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Some back pressure is good down low. /forums/images/graemlins/peace.gif
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Once again, bullshit.
Provide just one reputable source that states otherwise and I'll retract my statements.
Anything you can do to reduce backpressure will improve power and efficiency.
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Do you happen to have a dyno? Try it!
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I don't need to. The scientific process doesn't require that you do an experiment to verify every known law of science.
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I could be wrong but I think in near stock configurations, which we have, exhaust valves need some backpressure to work correctly. And at low RPM's no back pressure causes a parasitic lose to the motor since the exhaust valves need the back pressure to operate correctly.
I'm just trying to remember what an engine builder told me once.
This all goes out the window at higher RPM's when the parasitic lose is negligible due to the rotational momentum of the motor. Also a motor can be built to run with no back pressure.
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Meaning no disrespect to you in the least bit, that is the biggest bunch of nonsense that I have ever heard.
The exhaust valve has a spring to close it. It doesn't need exhaust back pressure to close the valve. It will do so when the cam moves, allowing spring pressure to pull the valve closed.
It is nearly scientifically impossible to build an engine that will have NO backpressure. The exhaust ports create some sort of backpressure to begin with. Without SOME pipe, the head will be less efficient at scavenging the exhaust gasses from the cylinders following combustion, but anything after that, ESPECIALLY a muffler, is restriction.
I'm not out here to say that everyone needs to run straight pipes, or open headers, because that is just not practical for the street as it is too loud.
Go to the strip though and you'd be hard pressed to see someone run anything but open headers. They're not losing any low end power by doing so, in fact, they're gaining power from idle on up by doing this.
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Tim,
For the most part this is a four wheel drive site. Race cars and four wheeler's are totally different when it comes to a properly built motor. Typically 4 WD engines need more torque down low. It amazes me on how many kids want and do build their 4 wheeler engines to produce high rpm's with gobs of hp. Torque is where it is at in most 4 wheel and street engine applications for that matter.
I have built and run test on my engines, including my current 350 Chevy engine with many scenarios. Stock exhaust manifolds, steel headers, ceramic coated headers etc. The best performance and torque from these tests where; ceramic coated headers, 2 ¼” tubing from the collectors back about two feet with crossover pipe. Then 2 1/2” tubing for about 1 foot to the mufflers then 2 ½” tubing from muffler the rest of the way out behind the rear wheels.
There are many other factors to take into consideration, such as; the temperature and speed that the exhaust gasses exit. For example; regular steel headers cool much quicker than ceramic coated ones do. If this is what you are referring to back pressure, I would agree with you that this can cause too much back pressure.
I agree with you on one of your opinions though; Race cars with lots of horse power and rpm’s have different requirements and can run open exhaust. This is not the case with most of our stock or slightly modified engines.
I noticed on a few of your posts that you appear to like to argue; your opinions as well as mine are not always going to be right. There are far too many scenarios to be right in every case. /forums/images/graemlins/peace.gif
http://www.iamnotageek.com/showthread.php?t=58653
