Lonestar382,

It will be interesting to see an "apples to apples" comparison in your situation. That would be using the same props in the same water/load conditions that you ran with before the boxes and after with boxes.

I would not even consider the numbers National gave you ... could be different fuel load, different ambient air temps, different wind/wave conditions, too much trim (you will loose speed if even slightly overtrimmed with boxes).

When I first ran my 382, I had some slightly dinged-up "labbed" 28's that came on the boat. They slipped bad below 3000 rpm, had crappy mid-range, and WOT was only 80 m.p.h. @ just over 5000 r.p.m. When I traded to my unlabbed but mint 28's, I gained almost 400 r.p.m. and 4-5 m.p.h.

Who knows what condition the 26's were really in. Don't sweat it until you run it yourself ... look at the numbers John B posted with the Hydros. I think you will be happy in the end!

Wags
 

They are the Quad IV X. No difuser ring.

As far as bow or stern lift, I haven't a clue.

Lonestar,

You should call Formula 260 724 9111 (Darryl Johnson), and ask if the motors are raised when the boxes are installed. If they are you may want to consider a higher x dimension on your boat. This would be shorter drives, like 2'' shorter, and use drive spacers if you have planning problems. They can help you determine this from their testing.

Reddog,

What motors do you have in your 382?

Thanks, John B

thanks for the tip John.
I was wondering that myself. Would installing the XR Sportmaster lowers help me out any at all?

Now, about this X dimension topic, could someone please describe what this refers to and how to measure, change it.

I know I sound stupid, but if I don't ask, I'll never know.:rolleyes:

Corey

Corey,

X dimension is the distance between your planing bottom and the prop shaft when your drive is level with the bottom. The higher the prop shaft (smaller x dimension) the less drag and therefore more speed you will have. Unfortunately as you go up the ability to plane off, without slip, is reduced. Compromise! The extension box, set back, allows water to get to the prop so you can plane off with a higher drive height. If you just put the extension box on without a drive height increase you will lose speed!

So you go back and up with this procedure, then you gain speed.

I would guess your prop shaft should be 3.5 to 4.5 inches below the actual boat bottom, not the step, to achieve the best results.

Sport masters, due to their design, will actually slow you down if you stick with the same, stock, length. The short ones will help however the Imco's are better for top end performance.

Why don't you measure yours and let us know what it is?

John B

thanks a bunch, that is the first time someone has ever explained it to me. The boat is on the road right now and should be here Friday. I plan on spending all weekend on the boat going over everything so I will definitetely get back with you on the Xdimension.

Let me make sure I have this right, I measure the vertical distance of the prop shaft to the planning portion of the hull while trimmed neutral?

Sorry I'm going back to elementary on this, just learning as I go.

thanks again
Corey

Corey,

That's right. When Formula installs Stellings boxes at the factory they raise the drive about 2 inches higher than the others. This is were the gain in speed comes from, not by having the drive further back at the same height.

John B

John B,

I'm running 510 c.i. Sterlings turning 645 H.P. @ 5800 r.p.m. on the dyno. I think there is more speed available with some massaging of the props and higher r.p.m., but I really don't want to turn the motors/drives that hard.

Ed at Sterling wants me to crank the r.p.m. up a bit to get more out of the motors, but it's like I explained to him ... the harder you use your body, the sooner you will need to come back and see me (I'm a physician). He had to laugh and couldn't disagree with me!:D

Well I had the boat in the water today for a few minutes and here is what I have seen thus far. When the boat left it had 28" Bravo1's and ran 72@4800rpm.

today I was able to grap 70.6@5400rpm on...24"Bravo1's.

I am going to install a set of 26"wheels tommorrow and pray that the weather clears up long enough to try them out.

I talked with Sterndrive Spec today about IMCO shorties, and was a little blown away by the price. Hopefully I can find someone who can give me something for my stock lowers to help the cost a little.

Corey

Corey, At 5400 you may be up against the rev limiters. What motors do you have?

JB