| Author |
Message |
    
david
Member
Username: olmo40
Post Number: 8
Registered: 04-2008
| | Posted on Sunday, May 18, 2008 - 02:43 am: | 
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Hypothetically ,Anyone know what max compression i could run safely in a 15hp Merc 2 stroke . |
ikia
Visitor
| | Posted on Sunday, May 18, 2008 - 07:08 am: |
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Not sure why you are asking this question, are you looking at doing some modifications??? Like shaving off some of a cylinder head that does not exist. |
david
Member
Username: olmo40
Post Number: 9
Registered: 04-2008
| | Posted on Wednesday, May 21, 2008 - 09:21 pm: |
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These motors dont have cyclinder heads ,However there are 2 3/16 or there abouts holes in the exhaust side of the motor under the exhaust plate ,im told you can block these up to increase compression ,i was wondering if this was a safe modification |
Graham Lamb
Senior Member
Username: galamb
Post Number: 3220
Registered: 05-2007
| | Posted on Wednesday, May 21, 2008 - 11:28 pm: |
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Are you trying to reduce horsepower?? That's what your idea would accomplish. This is a two stroke and needs to inhale and exhale unobstructed.... |
david
Member
Username: olmo40
Post Number: 10
Registered: 04-2008
| | Posted on Thursday, May 22, 2008 - 12:08 am: |
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Not trying to decrease hp,A dealer told me the 2 holes were to make it easier to start,blocking these up increased compression and performance?? |
Graham Lamb
Senior Member
Username: galamb
Post Number: 3221
Registered: 05-2007
| | Posted on Thursday, May 22, 2008 - 02:38 am: |
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Well I own a 1991 15 horse and have played with it and my pair of 9.9's for years. Have also taken alot of guys money to upgrade, hop up and improve the performance of their small Merc's because "some guy" told them it could be done and they wouldn't let me talk them out of the changes.
But let's get serious here. It's a 15 horse motor. A good tune up and a properly matched prop will do far more than trying to make any mechanical modifications to the motor.
I run mine on a 14 foot deep v hull. It pushes a total weight of about 700 pounds including gear/junk and me/wife.
With the 9.9 on the back my gps marks a top speed of about 17 mph.
With the 15 on the back, on a good day can get 20 mph.
Think about that for a second. A 50% increase in horsepower in this range results in a 3 mph gain at absolute top end.
You are talking about playing with a 16 cu in powerhead, you aren't going to get much more horsepower out of it no matter what you do - it's already at it's realistic horsepower limit - barring "major" modifications.
What can you seriously expect to improve upon by blocking a couple of holes - certainly nothing that you will notice in terms of "on boat performance" - you can't turn this into a 20 or 25 horse.
So why run the risk of possibly damaging the engine. If you really want more power, sell it and buy something bigger...
Any chance that dealer was trying to talk you into buying a new engine????? |
david
Member
Username: olmo40
Post Number: 11
Registered: 04-2008
| | Posted on Thursday, May 22, 2008 - 02:52 am: |
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Good advice .It just didnt sound right to me hence my post,when you are not an expert like me a little bit of advice can be dangerous.Think i will go and polish the bottom of the hull.He wasnt trying to sell me anything said he had done it to another motor and it made a noticeable improvement . |
Graham Lamb
Senior Member
Username: galamb
Post Number: 3223
Registered: 05-2007
| | Posted on Thursday, May 22, 2008 - 03:00 am: |
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The most noticable improvement I have ever seen on these is by adding a thermostat. Merc saved a few cents on their 15 horse and under models by leaving them out at the factory.
For 20 bucks you will get a way nicer idle and save a bit of gas to boot.. |
david
Member
Username: olmo40
Post Number: 12
Registered: 04-2008
| | Posted on Thursday, May 22, 2008 - 03:08 am: |
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Got one thanks again |
