Cutting Bravo Lower (it's done!!!)
 

Okay, after many trials and tribulations; the lower is ready for testing. This project forced me to buy a new tig machine to finish it up ( hence the delay). I am still not too sure about the cavitation plate, though. I stepped this one up, but I think I may just cut it off later. Keep a look out for Tommy V's posting ' cause I'm shipping it up to him tomorrow so he can try it out.

Dam, shure looks nice Max.

Beautiful work! How about a nose cone, low water pickup, and a 2" longer skeg.

Thanks ragtop and Marty, actually it is not as clean as I'd like it to be. This drive was pretty rough when I picked it up, corrosion pits, scratches, grinding marks, etc. But it was ideal for some R&D. I certainly didn't want to cut on a new one. As for the other options, I will try a nose cone and longer skeg later. I can't use a low water pick up due to the shallow water Get into sometimes.:rolleyes:

Looking good Maxx, You might be surprised with a larger cavitation plate. Since the drive is shorter maybe it will help keep the prop from ventilating and maybe help with the hole shot. I'm not sure what it will do on the top end.:cool:
I want to see how this does. I'll be waiting for the results.

That will be an interesting comparison. I'll try it with and with out the cavitation plate. May be a mute point though since the Bravo has that plate on the upper.

Maxx that looks factory. How much power is Tommy V applying? Greg

John, that does look great. Would you have any problems modifying one with LWP and a nose cone? Looking forward to the results.

Shawn

Maxx looks great cant wait to hear the results of some testing. best of luck with it

WOW Max you the Man!!!!!It looks great are you thinking of doing these as a side line???or just for yourself????what kind of cost would you charge to cut lowers?????

IM THE GUY TRYING IT ON A BOAT WITH 550HP AND A XDIMENSION WAY TO DEEP SO ILL POST RESULTS AFTER INSTALLING IT TOM

Maxx,
That lower looks good. Can't wait to hear the results. I've got one thats a good candidate.
Any idea what kind of cost ?

TOMMY V what type of boat are you doin the testing on??

Tom, I'll be dropping it with UPS in a few minutes they should be here antime now. Dyno, yes I will be doing these and other things, hopefully, full time when I retire from the PD; send me an email or call me at 757-739-5196. However, before I do anymore I want to run this one through its' paces and look for any weaknesses or any changes that need to be made. I would hate to send out anything that hasn't been tested again and again and have a failure. Tom's boat is a good candidate, he has the right amount of HP for a Bravo 1 and his X is way deep. Shawn, I don't for see any major issues with a LWP; it would just take a little more time.

Testing?
 

Youuuuuuu don't need no stinking testing.....! What you need is some marketing!:D

Brad, seems to me I've said something similar like " Badges, badges; we don need no stinkin badges" Wait a minute, I was mistaken; that was from The Treasure of the Sierra Madre. But, I may have said it once or twice.:p

well Maxx I look forward to the posts on the tests, will Tom be water testing yet this season?????I'm volenteering for the test on a twin engine set-up!!!1993 Sonic with twin 454's at around 500 hp each. The factory told me I could run a 2" shorter drive no problem....

Dude that is some amazing chit you just did. A big high five for you on that one!!! Keep us posted as to how it goes. Maybe you can do TRS drives as most of them are WAY to deep into the water :D:D

Jon

Thanks Dyno, Audiofin. We'll see how well it works when TommyV tests it out next week. The gears shimmed up fine I ended up with .055 on the pinion and didn't have to change the driven gear shims at all.

John it looks great. I'll be ready soon. Going to try to get out at least one more time if the weather cooperates.

Maxx

Great work! It's not easy, I know. Research and development is 1% inspiration and 99% perspiration. Let us know the propshaft location below the hull. If it's deep you're probably using a 3 blade prop and raising 2" will not cause blowout. The before/after comparison is really only valid if you can keep the same prop and spin it faster. If you think you might actually increase speed enough to move up in pitch, test the higher pitch prop before switching the drives.

Good luck!! Watching your progress helps keep me moving on the intercooler thing.

