-20-08-2005/

 

Exhausts – Basic information Keith Calver 20/08/2005:-

Little or Large?
"We can now apply our newfound knowledge of exhaust gas behavior to selecting a suitable system. Despite the plethora of systems available, the most reliable from a performance increase point of view will be those that have been around for some time; largely because more recent systems are either copies (generally poor ones), or purely made for aesthetics (huge bores and multiple tail-pipes). The longer-standing exhaust systems manufacturers established long ago the optimum sizes, shapes, and lengths as far as exhausts for Minis go. Boosted by the sheer volume of folk racing, rallying, and tuning them. Consequently they’ve been distilled into a few very effective systems.

Size-wise, a bore diameter of 1.625” is more than ample for practically any road engine. Right from 850 up to 1400+, where power outputs don’t exceed 125bhp or so. Even then, going to a bigger size – say 1.75” or 1.875” bore – will only gain a few extra horses right at the top end of the rev range – OK on a racer where the engine is flat-out all the time, but on a road car the benefits of increased gas speed and getting a hot cam pulling power in earlier far outweigh the slight hp gain. Conversely, fitting a 2” system to a small-bore engine (850/998/1098 based) will actually loose power because of it’s relatively small through-put of exhaust – the huge bore increase prematurely slowing the exhaust gases, bringing about the unwanted effects outlined earlier. Using a 1.5″ bore size instead of the more common 1.625″ can have marginal gain on a small-bore engine. But I stress these are small. The uncommon pipe size being reflected in its price. Given the choice of the two different lengths generally available, the longer side-exit type almost always gives the best over-all results."

Full article here:-

https://www.minispar...ver-20-08-2005/

Edited by mab01uk, 13 March 2025 - 10:42 AM.

[coopertaz]

go to maniflow website, have always found these exhausts well made.

[beardylondon]

I’ve got a stainless steel Playmini exhaust which I fitted in 1999, only covered 10,000 miles, but it is still in great condition! It’s a single box and a bit noisy for my now older ears!

[Cooperman]

For a 2" dia exhaust system you need to be using over 6000 rpm a lot of the time.

Exhaust technology shows that the exhaust gas molecules need to move at an optimum velocity and the larger the bore, the slower they go at any specific rpm.

For a 1275 to 1330 cc engine, at, say, 4000 rpm the best inside diameter is 1.625".

Now moving on to twin final outlet pipes. These need to have a cross sectional area the same as the area of the main pipe. To have larger twin outlet pipe diameters causes the final output of exhaust molecules to slow considerably which increases back pressure and reduces exhaust efficiency. For a twin final exit the pipes need to be around 1.25" diameter, about the same as a standard 850 exhaust pipe, if the exhaust is to work as intended.

Most big exhaust systems with a large bore and/or twin final output pipes are best known as 'power sapping noise boosters'.

[Designer]

Hi,

 

'power sapping noise boosters'.

 

In other words    "All fart and no action"

 

Paddy

[Java_Green]

For a 2" dia exhaust system you need to be using over 6000 rpm a lot of the time.
Exhaust technology shows that the exhaust gas molecules need to move at an optimum velocity and the larger the bore, the slower they go at any specific rpm.
For a 1275 to 1330 cc engine, at, say, 4000 rpm the best inside diameter is 1.625".
Now moving on to twin final outlet pipes. These need to have a cross sectional area the same as the area of the main pipe. To have larger twin outlet pipe diameters causes the final output of exhaust molecules to slow considerably which increases back pressure and reduces exhaust efficiency. For a twin final exit the pipes need to be around 1.25" diameter, about the same as a standard 850 exhaust pipe, if the exhaust is to work as intended.
Most big exhaust systems with a large bore and/or twin final output pipes are best known as 'power sapping noise boosters'.

Interesting thoughts. Theoretically, the diameter should most likely be reduced along the way in order to keep up the gas speed as the temperature drops.
I wonder if a 1.625" diameter also is the most ideal one for a supercharged engine delivering beyond 125bhp at top end but mainly uses the massive torque at a lower rpm...!? I haven't come to an conclusion on this yet....

[stuart bowes]

I don't pretend to know much about this but i did once have someone tell me, with forced induction (possibly just turbos?) back pressure isn't an issue, you just want a nice big pipe to get the gas out asap

 

that might have just been nonsense though ? 

Edited by stuart bowes, 14 March 2025 - 03:42 PM.

[Java_Green]

I don't pretend to know much about this but i did once have someone tell me, with forced induction (possibly just turbos?) back pressure isn't an issue, you just want a nice big pipe to get the gas out asap

that might have just been nonsense though ?

It is valid for a turbo!

[Cooperman]

With any exhaust system the important thing is the molecular velocity of the exhaust gases. It's a long time since I did fluid dynamics as a student, but the technology has not changed.

Without doing complicated calculations, you simply consider the engine size to be basic capacity multiplied by the turbo boost ratio at the point of maximum power/boost.

Then you size the pipe to suit, bearing-in-mind that it's always a compromise.

The diameter should be the same from the point where the exhaust system becomes a single pipe to the final outlet.

As a guide, if the ideal diameter for, say, a 1275 engine is 1.625"c, then with a 5 lb/sq.in boost pressure, multiply the engine capacity by 1.33 and use the resultant volume for sizing the exhaust.

What you don't want is an engine which will be operating at an optimum rpm of 4,500, but which has an exhaust diameter for a similar sized engine revving at 6,000 rpm. Probably a 2" pipe diameter would be about right.

Moving on to twin final outlets, there is a thing known as 'Bernoulli's Principle' which states that when the velocity of a fluid moving along a pipe is slowed during its flow, the pressure increases. Thus if the final outlet(s) is of bigger cross-sectional area, the  pressure increases and the molecular speed is reduced, which reduces the inertia of the exhaust gas molecules and thus causes a loss of power. For best performance of the system, the diameter must be constant right to the final exit.

This is a bit simplified and there is a lot of exhaust design content available on the web if you want to delve into the subject.