| Enginetype:
Outboardgas
> motormodel: Johnson Fastrike
150
> Serialnumber: '98
> Configured: single
> boatmodel: Sprint 286
> Boatlocation: garage
> typeofneed: Adding Toys
> Need_Other:
> TechQuestion: Submit Question
> repairsdone:
> none
> Comments:
> What are the pros and cons of
opening up the exhaust on my motor? Actually, if I do add that, I'll
used Bob's machine shop's exhaust plate, so that I can put the plugs
in to quiet it back down when needed. If you would like to see the
part I am referring to, go to their web site. http://www.bobsmachine.com/index.htm
> Click on "transom
savers" and scroll down to exhaust housing.
> I've asked around, and opinions
varied widely. I've heard that I might not see any results, and I've
heard that I would pick up possibly 400 RPM. So, my question is: What
kind of benefits should I see from doing this? I know it will be
louder, and that really doesn't bother me. Also, are there any downsides,
like as far as the life of the motor goes. I was told that there is
not, but it seems to me that with the air flowing faster, the motor
might run a little leaner. Thanks.
Our Answer:
Results would be dependant upon
quite a few factors.
First, if you use a prop that needs
exhaust pressure to cavitate the prop during take-off, than this
exhaust relief system will most likely slow the hole shot down. The
performance of these type of props also depends on how the operator
uses the throttle, anyway. Aerated props work best if the operator
guns the engine for take-off. Thereby, forcing a lot of exhaust gas
around the blades of the prop.
If you are using a surface running
prop and have enough engine height and trim to get the prop out of the
water, at full power, then the benefits of an exhaust relief system
would be negligible. Surface running props already relieve exhaust
back pressure, at full power, by their design.
If your boat is a transom heavy /
extremely hard to plane boat and you already have a properly matched
aerated prop and are using it correctly... then this exhaust relief
system "might" help to relieve "excessive"
back-pressure during take-off.
I am not aware of any harm that
could be done to the engine, itself, by installing this type of kit,
as long as the engine is tuned properly and operated within specified
RPM range. However, benefits achieved would have to be analyzed on a
case by case basis.
Hope this helps. Let me know if you
need more.
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