Large Baffles

[rancid]

You never want backpressure, why would you? What you want is the exhaust sucking out the spent gases and drawing in the fresh gas/air mixture. But this takes "tuned exhaust", the correct cam overlap and right sized carb/TBI.
Real world, the EPA DOES NOT want ANY unburn't fuel leaving the combustion chamber.
So you get cams with little overlap and restrictive exhaust to keep some exhaust in the CC.
Its easy to slap some pipes on, RE-cal fuel and go. But, you still need the correct cam overlap, correct exhaust scavaging and right sized carb/TBI to be right.
As far as reversion goes, theres pages upon pages on this. Best reading is from Buddy Reher of Reher-Morrison Pro Stock fame. Their engines actually get 105-110% V.E.
wilks3
:USA

finally.... A+++

 

[glider.]

Guys, not to rain on your parade but from what you are posting here, your opinion is that NO back pressure will run better than a system with back pressure??

Granted on the strip you have a point but for a street bike it just doesn't work.

Where then do all the bikes running drag pipes that have problems and install either lolli pops or AR cones or small baffles fit into your theory?

 

[wilks3]

Because you are going back to similar exhaust back pressure for that engine. If you changed cams to short duration, low lift with moderate overlap, then you wouldn't need the lolli pops/AR cones. Everything is a package, change one thing, you have to change everything to make package work correctly. What do you want? High RPM high hosepower or low RPM street torque? Which package do you want?
wilks3

 

[glider.]

Because you are going back to similar exhaust back pressure for that engine. If you changed cams to short duration, low lift with moderate overlap, then you wouldn't need the lolli pops/AR cones. Everything is a package, change one thing, you have to change everything to make package work correctly. What do you want? High RPM high hosepower or low RPM street torque? Which package do you want?
wilks3

"Because you are going back to similar exhaust back pressure for that engine"

Then you admit that back pressure is needed then. It seems contrary to your last post.

I think you are way off track with your packages and cams. We're talking a street bike here with the exhaust being the topic. Let's keep on topic here. Things change when you get into cams etc but reference is to a street ridden bike with street exhaust and baffles removed verses baffles installed and backpressure.

 

[wilks3]

OK, When you use the lolli pops or AR cones in drag pipes, you are in effect adding back pressure to that exhaust system to make it like the stock one.
wilks3

 

[glider.]

OK, When you use the lolli pops or AR cones in drag pipes, you are in effect adding back pressure to that exhaust system to make it like the stock one.
wilks3

You never want backpressure, why would you?

So why then would you add back pressure if it's not needed ? Aren't the statements you made contradictory?

 

[wilks3]

No. You are adding back pressure to the drag pipes on "that" engine.
Back pressure keeps a fresh air/fuel mixture from getting into combustion chamber. I.E. EGR valve.
wilks3

 

[glider.]

No. You are adding back pressure to the drag pipes on "that" engine.
Back pressure keeps a fresh air/fuel mixture from getting into combustion chamber. I.E. EGR valve.
wilks3

By your own reasoning then back pressure IS needed for the engine to run right like I have been saying all along and you disagreed with.

Originally Posted by wilks3
You never want backpressure, why would you?

The EGR system you mention (in cars) re circulates exhaust gasses back into the intake for emissions reasons and has no bearing on backpressure (due to baffles) like I am trying to explain. Your reasoning doesn't make any sense in this thread especially with this remark "You are adding back pressure to the drag pipes on "that" engine" as well as the cam overlap statement you posted too.
Well it's rather obvious to me "that" engine (as you put it) needed the back pressure to run properly. Without some backpressure you run into a reversion problem and your bottom end torque will be low. Before we get into tube length and size also that effect flow, read the link added below.

Read the info in this link and maybe you can understand where you are going wrong.

Harley Davidson Community

 

[rancid]

Mr. Data, how many hours have you spent on a dyno and how many exhausts have you built? the age old saying "she needs a bit of backpressure to run right" is gone. the only time i read something supporting backpressure is from a journo who thought "well thats what all the old riders keep saying" or a punter that read it and said "well he writes for a big mag so it must be true", yet everything you read from tuners and exhaust builders says otherwise. guess the guys at the mags know more than the guys building pipes. circuit racing requires a good spread of power, not just top end. dont think jeremy burgess is asking for more backpressure in rossi's ducati.... or any of the other 14 or 15 bikes he has chiefed to world championships. the dumb rods across baffles and silly things like that arent creating pressure they scatter the negative wave that you too could enjoy the benefit of to mask dumb choices and bad designs

 

[glider.]

Again let me repeat what I have said before to you and wilks3

We are not talking about race bikes, drag bikes etc.

These are street bikes in a mild tune that I speak of. Race bikes are a different criteria completely and I understand that completely.

Hard to make a point with you guys when you don't see what I am referring to and keep coming back with different scenarios trying to make a point.

I think any further conversations would be a waste of our time so let's end it here.