Tom

Thanks Tom, appreciate the comments. I think helping each other and keeping costs down is what this board is all about. We have seen some great posts lately. Alfster showed us his steering system that was truly a fantastic project (we'll be working together on that to get it in to production) Just keep plugging away and don't give up. :D B.R.S. give me a call.

Maxx, looks good! Best of luck on your testing. Let me know how your steering system works out.

I'll keep you posted, Steve. I am working on the stainless cylinders now. Pretty much have everthing together I'm just waiting for the machine shop to free up a cnc lathe to produce the glands. Give me a call or stop by when you get back down to Norfolk. :)

RIGHT ON JOHN!
 

:) :D :) :cool:

THE BOAT IS A 27 FOOT IMP WICH ORIGINALLY WAS A ALPHA SSDRIVE TO ABRAVO KNOW I AM 4''TO DEEP HEAR IS A PIC 454 30 OVER 10/1 PISTONS HYDRALIC ROLLER CAM DART PRO 1 HEADS BRODIX INTAKE AND HOLLEY 850 CARB DYNOED AT 530 HP WITH THE CHANGES BOAT SPEED STAYED THE SAME 54MPH TOP SPEED NOT GOOD

With the shorter bravo it stayed the same?

Man Tom! I had forgotten just how deep that drive was. As you said, you may have to raise the X and use a shorter lower.

Maxx

I think you need to find a different boat with less variables for back to back testing. You have a great idea and I would hate to see it ignored because of one inconclusive test. What does 4" inches too deep mean? Where is the propshaft before and after? How heavy is this boat? What is the torque curve of the modified engine, etc.

I'm sure you could find a volunteer on the board with a more "typical" boat, a vee hull with stock power, well known characteristics and best performance with a Mirage three blade. If the boat just starts to blow out on turns then the X dimension is about right. At this X dimension a Bravo four blade will be slower on top end although usually better at everything else.

Form this starting point, when you raise the drive 2", the boat will be faster, but the three blade will probably blow out too much in turns and will be hard to get on plane, especially with any load. Now you put on the Bravo four blade and get back the planing and turning ability while keeping most of the top end gains. This is exactly how the manufacturers have used the four blades and raised X dimensions.

The test report should give the position of the propshaft before and after, GPS speed, verified RPM etc. Any changes in trimming ability with the raised drive should also be noted. You could try Hydromotive props; I found they were a bit faster but did not carry the bow as much and as a result were a little scary handling in some conditions.

I suspect the gains on older, heavier boats will be small. Since you only have one drive, the test boat is obviously single engine. It may be that you have to be going faster to begin with. At slow speeds, hull drag is the biggest factor. At higher speeds, as the hull rises out of the water, drive drag becomes a bigger percentage of overall drag, so improvements here may be more noticeable. I suggest stock HP500 power in a smaller boat. You would probably be going 70+ already.

You may have already come to these conclusions yourself. In any case, good luck!

Tom

John. you also might need to keep an eye on your water pressure as the pick up is also raised.

Shawn

Tomcat, I appreciate your input on the testing. However, my purpose for testing, at this point; is durability and Tom's boat fits that bill perfectly. I believe that most performance boaters are aware of the pros and cons of a raised X dimension as proven by the popularity of the Imco units. My goal is to provide a less expensive and durable alternative. As you have mentioned, hull design and stock X dimension will be a factor in whether someone should consider a 1 or 2" shorter lower. I plan to perform a detailed performance test on my boat (1989 Chaparral 2350sx) at a later date, but bear in mind that the gains I may see could be totally different from another boat with a more aggressive hull design. I will post all of the performance results and thanks for the encouragement.

Shawn, I was able to compensate for the water intake issue.

