Exhaust Dynamics

When it comes to exhaust systems, there are so many different variables that determine how the pipe will perform. <br /><br />Take looks and number of pipes in the system out of the equation, what would you point to as being the MOST important variable in exhaust performance? Is it cam duration? Pipe diameter? Pipe length? Valve size? Cubic inches? <br /><br /> I am asking this for a few different reasons. One reason is I am trying to ascertain on what my starting point should be when picking a system for my builds. I will have one engine built here shortly with another one to hopefully soon follow.<br /><br />Thanks for reading and sharing. Let's see what shakes loose.[emoji54]<br/>

They are all part of the package and should compliment each other to get the most out of your engine...

I think it depends on the engine and its design drawbacks as far as which exhaust performance element is most important in that case. A great cam with poor head flow will nullify the greatest exhaust system. I guess the proper ratio of flow versus backpressure to achieve most power output on a dyno for your engine, but that is a sum of all the elements you mention. I would guess exhaust pipe diameter and cam timing/selection as the elements I would say are universal to all motors big and small as the starting point for performance. This is a definitely a BaggerPaul question. Sorry for being vague.

valve timing duration overlap and lobe seperation ! exhaust valve size and port crossection area . the bigger the pipe the slower the exhaust flow ! just like a garden hose and water flow . if i pinch off the end of the hose i can push water across the yard so if the hose end is to big the water hits my feet . k-i-s-s way of thinking works well here . exhaust valve and exhaust port is just a part of the pipe on a harley engine !

But pick one variable.

big on e for me would be exhaust duration

Guess I was close...

chew on this for a moment? why do stock engines responsod well to exhaust changes . most customers are very happy after a stage one and just any old map or jetting .add a stage two with cams now a full tune complaints about it being soft or jerky on the bottom . not being smooth . well its the longer duration and intake close ! the big exhaust dont play well .

So basically you are saying go opposite. Long duration, smaller pipe? Shorter duration, bigger pipe?

in a way what im trying to get across is that you can get away with a larger than needed exhaust system in the cam is very short in duration.
Smaller diameter pipes flow less volume than larger ones, but the exhaust in the smaller pipe flows faster. Until you reach the RPM where the sheer volume of exhaust gases require bigger primary tube diameters, smaller tubes will scavenge the cylinders more efficiently. If you're using the engine in the 1,500 to 3,500 RPM range, which is typical for a street-driven vehicle, you definitely want 1-1/2" to 1-5/8" primary tubes for any small block and 1-3/4" to 1-7/8" for a big block engine. Any bigger and you'll lose a considerable amount of low end torque. beyond 3,500 RPM it is a question of where you want the power peaks.

If you're not going to do competition drag racing pick a pope that has the sound , look, and good quallity you're going to enjoy

Hope Charlie46 meant pipe not pope, no need to throw in religion(lol) We all want THAT sound with performance. there are so many factors but not quite enough will usually work better than to much. P/S we all want more.

The pope has a Harley

With or without a sidecar???

The shape of the header pipe.
And the size of the muffler, and if it holds in any back pressure in.
Choosing the wrong muffler can hold you back a little, and it can hurt in in different ranges of the rpms.
Baggerpaul ought to be able to explain it to you a little better.

If you get the pipe too big Its not gonna help you.
Cam duration is totally different.
You can get a Woods 222 cam that will work great with stock heads and stock motor.
But if you go with the Woods 555 cam, it s the same cam but has more duration.
And to make it turn on you need more compression.

everything has to work in Harmony. You just don't throw things you like together.

A head man or a builder or tried and proven kits are a great way to go.

Sorry guys, this conversation didn't work.

Thanks BaggerPaul for being on point.

I didn't read the whole post.

But I do call a exhaust mfg and talk to them about their product.
I don't tune bikes like Baggerpaul does.
So I can't explain it as well.