I posted this graph several years ago.

http://www.britbike.com/forums/ubbthreads.php?ubb=showflat&Number=268898&page=1

It compares the calculated lenght for Blair and Vizard.


There are two things I would add from my experience.

Firstly as several others have said the inlet tuning needs to match the exhaust. For road racing I think you should tune the inlet to fill in the low points on the hp curve from the exhaust lenght. For example - tune the exhaust for a 6800 rpm and the inlet for 6300. This produces a smooth curve.

Secondly possibly the most important thing of all. Vibration of the carbs. With the long inlet tracts you will probably find the carbs vibrate badly. They are out on the end of a long tube and can really buzz at certain rpm. You must mount them on good quality Mikuni type rubber connectors and support the carbs so they can move but not buzz! If you find you are getting a misfire at the end of a long straight with the throttle wide open you are probably getiing frothing in the carbs and fuel starvation from vibration. (I assume you have already tested to ensure you have sufficient fuel flow through the lines fuel taps etc.)

This is really important to check this or all your tuning tests may be misleading!

Anyone wanting do this stuff must read the back to basics paper here. It is excellent!

http://www.profblairandassociates.com/RET_Articles.html

Last edited by johnm; 03/24/14 5:15 am.