| Author |
Message |
    
craig griffin
New member
Username: griffo0246
Post Number: 1
Registered: 11-2009
| | Posted on Friday, November 06, 2009 - 02:14 am: | 
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I have a 40 HP Mercury lightening XR outboard and it is a rebadged Tohatsu. The Tohatsu 40 and 50 hp are the same motor with different jetting, inlet manifold and throttle cam.
The 40 hp lightening xr has the 50 hp jetting and throttle cam. Though the inlet manifold restrictes the intake to half the size of the carby throat.
Is it just a matter of fitting a Tohatsu 50 hp inlet manifold to increase the HP? Or is it possible to cut/grind the inlet manifold restriction plate area to acheive the same result? If so to what size?
This will obviously be done after the warranty period expires. |
Fastjeff
Senior Member
Username: fastjeff
Post Number: 7089
Registered: 09-2003
| | Posted on Friday, November 06, 2009 - 04:38 am: |
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Obviously! Most manufacturers make their larger hp motors less so by restrictions (instead of visa-versa). I'll bet grinding the intake out would not be hard to do, but other restrictions might be lurking in there as well, like the exhaust tuner: it could be tighter.
Jeff |
JB
Senior Member
Username: beckerjs
Post Number: 2041
Registered: 11-2005
| | Posted on Friday, November 06, 2009 - 09:48 am: |
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Graham has had some good write ups on these mods. It goes something like when you take a xx motor and turn it into an xxx motor you acheive a 2% gain. That gain at WOT will net you 1-2 m/h increase. Long story short is its just not worth the time and effort or taking a chance of messing a perfectly good engine up. |
craig griffin
New member
Username: griffo0246
Post Number: 2
Registered: 11-2009
| | Posted on Thursday, November 19, 2009 - 05:28 am: |
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found out that it was losing power at WOT. Butterflies were going past horizontal and the timing was incorrect. The boat would do 29mph with the tide and wind but drop down to 25mph against the tide and wind. Once the throttle linkage and timing was fixed the speed increased to 31mph with tide and wind, 29.8 mph against the tide and wind.
I originally was not impressed by the performance of my new outboard, hence why I asked the question. Now that it is performing as it should, there is no reason to modify the engine.
Thanks for you input. |
jamie campbell
Advanced Member
Username: outboard_doctor
Post Number: 763
Registered: 02-2009
| | Posted on Friday, November 20, 2009 - 03:47 am: |
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Change the manifold or mod it will you notice an inprovement in accelleration and speed...it isnt going to cost anything and you dont often get something for nothing |
