Biciboyz

I have a 1987 Baja 240 Sport with 454 Mag in it with a Mirage 21 P prop on it. Couple of questions. What is the max RPM I should be getting on that engine? Right now at max I am getting 4000 on the RPM gauge. Is the 21 p proper the correct one? I have read that maybe 23 p is the one I need. Will the 23 p porp let me get that extra RPM out of the motor?

Griff

More pitch will decrese rpm. 1" of pitch = 200rpms.

That would have been a 330hp engine in 1987. You want to spin it about 4800rpms and with a 21 Mirage, you should be able to get close to that. I suspect you have a tired engine or are not trimming it up enough.

captain girt

maybe your tach is off

astar77350

I have an 88 baja 240 sport 454 mag. you should definately be in the range of 4800 rpms, and with that size prop you should, key word should, be exactly in that range. Read through some of the posts from my thread that I posted a few weeks ago, it might be helpful.

http://www.offshoreonly.com/forums/g...ped-wrong.html

blue thunder

1987 would be an alpha drive. What gear ratio are you using? I believe a 1.3:1 was common because they were stronger and the alpha was on the edge with a BBC.

Biciboyz

Don't have a clue on that one?
Would that be marked outside on the drive any where?

Biciboyz

Thanks ....
Went throught it. So where are you now ...what have you figured works and doesn't?
21 or 23?
3 or 4 blade? Thinking it is 3 blade
14 1/2 or 14 3/4 diameter?
Difference between Mirage and Mirage Plus?

bajabob

your rigth. 136drive and they use a19cleaver prop back then or try a 19 mirage

Planetwarmer

My 1987 Donzi 22C has the 454/Alpha combo. I run a quicksilver 21P cleaver 3 blade turning 4600 at 63-65mph

astar77350

Im in columbia sc, boat on Lake Murray. I'm still in a guessing game right now as to what set up I like. I do know that my 4 blade 23p is giving me the best fuel economy. I'm able to run 35 to 40 mph between 3000 and 3300 rpm. but as for top speed i was only able to get to about 53 or 54 at 4200 rpm. I ran the 21p laser II and wasn't pleased, but one thing that was good was that it really opened the engine up and i was able to cruise in the 4800rpm range for a short period, I think that helped because when i took the boat out this weekend with the 4 blade back on, i was able to get to about 4400 rpm and about 58mph. A friend of mine has a mirage 23p 3blade alluminum that I'm going to borrow, i will let you know how that goes, not sure how i feel about alluminum but we'll see. keep me up to date as to your findings as well.