1985 DD 6V92 TA turbo modification question

[joesig]

I was told that a modification was performed to the twin 1985 DD6V92 TA's on a boat that I am looking at by changing from air cooled to water cooled turbo's including the entire exhaust system, anybody ever herd of this modification? It's on a 42' Chris Craft .thanks, joesig

[Genesis]

Yes. I considered it (briefly) when I was already in the position of re-doing my exhaust (due to age.)

It's a hella-expensive changeover. It DOES produce a safer system (the turbo is no longer red-hot during operation) and allows, if desired, going to a bypass blower and cranking output a bit more (I do NOT recommend doing that) but it also comes with some minor costs including more rotating mass in the turbo and thus a slightly slower spool-up time.

The water-cooled turbo is a bit less efficient due to the lower temperature internally (energy extracted is directly related to the temperature delta across the turbo) but that's not a major factor.

Done with OEM parts (manifolds / riser components) I would consider this to be neutral to a slight positive in terms of configuration. The single turbo design was a later-year factory configuration, so this can be done "properly" rather than "garage-shop style" and if so, its fine.

The other factor is that the twin-turbo setup did have a minor issue with oil pressure and flow in that from the factory the turbos are fed off the opposite sides of the oil gallery. One tends to be OVERfed somewhat with oil which can lead to excessive oil bypass and consumption, and the other can be starved under certain conditions when coming down from high output to idle quickly. This risk can be controlled by reasonable operation (don't cut an engine running at high output straight down to idle if you can avoid it) and is a relatively minor issue as well. What would be ideal for the twin-turbo setup would be to feed both from the high side through a pressure regulator that held oil pressure at a constant 30psi or so, but I know of no reasonable set of aftermarket parts to do that, so I left mine alone and used the "judicious hand on the throttle" solution.

[joesig]

Genesis,
Thanks for the information on the turbo conversion question, All work was performed by a reputable Detroit shop using all Detroit parts (I have the receipts)about 4 years ago. All other DD 6V92 TA's that I looked at had the hot turbo design with the silver wraped heat shielding on the exhaust, I did not see this on this boat.
Thanks, joesig

[SKYCHENEY]

joesig,
Just curious, what did they spend to convert those over?

[joesig]

joesig,
Just curious, what did they spend to convert those over?

It looks like the parts alone were a little over $10K. The total was around $40K but a couple of other things were done to the boat during that repair.
joesig

[Genesis]

That'd be about right, plus the new exhaust collectors (!)

When I priced it the exhaust system + turbo changes ENGINE ONLY were about $5-6k PER MOTOR.

A set of exhaust collectors at the time was ~6-7k as well, so you're talking $15-17k for the PARTS, assuming you do the install (you can, its not hard.)

[Fanfare]

Not only is the turbo water cooled, so are the exhaust manifolds. This really reduces the engine room heat while running. The cooling stops when the engines do, but usually by then the engines have idled some and a lot of exhaust heat has gone. Switch on the engine room blowers or add exhaust fans and a huge load is removed from the air conditioning.

[REBrueckner]

When the exhaust manifolds develop and internal leak, can cooling water leak back into aft cylinders as it can in naturals?? That's a significant advantage in my mind for the standard DD "hot" turbo approach. If so it's enough to turn this configuration to a negative for me.

(subsequent Edit note: must have had a senior moment..I was thinking "riser" but posted "exhaust manifolds"...)

[Genesis]

Exhaust manifolds on Detroits with dry turbos are fresh-water (coolant) cooled - no difference there.

The risers on the dry turbo system are hotpipes and require insulation blankets.

Any coolant-cooled system is fine as it should outlast the boat provided you run properly-inhibited coolant (or water with proper inhibitors)

[SKYCHENEY]

Not only is the turbo water cooled, so are the exhaust manifolds. This really reduces the engine room heat while running. The cooling stops when the engines do, but usually by then the engines have idled some and a lot of exhaust heat has gone. Switch on the engine room blowers or add exhaust fans and a huge load is removed from the air conditioning.

Jim,
Are your 6v92's of the wet turbo design? It sounds like you have first hand experience.