Exhausts

[Esceptico]

I've seen references to 4-1 and 4-2-1 exhausts. Please can someone explain why the latter seems to be preferred or what advantages it is supposed to bring.

[Gingerbread Man]

4-2-1 is meant to favour mid range power, where as 4-1 favours top end power.

[DCL]

Where the primaries join, and the diameter changes, a pulse is reflected back and this can be used to extract more exhaust gas. If you have two collectors, there are two pulses (although weaker) that can be used and generally this means a wider power band. One way to think about it is that the area under the torque curve remains constant, but the shape changes.

That said, exhaust design is such a complex thing (in an NA tuned engine) that both setups can produce good results.

Edited by DCL on Friday 26th February 11:51

[DVandrews]

In my experience a 4-2-1 is the only sensible option unless you are craving an extra 2-3BHP at the top end traded off against a mountain of mid range torque. In back to back tests a 4-2-1 can gain 10-15% extra mid range torque over quite a large rev range. If you examine the torque curves between the best 4-2-1 and best 4-1 (and I have) the area under the torque curve with a 4-2-1 is much more substantial and in the area where the engine is most used. The only negative is a small drop off in the last 500RPM of around 1-2%.

In short, get a good 4-2-1 and reap the benefits.

Dave

[radical78]

the long 4 to 1 is about 2 seconds a lap quicker than the standard short one

[BertBert]

radical78 said:

the long 4 to 1 is about 2 seconds a lap quicker than the standard short one

Really? 2 seconds on any lap? Impressive at BH, less so at the ring

[tomwoodis]

Interesting info that Dave, thanks for sharing. Are your comments specific to the K series or would the same be found on Duratec cars?

Tom