A common example of backpressure is that caused by the exhaust system (consisting of the exhaust manifold, catalytic converter, muffler and connecting pipes) of an automotive four-stroke engine, which has a negative effect on engine efficiency, resulting in a decrease of power output that must be compensated by increasing fuel consumption.Ahh the old back pressure myth again
if your trying to impress, u might pick somebody else.They were all motorcycles except the V stock NHRA national record holder I prepped the block on. Lots of 2 stroke experience too. One of my favorite Smokey Yunick quotes is: an engine doesn't know what name is on the valve cover. I doubt you have the experience or the mind to comprehend that though.
"All it takes is a little practical experience to blow the he!! out of a perfectly good theory." --- Lloyd Rosenquist, charter member AWS, 1919.
"As soon as exhaust hits the air outside of the end of the pipe, slows way down, which causes a build up in the pipe that has to be overcome "Back on my wrecked bike when it had drag pipes, I used those inserts in the end to bring back the low end (bike had straight pipes when I got it and I couldn't afford a new set of pipes at the time). The ones that go in the end of the pipe. When you say torque cones, for a second I thought you were talking about the snake oil inserts that go up by the heads (those don't do anything).
The lollipop baffles in the end of the pipe work, depending on the pipe. There's two things at play, one is the harmonic reversion you mentioned (which could be remedied by as little as a screw or bolt in the end). The big thing these particular inserts do, is increase exit velocity. As soon as exhaust hits the air outside of the end of the pipe, slows way down, which causes a build up in the pipe that has to be overcome (the engine has to push it out, which is why it's more a problem at lower RPM). It's a problem with larger diameter pipes because although more free flowing (good at high rpm), they have a lower velocity (which is why the exit slow down is a bigger problem). The lollipop increases velocity just before where it would slow down as well as increases scavenging in the end of the pipe, helping to prevent that pressure build up.
The result is a smoother bottom end and eliminating some of the low-end sag (assuming it's caused by an exhaust that's too big for the engine and rpm range).
Your welcome. The torque inserts have their own site where they explain how you can also adjust the position of the plates to change the tone or to help with low end torque the most. I can only go by what I have experienced myself and if others do not agree it's no loss to me. They are called "torque inserts" not sound inserts but they do help on both.I agree. There are a lot of variables to consider beyond what "racers" do on a street machine that will rarely run at full throttle. Physics is not always user friendly. I used to teach physics and physics plays a large part in my current employment. Test and verify is the only answer. I felt DK documented their test and verify of this product with a healthy amount of dyno runs. Even then I do not preach the power numbers and kerp it to the reason I purchased the inserts. To control the decell popping and improve the sound. Which they did fantasticly. If I am getting more torque its a bonus. Thanks for your reply.
Never mind that they call it "back pressure".
To oversimplify it, you get better performance in various RPM ranges based on diameter and length. For street riding, if you put a too high output exhaust, that's where you lose power through the loss of scavenging and velocity, not back pressure.
And to be clear, these inserts don't give you more torque, you can't just slap them in any exhaust for more torque, they just give you back some of the loss when you have the wrong exhaust pipe (usually too big diameter) for the engine/cam setup for your application, which is really only a bandaid on the problem. But they aren't really creating back pressure, they're sort of correcting oversizing (for the intended RPM range and cam) and helping with some scavenging. It's more like what stepped headers do: not add back pressure, but add scavenging. That's why they go at the end of the pipe, where the everything has lost the most velocity. And it goes without saying, the proper exhaust for your setup would produce more power than a modified wrong exhaust.
Exhaust isn't that complicated to understand the basics. Yes, they can get complicated and there can be a lot to them, but...
"The reason why some old timers have said things like 'you need some back pressure to make power and torque' in the past was... well if you have like a really huge, way oversized exhaust, you lose your gas column inertia..." (key part here being "oversized exhaust"). Also "the trick is to get as much velocity through the pipe with as little back pressure as possible, a lot of that is in the correct size tubing for your engine":