91-GS
Proven Member
- 1,390
- 65
- Jan 12, 2013
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Paris,
Tennessee
Have been reading a bit about how exhaust gases act in the system and learned that the so-called "scavenging effect" greatly increases low-end torque. The effect is produced by pulses of gas that create vacuum behind themselves as they rush through a pipe. That vacuum helps to pull exhaust gases out of cylinders to allow, reducing energy losses associated with pistons having to push the gases out.
Have also learned that as engine speeds up the smaller-sized pipes create alot of drag that hinders performance. So a larger pipe is needed for higher revving engines.
What are some of the choices when it comes to getting the "best of both worlds" and combining scavenging effect of a small pipe with free flow of a large one?
One thing that comes to mind is a valve that diverts gases into a smaller pipe al low RPM and into a larger one at high (or just dumps it outside). There is a drawback to this, however, in the fact that if the car is a street car then it practically needs two separate exhaust systems.
Another idea is to have smaller pipe right after the header where pulses from all cylinders get together and help each other. After some lengths the small pipe will go into a larger one since a pulse is already past the small section (and pulled another pulse in it's place) and is no longer "useful". So now it can rush out unrestricted more or less. Issue with that however is the tuning since lengths and sizes of all components would have to be tuned to that exact engine setup, unlike the valve idea where it is simply a matter of opening/closing the valve at different times and tweaking that timing for best performance.
What else can be done?
*Please note that this thread goes together with this intake design thread
Have also learned that as engine speeds up the smaller-sized pipes create alot of drag that hinders performance. So a larger pipe is needed for higher revving engines.
What are some of the choices when it comes to getting the "best of both worlds" and combining scavenging effect of a small pipe with free flow of a large one?
One thing that comes to mind is a valve that diverts gases into a smaller pipe al low RPM and into a larger one at high (or just dumps it outside). There is a drawback to this, however, in the fact that if the car is a street car then it practically needs two separate exhaust systems.
Another idea is to have smaller pipe right after the header where pulses from all cylinders get together and help each other. After some lengths the small pipe will go into a larger one since a pulse is already past the small section (and pulled another pulse in it's place) and is no longer "useful". So now it can rush out unrestricted more or less. Issue with that however is the tuning since lengths and sizes of all components would have to be tuned to that exact engine setup, unlike the valve idea where it is simply a matter of opening/closing the valve at different times and tweaking that timing for best performance.
What else can be done?
*Please note that this thread goes together with this intake design thread
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. Couple that with your "scavaging" and you could have a significant increase in overall power.
Oops
