-3 modification who can do this
 

I need to have the cavitation plates on my IMCO SC drives modified to run -3 lowers. Does anyone know who can do this?

WOW - your going all the way to -3. That is a serious change in prop height.

You trying to beat me in prop shaft height?

Ha- I was running -2 last season and I was still deep. I'm pretty sure I can pull off -3's, that will put my shafts 4.5" below the hull. I think you still have me beat!

WOW they were deep. That extra inch should make a noticeable change.

Yes they were, I started out at 7.5" below. Last year with the -2's I could still run Mirage props without any issues getting on plane. In big waves I had to work the throttles, but thats it. I only tested the Mirages, I never left them on. I ran Bravo's all summer and never once blew out the props. That told me it time to go higher!

Did you use a lot less trim with the shorter drives?

For the most part yes, Past 6 i really didn't notice any speed gain. It would have been nice to have run the boat with the old motors and the new drive set up to see what the real gains were, but that wasn't really realistic. I really think this extra 1" will make a difference, my drives were DEEP, which is one reason why I think these boats are not that fast with big power. Once I get the drive height correct I think I will see a bigger improvement in speed.

The Bravo Shop can do it.

Thanks! I'll give them a call.

I believe IMCO will do it also.
I know you can order a SCX upper modified to fit a -3 lower.

I called bravo shop today about it. They said, they have done it and never again. The cost would have been the same as just buying the -3 lower portion for the SC upper. The Imco is a split case and you can just bolt on a -3 section to change the cavitation plate. If that's the route I need to go, it will go back to a -2 and be done with it.

I didn't know what the mids cost and I just looked and saw they are about $1100 for the -3 mid section from Imco.
I'm sure by the time the Bravo Shop mills, re welds and paints them, he probably has at least 8 hrs into each one, so realistically, its just not worth it.

I just got a reply back from another drive shop and the quote was half of what Bravo Shop quoted me. But he said the same thing, it's a lot of time to mill and re-weld everything. $500 a drive may be worth it, in order to get the prop height up a little more.

I got a sawzall and some JB weld.
You got the beer.

Ha- I've been thinking the same thing. I have 3 IMCO SC's, and I've thought about experimenting with one of them. Either way, I have to decide what to do because it's time to buy the lowers!

Ok- I've been doing a lot of research on this topic, x-dimentions ect. the past few days. On the Power Play forum, one of the factory guys was discussing x-factor depths on the 33. When bravo props and dwp lowers came out, they raised the X by 1 3/8" and picked up 5-8 mph all things being equal. I know that there is big speed to be found with the proper drive height. With that said, I'm going to try and cut the upper over the weekend. I was looking at it last night and it doesn't look as difficult as people make it out to be. I've got three of these cases so it it works- great, if not- oh well. I'll report back on the progress!

I will be curious how this comes out. I am fixing to do the same thing but have not ordered my -3 shorty yet. The research I have found makes it look that a stock B1 upper can be modified pretty easy to fit the -3. I have not yet found any good pictures or write-ups to confirm that though.

Tinkerer has done that mod on his B1. If he sends me a picture I will post it. [email protected]

This is the modification to clear a Bravo prop.
I have since modified it further to fit a Maximus prop.
You need 1/2 inch clearance between the blades and the underside of the cav plate.

[ATTACH=CONFIG]566000[/ATTACH]

I will post a picture of the final mod. later.


It's later

[ATTACH=CONFIG]566001[/ATTACH]

[ATTACH=CONFIG]566002[/ATTACH]

The above fits a Maximus prop
I just bolted on the SS cavitation plate and cut off what hung below, removed the plate and then used a orbital sander to clean it up.
After you cut it off you lose the ridge that holds up the back of the cav plate so make sure you have at least 1/2 inch clearance to any prop.
The prop getting on plane causes a LOT of suction and will pull the cav plate down into the prop if it is not high enough. Ask me how I know.

What I have planned is going to work perfectly. My idea is similar to what you did originally. Have you noticed any ill effects with the flip up on the end of the cavitation plate? I believe the SX4 is very similar to that.

OH and I took the sawzall to the back of my prop also.
This is my OLD bravo 28 that is off of the SCARAB and it doesn't owe me anything. I figured I would do all of the experimenting on this on. Then I ordered a new one like it from BBlades. New one is a 30 though.

My props are SO high it doesn't do much at all. It is there more to shield the prop - labbed props are sharp.
Anytime I pull up to the beach I make sure to tell anyone that is near the back of the boat to be very careful because my prop is much closer to the surface not four feet down.

Well I'm going to order some aluminum plate and make my own bolt on cavitation plate. I'm going to build it similar to how merc build the sportmaster plate. They have it also bolt to the rear of the housing as well as to the existing cavitation plate. That way, you don't get the sucking issue you were describing above.

As for your drive height statement earlier I tend to agree.
Last year I was having a conversation with two other owners of 26 Daytona's and they both had approximately 800 to 850 HP. They were doing 95 consistently that I was doing with one of YOUR engines ( 650 HP ) I now have the same HP as they had and I can do 108 with half tanks anytime and 112 under ideal conditions.

Ideal drive height does have one drawback though. My boat wouldn't get on plane at all with a 4 without the extra negative trim mods. It would get on plane with the Maximus before the negative trim mods about the same as it does now with the 4 blade.

Yes, building more power is only half of the equation, look at your scarab vs my formula. Mine is smaller and a bit lighter, but as of today, 7-8 mph slower with the same engines. I'm willing to bet that I'll make up most of that with the right drive height. Better exhaust this summer isn't going to hurt things either.

Post a picture of the back of your drive that you want to cut up.
Is the SC upper the same height as a bravo drive?

The standard SC is the same, then you can also buy the -3 which is notched.
[ATTACH=CONFIG]566003[/ATTACH]
[ATTACH=CONFIG]566004[/ATTACH]

You could just cut flat to the top of the cavitation plate then cut a little higher in the shape of a V ( another words cut a wedge out of the back of the drive just above the cav plate then cut from the bottom or just bend it up and weld around the top and repaint. looking at how thick it is you will have to at least surface cut the bottom where you want to bend it up. You will want to grind off the raised portion underneath.

I have a large Delta Unisaw that I think I can use to do some of the cutting, so I get nice clean cuts. Tomorrow I'm going to investigate and see if that will work with the correct blade. D-Day has arrived.

Easy mod with the right tools.
I need to buy a welder that will do aluminum.

Thanks for the pictures that looks to be easy enough. Question: If your worried about the cav plate getting sucked into the prop can you add a bolt on angle (or block) on top of it right in the middle of the cav saddle and bolt it to the drive?

Step one is done. I just ordered the bits so I can mill this flat with my mill/drill and then I'll start building a new cavitation plate. I was going to just reuse the one I cut off, but I have an idea for a bolt on plate so I don't have to have anything welded.

I guess the angled-up cav plate doesn't act like an upside-down trim tab and try to pull stern lower?

-3 Imco lower can bolt to bravo1 upper. cutting clearance for prop is easy with a portable band saw. measure, mark, measure, mark recheck 3 times. I've done 2

Any updates on how this is coming along?

Cutting sounds easy enough. What did you do for a cav plate solution?