Going labbed?
 

I have a 31 formula with stock 454 mpi, I was wondering what I would expect going from stock 28 4 blade to labbed 30's, I want to loose about 200 rpm and not loose any speed, however it would be nice to gain a little mph, im hitting my rev from time to time, it seems like more often than not.

The assumption here would be you are running Bravos. If so then a switch from a non lab 28 to a lab 30 would net you a small speed gain while keeping the RPM the same. If you want to drop the RPM by 200+/- then going to a non lab 30 should work, or possibly a lab 32.

Basic recipe here: 2" of pitch equates to about 200-250 RPM on most boats with the Bravos. The Merc lab process will also increase the RPM about the same 200-250, and most often will result in a few MPH gain. Not every shop will use the same process to "lab" a prop, they all have their own way of doing it. The Merc process is somewhat generic in that they do not generally do them for a specific hull / power set up, that's where the custom shops come into the picture.

A friend has had good results working with BBlades on his Formula, you might try to contact them.

Keep in mind that labbing will make the blades thinner and more susceptible to breakage.

Brett at Bblades has been great to work with regarding labbing. Custom labbing is the only way to go.

What rpms are you turning now that you would want to decrease it by 200rpms??? Running the engine very close to the limiter is the best.

General rule is 1" pitch =200rpms

Standard Labbing will add 200-300rpms in most cases.

Sounds to me like a mildly labbed 30 would be just right for what you want. You could also have your 28's tweaked to 29's which would be less expensive.

Well if its at all cool out im bouncing the rev at 3\4 throttle, on the hottest day it will do it with the right water and fuel, Im just trying to take it down a little and possibly gain a mph or two and help out my midrange, and I thought a labbed 30 would be about right.but I just do not know enough about the labbed blades.

I have a set of labbed 32's that would probably work in cool weather if your hitting the limiter at 3/4 throttle.

Get BBlades to send you some test props and call him to discuss your best options.

Test some props before spending your coin on them,not all boats respond positively to labbed props,especially heavy ones. Wags 382 was running stock 28's on his formula,bought 30's that were labbed,boat was about the same at wot but revved higher,slipped badly at midrange cruise,after tweaking and re-tweaking the labbed 30's he finally gave up,was a 1800$ experiment that went bad,Smitty

I was not impressed with labbed 30 b1's on my 382.
The original stock 28 from 1998 out performed them through the whole range.