Bespoke exhausts

[NigP]

Can anyone tell me, or direct me to a website which will enable me to find out what the advantages/disadvantages of 4-2-1 exhaust system over 4-1 system.

 

Cheers

[tcrawford]

NigP,

 

Basically a 4-2-1 will give you a better mid range power figures at the

expence of the top end.

The 4-1 will then give you a better max revs power figure at the

expence of mid range.

Look at motorcycles at the race track, all 4-cylinder bikes will run 4-1.

However when doing long distance racing the 4-2-1 will come out to play.

Everything about engine tuning is a compromise its ultimately your

decision about what you want i.e. BIG numbers in B.H.P. to talk about

down the pub or something thats useable.

Dont get me wrong, both systems can be used but on a highly tuned

engine the above rule does apply.

 

Hope whatever you fit makes lots of noise.

 

tcrawford.

[DanB]

Actually, almost all 4 cylinder race bikes use a 4-2-1 system but with very long primaries. For instance, this is a picture of the Akrapovic system for the Fireblade, as used by many Fireblade race teams:

 

http://www.akrapovic.net/honda%20954%20pipe.jpg

 

Honda Racing's own exhaust system for the Fireblade for the years 1999-2001 were all 4-2-1 systems - I know this, cos I've seen the original drawings...

 

Dan

3 broken ribs and no Fury.... 🙆🏻

[Pierre Gillet]

I am envisaging fitting a Caterham 4 2 1 collector and a Raceco titanium box.

Will they fit together straight away?

 

Pierre

[Rob Walker]

Pierre,

 

I have a Caterham 421 collector that is surplus to requirements its offa 2001 SLR and in perfect condition.

 

Rob

[Pierre Gillet]

Rob,

YHM

 

Pierre

[Pierre Gillet]

Rob,

I am unable to send you a mail.

Please contact me at : Petrus7@aol.com

Cheers,

 

 

Pierre

[elie boone]

Pierre, It's probably due to bad wheater that your e-mail could'nt cross the channel. 😬 😬 😬

[JimmyRocks]

but does that mean that tccrawford is right

ie would a 4-2-1 exhaust give me noticeably more mid-range grunt 🤔

 

Mines a 1.6 unmodified roadsport with 5-speed box. Only road use (so far)and I rarely get close to the top of the rev range, so it would seem to suit.

 

 

 

James

Yellow Roadsport 115, 5 speed.

[Pierre Gillet]

Elie, not so easy to send an email with the email sender of the forum. Did you try?

I finally suceeded

 

Pierre

 

Edited by - Pierre Gillet on 12 Sep 2003 20:11:48

[elie boone]

Pierre, Never had any problem, maybe the Blat Chat sever has some problems with the French language. 😬

[c21vhpd]

This page might help. I confess that I never really got to grips with it, and I think the guy that wrote it ended being unhappy with his exhaust in the end, but if it helps your understanding...

 

To whet your appetite:

A 4-2-1 set of headers, as with any tuned header, relies upon constructive interference of positive and negative gas pressure waves to assist in scavenging. This basically means that an exhaust port open to low pressure in the header which assists the flow of exhaust gases out of the cylinder and sucks in a greater charge for more power. With a 4-1 header the length of the primaries is such that a high pressure gas wave will flow to the collector and reflect a low pressure gas wave so that it arrives at the exhaust ports at exactly the moment when the next cylinder is opening its exhaust port at peak power rpm. A 4-2-1 header's primaries work in exactly the same manner, but the collectors are shared across pairs of cylinders and the primaries and collectors are tuned in length and diameter so that negative gas pressure waves coincide from the end of the primaries, the end of the collectors and the combined length of primary and collector to provide improved scavenging at lower engine speeds as well as at peak power rpm. As with a 4-1 set of headers the lengths and diameters of the pipes are critical in determining the resonant frequency of the system, but unique to 4-2-1 headers the pairing of cylinders is vital to generating the correct sequence of low pressure gas waves.

 

Honda Passion Orange, 640kg , and proud of it

[JP]

Nigel,

You should have mentioned that you have a cross-flow 7. I think(?) that the ideal set up for these is the 4-1. I don't think they react in the same way as a K-series to different exhaust configurations...no doubt someone will be along to correct me soon...