|
took my post out of the mix. Not fair for some whom are trying to help rather than a distraction. Anyways
|
Originally Posted by SB
(Post 4630575)
Excuse the french...What ? H O L Y F U K !
From where ? Nicaragua ? Lol. good news is I’m not going that route and just taking care of the rot myself. |
Those prices are cheap ! Forgot to add that part. Not sure how the work would be for that. LOL.
|
way way cheap.....
|
Ok Guys, Heres the update: I’ve been busy with the boat chasing my tail on a bunch of stuff with the Alpha One and just going through the motions fixing things that aren’t right and then creating new problems or noticing new problems but today I finally got her out on the water. I hadn’t had a chance to do a compression test or change the plugs but today’s trial was mainly focused on an overheating issue I had and a shift cable issue. The good news is, both of those problems are fixed and I had a solid 2 hrs on the water today just putting around. Halfway through my trip I did get a short chance to open her up and see how she’d do with the new prop on her (it’s a 4 blade, 14x21). Tre space to run wide open was narrow and short so I didn’t have the time to mess with trimming out the drive so it was done at the full lowered position. She topped out at 31mph at 3k rpms. I’m thinking trimmed out I could’ve maybe seen 36/37 at around 3500 rpms but who knows. So I took her home to do a compression test and change the plugs. The results of the compression test are all between 160 and 170psi. But I’m still a bit confused as to why she’s running so slow. With decent compression numbers and a 21p prop I’d imagine she’d get going a bit faster. Am I missing something? And after doing the plugs if I can’t get much more speed out of her what other problems should I be looking for? Thanks again for all the help guys. |
4800 rpms for max Mercruiser OEM 5.0L run when correctly propped and with solid engine.
Make sure your throttle plate at the carb can fully go wide open Outdrive trim and trim tabs -- are you using those correctly ? and or do they work properly ? Ignition firing on all 8 very strong sparkall the time ? . Ignition components might need to be changed out. Cap - rotor - coil and plug wires - sensor under the rotor. Fuel pressure at wot is ?? Possible a remaned prop and pitch is way off from stamped 21 pitch that is shown. Possible big weight gain for the hull - weight however How is the bottom of hull ? Next and VERY POSSIBLE as I seen this many of times with used boats - Owner and or seller buys any outdrive to get it sold no MATTER WHAT GEAR RATIO IT IS and of course as cheap as possible in price for that outdrive. You might have the wrong gear ratio set up in that Alpha outdrive. |
Originally Posted by BUP
(Post 4636280)
4800 rpms for max Mercruiser OEM 5.0L run when correctly propped and with solid engine.
It turns out, this is a 5.7 l31 vortec truck motor someone dropped in. Make sure your throttle plate at the carb can fully go wide open This is the next thing I need to do, right now it only opens about 80% due to the angle of the dashboard it’s mounted on Outdrive trim and trim tabs -- are you using those correctly ? and or do they work properly ? Outdrive trim works, trim tabs may or may not work but I’ve left them in the full UP position and don’t use them. Ignition firing on all 8 very strong sparkall the time ? . Ignition components might need to be changed out. Cap - rotor - coil and plug wires - sensor under the rotor. The ignition is the next direction I’m planning on tackling. New plugs made a 9mph difference from 31@3krpms to 40@3600rpms. Going to check timing next and then move to distributor. Fuel pressure at wot is ?? Not sure, still need to check Possible a remaned prop and pitch is way off from stamped 21 pitch that is shown. Prop is brand new 4 blade 21 pitch quick sliver aluminum. Possible big weight gain for the hull - weight however How is the bottom of hull ? Ive pulled out one of the bulkheads and have checked the interior hull, it is good and not holding water. The outside/underside of the hull is spotless, I’ve cleaned her up really good. Next and VERY POSSIBLE as I seen this many of times with used boats - Owner and or seller buys any outdrive to get it sold no MATTER WHAT GEAR RATIO IT IS and of course as cheap as possible in price for that outdrive. You might have the wrong gear ratio set up in that Alpha outdrive I’ll need to double check this with SEI based on part numbers but it looks to be a legit job. It’s a very new looking SEI 106. . Not completely apples to apples as I did trim out a bit on this run but before trimming at all she got up to 36mph so the plugs definitely needed to be changed. Next to item to look at appears to be the rest of the ignition starting with the distributor. After that, if it turns out that it’s fine but I’m still not getting correct speed/rpm for this motor would I be correct in assuming that the engine is just under powered for the 21p prop? If that’s the case and the boat just needs a different pitch prop or more power, I’d be inclined to spend the money on a camshaft vs a lower pitch prop. Is there anything wrong with this logic or am I missing something? |
Thanks to all the guys that chimes in with advice. After following most of your advice and some general tinkering I think I’ve got her dialed in. I think I need to go down from a 21 to a 19” prop but otherwise she’s running great. I had her out today and saw 50mph on the gps at 4200 rpms. The golden ticket was checking the timing, someone had set it to 40* total advance... just brought her down to 32* and boom, she ran like a top. Thanks again guys |
I just came upon your thread. Want to agree with the 19 pitch prop idea. My boat came to me with a 1997 350 mag and needed a 19 to get wide open rpms of 4700. I imagine your boat isn't as heavy as mine so I'd expect a healthy 350 to pull a 19 to 4800 or so.
|
Do SBC Vortec like 28°-30°? I believe the BBC Vortec like a little less timing.
|
| All times are GMT -5. The time now is 08:06 PM. |
Copyright © 2026 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.