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170 inner exhaust

Posted: Wed Apr 09, 2008 12:31 am
by rosbullterier
I am converting a 170 to standard shaft.
The following question might make sense.
Inside the exhaust tube is another exhaust tube. This smaller exhaust is shorter than the longshaft exhaust outer but does the standard exhaust outer have a shorter inner exhaust than the longshaft exhaust outer?

Posted: Wed Apr 09, 2008 3:25 am
by GregBda
Yes. About 5 inches shorter.

Posted: Wed Apr 09, 2008 10:26 am
by rosbullterier
Thank you Greg.
5 inches - thats quite a lot. It might alter the sound a bit - but would it affect the performance?

Posted: Thu Apr 10, 2008 5:27 pm
by Charles uk
The inner exhaust on a short shaft is 12" long & 16" for a long, now I can't remember if the measurement is from the top of the mounting plate or the length of the projecting tube.
But you should be able to tell from the length of your long shaft one.
The face of the mounting plate where it fastens to the cylinder is very prone to salt water corrosion beware, there is a lot of work recreating one of these.

Posted: Thu Apr 10, 2008 10:47 pm
by rosbullterier
Yes Charles I started to try to dismantle the inner exhaust mounting plate which is corroded and though better of it as there was no purpose in its removal.
I have read on a 'racing site' that that a bigger exhaust produces more power and it would be beneficial to change to a longshaft exhaust.
I would like the convenience of the short shaft, but would this noticeably restrict performance?
Hopefully the engine is starting with 7hp and I am not in your hydroplane league!