43 replies to this topic

[Skortchio]

Small to large = less pressure and less velocity, I get that.

However, you said

[If the end pipe suddenly has increased cross-sectional area then, according to Bernoulli's Theorem, the gas velocity decreases and the pressure increases. This causes inefficiency and loses power.

The issue is to do with the exhaust gas inertia. When the velocity decreases as the gas passes into a larger pipe, the local pressure increases and the velocity and hence inertia of the gas molecules decreases.

Which is where I'm not following, small into big cannot equal more pressure.


I'm still a little miffed that the end tip alone can alter the economy so much, given that for effective length a centre exit system is shorter and they don't suffer the same fate.
If it's due to the total effective silencer length, then perhaps cutting the tail tips shorter would help.

Edited by Skortchio, 24 July 2012 - 09:21 PM.

[minimarco]

Now that you mention Keith Calver, I remember reading him say the side exit length is actually a pretty good one (perfect?) for a mini, but the center exit is a bit too short.

edit: must be somewhere in here
http://www.minimania...SIC_INFORMATION

http://www.minimania...zing_and_styles

Edited by minimarco, 24 July 2012 - 09:23 PM.

[Skortchio]

Those losses were with a mere 2'' system by the way. He also commented on the dramatic increase in noise

Complete system, that makes sense enough. But this is about choice of end tip on a full 1.75" system.

While the side exit length has been shown as optimal, surely a side exit with marginally shorter effective length, due to the extra volume of twin tip would still be greater than that of a centre exit with a single exit?

[Jakeclubby]

Ummm so should i do it?? :/

[Skortchio]

Ummm so should i do it?? :/

It's up to you man, it's your car. It's not the optimal but it's not the worst either. Better than the 3" one you have for sure!

[konyo]

Ummm so should i do it?? :/

I would

[Cooperman]

I can't do more than explain the science. If you doubt it then think about how a spray gun works, the diameter decreases, the air velocity increases and the pressure decreases and sucks up the paint into the airflow. With going from smaller to larger the velocity decreases and the pressure increases. That is the laws of physics and DTM can't change that.
If you fit a large final exit, for what reason I can't imagine, then power will be lost as identified by Keith C.
That is the absolute truth and I'm sorry, but it can't be altered.
Why do people want to fit those huge final outlets anyway? They look very odd to anyone who knows anything about auto-engineering and design and make a lot of unnecessary noise.

[mini-luke]

Those losses were with a mere 2'' system by the way. He also commented on the dramatic increase in noise

I know it's a personal thing, but I can't understand why anyone would want to put huge exhausts on what is a genuine classic car just to make a lot of noise! What style statement is the noise supposed to be making?
Do you have the actual figures as identified by Keith C.? I do know they were quite significant as a percentage of total potential power.

Here is the theory behind exhaust size: http://www.minispare...c8-f023afec0348

And data on exhaust testing. Max loss varied between 4-7hp depending on the 2'' system and number of boxes.

http://www.minispare...4a-71fe260530b6

[mini-luke]

Anybody wishing to argue the toss should read and understand the theory behind exhaust diameter and how pressure waves are reflected back down the system in the first link above.

[Skortchio]

Interesting read, Luke.

It would see the test was using a full 2" system based on the notes regarding the bends in the pipework. Even then it indicates that it will give better performance than a single box side exit RC40 in the bottom end and about equal at the top.

Not a bad sacrifice if you like the look and should you go with Maniflow and get a full 1.75", mid box pipework with just the large exit tip, I'd imagine the loss to be even less.
He does also state in the article it is a budget system and not a well engineered one, such as Maniflow.

Based on the supplied information, this supports my original statement. Providing your headers (LCB) and pipework are of the ideal size (1.75") and you run a twin silencer system, the overall loss will be minimal.

If a small loss of power for asthetics is something you can live with, that is personal choice.

Edited by Skortchio, 24 July 2012 - 10:04 PM.

[mini-luke]

that is personal choice.

Absolutely - if you read that and mane an informed decision that's up to you (not - ''oh I had a 3'' manifold to tailpipe fletcher and it made it faster''!)

[jaydee]

never mind all of the technical stuff, my theory is this.....dtm exhausts look and sound naff.......thats the quick and simple answer....

The bigger the better..powaaaaaaaaaaaaaaaaaaaaaaaaaa

I had to put a cooper freeflow to stay within noise regulations and some people on here are debating whether or not to put double cannons LOL

[DEXISWOLF]

Think I will stick with my twin cherry bombs (says the chap in the corner)

[Mini_Magic]

Seriously, you're not going to notice a difference on the road except for the noise.

[Cooperman]

I think a 5+bhp power difference will be noticed. After all, most people fitting a so-called 'Stage 1' kit will gain about that much extra and say they notice the difference.