Turbo is add on, 15-20 psi, runs great when boosts up, almost zero blowby at idle or revving not under load
The reason I asked about the turbo added to a non turbo engine is that there are a lot of INTERNAL differences between a factory turbo engine and a factory non turbo engine.
One: the compression ratio is
usually less on a turbo engine than a non turbo engine. Instead of 22 to 1 like the non turbo Kubota has to about 16-17 to 1 compression ratio.
Two: A turbo engine usually has oil squirters that are aimed at the crankcase side of the piston crown to quench the added heat out of the piston crown.
Three: The pistons are generally beefier to handle the extra load and some use steel piston ring lands cast into the piston.
Four: When a turbo is added to a non turbo engine, the maximum SAFE boost is around 5-7 psi MAX.
Why I asked about blow-by is to see if you didn't burn a piston or in the worst case, burn a hole through the crown of the piston. That's why turbo engines have piston quenchers AND a larger capacity OIL pump to give plenty of flow to the quenchers as well as lubricating the bottom end.
Five: A turbo engine with mechanical injection generally had a boost activated aneroid can on the injection pump that controlled the enrichment of fuel depending on boost pressure. If you look at an old, 5-cylinder Mercedes turbo engine, they had a diaphragm on the injection pump that hooked up to the intake manifold and sensed boost pressure. We used to break the seal on the aneroid and turn the fuel up a little bit. It really woke up the 5-cylinder Mercedes engine. Cummins also used the same principal to add fuel under boost on the 5.9-liter engines that were used in Dodge pickups. Both used Bosch injection pumps. I would turn up the fuel on the 5.9 Cummins too.
Looks like a neat set-up. Could you post some pictures of the whole watercraft?
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