increasing compression on a 59ci merc

[fs5]

hi guys ,i want to try raising the compression my 55 merc its basically the same as a merc 60hp.
i have a couple of ideas ,my first is fitting domed pistons.dose anyone know if anyone makes domed pistons for these motors?
the other idea i have is getting the block barrel bored.if i do this ,this will lower the the ports .if i went this way,i reckon i'd only take a max of .030 off .would this much have a real effect on the port timing?
also i was thinking of getting the pistons fluted to help raise the exhaust and lower the intake ports?
my motor is pretty much stock,it had a hone and a re ring and its done about 50 hrs .it only pumps 115 psi .i'm trying to get around 140+ out of it.
thanks for any help.

[proprider01us]

On my 44ci Merc, I had Jim Ruck crush the block. Not real sure how the process works but he was able to bring my block to the minimal cc's spec allowed in stock racing. Give Jim a call.

[zul8tr]

hi guys ,i want to try raising the compression my 55 merc its basically the same as a merc 60hp.
i have a couple of ideas ,my first is fitting domed pistons.dose anyone know if anyone makes domed pistons for these motors?
the other idea i have is getting the block barrel bored.if i do this ,this will lower the the ports .if i went this way,i reckon i'd only take a max of .030 off .would this much have a real effect on the port timing?
also i was thinking of getting the pistons fluted to help raise the exhaust and lower the intake ports?
my motor is pretty much stock,it had a hone and a re ring and its done about 50 hrs .it only pumps 115 psi .i'm trying to get around 140+ out of it.
thanks for any help.

Have you ever cc'd the stock combustion chambers with pistons at TDC? This info would be needed to see where your base cc's are regardless of how you intend to raise it. Easy to do with light oil and a graduated cc burette or a simple cc graduated syringe

If cc's are known it is an easy calc to get the compression ratio at full stroke as well as to the top of the exhaust port if the dimension is known to the top of the exhaust port from the crank case split surface (centerline of the crank). I assume this is a split crank case merc.

From there it is easy to calc an expected compresion pressure for an engine with good ring seal (and you can check the 115 psi you read) then you can see what cc's are needed to get you close to your desired crank pressures.

[fs5]

nah mate,i havn't cc'd the combustion chamber .i was kinda hoping someones been there done that before.i assume the 40/50/55/60 59ci motors run the same bock crank and pistons ,from what i have researched .
there's some good engine builders over there in the states ,but "NO" one dose anything with them over here.
on another note ,dose anyone know if the 60hp mercs have decompression ports?
thanks for your replies

[Lil' Blue Rude]

I'm pretty sure the 60hp do have the compression relief notch cut in the exhaust. The 2005 I looked at did.

[fs5]

I'm pretty sure the 60hp do have the compression relief notch cut in the exhaust. The 2005 I looked at did.
thanks mate

[Fastjeff57]

You can see that decompression port in this photo.

Jeff

[Jackson]

Doing away with that notch doesnt make much diff at all. It helps but u will never c a gain.

[sabine river killer]

you can swap them with the sleeves from a 55 seapro or take those out and weld up the slots and put the sleeves back in

[Jackson]

A 60 has the good sleeves already in it.

[fs5]

that pic looks exactly the same as my exhaust port .
jackson i have researched as much as i can ,and basically a 55 seapro is a 60hp other then timing and jetting.the only thing i can't find a part number for is the sleeves ???
when my motor was apart after flipping it,i posted a thread about modding it and was told to take the ports to the wall .i remember poking my finger down the block and there was stuff all between the sleeve and block casting ,i know it was only my finger but it would have been under .020 thou it just felt like a very small bur . ??? my mate doing the motor said not to worry about it?
thanks for your replies.

[Jackson]

that pic looks exactly the same as my exhaust port .
jackson i have researched as much as i can ,and basically a 55 seapro is a 60hp other then timing and jetting.the only thing i can't find a part number for is the sleeves ???
when my motor was apart after flipping it,i posted a thread about modding it and was told to take the ports to the wall .i remember poking my finger down the block and there was stuff all between the sleeve and block casting ,i know it was only my finger but it would have been under .020 thou it just felt like a very small bur . ??? my mate doing the motor said not to worry about it?
thanks for your replies.

That's what I'm trying to tell u is that they have the same sleeve. If u can send me just ur power head I can get the compression up and get alot more Hp and torque out of it for u.