Can I lower my peak power rpm with a 4 hole spacer?
 

Im a little over propped and its currently being labbed. If I still cant get it into my recommended power rpm 42-4600, would adding a 4 hole spacer help by bring more power in at 4200 and possibly letting me spin it higher? I have one, just need some gaskets. Im right at 4200 now. Motor is a stock 330hp OMC 454 with a Weind Stealth intake and Holley 750 mechanical. Will the spacer screw up my power valve sizing? I just hate to lose my cruise speed with a small er pitch and dont want to spend the $ on a boat Im going to sell soon anyway.

It works sometimes, and other times it doesn't. The Weiand Stealth has a pretty big plenum and a four hole spacer might not help. You aren't going to screw up your calibrations by trying it (unless you have that carb jetted perfectly now, and who does?). Is the exhaust crossover passage blocked off in the intake manifold? That could help a little.

You might have to try some different ignition timing settings (34 - 35 degrees BTDC @ 3500 rpm), and install some extended tip spark plugs (Champion RV15YC4 gapped at .045). Do you have a non restrictive flame arrestor? A K+N marine air filter with a stub stack might help. Change to synthetic motor oil for a little performance boost. Keep the air inside your engine compartment cool by running the bilge blowers all of the time.
Good Luck
Dennis Moore

Thanks Dennis, I have almost exactly what you have recommended. K&N arrester w/stub stack, full time through hull exhaust, AC Rapidfire plugs, Mobil 1 synthetic and I even added two bilge blowers that suck in air from outside and blow it directly on my flame arrester (that was good for about 1.5mph). I think Ive rung everything out of this thing I can w/o opening her up.
The ignition system is this goofy Spitfire ECM. Doesn't matter where you turn the distributer, the ecm corrects and puts it back where it wanted it. Do you know of any way to advance timing with this type ignition short of changing it out?

Mr. Demeanor,
Even though it's a lower rpm "330", I sure think that if you are not even turning 4200 your best bet for improvement is a different prop. Most marine engines seems to perform best when running near the top of the recommended range.
The Stealth manifold from what I understand is more of an upper range dual plane and may not have been the best choice over stock if you haven't done any other mods to the motor. An Edelbrock Performer (not the Performer RPM) used to be the hot ticket for the 330, good for 15 to 20 horsepower compared to the stock cast iron piece. They are cheap too, at Jegs or Summit.

I live in your area (Libertyville) and have some props sitting around that I can't use any longer. Maybe one of them will work for you. What are you running now?

Rich

35/25, thanx for the offer. I tested two props yesterday. My current prop is a 19pitch Rev4. I tested a 17pitch Rev4 and a 19pitch Offshore. I spun both of those to 4800rpm with a full load. Chicago propeller is working a deal with me on 21 offshore that should do the trick. Should put me at about 4500rpm and maybe 4600rpm tweaked a bit. This all just came together today. I love the Rev4 but a 19 pitch turns like a 21 or a little bigger. I lost 600 rpm going from the same pitch 3 blade. The blades are huge on the Rev4 if youve never seen one.
I would still love to get more rpm of course but with the boat for sale and a move to Florida soon, its not a top priority. I was hoping someone might have input one my ignition timing ?????

I have an old, but in excellent condition, Mirage 3 blade, 21 pitch. I had it on a 243 Cobalt with 300 horse ("330") Merc 7.4L and turned right around 4600 rpm. Would unload it cheap.

Rich

I already tested one. My boats real heavy and the 3 blades just dont work well. I have two for sale. Thanx again for the ofer though.

I was looking for a 21 pitch prop to get labbed and I found this thread. Do you still have this prop for sale?

Bryan

I'm looking for more RPM's also I currently have a 21 pitch mirage plus. I was considering buying another one to get labbed or going to a 19? do you still have any props forsale?

I doubht it. This thread is 4 years old and he's not registered anymore.