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Re: I cannot fathom how exhaust flow can cause vacuum... Posted by John Williams [Email]  (#1982) [Profile/Gallery]
(more from John Williams) on Wed, 31 Jan 2007 11:46:12
In Reply to: I cannot fathom how exhaust flow can cause vacuum..., Chaz, Wed, 31 Jan 2007 10:49:52 Members do not see ads below this line. - Help Keep This Site Online - Signup |
I thought that is what scavenging in the engine is all about, how the exhaust can create a vacuum or low pressure side that aids in pulling in more air/fuel into the engine and increase flow and power. I know on a tuned exhaust system, this is what is being tuned and the effect is on the scavenging of that engine. I also know on two stroke engines a tuned exhaust pipe can add up to 25% more power from that engine over a stock non tuned pipe. The effect is on the scavenging of that engine and it helps pull in more air and also get rid of the burnt gasses by pulling them out faster in that tuned area. That is my understanding of a tuned exhust manifold, its similar to a tuned pipe, it will have a certain rpm area where that pipe works best and it will aid in the scavenging effect and actually make more power in that tuned area, which is usually higher up in the rpm band.
By tuning the header, you can change the point in the rpm band where it makes the most power. You can have it make the most power a little lower or a little higher in the rpm band by shortening or lenghtening the header primary tubes. This is all relative to the load on the engine and where in the rpm band that peak load is located. The idea of tuning a header is to fine tune the peak load and power of the engine to the header so that the best scavenging of the motor happens at the best spot in the rpm band so that the motor makes the best power. Shorter header usually means better top end flow and speed and longer header means better torque and may be a little lower in the rpm band.
To tune a header you have to know what you want, max flow up high for better high end power output or better low end torque for better low end output. Then once you know what you want, you would have to start making the header longer or shorter and tune it for maximum performance for that engine and set-up. It usually takes trial and error and some of the header tuners will just start at a point and then make changes in the header and try again and again and again until they maximize the performance they are looking for and once you go a litle too far and the peak power drops off, you come back a hair and you are set. You now have a tuned header for that application.
That is my understanding of a tuned header... John
posted by 75.71.190...
, Tue, 30 Jan 2007 14:34:02
, Thu, 1 Feb 2007 20:02:39, Fri, 2 Feb 2007 16:00:05, Fri, 2 Feb 2007 12:00:27
, Sun, 4 Feb 2007 13:50:18, Fri, 2 Feb 2007 12:18:40, Fri, 2 Feb 2007 07:44:17, Wed, 31 Jan 2007 11:46:12 <-- Viewing This Message, Wed, 31 Jan 2007 12:36:21, Wed, 31 Jan 2007 12:23:24, Wed, 31 Jan 2007 17:23:55, Wed, 31 Jan 2007 19:47:44, Thu, 1 Feb 2007 13:01:29, Thu, 1 Feb 2007 10:08:02, Thu, 1 Feb 2007 08:53:29
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