Herring says there are some 1075 boats w 6 blades out there but he says it depends how they are setup , there again why ???

Well I did learn that from you RB

And you did tell me to do the spacers

That's why I am following you to Miami
Because you are the man

Thank you for all you have done

RB you have a 1075 boat will you take it from here please

Its just that Herring couldnt give a definite answer ! trial and error im shure .

1 bar vs 2 bar is quite a bit of difference, 14.7PSI. Is the engine with less pressure the one that was loosing grip over 5.5 trim?
Less pressure could be aerated water to the pick up, and prop.
Or a restriction? causing water to not flow cleanly into the drive and "spill" over the inlet causing the prop to lose grip.
Or a restriction in the coolant path causing higher pressure and lack of cooling to a particular area, excess heat, and the knock sensor issue.
As far as the indicators, turn the label over.

We have 2007 42' Lightning with 700sci's (stock), SSM6/NXT, Hering 6 blade 37pitch props also.
X dimension = "22 7/16 x 18 1/2"

98mph with 5 people and ~half tanks gas, but didn't stay on it to play with trims.
"Drive trim on 3.0 Smartcraft, Planes 2.5 Mechanical"

It does run into stock rev limiters alot up there, eventually went into "hard limp" mode so had to stop, shut off motors, refire to reset the computers due to too many rev limit bumps.
Clearly to get 105mph, we need less proplslip than we are getting.
(Speedo Tattletale Recall is at 104mph, the prior owner clearly has had it there...I seem to recall he had drives more down/in than 3 though, I should call him about it)
I also noticed a "low fuel pressure" warning.
We can only get 89 octane gas in Milwaukee...are people adding Octane Booster to get toward 91?

Fountain test had it at 105mph 5350rpm, drives 5.5, tabs 2.5, 7.4/7.1 lbs boost port/stbd, 45psi water both.

My boat has both trim tab and outdrive MECHANICAL indicators working, but
Smartcraft only has OUTDRIVE numerical display; the trim tabs are not input into the Smartcraft display.
My boat does NOT have the GPS speedo inputting to Smartcraft, so I get no prop slip data either.

QUESTION 1: Tried to see the wiring up under dash but can't see where the GPS speedo should hook into Smartcraft, is that one wire OR is it a Harness Connection?

QUESTION 2:
Should I be using the SMARTCRAFT drive position (3 supposedly neutral/highest speed) or the MECHANICAL drive position to get top speed?
We have the same "opposite" numerical situation on our outdrive position (mechanical vs Smartcraft numbering of drive position, they do NOT match up, max in/bow down is 0.0 on Smartcraft, we've been going to 3 on Smartcraft for "theoretical best top speed position", is this RIGHT?!)

I will have to go to the boat with a digital level and see what "true neutral" is for drives, mechanical AND Smartcraft, to understand this.

We haven't top-speed run too much at all, as we have been "learning the boat" and sneaking up on speeds, handling with great respect for safety before doing alot of all-out top end (for us--I know there are many much faster boats :) ).

Thanks as always to the experienced people here for your thoughts and answers!

XWING.

I have a Fountain with the same setup and also run on Lake Michigan. Not sure about your X dimension numbers though. You need to measure from the crankshaft center line to the bottom of the hull.

Port Washington has 93 octane or you really should consider having your ECM's re-programmed to run on 89. Mercury has a program for this and the HP loss is minimal.

Your GPS antenna has a battery to store the satellite maps that has probably gone dead. Livorsi in Grayslake can replace it for you and that will probably fix your speedometer issue.

The SmartCraft drive trim is the most accurate but you need to calibrate it. Check your manual if you can't figure out how to navigate through the menus.

You need to make a note of the indicator readings when the tabs are parallel with the bottom of the boat. That is the highest you should ever raise them.

At high speeds my boat runs best with the drives level and my tabs level or just below. It sounds like your drives might be a little too high if you are hitting the rev limiters at 98MPH. Please note that very small changes in drive trim can make a big difference in speed / RPM. I have seen similar speeds as your Fountain test sheet so I think they are attainable.

I run out of North Point and head to Milwaukee fairly often, Hope to see you there.

GF?

Got Freedom:
Thanks!
I am surprised there is only 89 octane around MKE, maybe someplace has 91 or 93. Milwaukee Skipper Bud's and South Shore Yacht Club are only 89 too.
Torco octane boost could work, looks like 5 gallons=640 ounces costs ~$300
40 oz Torco in 100gal gas make 89 into 91 octane based on their charts.
5 gallons = 640 ounces = 1600 gallons, adding 18.75 cents/gallon to 89 octane gas cost.
Will likely do this.
We just have the Livorsi GPS speedo, not mapping GPS...but will call Livorsi as you've recommended.
Will have to see what putting the drives down a little does to speed/slip.

I hate to remap the motors for 89 octane/less HP. We WERE thinking about doing Whipple Stage 1 reflash to help under 3000rpm torque (doggy down there with torque management), but not keen on paying $2095.95 TWICE for the exact same computer program. I do computer programming on my cars on dynos...and I reflash (takes 5 minutes) every time I take one still under warranty to dealer, so "$4191.80 for "2 motors", instead of counting it as "one boat getting same programming" is hard to swallow.
Pure profit at this point obviously, "whatever the market will bear" and all, but...

Well we are headed to Miami for the run I let you know how it goes

Been a whie since I have been here. It is great to see your comments and also about the spacers. I find it very logic that the boat handles better with the spacers. But What really accoundt is the prop grip, as having the skeg a little further down should not make much of a difference (in my opinion - maybe I'm wrong). So in essence, I would very much like to have the max prop diametre with the std (extreme) X-dimention. So what is the biggest diametre you can have on a No6 drive? Also, wouldn't a 5 blade be less restrictive than a 6 blade prop? If increasing the diametre, you will get better grip and by going to only 5 blades, you would reduce the drag by the blades..? From looking at the props on "our" 42, it seems that they do not have very much rake. I would assume that a long Vee bottom would run faster with a prop with much rake (more bow lift) as the shafts are so high in the first place..? Am I right or wrong here?

Anyway, in our case, we need to have better fuel for testing before we do any modifications.

Regarding low fuel pressure.. I know the high pressure fuel filters on top of the engine need to be replaced quite often to manage to deliver the right amount of fuel. They are cheap elements and easy to replace.

Happy new year everyone!

Here is a video from a private boat race witha very fast Fountain 38 Lightning with 2x700 with a whipple kit.. It runs 124 mph and accellerate like a rocket! We had some problems passing it with the black MTI in the strange wakes from other boats.. :) http://www.youtube.com/watch?v=Nj7WdiMPVro