I have my engine running good, its a fishing motor and is running as good as they come.
its got the large carbs and runs very smooth and picks up straight away, so pretty good.
hole shot is fantastic as too is the mid range, but I was hoping for a bit more top end rpm.
now I want more power if possible and I thinking upping the compression might be the only way to go for
just a bit more top end power without stripping the whole lot down.
Mine is the later 56 cu in oval port 3 cylinder with the one piece head (looks like 3 but is just 1).
There is no option for changing engines or messing around with port work ( apart from a slight angle on the tops)
The seam inside the block behind the sleeves will be gone, but will be keeping the exhaust reliefs for the idle so as
the engine can still be used for slow trolling when needed.
I have a spare cylinder head to play around with that needs skimming big time, the engine it came off was blown on the
middle cylinder and this head has some severe pitting on the middle squish area.
There is no pits at all in the combustion chamber itself, but this head would need around 1.5mm taken off.
so that's around 60 thou +/- a bit.
if the compression would be too high to run pump gas then maybe I can mill out the combustion chambers a
touch to compensate and bring it back down a touch.
the very deepest pits are 1.5mm
what I am after is as much compression as possible but has to run on pump gas !!!
AV100 is far too expensive here and hard to get hold of.
The compression and im getting at the moment is 141 -143-142, I am wondering what would I get with 60 thou
shaved off a head. ?
I know the sst60 has a thinner head than the fishing motor, but that also has a shaved deck/block to give its
higher compression.
I have been told before that the heads can have as much as 80 thou taken off without any problems regards the
water jacket. but I dont know if this could run on pump gas and what compression would be
so my questions realy are
1 /what amount of compression difference would I expect to get with 60 thou taken off
2/ would this then still run on pump gas. ?
3/ what sort of power gain would the higher compression give. ?
4/ how much thinner is a sst60 cylinder head to the normal fishing motor head.?
5/ can the combustion chamber be milled ? and by how much ?
6/ is there an option for thicker cylinder head gaskets available ?
I know its a lot of questions, but I am curious to is this worth trying to get more power, or atleast give me a
spare cylinder head for in future if needed.
getting spare heads over here is not exactly easy for the 56 cu in.
at the moment this is scrap unless skimmed by a good amount. 60 to 70 thou !!!
here is a couple of pics of the offending head, a friend of mine is willing to mill it when he gets his new mill.
WARNING THIS IS A SAD LOOKING HEAD THAT HAD BEEN ABUSED ( need to make it good again )
First, raising the compression will not give you more top end speed. You will gain low & mid range torque for better acceleration, but not gain on the big end. You can mill as much as .0125" or 3+ mm and not have water jacket issues. The SST-60 has a pocket depth of 0.450" +/-.010"
Glad to help.