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SilverBack
01-10-2008, 07:53 AM
I just saw one of these on ebay and was wondering if anyone has tried one on a single engine BBC Z boat?
I found a thread from a couple of years ago where they were talking about sterling boxes but not about IMCO. They were talking about BH drives and not others also.

I am interested mainly if you have run one the 3" of lift.

Does this do better than just running a shorty? What about the steering? Do you have to go to external steering?
Thanks!!

http://www.diamondperformanceparts.com/product.php?productid=16820&cat=258&page=2

http://www.offshoreonlyclassifieds.com/extension_box_with_torsional_drive_line_diamond_pe rformance-o20602-en.html

The Hedgehog
01-10-2008, 08:10 AM
You will need steering for the box. From what you sound like you are doing you will need it anyway!

I would love to know the answer to that. I would also like to know how the 26ZX hull likes them.

I hear that step hulls seem to like them and when it comes to non-step, some do and some don't. There is a guy on OSO that spends tons of time in research dialing in his 90+ mph Baja, it hated the extension box. I talked to a guy that put one on a Stingray and it loved it.

I have my engine out right now so it would be a great time to know.

SilverBack
01-10-2008, 08:17 AM
BGZX
I thought that you would already be looking into something like this when I saw it. I was talking to Scot V (HorbourMaster) and it sounds like it might be just as easy to reglass the transom and raise the X. If you already have everything apart it may be just as easy and about the same price.

I am new as you know and these looked interesting to me.

The Hedgehog
01-10-2008, 09:23 AM
BGZX
I thought that you would already be looking into something like this when I saw it. I was talking to Scot V (HorbourMaster) and it sounds like it might be just as easy to reglass the transom and raise the X. If you everything apart it may be just as easy and about the same price.

I am new as you know and these looked interesting to me.

I have looked into it.

You can reglass the transom and raise the X. That works well on the classic hull. Once Donzi started putting steps in the hull they raised the X themselves. Any higher for me and I will blow out. That is probably why I will go with an IMCO lower in standard length. Jamie is having issues with that on his big power ZX and is having to space his drive down.

I considered doing it on my x-18 when I was redoing the transom and it would have been a free 5 mph. Well, nothing is really free. I would have sacrificed some drivability and then had clearance problems with the hatch. Since I already had a Bravo drive, I decided I could always throw a shorty on later. The other downside is that will bring that heavy engine up 2-3" raising the CG.

One of the reasons that the extension box works well on a step hull is allows for a higher X since the prop is further behind the hull turbulence. This is the same reason notched transoms benefit speed. This has some benefit on a non-step as well.

One thing to consider when playing with the x and boats longer than 22 feet is bow lift. Higher x (or shorty) = less leverage below the surface. If you can't carry the bow, the hull drag will offset the reduction in parasitic drag you get from reducing the amount of lower unit in the water. It will also likely bow steer and have a host of other handling issues.

Will it work on a 24? I dunno, but it is certainly worth looking into. If you like to do some work, play around with a bunch of props and spacers it would be a fun exercise. Brian Rose did the shorty experiment on his 27ZX and picked up 2-3 mph in the end. He and I are both kicking around the extension box idea. The reason I like the shorty idea is that if it does not work, you can sell it all and go back to stock. You can do it with an extension box too but the work will be a major PITA.

One more thing to consider is that a IMCO lower has a hydrodynamic benefit over a stock merc. I am guessing that this comes into place somewhere in the high 70's - low 80's. Big Griz has done some testing on this and probably knows the mph benefit. Maybe he will chime in.

MOP
01-10-2008, 10:31 AM
BGZX
I thought that you would already be looking into something like this when I saw it. I was talking to Scot V (HorbourMaster) and it sounds like it might be just as easy to reglass the transom and raise the X. If you everything apart it may be just as easy and about the same price.

I am new as you know and these looked interesting to me.

The nice thing about the boxes is the engine stays low and no modification is needed to the hatch, something to think about.

Phil

BlownCrewCab
01-10-2008, 10:48 AM
We added stellings box to a 24 Corsa (former Hogs Breath) no step, but did start with a 3" high X. the box didn't give any more speed, but did LOSE the ability to carry the nose. which in some rough water conditions wasn't too bad cause it wouldn't fly the nose bad when launching off a wave with positive trim. Boat owner thought it was/looked cool and he was payin so I put it on for him.

SilverBack
01-10-2008, 10:52 AM
Blown Crew Cab,
I thought crew cabs were always faster with a turbo??
I saw that you sold your boat. It looked like it would really run!! Where are you in TN? Are you working on any other projects?

BlownCrewCab
01-10-2008, 11:55 AM
I actually decided on a STS Turbo, at the last minute decided to go with the Magnuson supercharger cause I wanted my power right now, not waiting for it to spool up. it couldn't have worked out better, I have smoked a turbo porsche, a drag car camaro, numerous others. as far as projects go my next will be a cat 21, 24. the wife didn't like to chine walk, so I'll get somthing about 30mph faster that doesn't chine walk, won't she be suprised :)

Pismo
01-10-2008, 03:57 PM
I would think to raise the x it would be better to go Imco Shortie and leave the engine where it is. Keep the engine CG low. Reglassing is major work comparatively and you cant go back to stock if it doesn't work.

BlownCrewCab
01-10-2008, 04:48 PM
running a boat with a 2" high X dimension isn't exactly the same as a boat with a 2" shorty drive. where the transom assembly is mounted on the transom has subtle differences. the higher assembly pushes the boat forward from a higher point which in turn helps hold the nose down. (just from lost leverage) where a standard set up using a shorty drive pushes forward from a lower point. if I had a choice I'd allways go with the higher X, but thats just me, I don't like the nose flying in the air when jumping waves. and you can allways put a spacer to go back down. yes the motor is higher, and the longitudinal cg is higher, but only 2 inches, not somthing you'd really notice unless you took all your turns on the edge of control (which somtimes I do :) ) Maybe I should get a partybarge instead of a Cat.