RonA

I have a 242 ss w/ a small block 350 .I seem to reach about 45 mph w/ a 19 degree prop at 4400 rpm. I'm curious to hear from other small block owners of there top speed , prop size and rpm. I know these are heavy boats but I would like to do about 50 mph. Thanks,Ron

32storm

In 1990, the F-242SS with a Volvo 271 DP(270 HP small block)was rated at 50 MPH with a 21" pitch prop. With 350 magnum & mercruiser it's 48 MPH. Is your 45 MPH based on speedo or GPS?

mopower

Ron,
Sounds like you could use Sheikmans engine

RonA

The speed was with a GPS . I wonder if I can turn a 21 degree prop without too much sacrifice? Thanks the replies,Ron

cuda

If it is only turning 4400 with the 19, I think the 21 will be slower.

Iggy

What model 350 are you running?
I have a 206 LS with the 270hp 350MAG turning a 21" Mirage. Top end is 58mph@4800rpm.
I know mine is smaller and lighter but you should be able to do better than 45.
BTW 4400, I believe, is the low end of the max operating RPM. If you go higher in pitch you'll over stress the engine. Remember: for every two inch pitch increase, RPM drops 200.
Sounds like you need more power and torque.

A Formula rep said the Mirage prop I have is wrong. It should have a 19" Laser II. Their data says mine'll run 56 mph with it.

mopower

Cuda and Iggy are right ...21" will be too much load on the engine. You'll be turning 4100/4200 rpms and may even have a hard time getting on plane
Actually , believe it or not , a 17" or 18" if possible may do better.
But then again it may only increase rpm's and give you the same speed . Best bet is to try to borrow one from a friend (or enemy) before buying one

mcollinstn

Ron,

#1: it's not degrees, it's inches of pitch. A 19 pitch prop will theoretically move 19 inches for each revolution not taking into account any slippage.

#2: Are you running a stock aluminum prop or a stainless prop. If stainless, which model (Laser, Mirage, Mirage Plus, Bravo1, Revolution, etc - it may not even be a Mercruiser prop, it could be a Turbo, Michigan, etc).

#3: Is your prop in good condition?

#4: is your top speed measurement done at Wide Open Throttle, with any trim tabs full retracted (up) and drive trim angle at a moderate to moderately high positive (up) angle before ventilation? If one or more of these factors is not optimized, your measurement is not valid.

#5: are you boating at a high altitude above sea level? this will destroy performance.

We need this info before we can help with a diagnosis.

BAD-HABIT

My F3LS ran 47 GPS in good conditions....I went with the stainless marine exhaust straight thru hull and got 49.5 Gps. After building a 360hp SB roller Im at 54 GPS but I still have probally 2-3 mph left that I just have to dial in.....As for Prop's try the Michigan Attwood Ballistic prop...I got my best times concisently with them all the while comparing them to Mirage and Miarage Plus props......I havent' heard ANY thing bad about these props especially on our hulls.....Just a thought. Seems like the LS hulls like about 12-18 hp per MPH.......Keep us posted

mopower

I've run the Ballistics on my Four Winns Liberator which is quite similar in design and had very good luck with them