What am I doing wrong here???
I have a Baja 342 - with the 33 Outlaw hull twin 525 HP engines and I have Stellings boxes with -2 in shorties. (mid hole on the Stellings box))
I have a prop height of 3.25 and not getting great numbers - running bravo 4 blade.

What prop height have you seen the best results with?
Is the mercury lower or IMCO lower better? (Want to get the best bow lift)

Numbers:
With 496 Mag Ho's Before upgrades
All GPS
3500rpm @ 50.2mph
4000rpm @ 60.1mph
WOT @ 71.8mph

With 525+ HP Stellings boxes and IMCO shorties
All GPS Prop height 3.25in
3500rpm @ 41.8mph
4000rpm @ 50.4mph
WOT @ 64.7mph

With 525+ HP Stellings boxes and IMCO shorties
All GPS Prop height 4.25in Stock mercury lower
BAD porpousing and felt like the anchor was dragging handled like crap!
3500rpm @ 42.8mph
4000rpm @ 52.4mph
WOT @ 68.6mph

I do not have any experience with Imco shorties. However in my experiences with the Merc stuff, you really need to be running better than 90 or so to get any gains from the sportmaster shorties on a baja hull. The increased surface area of the longer gear case and the longer skeg will typically slow you down at speeds of less than 90. That being said, I would concentrate on dialing in your standard lowers. Or someone else on here may have experience to rely on with the Imco stuff.

thirsty thirsty

Trim position is going to be a critical piece of the puzzle. My experience is 2 to 3 degrees positive is optimal with 4 to 5 degrees positive max. You may need a little less with the additional leverage gained by the boxes. Use a digital level on the chines and the cav plate to figure out where you are. If you are over trimmed trying to pry up the nose and gain rpm, then your going to porpoise like a b!tch.

thirsty

Something else to check (and it is amazing how many times this is wrong by a lot!!!) is the drive toe AT OPTIMAL TRIM. Many people will set the toe with the drives tucked clear in. As the drives trim out, the tow will change if the drive centerlines are not exactly parallel and they often (always) are not. Typically Bajas like about an 1/8" of toe out (ie 36" at the nose 36-1/8" at the prop shaft tip) at optimal trim.

Once these items are checked and baselined, then I would start playing with props and drive height. Keep us posted on how it is playing out.

I would try a 2" spacer with the imco shortyies and IF it feels like its dragging and gains no speed but your slip drops back to what it was before the boxes its time for the boxes to come off and become somebody elses problem. I too have rerigged my boat (a 2000 272 baja w/BIG power) with a stellings box. It ran 89.5-89.8 any day of the week before the box and would run 92.5-92.8 running light. After installing the box it would barely break 86-87 mph,porpoised badly,would no longer carry the bow etc. I put a 1" spacer on it which helped return the handling and ride BUT slowed me down even further to 84 and change. Not every hull works well with exstension boxes,yours might also be one of them,I'm sure you don't want to hear this though. Make sure and try a assortment of props before giving up however,maybe a 5 blade hydromotive would bring your slip back down and speed up,its obvious your prop slip is way up,either prop is just too high or somehow the water is disturbed 12" back because of something about your hull design. The prop experts felt my padded bottom on my boat was the reason why the box didn't work for me,Smitty

smitty's boat did not work well, but they seem to work on the 24 ol/ 25ol/ 29ol and some of the bigger boats I am pretty sure there are a few 33ols with them and one 36ol that was here. I have a 2'' imco shortie and love it went from 76 to 83.2 gps with it and carb change ran out of prop. when you use a box you go up a min of 1'' most guys go 3'' from stock the 25ol that stephen owns has a 2'' shortie plus a 3'' higher ex box from imco so far he lowered it one 1'' so he is 4'' above stock. I was going to try a box but am building a 1000hp 572 it looks like this winter.

My 29 loves them! I have the boxes & 3" shorties.
That is the gamble with boxes. They work on some stuff & they don't on other stuff.
Sometimes you gotta throw a bunch of money at it to get it to work or you can just go back to no boxes.

5 blades and inside rotation

Don't be afraid to use tabs if it porpoises a bit...mine
runs fastest with tabs between 3-4 ( 380 k-planes)

I knew one of you guys had the set up, what do you have standard boxes with 2'' shorties or ???? to help the guy out

Is that what worked on your 33 ol or a 342 baja like the one in question? Honestly from the speed loss he is suffering it will take a miracle to get the speed back to where it should have went to (go from 64 to 80 ish). I think the boat can't get enough bite or leverage to carry the bow now,maybe the 5 blades will do it. Like Jason Smith has stated,there are hulls that boxes don't work on. Try some 5 blades and if you don't make progress at least you will know. Everyone told me before wasting my time installing a box how great it would work,after I did it then I realized I was breaking new ground. Your going to have a hard time finding someone who put boxes on a 342 to give you actual set-up info but I hope you do,Smitty

I have some P5x's for sale you might want to try. They supposed to get traded for some labbed 30 Maximus wheels, but you are welcome to try them.

The 342 hull is the same hull as a 33 Outlaw hull. Believe it or not, google "342 Stellings Box" a ton of this boat was produced from the factory WITH Stellings boxes but of course I cant call the DAMN factory cause of the Fountain buy out... And I am pretty sure fountain cant help. Stellings knows nothing... BUT! with the boxes and HP 500's it runs 80! I just have to get there with IMCO lowers.

Dont forget what I overlooked. The IMCO 3 inch raised is 1 inch higher than the stellings. The stellings gives you the original height, then minus 1-1 for a total of 2 so I am still an inch off with stellings to IMCO comparison. I just have to get the speed with the IMCO lowers the Mercurys are too deep. I am pretty sure since I buried the throttle and had no slip on takeoff and it shot outta the water like a bobber. IMCO told me it was soo deep that it was slipping cause the cavitation plate was buried too deep.

I am going in half inch incriments from 3.25 all the way to 5.25 and testing two sets of props the whole way.

Anybody want to buy any lightly used IMCO spacer plates? I have almost every size! (I am serious) 1/2inch, 1 inch, 1 1/2 inch and 2 inch