33 replies to this topic

[wiltona79]

I am looking to replace my standard exhaust system for something a bit more sporty.

 

I really like the sound of the exhaust system in the video in the link (RC40) but don't want compromise the power (some systems seem to reduce power?).

 

 

I am a little confused though as weather to run a single box system, should I replace the manifold for an LCB, remove the CAT etc.

 

Any advice on the best system to run for a 1275 and where to purchase.

 

 

[998kid]

I have a rc40 with manifold and link pipe for sale if you are interested. Side exit

[freshairmini]

Full maniflow kit. Great quality and great customer service. Ring them up, tell them what you've got and they tell you what you need!

[Cooperman]

+1 on full Maniflow twin box 1.75" diameter system. And don't add a large final exit pipe unless you want to lose a few bhp. It needs to be 1.75" internal diameter right to the final exit point. The reason for this is a bit scientific, but I'll explain it if you so wish.

[IainStallard]

Is there that much of a difference in quality between an RC40 and Maniflow? Surely if the maniflow box got scratched, then it would start to rust seeing as its mild steel?

[Tamworthbay]

Maniflow stuff is superb quality. My old mini is till going strong on its maniflow ten years on.

[Mighty made]

I've had both RC40 and Maniflow and both are fine.

 

If you have a traditional cast iron manifold, then either a LCB or a Maniflow will work well as a replacement,

along with a new inlet manifold.  

 

Minispares will give you a 7.5% discount if you are a TMF+ member (worth it for £5 membership)

[Dusky]

+1 on full Maniflow twin box 1.75" diameter system. And don't add a large final exit pipe unless you want to lose a few bhp. It needs to be 1.75" internal diameter right to the final exit point. The reason for this is a bit scientific, but I'll explain it if you so wish.

http://www.minisport...ncer-2-dtm.html

 

 

But with 1.75" pipes ... WOuld it still be rubbish(bacause of the twin exhaust)?

Edited by Dusky, 14 January 2014 - 06:06 PM.

[Cooperman]

No, it's a single exhaust pipe all the way. The expression 'twin box' is because there are two separate exhaust boxes in series. A twin pipe final exit is often called a 'power-sapping noise booster' as it is just so inefficient.

[Dusky]

Hmmm, so no gains from my exhaust? except for the roar

[Cooperman]

No gains, actually some loss of bhp due to the over-large exit pipe.

What happens is the molecular velocity along the pipe is at its optimum in a 1275 with a 1.75" internal diameter pipe at around 5500 to 6500 rpm.

However, there is a thing in physics called Bernoulli's Theorem. This says that when a fluid passes along a pipe, if the diameter increases the velocity decreases and the pressure increases. This pressure reduces the ability of the fluid (the exhaust gases) to exit at the right speed and it created an undesirable back pressure. If going larger at the end increased power all F1 cars would have it, but they don't.

Imagine trying to get water from a 1" hose pipe and putting a large 2" outlet pipe just on the end. Imagine how inefficient that would be.

[Seba5tian]

No gains, actually some loss of bhp due to the over-large exit pipe.

What happens is the molecular velocity along the pipe is at its optimum in a 1275 with a 1.75" internal diameter pipe at around 5500 to 6500 rpm.

However, there is a thing in physics called Bernoulli's Theorem. This says that when a fluid passes along a pipe, if the diameter increases the velocity decreases and the pressure increases. This pressure reduces the ability of the fluid (the exhaust gases) to exit at the right speed and it created an undesirable back pressure. If going larger at the end increased power all F1 cars would have it, but they don't.

Imagine trying to get water from a 1" hose pipe and putting a large 2" outlet pipe just on the end. Imagine how inefficient that would be.

 

Or to make it sound even simpler, putting your finger over the end of a tap / the hose pipe to make the hole smaller makes the water come out faster and go further

[Cooperman]

Absolutely, reducing the cross sectional area increases velocity and decreases pressure. It's the way a spray gun sucks the paint up from the canister into the air-flow by reducing the area to increase the velocity and create a lower pressure which sucks the paint up.

How these exhaust manufacturers can describe an inefficient exhaust as a 'performance system' is strange and contrary to the Sale of Goods Act as they are not fit for the purpose for which they are advertised.

You could have twin exit pipes for a 1275 engine, but they would need to be around 1" diameter each, or whatever diameter equates to 50% of a 1.75" pipe (can't be bothered to calculate that at this time of night!).

[Vipernoir]

One big advantage of an RC40 over a Maniflow system is weight.

 

Maniflow seem to make their systems out of cast iron in comparison to the RC40 - I've lost count of the number of cotton reels and centre hangers I've changed with a Maniflow fitted, but never changed one in 9 years on the car with an RC40.

[Cooperman]

And the twin-box RC40 is a bit quieter than a twin-box Maniflow.