My boat has 400+ hours with Stellings boxes and the original drives. The first 100hrs was with 750hp. The last 300hrs has been with 502mpi's.

Yeah well I ran the Barvo 1 4 blades at 3.250 inches and got 67 MPH then rant he 5 blade maximu and got GREAT midrange rant at 70 MPH WOT and still off by 10 MPH

Broke the upper downshaft tonight! fkn hate my boat - I am over this sht! I was at 72 before and at 68 now with boxes and 200 more HP...

i have had good luck with the stellings on my single step fountain 35, boxes are in top hole with stock bravo drives running hydro 29 q4 props turning in, its a pain to get on plane but handles great at speed. What did you do to the engines? are you sure they are running right ?maybe try some small props and see if they turn max rpm. also try some hydro q4 props if you get on plane easy then your drives are not to high. if you cant get on plane then they are to high. are your drives toed in or out 1/8"?

The reason wy the downshaft broke is probable because of drag or blowout . That is also wy your speed is of.
First of all you did to many changes at once.
More HP ,then run it stock,- ad boxes at stock hight with stock lower,- now go up step by step ,if it gets better but u whant more then try lower case but go to stock hight with the box again and just try going higher again untill the optimim is reached.
If u try so many things at once how will you know whats wrong?
If you dial a boat in you have to do it step by step ,piriod !
First of all ,stay calm.:ernaehrung004:
If you wanna get your boat dialed in correctly ,let me know.
Scott.

I feel your pain,like I mentioned in my post in the Baja forum,I put a stellings box on my 272 single with big power,lost a solid 6 mph. In my ENDLESS misery of testing different props and spacers I ended up also shearing off a billet prop shaft trying to turn a maximus prop. The maximus gave me great cruising speed but still didn't bring the top end back,I hope you find the right combination,I finally gave up,Smitty

Ding, Ding, Ding, we have a winner!

Let me know if you deciode to get rid of the boxes, I am looking for a set.

no i do not.

how ever i have never seen any improvement in performance from boxes at the speeds your discussing.
only at higher speed do they make a difference and not big ones. the c.g must be considered when doing what you are doing. as i said leverage helps more than anything and is efeected most by c.g .

pulling the engines is most likely why you did the boxes at the same time, but as stated above too many changes dilutes your results of what worked.
i would say to pull the boxes and stick the stock lowers back on. most likely will run the fastest.
check with baja to see what speeds your boat with what ratio and x-dimension are running from the factory.

The boxes are still on with the stock lowers now at 5.5 inches. I know this is in the basement but the boat is running 4-6 MPH faster thru the whole rpm range (keep in mind the stock prop height on a larger Baja is 7.5 to 8.5 inches).

Also, I found out why the boat seemed down on power. We hooked it to a scan tool and the damn Stellings boxes universal joints are setting the knock sensors off - they retard the timing 20 degrees. Hows that for robbing power...

It seems like something is wrong with the drive line....noise? The u-joints in the drive shafts will not last long if you have much angle on them. The carrier bearing must also be set/shimmed with the Bravo alignment tool. If your boxes are 10+ years old, getting perfect alignment may take custom made angle shims...Stellings had machining/jig issues. Here is an easy method to check your driveshaft angle.
Buy/borrow a inexpensive digital level, move the bow by raising or lowering the trailer jack until the engine is level (the edge of head is generally a good reference place). When the engine is level, now see what the angle is on drive shaft....or measure from current boat position and do the math.
Short term, any driveshaft angle will likely work for testing, long term the u-joints will not last with a big angle. My data comes from experience and mostly from a Dana/Spicer engineer that said that a big HP in 6-10,000 lbs boat at high RPM was a crazy use for automotive designed u-joints and was WAY past any design criteria or intended use for any u-joint in their product line:eek:. His recommendation was a MAX of 2 degrees. I run mine at .5 degrees and replaced the u-joints every season when I raced.
Based on your recent engine issues, are you sure your testing with the IMCO -2" lowers is valid? There should have been some speed at the raised X unless their are other issues like excessive porposing (balance), hook in bottom, etc.
Going forward, try and only make one change per test. If you can borrow drive spacers, the testing is much easier. When you find the "spot", now move the boxes, engine height, re-rig, etc.