chuck21401

I posted this message on the Formula owners OSO forum and received a couple of replies...thought perhaps I get additional feedback by posting over here.

I have a Formula 1989 242LS with a 454 magnum (365 HP)

I'm running a SS 21P mirage prop. (part #48-13702 A40; what does the A40 mean? I've seen different suffixes for this part number)

At WOT, tabs up and drive trimmed I'm seeing 53mph on GPS. This is with 3/4 fuel and 2 people. Boat weighs 4300+ and has 8' beam.

The tach shows 5300+rpms which is too much; book says max RPM should be between 4600-5000.

I'm thinking about trying a 23p mirage prop. (Would I get a mirage or mirage+, what is the difference?) Should I consider a four blade prop?

What are other single big block 24' owners running?

Top speed isn't that important as I wouldn't keep it at WOT for long, but rather I'd like to bump up my cruising speeds in the 3000 to 3500rpm range.

Also, how long is it safe to run at WOT? ("until the motor grenades" Yeah I know that, but really, how long do you run at WOT?)

Chuck

zog02

Chuck,

I have an 89' 223LS with a regular 7.4/ 330 hp. I run a Mirage 23 pitch and it has no problem reaching WOT. (4600) My top speed is about 59-60 on the GPS with 2 people, 1/2 full of gas. The WOT for your engine should be between 4600-5000. The general rule of thumb is a loss of 200 rpm for each 1" increase in pitch. I have no idea what your boat is like coming out of the hole. I am guessing it is like a dragster. As far as whether to get you a 3 or 4 blade.....3's are almost always faster on the top end but the 4's help you accelerate faster. If it was me I believe I would go with a 3 blade 23 pitch mirage or a 4 blade 24 pitch mirage. I have heard people talk borrowing props from Merc dealers to test them out. Check this site... http://www.mercurymarine.com/propellers

Good luck....hope this helps.

Drew

chuck21401

Drew,

Good information, I'm leaning toward the 23 mirage. Glad to hear that you hit 59-60 and can get WOT with your prop. A local shop will let me try props, so long as I agree to buy one. Boat has pretty good acceleration, not quite a dragster. I put the tabs down and drive down before trying to get on a plane. I take it slow with 3/4 throttle.

I just bought the 242 formula. Great boat so far.

Chuck

Dave F

I used to own a 242ls. I used a 23 mirage with a 1.5 bravo and 500hp turned 5200rpm consistantly

When it had the 454/330 and a 1.36 alpha it used a 19 Quicksilver prop with a full cup. Which is what the "plus" means, cupping on the blades.
That setup would turn 4600 consistantly.

DAVE

chuck21401

Dave,

Wow, so what was your top speed with 500hp?


Chuck

Dave F

top speed with the 500hp/23mirage was a consistant 69-70.
I later procharged with new heads, cam and other goodies and topped out around 93 with a stock 1.36 bravo and 28 4blade bravo. around 900hp.

DAVE