Header primary pipe length

[subike]

I am about to rebuild my 4 -1 headders, and after looking at some of the pics posted of XS11's
I noticed differences in the lengths of the primary pipes to the collectors.
Some were short, as in ended at the collector just behind the oil filter, others were longer ending at the G Box sump.
Now this got me thinking,
From experiance with Cage motors, short primarys gave top end tourqe, long primarys bottom end tourqe.
I am interested if there is a power difference between short and long in the same way for the XS11
I am interested in low down acceleration power, at the cost of high top end speed if nesessary.
SO before I cut up my existing 4 - 1 and just reshape it to what looks better than the doggy job it is now,
what is better for lower end power
short?
long?
why?
And what size can should be clamped on the back of the collector,
again, short or long.
Cheers!

[TADracer]

Just another tuning point.

My initial thought would be that if you want low end torque you would probably want to stay with a longer length and a smaller diameter collector and keep some sort of baffle in your mufler. This will help keep a bit of back pressure which will help develop torque. But having said that, a header is but just one tuning point. If you change it then you must consider everything else in the path of the airflow, like intake arrangement, carb jetting, cam timing, etc, etc, etc in order to get exactly the performance you want. So, be ready for a tuning session.

[Dennyz]

My experience has been that muffler selection has much more impact on torque than primary tube length on a stock XS motor.

I played around with an old 4:1 with primary tube length and could not tell any difference (without a Dyno). Oil filter access and ground clearance (in the turns) was a bigger issue.

[subike]

Re: Just another tuning point.

Originally posted by TADracer
My initial thought would be that if you want low end torque you would probably want to stay with a longer length and a smaller diameter collector and keep some sort of baffle in your mufler. This will help keep a bit of back pressure which will help develop torque. But having said that, a header is but just one tuning point. If you change it then you must consider everything else in the path of the airflow, like intake arrangement, carb jetting, cam timing, etc, etc, etc in order to get exactly the performance you want. So, be ready for a tuning session.

Yeap agree with you there, Once I have sorted out the headers and muffler , I know that carb jets and timing adjustments are next, I am even going to look at the possibility of changing the Velosity stacks to bring the power on earlier.
I will have the use of a dyno to do the final tuning.
I will post the full results when completed.
As I am only interested in acceleration, I am prepared to loose top end and ecconomy out of this adventure