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Marinizing 7.3 Powerstroke's Is there a kit for this?

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Old 11-30-2007, 01:01 PM
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The problem with the drives is not whether or not they are strong enough it the gear ratios. That's why the Condor that is for sale is slow.

I'll give you an example of what I mean and why the strength of the drive is less not the main problem.

T = 5252 x HP / rpm - so as RPM's go up T goes down.

When you run your gas boat it turns 5,500 rpms throught a 1.5:1 reduction = prop speed 3,666 rpm right?

Take that 7.3 L that turns 3,500 rpms through the same 1.5:1 gear set = prop speed 2,333 rpm right?

What we & the Europeans did was to increase the prop speed with overdrive boxes. Go back to T equation on top, if I speed up the RPM's before the outdrive the outdrive sees less T. An outdrive only knows T & RPM not what is making those numbers.

The only trick to making a diesel boat fast is prop speed, not stronger drives, bigger props, etc, etc. We always argued the bigger prop theory - the bigger the prop the more strain and the harder to throttle, engine can't respond quick. It goes back to blower vs turbo. A blower makes constant boost controled by RPM a turbo makes boost by exhaust heat - once you life the throttle you loose the heat, loose boost the bigger props make it worse.

We even had Speedmasters (he still have them) make us a set of O/D TRS drives by truning the top gears around (I know it's not simple, you need make bushings for the small shaft and turn the latger down). These were never tested as a simple O/D box on the tranny allowed us to run 1:1 drives such as #3, 4's etc.

If anyone wants to tackle a diesel preoject I have notebooks full of data and would love to help you out.

Joe
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Old 11-30-2007, 03:13 PM
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I'm a turbine guy, not diesel, but wouldn't it be better to utilize the Cummins 6-cylinder than the 444? They adapt much better to mods, and as everyone should know, a 6-cylinder engine has a significantly better power overlap than a v-8.. Weight is weight, and diesels are heavy, so why not go with one that makes more hp and torque?
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Old 11-30-2007, 03:39 PM
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jafo

Your right about the Cummins B better engine. In theory the 7.3 should make great power. Back in the day we could run a mechanical 7.3 at about 380 hp hour after hour after hour on the dyno and that took 2 years t get it there. You can never get real hi-HP from a 7.3 for long periods of time. The PC style heads can't make great power and the more you push them they'll crack. With DI heads those engines have alot of potential.

We made a supercharger manifold for 7.3 once, it worked fine by couldn't get enough boost no matter we tried - the concept though was great.

Maybe today with those Whipple chargers it can work?
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Old 11-30-2007, 07:36 PM
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mercruiser used the 7.3 for a few years i'm sure all the parts you need are around somewhere
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Old 11-30-2007, 09:08 PM
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Quote:
Originally Posted by HabanaJoe View Post
What we & the Europeans did was to increase the prop speed with overdrive boxes. Go back to T equation on top, if I speed up the RPM's before the outdrive the outdrive sees less T. An outdrive only knows T & RPM not what is making those numbers.
Where did you get the overdrive boxes? Also didn't it require moving the engine forward to accomodate it?

Michael
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Old 11-30-2007, 09:36 PM
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Quote:
Originally Posted by HabanaJoe View Post
jafo



We made a supercharger manifold for 7.3 once, it worked fine by couldn't get enough boost no matter we tried - the concept though was great.

Maybe today with those Whipple chargers it can work?

didnt detroit diesel also try that on quite a few models
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Old 12-01-2007, 12:28 AM
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Quote:
Originally Posted by HabanaJoe View Post
a turbo makes boost by exhaust heat -
Wow, I had no idea that the heat from the exhaust was what made boost, I acutally thought it was the exhaust gasses that were exiting the cylinders that were spinning the compressor and building boost. Convection turbos sound cool!!!

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didnt detroit diesel also try that on quite a few models
Detroit ran the blowers on the old 2 strokes more as a way to keep an intake charge and clear away the spent exhaust gases and bring new air into the cylinders. The '71 models were straight blowers. The -92's brought in a turbo feeding the blower that actually built boost for more ponies.
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