If diesels are setup correctly it seems they can perform, many are sceptical because of there weight that they are no match for gas motors.

https://www.youtube.com/watch?v=TQ6f...K4kQ604ejSJ_aQ

Cool thread.

Thanks for sharing that Video Jay. I've not seen it before, but defiantly has the right sound we're going for...

When I was looking to do ASD8's and Duramax's in the 38' cat. The 2-spd ZF was once top of my list due to boat weight and transmission output shaft location. It's always a tough call between a single speed and a two speed behind new diesels. While I feel we could get these turbos lit by providing aeration to the props, you also run the risk of smoking like a cruise ship at lower speeds tying to light them.

My small boat with the 1:26:1 XR and 37p x 15.5" suffered from spool issues when I first purchased it. They had ditched the VNT setup for a GT4094R turbo. Just adding an air filter caused it to have trouble spooling, before switching to larger injectors.. But once you got on plane, it ran great. Reason I added a velocity stack setup after re-rig. I learned how fine that spool line can be in a boat. Where a two speed helps the spool time by allowing RPMs to build much quicker at lower propshaft speed. However, I don't need a 1.8:1 ratio 1st gear to accomplish this. That's what keeps screwing with the math.

Second issue I've ran into with transmissions is location of output shaft. While the ZF you posted above fits perfectly with the Arneson's, not so much with a 15-19" X-dim on a typical drive. Below is the gearbox setups out of the WMD's. On the left side we have reverse rotation unit, on the right [3 gears] is the engine rotation unit. There is a 6" offset from input an output shafts. Those "were" mounted inside the drive box for a 21" X, but can be move inboard to transmission end. However you still have to deal with 6" of height somewhere.

[ATTACH=CONFIG]558526[/ATTACH] [ATTACH=CONFIG]558527[/ATTACH] [ATTACH=CONFIG]558528[/ATTACH]


To get the prop where we need at speed, the drive input shaft sets 17"+ above the bottom. With the old #6 that would been 18.6". But now we add a 6" gear case and are at 23" off the bottom. Meaning the engines get raised 4" from previous OEM height. These custom diesels have some serous rotating mass compared to a std BBC. If I could ditch those gear boxes, there is just enough room to lower the engines 2" and run a 1:1 final drive. Thus likely working perfectly with either a single Velvet or 2spd COAN trans setup. However, something's gotta spin backwards in there feeding one of these drives...

So rather than jack the CG way up, I'm playing with moving the engines closer together to cut a couple inches off that height. The dry sump gear boxes will operate at any angle. Then we maybe gain another inch with driveshaft offsets. But this is where the #6 drive would have been more plug and play friendly in this side by side vee environment. If these engine were dry sump, that would allow us to drop them straight down and lower the CG significantly.

[ATTACH=CONFIG]558533[/ATTACH] [ATTACH=CONFIG]558530[/ATTACH] [ATTACH=CONFIG]558531[/ATTACH] [ATTACH=CONFIG]558532[/ATTACH]

Here is a few pics of the first long block assembly.

[ATTACH=CONFIG]558534[/ATTACH] [ATTACH=CONFIG]558535[/ATTACH] [ATTACH=CONFIG]558536[/ATTACH] [ATTACH=CONFIG]558537[/ATTACH] [ATTACH=CONFIG]558538[/ATTACH] [ATTACH=CONFIG]558539[/ATTACH]

Engines looking great are you going to dyno it when ready?

Yeah just waiting to pick up all the powder coated parts then it's off to the dyno. Took a bit of time, but I found someone with a correct setup to run them loaded for extended periods.

Sound great can't wait to see the figures.

I have been through all of these headaches you are experiencing trying to get my engines as low as possible.
I ditched the BBC offshore engine mounts and fabricated aluminium channel for the outboards mounts and fabricated large aluminium hanging brackets bonded to the tunnel for the inboard side as I didn’t want to drill mounting bolts through the inside of the tunnel .This enabled me to mount everything cleanly without compromising the strength of the tunnel itself and allowed the engines to sit as low as possible.
I still didn’t get them as low as I wanted as the ZF305 has a sump that is 6” lower than the output centreline, causing my X to be 2-3 higher than I would like.
One consolation is that my drivers are sitting on a ten extension boxes and the BPM stern tube is 6” longer than a regular Arneson so my prop is 16” further back than a regular setup, my props are running in cleaner higher water.
I thought I would try the setup out before make any further alterations, worst case scenario if the X turns out to be too high is to run ASD8-6 boxes.
Are you running solid or shear mounts? I went for shear but we will see how they perform.

I hope you don't mind me posting on your thread, just wanted to share my experience incase others do a similar build.

No problem Jay, I appreciate advice from anyone who's done this type setup before. Believe me I've hit up all my buddies in the industry multiple times. Most still answer my calls, so must be at least somewhat interesting project... lol

I've already spent more time on driveline setup than I ever expected. The boat was rigged offshore solid front and rear plate mounts at a standard #6 height with Merc mounts. Being a plug in setup, this also meant things were set further towards the transom. Moving things forward a couple inches wouldn't be a problem, if the stringers were symmetrical. However the center one was reinforced only where front mounts bolt up. Moving the engine mounts forward only an inch means glass work.

[ATTACH=CONFIG]558687[/ATTACH]

I thought we had a couple good height compromise locations picked out by setting the engines closer together. Then these two boxes I'd been waiting for showed up. The headers are 1.5" wider than I expected, cutting out the option of moving these engines closer together now. Even with custom oil pans, can't get low enough either because the bell housing hits another stringer. So,, the choices now are raise them 4", or stagger them.

[ATTACH=CONFIG]558688[/ATTACH] [ATTACH=CONFIG]558689[/ATTACH] [ATTACH=CONFIG]558690[/ATTACH] [ATTACH=CONFIG]558691[/ATTACH]

Time to pester some pros again. :readinghelp: