So you have a 353 with 770 hp on boxes running 30P Bravos at only 82 mph. That's just a little more mph than the stock HP500's would get you.

I know you mentioned a dyno, but it almost sounds like you're not making as much HP as you think. Or, you're getting tons of slip because of those boxes.

I run 5 blades and Im working on 4 blades now. No boxes. The 5 blades do lift the stern, but getting on plane and mid range is great. The 4 blades seem to be a little faster but I haven't wrung it out yet. Based on my boat, you should be in the high 90's with that much power, although mine is a later model and I believe they changed the X in the mid 2000's.

Hope this helps.

Sorry maybe I misquoted numbers my old HP 500a were dynoed at 535 and the new motors at 697 corrected HP plus more TQ and CID. I did speak to the factory a few years ago about the higher X dimension but never got a confirmation that they actually did it even if they did the boxes would more than make up for one inch of x you would think. I might have an opportunity to try to set of 4 blade Hydro motives 28 which I think will be more like labbed Bravo 4 30s. The only other thing my engine builder suggested is having the hull checked for hook but that will be in expensive proposition to change if we need to get it blue printed

Offshore performance in egg harbor did a 353 a couple years ago. A guy near me bought it. Did you put raised boxes or straight? If they're not raised you effectively lowered your propshaft height. Formula raised the x dimension 1" on boats that got boxes from the factory.

Good to know. My boat is a 99 and the boxes were on from the factory. I'm not standing in front of it but I'm thinking they are straight.

Wete any of the boxes adjustable? I seem to remember reading about this at some point.

Stellings are adjustable. I have them on my 353.

Excellent, I'll have to check. Do you know how difficult the adjustment process is or if there any special steps required? If everything from the boxes back will need to be removed this might have to be a fall project.

According to Scott Smith at Formula the X Dimension on the 99 353 with boxes was 18 inches and 1/2 inch higher than non box boats. I measured my prop shaft height from bottom of hull directly in front of drive to the nose cone point and got 4.5 inches. Some people I've spoken to say this seemed too deep but they were not familiar with the 353 stepped bottom. Does anyone have their numbers handy for comparison? Thanks

I'm interested in what you come up with. I just picked up a 2000 353 with 500's / 30" Bravo 4 blades... Low water pickup 1.5 drives.
With just a quick run before layup it ran 79-80 at 5100rpm. 1/2 tank if fuel. Slip seems high. A friend asked me to check the depth of the drives and they seem pretty low. Gets on plane very well. Was on an 06 with 496HO's and it had a hard time with any tab involved. I played with shorties on my 42 a while back. Didn't carry the bow well. So if I did anything from here I would try 4 blade Hydromotives first. Or might be too much gear case too low and having a hard time pushing it through the water. I'm going to check drive alignment for the hell if it also. We'll see...

I spoke to some other people and 4 to 4.5 inch propshaft depth seems to be correct for this boat with boxes The 496 353s were a pricepoint offering imho and are fine cruisers but have a tough time getting across the high performance threshhold since its not a light hull. As for the props I think most people with good power are running labbed Bravo 30's or Maximus 5s but like to keep their little secrets. I heard formula used Hydromotives on their race boats back when they were campaigning but the right size Merc prop should be just as good since its mostly in the labbing.