View Full Version : New motor, first start today (vid) BBC 468, 10:1

04-07-2012, 10:21 PM
So for those who have followed my 24' Black Widow purchase, I obviously decided to trash whatever was in the thing (rusted up Gen VI, looked stock - not sure how it got so nasty for a fairly new motor! bent exh. valve, water in oil, etc etc)

We finished throwing together the accessory system and ignition pieces today and finally started her up. I bought the engine from a friend and it had already been run-in a bit on the dyno (months ago) but it was nice to see everything come together today.

I finished cleaning the bilge and re-running some new electrical to the dash area, as well as checking operation of the bilge and float. She could be in the water within a week!!!! :nilly:

Some info on the build: assembled by Gardener Performance @ .060 over to 468. .510 lift and 226 deg. intake and 236 deg. exh. @.050 on 112 centerline, roller rockers, all forged internals, dimple rods, SRP 10:1 pistons, heads are GM Perf w/ inconel valves, Sea Demon 830 carb, stainless marine exhaust.


This is my first DONZI, first I/O boat, and first big block V8 - so excuse my enthusiasm haha I'm freaking excited.

Morgan's Cloud
04-08-2012, 08:18 AM
Sweet .. Nice looking/sounding motor .

Just a tip though , and maybe a clue as to what might have messed up the original motor .

In single installations as you go up in size in a deep V the engine height in relation to the waterline gets into the danger zone and you need to go with extensions on the risers to keep them up high.

I've seen a few boats loose their engines this way ... from the factory , and one was even a Donzi !

04-08-2012, 08:38 AM
I highly suggest you get at least 8" longer tails with that camshaft with the water exiting at the end of the tails..... if you look CLOSELY at your video, your clearly getting reversion just running it on the hose....


04-08-2012, 09:10 AM
You say roller rockers! Is the cam a flat tappet? If it is a flat tappet it should have been run up to 18-2000 RPM for about 15 minutes, they rely on splash for initial break in with a roller it does not matter. Once you get it in the boat you need several hard pulls to seat the rings, don't baby it or it will be a smoker. No extended high RPM varied up and down is best for about 10 hours at which point an oil change is in order then have fun!

+1 on the risers real important!!!!!!!!!!!!!!

04-08-2012, 09:13 AM
Man just re watched the vid that thing is sucking up bad!

04-08-2012, 10:22 AM
Thanks for the comments and concerns anyone, it's great to look into this stuff before the boat hits the water. While I'm still not sure if this is going to be a buy/sell type of boat project, if I DO keep her I'd like everything to be bullet-proof so I can really enjoy this setup for a long time.

MOP - she's a flat-tappet setup and it was run-in on the dyno previously. Honestly that's not the "real" first start video :jestera: - it wouldn't idle at first and we changed a few things, but my tech did mention not babying it when I start the engine.

How will a motor like this handle extended idle situations? There's one boat ramp through a no-wake creek here and it takes ~20 min to get out into the bay. I'll run her on Lake Anna with my friends so I can continue the break-in, but I'm thinking down the road.

I'm looking into the reversion issue. Are you talking about at the end of the video when the motor is coming back to idle and the water stops coming out? I did notice that some weird things were going on - I honestly thought those weren't my tails and was a little shocked when I realized that's all they are!

I'm going to contact SM and ask if this has been a problem in the past and if they have some other risers. I'll measure my clearances as well. The previous motor was very basic and while it was a 454 it was probably running ~330hp (Vortech motor though, so probably some serious torque) - looked like a stock GM Vortech 7400 roller cam which I doubt had the kind of overlap to suck in the water. The bent exhaust valve is still our #1 culprit for most of the damage. People on forums mention everything from x-pipes to thru-hull water dumps and all kinds of other stuff.

04-08-2012, 10:29 AM
Morgan's Cloud - took me a second to digest what you were talking about but I think I've got it now. Besides the water "creep" and extended tail/riser issue, is the waterline comment related to coming off-plane and situations where it would be easy to suck up water?

I'm rather surprised how high the exhaust holes are on the transom, couple " above the top of the transom plate. I don't even know how she sits in the water yet honestly. :bawling:

Morgan's Cloud
04-08-2012, 11:26 AM
Yes , if the engine is too deep in the bilge without high enough risers the exhaust level on the transom is too close to the waterline. It can create problems when coming off plane and just when at a standstill with load shifting moving rearwards in the boat.
It can especially create trouble when trailer launching on steep / short ramps too .