bcfountain

how can you tell if your boat is overproped other than rpm.can you tell by time to plain,fuel consumption,idle speed?or even max speed.thanks.

monstaaa

all of the above

Griff

Its really only overpropped if it can't make it into the correct wot operating range of the engine. Planing time and cruise speeds are related more to whether or not you have the right type of prop on the boat.

monstaaa

if the prop is too big, it will take forever to plane. cruise rpm will be off. fuel consumption high. high oil temp and possibly water as well. top end off. rpm's low. no acceleration.

bcfountain

hey monstaaa,tell me what u think about my set-up.22pachanga,454.30 overw/blomer pistons..7.5comp,500sc merc cam,tbs 250 blower,6psi boost,1050 carb.stainless marine manafolds+risers.msd marine box.timming at 30*btd.28 bravo1 prop.the boat is 3400pounds.i can run about 78mph on gps on a good day at 4600 rpm.fuel comsumpton is bad....about less than a mile per gallon.do you think i am overproped.thanks ,brad.

Pat McPherson

You basically built a 525SC with a slightly larger blower.
You want that engine to spin 5000rpm+.
If the engine is tuned properly, you have too much prop.

Griff

You are not into the wot rpm range for the engine you have. Like was said, you have close to a 525sc clone. You should be making 525-550hp. You also should have no problem spinning a 28 Bravo1 to 5000+ rpms with your boat. I could spin a stock26 Bravo 1 to 5100 with my 525sc in 5200lb 28 Pantera. I would try bumping the timing up to 32-34*. A 525sc runs 35* of timing.

Also, your numbers don't really add up. Using 27" for pitch in the propslip calc to compensate for what Bravo 1's really measure and at 4600rpms/78mph, its 0% slip. I assumed you have a 1.5 drive. The speed seems about right for your boat with that power, but I think your tach could be off. I would verify the tach at higher rpms.

StillHaulin@63

When you consider the WOT operating range for the engine,
is the trim level taken into account,
or is a fully trimmed RPM level used for this analysis?

EXAMPLE: I can spin a stock 24p Bravo/1 at WOT at 4700rpm with 1/4 trim,
but when fully trimmed, my RPM level bumps 5000 on my 454 Mag MPI.

monstaaa

what gear in the drive

bcfountain

the drive is a 1.5.trim is about 1/4-3/8 out.its hard to say right on....h/p gimble assembly.i can keep triming and gane rpm,but speed falls off.i am hopping that my tach is not off,brand new,but anything is possible.could be the timming too,i run alittle low because of the gas around here and try to avoid the silent killer in boats....detenation.i will get at it this weekend.thanks for all the input folks......man i love this web-site.brad