12V71TI's to 12V71N's

[Walter P]

If your plan is to only do displacement speeds then I would NOT remove pitch, in fact adding some would probably be better since the operating temperatures would be about where they should be at 170 - 180. I understand that 160 will not do any harm either, but be careful of much less temp. Of course more pitch will present it's own set of issues at higher speeds, but you seem to indicate low speed pretty much all the time.

Perhaps the best thing would be to take care of those iron monsters and don't try to re invent the wheel.

Walt

[kwerges]

Sounds like (should the deal work out) we leave them alone and enjoy the boat as Hatt designed it. Randy, I'll be in touch to get Carl's numbers. Thanks...

[Boatnut]

Agree with the others - don't bother trying it. There are significant differences with the most-significant being the cylinder heads and kits. While it is certainly possible to put "N" cylinder kits into a turbo motor and remove the turbos (and then re-injector much smaller) I wouldn't do it.

If you're looking to detune the engines for longevity purposes the easiest way is to take a couple of inches out of the props. If you're looking to be able to run at hull speed without the loading being too light (and temperatures in the engines being too low for good service life) there's no simple solution that doesn't severely-compromise something else. The easiest answer is to accept operation in the bottom of the "transition" zone, typically around 1100 RPM, which will be materially above hull speed but present enough load to keep the engines reasonably happy provided you run 'em up to cruise power for 15 minutes or so toward the end of the day.

If you're running 10kts you're likely into the transition range - so long as you can keep water jacket and EGTs in the safe range (and you probably are with that operating regime) you should be fine.

Over 5,000 hours and then 3,300 more on the rebuilds (thus far) sounds like the owner knew what he was doing and is both set up and being operated in a reasonably-conservative fashion, assuming we're talking recreational service. I'd leave it alone.

I don't understand how smaller props will detune an engine, if this in fact true as I honestly don't understand it, but does this mean I can detune my grandsons hot rod car by putting smaller tires on the car? I really need to slow him down.

[Genesis]

Less pitch = less load presented to the engine (smaller = less pitch, not smaller DIAMETER necessarily)

[rsmith]

Ever see what the truckers do in winter they put cardboard over the radiators. If your that concerned about temps bypass some of the raw waterflow to the heatexchanger. Peronaly Even at 550rpm my engines come up to over 140 and I've trolled thousands of hours at 850 and never had a problem.When I Rb the engines at 6500hrs the heads and valves were clean.If the injector tubes had'nt been starting to leak I would have kept running them.

[saltshaker]

Ever see what the truckers do in winter they put cardboard over the radiators. If your that concerned about temps bypass some of the raw waterflow to the heatexchanger. Peronaly Even at 550rpm my engines come up to over 140 and I've trolled thousands of hours at 850 and never had a problem.When I Rb the engines at 6500hrs the heads and valves were clean.If the injector tubes had'nt been starting to leak I would have kept running them.

My 8V71N's would hold temp once warm but my 6V92TA's cool off to around 125 once you slow down under 1000rpms. I even put in different thermostats but they don't keep temperature up.

[Boatnut]

Less pitch = less load presented to the engine (smaller = less pitch, not smaller DIAMETER necessarily)

Let me try this again. I do not understand how lowering the load on an engine detunes it, seems to me the engine is still capable of producing rated HP. Detroit advised me that the best way to reduce power is to reduce injector size if possible.

[rsmith]

Let me try this again. I do not understand how lowering the load on an engine detunes it, seems to me the engine is still capable of producing rated HP. Detroit advised me that the best way to reduce power is to reduce injector size if possible.

Reduce the injector size and youl run lean and burn up the cylinders

[Ross Macdonald]

Just got in from a 10 hr. run at 1250 RPM. 16 GPH on the floscans. 12-71 tis. Manual guage temps 170 and heat gun shot on thermostats every hour during engine checks was 168. Don't know if that helps, but those were pretty steady over the 2 month cruise. We run stock 32x32 4 blade wheels. Ross

[Boatnut]

Reduce the injector size and youl run lean and burn up the cylinders

Makes me wonder why they make all the different size injectors. I'll have to discuss this reply with the Detroit guys as they are the ones that reccommended the resizing to me. given your responses maybe the not comming up to temperature might be caused by to rich a mixture, keeping the engine cool. I still don't understand how lowering the load detunes the engine.