Hi,
I have an 87 242 LS 454 with Alpha 1 outdrive. I’ve tried three different props ranging from a 14 x21 as 3 blade, 21 4 blade aluminum and a 19 x 4 aluminum with no measurable improvement in low end performance. Even with the 19 pitch the engine did no go over 43/4400 rpms. Any info, recommendations or suggestions would be appreciated.

Many thanks,
Tony S

Is that at the full trim limit?

No that’s at full trim down

thanks for responding

Tony S

I believe the info tag on the valve cover says 4,200 - 4,400 rpm max.
Most 242 owners prefer a Rev 4 prop. Your Alpha is most likely a 1:36 ratio. Try a 19 Rev 4, I bet you will like it.
Good Luck

Thats the standard 454 not mag (though with the alpha combo the called some of them mags) sothose motors redlined at 4800... when was the last time that motor was freshend up?

They never put the real Mag in front of an Alpha. Trust me I have owned 2 of these.
For reference see the following I copied from another site:

GM Marine Engines

Based on the same 454-cubic-inch big block Chevy, General Motor's Marine Engine division set up the motor specifically for use in boats. Because General Motors was not a boat maker, but a motor and automobile maker, their marine engines division often sold parts to companies specializing in setting up marine engines such such as Mercruiser.

Marine Applications

The 330-horsepower, marine 454 is different from the 454 automobile engine from which it was derived. Because boats have just one gear and very different power and torque requirements, everything that shapes power and torque characteristics are different: compression, valve-train, intake and headers. Water pumps for marine engines are specifically designed to withstand corrosion because the systems use open water for cooling and may contain salt, minerals and all kinds of chemicals. Marine carburetors are also designed so that fuel delivery is uninterrupted despite the extreme pitch of the boat during cornering. All electrical components must be able to withstand a hostile, wet environment.

454 Marine Specs

The GM marine 454 had a bore of 4.25 inches and stroke of 4 inches with compression ratio of 8.1-to-1. The engine breathed through a four-barrel carburetor, and ignition was provided by a Delco Electric unit. The marine 454 weighs 980 lbs and makes 330 horsepower, at its maximum RPM of 4,400

Does anyone out there have a digital copy of his Big Block Book . I got a 454 carb that I’d like to get alittle more out of.

I have the book somewhere, no scanner. What info are you looking for ?

If it's not a Mag motor you will only see 4600rpm if a 330 hp motor mag is more like 365hp@drive? Bring drives out and see of you get more RPM?

Okay...just to get past the maybe-uncomfortable-question...do you understand how to trim an outdrive? Meaning you start with it 'tucked in', full-down, whatever you want to call it, then gradually trim it up or 'out' after you get on plane?