| Author |
Message |
Eric Vartanian (Evartanian)
Junior Member
Username: Evartanian
Post Number: 192
Registered: 3-2002
| | Posted on Monday, May 19, 2003 - 3:20 am: | |
Found this at the ferrariusa.com site, still leaves some questions unanswered though:
>>The Maranello's insulated stainless steel exhaust system employs variable back pressure through bypass valves situated on the rear silencers. The bypass valves are electropneumatically actuated by the engine management system, based on engine speed and throttle opening. Varying back pressure makes it possible to optimize engine efficiency in various conditions. Greater back pressure allows higher torque under average load, while lower back pressure enhances full load engine efficiency.<<
Anyone know what they mean by "electropneumatically"? It looked to me like the valve didn't open electronically, or does it? Do computers play a role here? I was speculating that somehow it used the engine vacuum.
And I still don't understand how we get better low-range torque with increased back-pressure. (If someone knows and could explain, I'd appreciate your time)
Also, anyone have any idea how much influence, if any, the exhaust note/sound had in the development of this kind of system. I noticed in the archives the discussion of the various possible effects of throwing a Tubi or aftermarket on there. Were any conclusions made as to the effects? Reduction in efficiency/performance with just a kick-ass sound, or overall better? |
Jeff Green (Carguy)
Member
Username: Carguy
Post Number: 284
Registered: 10-2002
| | Posted on Sunday, May 18, 2003 - 10:05 am: | |
What I think can happen is if the flow is too good from lack of back pressure that the fresh incoming air-fuel charge can be pulled in beyond what is necessary and some of it actually passes through into the exhaust without being utilized. This would happen at low/medium revs when the timing events are not totally up to speed the the intake flow. At higher revs the timing events can exceed intake flow so then less back pressure is needed. I don't know what activates the valves but I'd guess it's simply pressure and not any type of electronic control. I remember hearing the exhaust system valves "bounce" or "pulse" at a track event where guys were beating the crap out of their 550s. It's a strange sound that would occur between shifting gears as the driver's foot came off the accelerator pedal. Those cars really need a louder system as they sound more like a "whoosh" of air than 12 cylinders at full song! |
BobD (Bobd)
Intermediate Member
Username: Bobd
Post Number: 1187
Registered: 3-2001
| | Posted on Sunday, May 18, 2003 - 9:27 am: | |
Thank you Google:
http://www.ukcar.com/sframe.htm?/features/tech/Engine/turbo/vario2.htm
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Eric Vartanian (Evartanian)
Junior Member
Username: Evartanian
Post Number: 191
Registered: 3-2002
| | Posted on Sunday, May 18, 2003 - 3:26 am: | |
So my understanding is that the point of this is that it "helps increase torque under part load and increase combustion efficiency at high revs" (italiaspeed.com).
I would like to know how adding backpressure accomplishes this, how the butterfly valve in the exhaust is controlled/functions, and if it serves any other purpose or has any side effects (of any nature).
I searched the archives with no luck, but if there is a good discussion of this somewhere let me know. Thanks.
Eric |
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