HEY TOM CAT
 

HEY TOM CAT FIRST OF ALL TEST WILL BE CONDUCTED WITH A 3 BLADE MIRAGE PLUS THE PROP YOU SEEN ON THE BOAT WAS A TEAST PROP THATS WHY IT IS BLUE INCASE YOU DID NOT KNOW I HAVE A GPS SPEEDO GAFFRIG AND WILL POST ACCURATE BEFORE AND AFTER INFO IM SORRY IF YOU ARE NOT HAPPY WITH THE TEST BOAT BUT IT IS NOT YOUR CALL I WILL TELL YOU BOAT WEIGHT ALL SPECS WILL BE AN HONEST TEST NOT EVERYONE HAS LITE WEIGHT HIGH HP BOATS ..THE RESON I HAVE THIS PROBLEM IS FROM LISTENING TO PEOPLE ON OSO WHO GAVE ME THE WRONG INFO THTS WHY AM SO DEEP AN ALPHA SS DRIVE IS 2''SHORTER THEN A STOCK ALPHA AND A BRAVO IS A 13/4 LONGER THEN A STOCK ALPHA WHICH MAKES IT 3 1/2 TO DEEP I KNOW I HAVE TO RAISE MY X DIMENSION AFTER TALKING TO MAXX HE AGREED TO HELP ... IF HE CHOSES TO RE TEST WITH SOMEONE ELSE THEN HE CAN DO SO TOM

HEY TOM CAT
 

TOMCAT THE PROP SHAFT FROM BOTTOM OF KEEL TO CENTER OF PROP SHAFT IS KNOW 10'' WITH THE SHORTY THAT I AM TRYING WILL BE 8'' BEFORE I DID THE CONVERSION FROM AN ALPHA TO A BRAVO WAS 6'' BOAT WEIGHT IS 5600 LB ANY MORE QUESTIONS

Maxx

Reliability is the most important thing. I just assumed the test was aimed at demonstrating a speed increase. Again, good luck.

tommy v

You need to relax a little. OSO is all about good (and sometimes bad) advice freely given in an open forum. My post was not an personal attack on you or your boat. I'm just trying to help, so take it easy.

WOW 10" bolow the keel. I've heard that problem with going from alpha to bravo and t prop ends up 4" lower if you just bolt on the gimble to the alpha location. Otherwise it requires glass work and raising the engine. IMCO was able to cut a bravo lower 3" shorter at one time. Your boat sounds ideal for durability/strength testing.

Can anyone else verify that the Bravo's are longer than the Alpha's? I also did the alpha-to-bravo conversion, and am not seeing the speed numbers that I expected. I was always told that they had the same distance between input and prop shafts.

"IM SORRY IF YOU ARE NOT HAPPY WITH THE TEST BOAT BUT IT IS NOT YOUR CALL ":eek: :eek: :eek: EEK! Him mad!!

Budman, I measured the two when I did the conversion and they where about the same distance between the two shafts. I believe the problem is that the Bravo just has a much larger lower. Thus, more mass more drag. BTW, cool dog!

Maxx,

Thanks, that makes me feel a little better about my swap. I was starting to think I was going to need one of you shorties. Still might - still not getting the kind of speed that I should. It is a 1.32 ratio with a nose cone - we are going to experiment with a 1.5 ratio in a week or two to see if that makes any difference. Gear ratios/prop selection has been discussed at length on this board before, so why not throw some more fuel on the fire? :D

That is my dog Buddy, at a pre-cruise party in Evansville, In. He also answers to "Budman", hence my username. I adopted him from the nearby humane society when he was about six months old. We think he is a lab/golden retriever mix, with maybe something else thrown in for good measure. He is a great dog - loves the boat. He is very happy in that picture because he just got leighed - twice! :D

Budman, that's what got me started on this whole project. I contacted my boat manufacturer and they informed that they move the X up 2" for Bravo / big block installations on the same model boat. I definitely agree on the 1.5 ratio, and you may want to consider removing the nose cone. I am going to try mine without a cone first and then install one with a minimal amount of epoxy and try it; then if the nose-cone is a detriment I can knock if off with a little heat.

That is my dog Maxx, hence mine name too, he's a full blood Chesapeake Bay Retriever ( we think, no papers ). Anyway, he stopped a neighbor's toddler from falling in the river one time, so I thought it would be kind of cool to put his picture up somewhere.