Why a 4 to 1 or 2 to 1 exhuast system?

[WesV]

Usually when you want to gain performance you go with a freer flowing exhaust system, ie: more pipes per number of cylinders (at least this is the old car addage I know). So if this is true on bikes as well which i suspect it is, why do you want to go to a 4 to one system in case of a 4cyl or a 2 to 1 system in the case of a 2 cyl? Wouldn't that cause mor backpressure and not allow as free flowing system thereby robbing HP? Please would someone explain?

Thanks for informing the ignorant!

[Dink]

Cross-section mostly, you will find most 4 into 1's have much larger pipe bore sizes than the stock 4 into 2 systems, this allows for far better "scavenging" of exhaust gases but utilising the pressure pulse of other cylinders.
Remembering that each cylinder has an individual header, that then collects into a single pipe; take a closer look at a V8 header, keep in mind that in automotive terms any header style system is gonna work better than a manifold.
So it comes down to, there is a weight advantage, there is a flow advantage, and most sound pretty cool to boot.
Dink
There is more than enough involved in all this to fill several books, so I have only touched on the most obvious.

[lhanscom]

and actually the best systems are 4 into 2 into 1 with 1, 3 and 2, 4 connected first then those 2 joined. Just more of the scavaging effect.

[Hap Call]

While this is very effective on 4 cylinder motors, the effect is reduced for 2 cylinder motors depending on the firing sequence and the crank design (i.e. 180 degree crank, 360 degree crank, etc)

Hap

[WesV]

So I guess my real question is:
Would it be worth the money to spend on a 2-1 system for my 450L or should I save it and just buy new headers? (The reason I ask is because mine are engulfed in rust! )

[Hap Call]

So I guess my real question is:
Would it be worth the money to spend on a 2-1 system for my 450L or should I save it and just buy new headers? (The reason I ask is because mine are engulfed in rust! )

Go with what is cheaper would be my advice.

Hap

[Dink]

How badly rusted are they? do they have holes? If not have them ceramic coated and forget about it.
Dink

[WesV]

The don't have holes yet, but the are rough enough I can't even run my hand over them. Very pitted and no chance of ever getting that chrome back that is why I wanted to replace them. What is that ceramic coating you speak of?

[Anonymous]

and actually the best systems are 4 into 2 into 1 with 1, 3 and 2, 4 connected first then those 2 joined. Just more of the scavaging effect.

This is the best way to do a 4-2-1, and will give you the smoothest torque curve. But a 4-1 will give you the highest peak torque and most horsepower, albeit with a lumpier torque curve. Depends on what you want in the end...