what part of the exhaust creates the back pressure? i have a 4in tip i want to put on, but if tht muffler is what causes the back pressure i wont take it off. but isnt it the presilencer?

 

Backpressure: something to avoid.

 

^ This. If you hear someone talking about back pressure being desirable, it's a clue that they have no idea what they're talking about.

 

the muffler is what creates the most back pressure. but ideally, and depending on the noise ordenance of ur state, u want as much of a free flowing system as u can get without being too loud.

 

The actual answer is; whatever part will flow the least amount of gas is the most restrictive. Not knowing your exhaust system, it could be the manifold, cat, muffler,pre silencer, dented section of exhaust pipe. It's almost never the exhaust tip though so a tip will almost never help.

 

Not that I want to stick my head out on the limb here - but some backpressure is needed for the operation of the 5th and 6th ports on a GSL SE right?

 

i have heard from SO many people that back prsessure on a rotary is a must....

 

AFAIK on piston engines some backpressure is desirable. There's a lot of debate around exactly how desirable it is, but I imagine it's maybe along the lines of how intake systems benefit from pulse resonance.

And since rotary still uses the same basic principles as a piston, I bet some backpressure may be beneficial.

And yeah, if you have mechanical secondary ports that use exaust backpressure, then it's pretty much a must.

[edit]

Correction on that, not backpressure, but rather some restriction is desirable. I remembered wrong, sorry. It's the velocity vs flow that's important. Wider exhaust diameter will have lower velocity - bad, but too narrow will be too restrictive - also bad. You want maximum velocity without sacrificing flow.

So now I'm not sure about the rotary, but I bet similar ideas apply.

 

rotary engines like free flowing exhausts, but as to HOW MUCH free flow, is up to where you want your power at.

more back-pressure (restriction) will result in an increase of low end power (good for take-offs) but will choke out on top end which results in less TOP SPEED.

and the opposite for free flow, it will kill the bottom end, making it somewhat sluggish on take-offs, but give you a greater top speed.

as to what would be a good balanced system for you, depends on your set up. for example, a system that would be considered "free-flow" for a stock engine, may be too restrictive for a ported engine.

 

All enclosed passages with fluid flowing through them will have backpressure unless they are magical frictionless surfaces.


Overall, exhaust restriction/backpressure is a flow impedement/resistance.
Abrupt changes in pipe/exhaust size, fouling, and baffles all act to impede the flow of exhaust. That is why there are aftermarket headers, pre-silencers, and mufflers, the most restrictive part of the exhaust system.
Also, try to keep your exhaust the same size. If you start with a 2" header, then go to a 3" midpipe, then a 2" header your exhaust will exhibit losses associated with the expansion and contraction and your system will require more pressure to flow the same cfm than if it was all the same. However, expansion chambers are designed this way to pulse with the engine in such a way as to tune the low end acceleration or top speed speed. This is done in the two-cycle world. Other words, if you do not know what you are doing, keep it the same. I just know some smart guy will say something to dis credit what I am saying.

I have read several times that some back pressure is required for the 5th and 6th ports to work properly. This is also on racing beats web site. You can wire them to always be open, but you will need to research that.

Don't buy an exhaust tip. They do nothing but make noise.

 

If you're asking because you're worried about your 5th/6th ports not working, I've heard really good things about these, http://www.pineappleracing.com/6-por...sertspair.aspx.

 

The inserts don't actually do anything to open the ports. You still need back pressure to open the ports with or without the inserts.