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They already have cars that have headers shooting out the sides with no need for a fancy exhaust system, however those would be impractical for street use for obvious reason like noise and safety. Look at the Amuse R1000, it's very loud but has very little in terms of restriction.
You have scavenging and backpressure confused, they are not related. If there was a way to have zero backpressure and have an incredibly efficient header that scavenges exhaust pulses to help draw in a more complete fresh intake charge at lower rpms, that'll be ideal. In no way would having backpressure in any amount be beneficial.
On a normal car, there's going to be some restriction (back pressure), with the assumption that your car is legal (CARB, smog, emission) equipped. Your example of a 4 inch exhaust system wouldn't be better flowing necessarily because an improper choice of piping (diameters) can lead to air turbulence within the pipes (versus a controlled flow) that may result in flow restriction(s). Reducing back pressure doesn't mean just up the sizing of all the pipes on a street driven car... it's not that simple.
A stock S2000 would be a lot more comfortable driving around daily on the streets, than one equipped with special header that has 4 individual pipes, one for each exhaust port running all to the rear, never joining at any point. That sort of system would be pointess as the engine can't benefit from the scavenging effect that would aid in pulling more of an intake charge at lower rpms (not to mention the complexity of the setup, and excessive noise).
Zero backpressure, an efficient header design that helps lower rpm performance (important for street driving) yet allows the engine to breath at high rpms are the goals most people shoot for. IMHO, Honda did it quite well already... though Toda and Mugen (both I'm familiar with) also have nice products as well.
You won't find anyone in the process of developing an exhaust system say anything like "well guys, let's produce a good exhaust system, but since it'll be used for the street, we need to add a little back pressure." Back pressure happens to be the result sometimes due to other factors, but it's never incorporated into the design itself.
Here's a better example. If you were to replace your existing mufflers with an original SuperTrapp muffler, put your car on the dyno and do a half-dozen pulls. Remove some of the plates (increasing back pressure) and repeat the dyno process. If the conditions of the dyno testing are done correctly, at no point will your car gain any power (HP or TQ) by increasing the restriction by using fewer plates. However if you uncap the muffler (so that it looks like a straight through glass pack), you'll record the highest numbers on the dyno. I've seen this done before on many different cars and I'll say again, back pressure is not good. Exhaust scavenging is good. Don't confuse the two.
Originally posted by l8brakr
I am not saying we need backpressure for the motor to run.
I agree 100%, no argument there.
From what I understood of the original question,
"What can be the negative result of reducing exhaust backparessure? Can a high performance muffler which reduces backpressure 50-75% be detrimental to the engine? valve train? intake system or....?"
The plain vanilla answer is no negative effects for power. It won't cause adverse effects to the valve train, intake system, etc.
There are other factors which could be answered good or bad, depending on the person. For myself, I don't like excessive or unnecessary noise that doesn't need to be there, as long as useable power isn't sacrificed. If there was a way for me to get the benefits of using an R1000 system but be quieter than stock, that's what I'd want. Others enjoy a louder tone.
Originally posted by Hyper-X
From what I understood of the original question,
That's what I suspected, you were trying to answer the original where we kind of hijacked but still on the same subject were discussing something a little different.
[QUOTE]Originally posted by Hyper-X
There are other factors which could be answered good or bad, depending on the person.
l8brakr, my research has moved in similar lines to yours. You might want to check out this article on Autospeed. These guys make a very free flowing (and loud) exhaust for max power. Then they add an exhaust valve to keep backpressure constant at a certain level. With some additional backpressure, mufflers seem to work better.
The power is down with more backpressure, but they also add a cut-out switch for WOT, when noise is not an issue.
That's an interesting idea, but I wonder about the reliability of a valve like that being in such a hot area of the car. I recall seeing something like this in a mag but I can't recall when or where.
Anyhow, I'd thought that you may enjoy this video, it's a repost but it's still nice. Watch the video first then scroll all the way down for some details.
See attached link discussing exhaust selection. http://www.newcovenant.com/Speedcrafter/up...ads/Exhaust.htm
I was actually looking for something that discussed the relevance of the length of a dragster's "zoomies" to power output. While more flow is generally speaking, better I wonder if 3 feet of dragster exhaust provides similar backpressure to a much longer, and smaller diameter system on say on a street car. 2000+hp is going to need a lot of breathing and if more was always better wouldn't the the dragster run bare exhaust ports? No scavenging required(unless the zoomie is just to scavenge the gases in the exhaust port itself). All big block headers are larger than small block headers which in turn are larger than the small displacement 4 and 6 cylinder headers. This implies that there are more than just volume concerns and that the largest piped systems, which most closely resemble the near zero restriction of the zoomies are somehow less desirable than smaller diameter systems, in smaller engines. The only thing I can come up with is the huge pipes, with insufficient gases to generate high velocity flow, would actually develop eddies in the exhaust gases as they cool and therefore are creating restriction in straight pipe! One comment in the Speedcraft article that I found interesting was exhaust flow selection affecting power output with long duration camshafts at low RPM and actual selection of an exhaust to get that specific effect. This may relate to the backpressure increasing torque comments where the exhaust system is altered to fight the low RPM characteristics of the cam. Backpressure adding torque may also relate back to carburated engines that had no ability to adapt to the lean conditions created by addition of low restriction exhaust, hence sudden loss of power and burnt valves. but I suspect it is the former.I know streetabilty is a concern for noise issues if nothing else but I am pretty sure that it is the low rate of power return after a certain level of exhaust flow is achieved that determines what the best available flowing systems are capable of. Unfortunately I don't have a thorough understanding of the synergy between cam profile and exhaust diameter selection but I can accept it as fact in spite of this.
Welcome to the forum!! I'm fairly new here as well. Thanks for the link I think it is supporting my theories (as long as I'm not selective reading). As far as dragster headers, I think they are there just to redirect the flames so the crew doesn't get BBQ'd when they fire it up. But seriously I would like to know how they came up with the length they use or if it is just an arbitrary number?
My sincere thanks and appreciation to all those who contributed to this link.
I learned alot. I will post pics re: new muffler installation when I have more time.
The setup gives me the low/deep tone I want. Again, many thanks to your
thoughtful responses!
01-24-2004, 07:57 PM
But seriously I would like to know how they came up with the length they use or if it is just an arbitrary number?
