OMC 56 Oval Port Specs.....Some very suprising results

[filthy phill]

Well today I got a bit of a shock when delving deep into the oval port triple block.
I measured all the ports on my 1995 oval port 56 motor. Cylinder block part number 0436908
I have read on a few places about how much smaller the oval exhaust is compared to the bridgeport exhaust. !!!....err thats not exactly right ...
Maybe some people need to get out their measuring tools before making such inaccurate statements.
The standard fishing motor oval exhaust is WIDER than the sst60 spec for APBA, the other ports are also slightly wider. ?
here is the results
sst60 exhaust width of each port is 1.075 x 2 = 2.150..........oval exhaust width is 2.185039 ( 30.5 thou wider )
sst60 Boost port max width is 1.255...................................oval port boost port is 1.29921. ( 44 though wider )
sst60 Transfer port max width is 1.5800........................... oval port Transfer width 1.633858. ( 55 thou wider )

Sst60 minimum exhaust port height from deck is 1.450 and max 1.520.......oval port height is 1.500 standard ( lower by 50 thou )
sst60 boost port height min.....1.860 and max 1.950..................................oval port boost port height 1.88976 ( within sst60 spec )
sst60 transfer port height min... 1.825 . and max 1.890..............................oval port transfer port height 1.948819 ( lower by 104 thou)

Not sure if the sst60 measurement for transfer top is with or without chamfer ???

exhaust and transfer port roofs are up higher than the sleeves, so are capable of being taken up to sst60 spec.


Going by these measurements, with a bit of work on the exhaust and a touch on the transfer port height, the oval port would be able to breath as good as
the sst60 motor than sst60.


ALL the ports behind the sleeves need to be cleaned up a lot and the sleeves themselves have some terrible edges on some of the top of the ports that are
more like a serrated knife edge than a proper nice clean port, they definitely could do with smoothing out.
OMC realy did not take any care when assembling the 56 oval port motors, no attention paid to detail at all.
Sleeves look like they have been put in without them being finished off nice.

The exhaust from the bottom of the block itself needs to be cleaned up inside as far as possible to get rid of some very bad casting marks, this can be
done with a small flexible shaft and brushes etc, not and easy task but it would pay off big time to let the gases flow better.
with the use of a tiny endoscope ( very cheap on ebay with 6 built in lights) a lot can be done to the exhaust as in polish it up to flow better.

for those who might be interested, I have made a sort of port map drawing to show the oval port versus the SST60 spec for APBA rules..
( nothing like true map or scale) just to show the port sizes and heights.