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  #61 (permalink)  
Old 01-27-2012, 06:03 AM
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Thanks for the response.

Im familiar with ZF's being able to turn both ways under full power. For a future project, I may consider building a LH engine in front of such a tranny.

For this one, the motor is done, with all of the RH components already in place (save for the cam). They arent necessarily hard to find (if you know where to look), and with the exception of the cam, no more expensive. Ive heard good things about the ZF, but the BW 72c is tried and true, especially in front of a big block.

To swap the rotation of this engine, Id be looking at a new timing set, starter, rear main seal, and transmission. Im also unsure of the ZF's length- we may need to pull our shaft and adjust the length too, if we swapped out the BW. All those items would cost well beyond the ~$500 premium for the RH roller cam (as compared to a regular LH roller)... not to mention, a lot more work. I think we'll stick with a righty for this project.

Just gotta make a decision on the cam!

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  #62 (permalink)  
Old 01-27-2012, 06:06 AM
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This guy knows 50 MPH on water is fast!!
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  #63 (permalink)  
Old 01-27-2012, 07:52 AM
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Ok well the 72c is a good trans. I see your point,you would defenetly have to shorten the shaft
Ive seen them behind 6V53 Detroits n they hold up.
Ok on sticking with what youve got,have you checked to see if you can change the BWs input rotation by just moving the thrust washers from front to rear or vice-versa,I know on big trans thats what we do.
Just for curiosity.Do u run the the spring torsional coupling on the 72C or a centa or vulkan?
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  #64 (permalink)  
Old 01-27-2012, 08:08 AM
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Quote:
Originally Posted by topwrench
Ok well the 72c is a good trans. I see your point,you would defenetly have to shorten the shaft
Ive seen them behind 6V53 Detroits n they hold up.
Ok on sticking with what youve got,have you checked to see if you can change the BWs input rotation by just moving the thrust washers from front to rear or vice-versa,I know on big trans thats what we do.
Just for curiosity.Do u run the the spring torsional coupling on the 72C or a centa or vulkan?
Another consideration I neglected to mention is clearance to the hull... anything bigger than the 72C wouldnt fit- its within 1/2" of the bottom of the boat. We also have minimal clearance between the output flange of the trans and the shaft log... just barely enough to fit the dripless packing system in there.

You can switch the direction of rotation on the velvet drives by indexing the pump. But you cant spin them full power in reverse. EI, the rotation of the engine (in fwd) has to match the direction of rotation of the prop. To turn a RH prop (required for proper performance with this hull), you need to turn a RH engine (with a BW), or find a trans that switches the direction of rotation (like a ZF Hurth or a PCM 1.23:1), allowing you to use a LH (standard rotation) motor.

Im not familar with your terminology (spring torsional coupling, centa, vulkan), but the transmission mates to the engine with a spring loaded damper plate, which we replaced with new last year. We do not use any dampers between the output coupling of the transmission and the driveshaft- these are not required on boats this size. When used in this application, its oftentimes a bandaid to cure the symptoms of a bad engine/trans damper or misaligned powertrain.
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  #65 (permalink)  
Old 01-27-2012, 02:54 PM
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Ok man I see what ur saying,the BW is what we call a Coaxial transmission rather than a drop down where the output is below the centerline of the crank by about 4 inches or so.
The damper you have in your BW trans,we call that a torsional coupling,on bigger transmissions it is either rubber or silicone.
But you probly dont need all this info,anyway good luck with your boat.
Its a nice one!
Most people dont realize just how much horsepower it takes to push a boat to 50MPH a 72 footer with a pair of 2000 series MTU engines is about 45 MPH at WOT at about 160 gallons an hour total fuel consumption.
ZF Marine bought my company out in 2000 n im long gone from there.
I still however work on go fast boats with big Diesels.
Regards Al
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  #66 (permalink)  
Old 03-04-2012, 07:41 PM
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I have a Velvet drive on mine and it's standard rotation. I could get a number once the snow melts off the cover.

I put a Comp XS268s solid flat tappet in mine because It was laying around, At the same time I bolted a set of L29 Vortec heads on the stock bottom end after rings and bearings, some roller rockers and a performer intake.

I never did like the angle the carb sat at so I bought an angle spacer or tilt shim that Glen L sells, http://www.boatdesigns.com/Tilt-Shim...ctinfo/90-410/

While apart I also wondered how you could get the oil to the dipstick full line without the crank running in oil all the time, after confirming it wasn't possible I built a larger sump , kicked out and level with the bottom of the boat.

All I can say is WOW and no issues getting to 58 mph... My Eliminator might be a little lighter than your boat but not by much. It's amazing.. Love it! and not as nice an engine as yours.
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  #67 (permalink)  
Old 03-04-2012, 07:52 PM
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No need to pull the numbers off the Velvet- all of them can be spun in either direction. You just need to index the pump correctly. Yours spins LH because its bolted up to a LH engine. Mine spins RH because its bolted to a RH engine. What it cant do is change the direction of rotation... so the prop rotation (which I am keeping RH) needs to match the engine rotation... thus, the RH engine.

58mph out of a ski boat is serious. HP is only part of the picture though- a fast hull will make up for lack of hp. I know of a 17' wooden inboard produced in the early 60's with a stepped hull that would run in the mid 50's with a stock 210hp y-block.
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  #68 (permalink)  
Old 03-04-2012, 08:01 PM
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Quote:
Originally Posted by TRBenj
No need to pull the numbers off the Velvet- all of them can be spun in either direction. You just need to index the pump correctly. Yours spins LH because its bolted up to a LH engine. Mine spins RH because its bolted to a RH engine. What it cant do is change the direction of rotation... so the prop rotation (which I am keeping RH) needs to match the engine rotation... thus, the RH engine.

58mph out of a ski boat is serious. HP is only part of the picture though- a fast hull will make up for lack of hp. I know of a 17' wooden inboard produced in the early 60's with a stepped hull that would run in the mid 50's with a stock 210hp y-block.

Yeah, that's what I was thinking but had to check. and my I thought you could change the pump direction. http://www.velvetdrive.com/techinfo/V7172/V7172pg1.pdf

why don't you want to change the direction of your motor? Drivers seat on mine is on the right hand side.. Perhaps not ultimate but I don't think it's really noticeable.

Last edited by airboat; 03-04-2012 at 08:08 PM.
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  #69 (permalink)  
Old 03-05-2012, 08:03 AM
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Never-mind, re-read the whole post,
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  #70 (permalink)  
Old 08-31-2012, 06:32 AM
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OK, time to bring this thread full circle...

After mulling it over, this spring we decided to bite the bullet and go with a custom RH roller cam. We freshened up the heads as well, with new Ferrea valves (SS intake, their version of inconel on the exhaust). Cam specs are on the order of .604, both I/E. With our high-ish (cam builder came up with ~10.4:1) compression, he erred on the side of a larger cam, in hopes that the longer duration would keep cylinder pressures down. Something to consider on a marine engine that is always under load, he explained (this guy does solely marine engines). HP is estimated to be in the ~480hp range.

Got it all buttoned back up last week with new custom Manton pushrods, and it we did final assembly this weekend. We still need to play with props a bit (we're not hooking up great with the 3-blade 13x14), but it pulls strong all the way to 5700rpm and just over 62mph on the GPS (best of 62.8mph thus far). It pulls a decent number of guys out of the water pretty strong too- so it will serve its purpose. Feeling pretty good about having it back in the water at this point!
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  #71 (permalink)  
Old 08-31-2012, 07:13 AM
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From Sunday... we had more pulling power than we had barefooters, but here's a 5-man attempt.

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