Prop Help 454 MAG?
 

I have an 89 Century Ultra I with a 454 MAG carb. and Bravo outdrive. Its stock except stainless marine headers and risers. I'm currently running a 23P 3 blade mirage prop, peak rpm is 5200 and I can get about 64 mph by the speedo in perfect water. Could I get a little more top speed with a different prop or is this ideal. The valve cover says 4800-5000 peak rpm I believe. Thanks for the help!

Check your speed with a GPS first...I doubt your doing an actual 64 mph...then go from there.

I would try a 25p Mirage plus prop, if thats an accurate top end RPM thats to high.

Sounds like you have the correct prop. Maybe get it lab finished or a little more cup. You can't go by the "Dream O Meter", GPS is much more accurate.

I think you have the right prop. It certainly doesn't hurt anything to be running a couple extra hundred RPM on flat water trimmed out. As you know when you have to tuck the drive in due to rougher water those extra R's come in handy. You can always try another prop however I doubt very much you'll gain anything and lose a lot of bottom end and mid range.

I am not real familiar with all the particulars of your boat however your speedo seems to be pretty accurate assuming your bravo is a 1.5. Regardless of what it says your set up seems just fine.

John

5200rpms is fine to spin a 454 mag. You could pick up some speed with labbing your current prop and adding pitch or getting a labbed 25. You're very close, so only try subtle changes.

Thanks to all. I'll keep my eyes open for a deal on a 25P to try.

I'm not sure i agree with that being the right prop for the boat. If you are going 64 MPH, that equals 16% slip, which can certainly be improved.

Quote:
You can't go by the "Dream O Meter",

Now that made me laugh,cuz it's so true, even though as I sit here with a broke motor with two bad heads.:drink:

Going from a Mirage to a Mirage plus will lower the rpm's by about 150 - 200. If you try to go from a std mirage 23 to a mirage plus 25 you will drop to about 4600 and the boat will be very sluggish in the acceleration dept and probably loose some top end. Look for a Plus 23 or a non plus 25 to try or possibly a Bravo 1 24"
Good Luck

Where are you located?

Albany, NY. I'm also questioning what prop I actually have. Its a stainless 3 blade 23P thats about all I know. I believe 23P are the only markings.

Does it say Mirage on it? If not it could be the old stye blades from the 80's. Mirage props are better, Mirage plus has more cup.

It does not say Mirage on it so that being said what should I look for? Its probably the stock prop that came on it in 1989.

23 Mirage Plus.

Ditto on that. The original mirage is akin to a labbed plus. Just a lot cheaper.

I believe in 1989 Mercury was selling the Mirage. Mirage Plus was a later release that was basically a Mirage with more cup. If it was me, I would work with the prop you have and send it to one of the prop specialist like Brett Anderson. He can put you right on the money with an exact top end RPM and reduced slip. This "labbed" process will cost no more than new prop(s) and will likely out preform any prop out of the box.

He said it does not say Mirage on it. I had a Quicksilver 3 blade on my Rinker, this was about 11 years ago. The blades are shaped different and they are a smaller diameter. It sounds like this is the prop he has. A Mirage is better suited for his application.

I just got my hands on a GPS this weekend. 60.6 mph on GPS = 64 mph on the speedo. at 5200 rpms. I will look for a 23 Mirage Plus I guess is the general consensus?

Good plan. You need a baseline with known prop.

That is why I call it the "Dream O Meter". Mine was about 3MPH fast when it worked. Looks like you are on the right track with the 23 Mirage.

So it went 60.6 mph on GPS at 5200 rpms with the stock 23P prop the boat came with new in 1989. I just put a 23P Mirage Plus on it. It went 60.4 mph at 5400 rpms on GPS with the Mirage Plus. I'm sure I could get the extra .2 mph the water was a little smoother the second time but very smooth both times. Same location. It was a little warmer out the second time and more humid. This isn't what I expected? I assume the higher rpm is because the prop is lab finished? It must be slipping more to run the same speed at higher rpm though? The one thing I did notice is it seems to stay on plane easier, cruise faster at lower rpms and I can trim it much higher before the prop starts getting air. What should I try next? I was thinking a 25P Mirage Plus??? Thanks.

If you are willing to spend more $ on props, I suggest you get a prop expect to work with you. No matter what you do with props, it sounds to me that you have likely maxed out your MPH...maybe an additional 1 MPH left.

Dont waste your money on a 25p mirage plus. I have that prop on my 26' Chris Craft Limited..except my warmed up 502 Mag with 4" thru hulls is making 500 hp or close to it, and it turns that motor 4850 rpm with that prop. What I'm telling you is your not making enough hp to turn that prop, and it will no doubt pull that motor down. I think youll be lucky to turn 4500 with that prop behind your motor. Work the 23..or try a 4 blade 21p.