My Buddy Has A 90 Nordic 23' Advantage With Stock Power 454 And Bravo 1.5 Drive He Is Spinning A 23" X 15" Wheel And Would Like To Go To A 25 What Do You Think He Can Get Away With In Size 26? 27? 28???

Current speed and RPM (?) would help us here.
Sounds like he's running a Mirage 3 blade. I recommend a Bravo 1 four blade, probably a 24"
Steve

He says he is turning 6k at wot and the non gps reading on the speedo is 70? +/- 3mph but I'm sure it's not accurate at all...

Doorshot,
If your buddy is in fact turning a stock 454 6K @ WOT, he won't be for long. Those are forged parts (internals) #s, and even then that is high for long runs, like a poker run.
I would:
a. check his tachometer against a shop tach
b. check his speed with a handheld GPS
c. find out which stock 454 he has (probably a 330). then you can prop for it's peak horsepower, which should be closer to 5K.
With corrected rpm and speed #s, we can calculate his prop slippage and recommend the correct propeller.
PS, this is a "no spin zone" . We're here help any of our fellow Nordic owners, but you can't get anywhere with questionable #s.
Regards,
Steve

Doorshot,
I just ran these #s through a prop/speed calculator, factoring in 14% slip (my estimate), and came up with 74.9MPH. If you guys can GPS the boat and check the tach, it would help. If the #s are correct this boat is way under propped.
Steve

We are taking it out this weekend and I'm loaning my prop to him 15x25 and I'll drag out the gps to see where we are at and yeah he drives it pretty hard "time bomb" waiting to happen...is there a direct correlation to prop size and rpm? and if the prop size goes up and rpm goes down how much harder is that on the engine?

Hey Doorshot, I think you mean 23' Venture, don't think Nordic built an Advantage. I owned a 92 23 Venture w/454 Mag ran a 23 pitch double cupped three blade Mirage. Speed was around 68-70.

Nordic Gary

When a motor is over revved, like this application, increasing pitch and reducing RPM will help engine longevity. Your buddy is way beyond the peak HP @ 6000 and running at reduced HP, and needlessly beating on his motor.
The key is to prop for peak HP/RPM. A mild 454 Merc should peak around 5K, or less.
It sounds like you are concerned about lugging (too low RPM) the motor down? That's not the problem here, it's excessive RPM.
Steve

It probably is a venture I didn't think that those boats went that fast! and zuckerman what are you doing up at 4:30 am?
that is way to early....but those motors turn low 5k? I just picked up a 1993 22' daytona eliminator with a stk 454 5200 rpm ok?

Doorshot:
I don't get up at 4:30AM even for sex or boating ...............
Post times shown are YOUR time zone (Pacific?), not mine (I'm CST). 5200 should be fine.
If you fill in your location on your profile, it will show beneath your avatar.
Steve