Hi
First off I'm a sport boat guy not a racer.....

I've seen lots of info on header length my question is if you shorten the header (I've seen lots of starting points from 11" to 13 1/2" - to center of band) shorthening header (to a point)raises the useable rpm range but loses torque? if I understand Mark's header info (very good by the way .. thanks )

I've read lots on shorthening pipe till you lose torque - how do you tell (by speed? by rpm?) .... would you not want maximum torque for 'bigger boats' (I have a couple 60" + Cats) and maximum rpm for lighter boats?

I understand wanting max rpm for light race boats (higher rpm = higher prop speed) but you need the torque to get boat moving to begin with specially with bigger boats with clutches .... is there a 'balance point' where you keep most of the torque for low end grunt but gain some of the rpm for top speed

I just don't want to shorthen pipes for max speed but have no torque to get up there where ...... what is a good starting point for 'torque' vs for max rpm ... and how do I know (apart from speed) when I've found that point?

Thanks

R. Peter

Peter,
First off, Welcome too MGB :drinks:

You need to understand that most utility marine engines such as Zenoahs, Sikk, etc are not really tuned in terms of exhaust duration too really take advantage of a tuned pipe. While it is common practice to fit one on these "Stock" engines, performance gains are marginal at best.
Not until you modify these engines with greater exhaust open duration or run a purpose built race engine such as the Quick Draw, J&G will you really see and hear a great difference in a Pipes tuned length.
That not to say on a stock engine you won't have changes with length fiddling, it just won't be anything dramatic

#1 issue most newer boaters fall for is BIGGER being better & faster and tend to run too much prop having pitch or diameter just beyond the horse power of the engine being run.

The more mildly tuned an engine is ( Stock verses Modified )broader it's overall power band and less reliant it is on boost from the pipe. Where as modified engines having less torque need and depend upon the pipes "Hit" to make horse power in the upper rpm range.

And YES, you are correct that Race caliber engines are in lighter and smaller boats that don't need a lot of torque getting up on step/plane, relying on the top end rpm turning a small prop to make the speed.

thanks Scott ,,, I was wondering the same thing

I think I will spend my time on props and set up and 'play with pipes' later I thought maybe I was missing out on some big power by not tuning my exhaust first ... my boats seem to run okay but with no one here (where I live) it's just me so I have no one to compare it to...

Thanks for me too

Randy

Thanks Scott ...