NigP Posted September 10, 2003 Share Posted September 10, 2003 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 Link to comment Share on other sites More sharing options...
tcrawford Posted September 11, 2003 Share Posted September 11, 2003 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. Link to comment Share on other sites More sharing options...
DanB Posted September 11, 2003 Share Posted September 11, 2003 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.... 🙆🏻 Link to comment Share on other sites More sharing options...
Pierre Gillet Posted September 11, 2003 Share Posted September 11, 2003 I am envisaging fitting a Caterham 4 2 1 collector and a Raceco titanium box. Will they fit together straight away? Pierre Link to comment Share on other sites More sharing options...
Rob Walker Posted September 11, 2003 Share Posted September 11, 2003 Pierre, I have a Caterham 421 collector that is surplus to requirements its offa 2001 SLR and in perfect condition. Rob Link to comment Share on other sites More sharing options...
Pierre Gillet Posted September 11, 2003 Share Posted September 11, 2003 Rob, YHM Pierre Link to comment Share on other sites More sharing options...
Pierre Gillet Posted September 11, 2003 Share Posted September 11, 2003 Rob, I am unable to send you a mail. Please contact me at : Petrus7@aol.com Cheers, Pierre Link to comment Share on other sites More sharing options...
elie boone Posted September 12, 2003 Share Posted September 12, 2003 Pierre, It's probably due to bad wheater that your e-mail could'nt cross the channel. 😬 😬 😬 Link to comment Share on other sites More sharing options...
JimmyRocks Posted September 12, 2003 Share Posted September 12, 2003 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. Link to comment Share on other sites More sharing options...
Pierre Gillet Posted September 12, 2003 Share Posted September 12, 2003 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 Link to comment Share on other sites More sharing options...
elie boone Posted September 14, 2003 Share Posted September 14, 2003 Pierre, Never had any problem, maybe the Blat Chat sever has some problems with the French language. 😬 Link to comment Share on other sites More sharing options...
c21vhpd Posted September 14, 2003 Share Posted September 14, 2003 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 Link to comment Share on other sites More sharing options...
JP Posted September 15, 2003 Share Posted September 15, 2003 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... Link to comment Share on other sites More sharing options...
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