MPH is lower than expected...

[diveboy]

Ok, here's the deal:

I own a 2001 32 Dominator that originally had 7.4 MAG's in it. I just replaced them with a pair of 500EFI's with 6 hours on them. I'm currently spinning Bravo I 30" props (not labbed yet).

With half a tank of fuel, 2 people on board total (including myself), running in approx. 68-72 degrees, in 2 foot chop, tabs all the way up, drives trimed all the way out, I'm only seeing a best of 82-83 MPH on a handheld Garmin 12 GPS at 5200 RPM (Gaffrig speedo reads 85-86MPH). If I try to trim the drives out any more, I bump the rev. limiter at around 5250 RPM.

I guess my questions are as follows: Shouldn't this boat be running faster, like 4-6 MPH faster with the current set up? I expected 87-89 MPH on GPS and am a little disappointed. The acceleration in the mid-range is fantastic but top end seems a llittle off. All the articles I've read on this boat (Hot Boat, Powerboat, etc.) show the boat running 88 MPH, however, they claim to have tested with 28" Bravo I props. I've read a number of posts on here by folks with the same set up getting much higher speeds on both GPS and the speedo. Also, for those of you running this combination, how are you getting 5400 RPM's out of your motor before hitting the limiter? Could my drives be out of alignment and scrubing speed?

Any thoughts on where I'm loosing speed would be appreciated.

Thanks in adavance!

[DaveSunsation]

Diveboy,

Pay attention to any weight added to the boat forward of the cabin door, (Cabin area).

If you have silent choice it is an exhaust restriction as well as angle tips - rubber flaps are the best.

Boats from the factory with EFI's have a different arm rest area that allows more air flow to the engines.

Boat will run faster in wind mixed chop.

Run fuel octane required, no higher as it will slow you down.

We also run Marvel Mistry Oil - 4 oz. per 10 gallons of gas.

Clean flame arrestors, some times they have dirt you cant see.

Spin props inboard, you will gain 1/2 mph but loose a little manuavering ability docking.

Lab props good for almost 2 mph

Bottom coating wax good for 1/2 mph

Synthetic oils after break in on engine and drives good for another 1/3 - 1/2 mph

Check postion of throttle plate at W.O.T

Leave tabs level with bottom of hull and limitors in.

We've seen 90 mph on gps with your package. Hope this helps in setting your boat up.

[Reckless32]

Marvel Mistry Oil? What's that about?...

Rick

I just put in a couple of new 500hp carb motors in my boat, tuned on the dyno. I also had labbed 30's and turned them 5400 until I chopped a log up for winter with them. They were 5 min. old. I used a cheap gps (neighbors) and got a consistant 88 mph and would touch 89 and 90.

Is everyone running Bravo 4 blades with there 500hp and above motors? I've been trying to get a set of Spinelli's dialed in and am having zero luck. I had my last set reworked over the winter to hopefully pickup a few RPM's. Well, I picked up about 400 RPMS (5000 up to 5400) and LOST about 1 mph. 86 mph on the GPS. I ran the slip numbers in one of the many prop calculators out on the net and came up with horrible slip numbers. if the pitch is indeed a true 31" then my slip is somewhere around 22%, while my old Bravo 28" calculates out to around 12%.

Does the Spinelli sound excessively high, or is the Bravo 28" suspeciously low?

-Bayley