Prop Advice

[GKricheldorf]

Is anyone out there running a 454 mag with an alpha one stern drive(1.32:1 ratio) been playing around with props? I'm looking for some tested results before i start spending money on props.

Currently i have a Quicksilver 3 blade, 19 degree prop on my Z25. WOT is at 4000 rpm and this yeilds about 58-59 mph depending on fuel level and 2 people.

[wytmike]

Are your speeds off a gps or the dash speedo.
They seem high. With that ratio and pitch it calculates out to roughly 48-49 mph. Pitot Speedos are usually optimistic. If I remember a 454 mag according to the manual should be running around 4200-4600 rpm. I'm running a 3 bladed cleaver on our Z25 right now with a TRS drive and it handles well. I had a chance to try a quad IV and it seemed to settle the boat down even more. Unfortunately it was a couple of inches too high and the boat couldn't pull all of it.

I think you would want to try and drop an 1" or 2" to try and get the revs up a little. It will help with your hole shot and also might give you alittle more on the top end. I don't think hydromotive makes a 17" or 18" quad IV but they may be able to take a 19 down for you.

Good luck,
Mike

[Darrell]

Your speed seems kinda high for 4000 rpm, Is the 58 mph on your speedo or GPS. With your numbers it figured that you should be @ 55 with no allowance for prop slip. With 10% slip you would be @ 50 mph. If your speeds are GPS I think your tach might be off a bit.

Darrell

P.S. on the last two boats I was very happy with the Mirage Plus 3 blades

[GKricheldorf]

Amazingly the speedo is very accurate. I have a Garmin Streetpilot GPS that reads out the same. I'm not 100% sure on the drive ratio. There was no sticker on the motor or stern drive that said what the ratio is so I called Mercruiser and gave them the sn#.

I'll take my tach and dwell meter out next time to see if the tach is accurate. If it is then I’ll see if the mechanic that the old owner used has any info on the stern drive.

Thanks for the help
Glenn

[wytmike]

Are your sure of the pitch of the prop? If it is a 19" pitch and it is a 1.32 ratio then your pulling around 5000 rpm. That would be high for a stock 454 mag.

[GKricheldorf]

That's what is stamped on it Quicksilver 48 xxxxxx 19P, sorry I don't have the numbers that are x'd, memorized yet.

I agree the math doesn't work out. My guess is either the rpm gauge is inaccurate or the gear ratio has been changed.

I did check the timing last Saturday and hooked up my tach. It did read 600 rpm at idle and I think that is where it should be. The dash tach read the same.