TomZ

iTrader: (2)

I had this under another topic but thought I'd move it out here in the open for discussion. TZ


Here's what I have and I need some prop advice... (19 year old hull technology, pleasure boat).

Boat:

'83 4 Winns 23.5' LOA, 8' beam
roughly 3500 lbs without fuel, holds 70 gallons.

Figure an additional 800 pounds fueled with me and my wife and toys, etc.

Performance with a dead 355 two years ago was about 45-50 MPH on the speedo (surprisingly, the speedo is right inline with GPS) depending on conditions. I was spinning a 17P Mirage with an Alpha One 1.50 ratio (yes, it's an Alpha and I know I'm playing with fire here). HP was "maybe" 200 or so. Like I said, it was rather toasted.

New motor (granted, have not been able to run hard because of bad gas, pings with load so I'm not loading it, another two trips will clean her out) spins 4100 RPM with no load (the engine is not working hard enough to open the secondaries at all) and runs 40 MPH going against the river current with a 21P Quicksilver QS3000. Boat is full of fuel, contains me at 190 lbs and my brother-in-law at about 165 lbs plus fishing gear and coolers.

New engine specs:

383 CID, 5.7 rods, 10.3:1, ported Vortec heads with big valves, Comp XE-274H (274*/286*, 230*/236*, .487/.490, 110*), Performer Vortec, 750 Quadrajet, jetted and tuned for the last stroker motor that died (jetting/metering seems to be pretty much on so far). Timing is set at 32* at 3700 (full advance). I did not have this motor dynoed, but a for-the-most-part-exact duplicate was run on my shop's dyno and produced 430hp and 460tq. Peak power was in the upper 5k range with peak torque coming in the mid 4k range (my cam was advanced slightly to shift the curve a little lower). The torque curve was very flat producing over 400 ft lbs at the 2500 RPM mark.

I'll be able to figure how the boat is running with the current prop once I get the bad gas out. I was told by a friend though that I'm wasting my time trying to test the 21P and that I should have moved up to a 23P instead. Any thoughts as to how it should be prop'd? Also, since my boat is ass heavy (as has been described by others with boats like mine) should I be looking at something that gets the stern out of the water more? My Mirage seemed to get the boat up more and this one seems to let the boat stay more in the water (though it gets on plane immediately, 2-2300 RPM is all that's needed to plane).

Thoughts?

Tom (sorry so long-winded)

TomZ

iTrader: (2)

And one quick note... according to the various prop calculators I am generating about 26% of slip. Is it that I'm unable to really test since I can't load the engine or what?

Again, thoughts and comments are appreciated.

Thanks!
Tom

TomZ

iTrader: (2)

Anyone??

tomcat

I'm not sure about the slip calculation but you won't really know anything until you reach WOT. I had a 236 Rinker with a 454 Mag that went ~65 mph at 5000 RPM with 23 Mirage. You may be making more horsepower but at a higher RPM so the 21 Mirage is the place to start.

jpclear

I would also say 21" Mirage (NOT Quicksilver) to start. If you feel that the engine was built and cammed to make max. HP in the high 5000's then that is where you should get your best performance. Look for anything you can "try" that will give you your 5600 to 5800 and then go to the different prop styles for bow or stern lift as needed. --- Jer

jpclear

I should have added that if you were talking BB then 5800 would be a bit extreme but a properly built SB should handle that OK. However, I don't want you to scatter it on my say-so. Rember; "only your dyno-man knows" --- Jer

FlyFast

Tom,

One of my questions with an alpha drive was what is the best prop to offload the stress in the drive? I had a volve penta years ago that kept blowing the tranny because the prop turned out to be the wrong one. I just have questions. No anwsers. I thought about trying a 25 pitch on my alpha but I was concerned it might be too much of a load on my alpha gears?

I would think a 23 would be a good starting point and with an aluminum prop it can be resized 2 inches for about 50 bucks.

With your motor a 25 would probally work but will that torque your drive too much? Your motor is really in bravo territory.

On my boat I think I could spin a 25 with a very light load but with a full load of people I like a 18 4 blade because it jumps right up on plane. My wife can drive the boat because there is very little bow rise and she can see over the bow. For top speed it is the wrong prop.

I think you have to experiment and sometimes the results are not what you expected.

Someone on this board will probally have a better anwser.

Good Luck

TomZ

iTrader: (2)

Again, the first thing I need to do it be able to get it up to WOT. I was hopefully going to get it there over the weekend, but with the weather being what it will be over the next couple of days plus Father's Day, it looks like it'll be a little while longer before the boat hits the water again.

You may have a point regarding drive loading. At the moment, the 21P does allow the the engine to run rather easy which is probably a plus considering that it is an Alpha drive. Next season a Bravo drive WILL be on the boat, but in the meantime I do not want to break the drive. I just can't afford to have it go to **** just yet. Then again, the boat it insured and it includes drive damage as well (they don't have to know that the engine is producing over 400hp... it looks nice and stock, except for the chrome valve covers and intake). I'll just be nice to it.

If the weather decides to clear up, I'll try and run some more of that crap gas out of there (a run down to Tim's River Shore for some crabs will probably do it just fine) and see what she does from there.

Tom