slate blue

In my lust for power, I'm looking into this relatively new area of 2 stage exhausts, S4 owners have the benefit of a variable intake system, Variocam owners have the a broader torque curve thanks to better breathing at low engine speeds, a stage exhaust seems to be the icing on the cake to deliver a broad power output.

If any of you have heard the Ferrari 550 Marenello or the 360 Modena at the point where the exhausts open up, it can be an ear piercing experience. So the obvious advantage is that your exhaust is tuned for around town or the track.

The link below gives some information on this subject.

<a href="http://autozine.kyul.net/technical_school/engine/tech_engine_2.htm#Variable%20exhaust" target="_blank">http://autozine.kyul.net/technical_school/engine/tech_engine_2.htm#Variable%20exhaust</a>

Does anybody have a schematic diagram of how this works or how it is controlled? I know the exhaust people who are going to do my exhaust do do work for the Ferrari dealer and would know,how the system works, but I like to do my own research first so that I coming from a position of some knowledge. Will this system be adaptable to our cars? Lets find out!All the best.
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slate blue

I don't normally post replies to myself but, I did manage to turn something up for those interested.

<a href="http://www.autospeed.com.au/A_0883/P_1/article.html" target="_blank">http://www.autospeed.com.au/A_0883/P_1/article.html</a>

Then the follow up article.

<a href="http://www.autospeed.co.nz/A_0893/P_1/article.html" target="_blank">http://www.autospeed.co.nz/A_0893/P_1/article.html</a>

The cost is about $200 USD which is more than fair if it works, I going to try to find out more on Monday, the magazine only tested the noise levels where as my main interest is power. If you keep the backpressure up at low revs does it matter how it works?

I would have thought the Ferrari system would work like the Porsche induction system Varioram. Just in reverse on the exhaust side. See link

<a href="http://autozine.kyul.net/technical_school/engine/tech_engine_2.htm#Variable%20Intake%20Manifold" target="_blank">http://autozine.kyul.net/technical_school/engine/tech_engine_2.htm#Variable%20Intake%20Manifold</a>

If anybody knows different please post it.

Max

Great info, this will take some time to look over. Well worth the research.

jpitman

First thing I noticed in the first article (which looks like it was written by somebody for whom English is not the first langauge?), is that he states the shorter exhaust length improves low end power. In the tuned exhaust 2 stroke world, shorter pipes resonate at higher frequencies, and improve high end power; longer pipes improve power at lower revs.
I may be wrong, but I dont think short pipes will work any different on a 4 stroke? Ever noticed how much low end power you lose when your exhaust system gets a hole anywhere near the engine end?
jp

slate blue

I managed to find a diagram of the Lamborghini exhaust, you'll probably need to scroll down on the link to find it, but it works like this; one of the pipes is resricted, until more airflow is needed and then the engine management starts to adjust the butterfly throttle to keep the backpressure in the system at the desired amount.

It also describes the reasoning behind having the pipes different lengths. I will find out more on this system since a guy that I used to go to Tech with as a mechanic apprentice works on Diablos' all the time.

<a href="http://www.lamborghiniclub.com/diablo6_gallery.htm" target="_blank">http://www.lamborghiniclub.com/diablo6_gallery.htm</a>

I think at this point what I would be interested in doing is this; You would need a car with a duel exhaust system, the system would use an x pipe and the valve for the system would be located towards the rear, I don't think I would use their electronics (from the kit)but the Motec system with a quick acting stepper motor controlling the butterfly throttle.

The way I concieve the system working would be to have at part throttle conditions one of the exhausts doing all the work and then when needed the throttle would open in no. two exhaust and give you the extra flow. Of course the system would have to be changed to take advantage of this, since the existing system is designed to be a compromise of all rev ranges and loads.All the best.
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Glenn Evans

The diagram for the Lambo shows a number of variables. Do you have a link to any formulae which use these to determine the effect on torque (and noise, I guess) and at what rpm?

The VariFlow Technology simply fits a butterfly valve in the existing exhaust pipe, without a second pipe. What are the disadvantages of this simpler setup?

slate blue

I can answer some of your questions Glen, the system will work with a single exhaust. It was actually invented by the fellow in Woolongong for the purpose to quieten the exhaust on his turbo car. The system was a single pipe system and the butterfly built up backpressure so that the mufflers would work more effectively.

Here is an except from the info I have gathered.

Calibration

Because the primary function of the VariFlow system is to provide high flow with low noise, we elected to carry out some noise readings as the first calibration step. Two sets of figures were taken - with the valve fully open, and with the valve in its shut position. (Although, as indicated last week, an adjustable stop can mean that the valve is never actually fully shut.) The noise readings were taken from 45 degrees behind the tailpipe at a distance of 1 metre, with the engine being free-revved in neutral.


Standard Valve Fully Valve
open Closed
Exhaust System

db(A)
Idle 57 80 78
1000 rpm 69 81 78
2000 rpm 73 91 81
3000 rpm 78 92 88
4000 rpm 80 98 89
5000 rpm 83 101 105
5500 rpm - 102 107

As you can see, the noise output was generally sharply reduced when the butterfly was closed, although there was an unfortunate clangy metallic buzz from the closed valve at 5500 rpm resulting in a 5dB(A) noise gain at these revs. But at 2000 rpm, the noise level was down by a massive 10dB(A), and it was also decreased by 9db(A) at 4000 rpm. However, when road backpressure readings were taken on the VL with the valve deliberately fixed in this shut position, the pressures were unacceptably high - like over 14 psi at full throttle at just 3000 rpm! But the contrast between the 'fully open' and 'fully shut' figures does show how effective at noise suppression the valve can be.

This test was done in the primary experimenting stage, If anybody has ever heard the new 360 Modena when the second stage comes in you'll realise the exhaust goes from being quiet to being ear piercing. So you achieve a quiet exhaust until high flow is required and then all hell sounds like it is breaking loose. The system has a number of adjustments, such as the amount of backpressure that is required to modulate the valve. Hope this answered some of your questions. All the best.

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Max

What kind of sound level meter are you using?

Max

slate blue

Hi Max, that info might be contained in the links I provided at the top of the post? I must admit I don't have time to check it at the moment. All the best.

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