2006 Tahoe 215 deckboat 4.3 MPI alpha one gen 2 prop question

[shackle101]

Hey guys so my current prop on this boat is a 48832832a45 14-1/4 x 21p normal rotation. three blade

I'm looking to upgrade to a 4 blade prop and wondering which pitch would be best to go with. The current prop is maxing out a little bit over 4k RPMS and getting a top speed in the high 30's.

I would like to see a improvement in speed, but maintaining pulling power. I've had a four blade prop with my older boat and hoping to get the better handling as well (in slow speed). I know with I/O it seems you really need trim tabs to get big improvements at slow speed, but hoping this will help somewhat. Any suggestions on Material? Obviously Stainless would be nice, but I'm fearful of hitting bottom and messing up the lower unit. Does this happen often?

Thanks!

 

[shackle101]

decided to go with a 19P 4 blade. It seems like the 21 might not be correct from factory. We only had 2 people on the boat and I think it was around 4200 rpm max. I do have a hydrofoil wings on it though.

 

[jkust]

Your engine is lugging. Even with what sounds like a boat that may have benefited with a 5.0 MPI option, the 4.3 shouldn't be lugging at such low RPM's. Stainless isn't going to do anything for you until you figure out why the engine is turning so slowly. Hydrofoils are generally frowned upon and even more so for I/O's.
There are two systems to mitigate damage from submerged object strikes...firstly is the system that allows the outdrive to raise up upon impact and return to its pre impact position and the second is the hub inside the prop that will sacrifice itself. I suppose technically the skeg itself is a system to protect the prop as well.

 

[steelespike]

No prop changes until we get accurate numbers.
The 4 blade isn't likely to improve top speed. To evaluate your setup we need accurate numbers.
your 21" prop at 4200 rpm would be "about" 45 mph. A 19" 4 blade at 4200 would be about 40.
Get rid of your hydrofoil And get us your lightly loaded rpm and gps speed with the 21"
Striking bottom depends on where you boat and the bottom material.
Soft bottom, mud and sand, a stainless prop may hold up better than al. but costs more to repair.
Hard bottom al. prop will be more forgiving.

 

[shackle101]

so what you guys might be saying is my engine might be undersized for the deckboat? Is this a known issue with Tahoe cause they put the 4.3 in them often. It's only a 21.5 footer about 3,500 to 4,000lbs. Yeah I guess I need to get better numbers and report back (and yes I guess I'll take the hydrofoil off, but I had good success with them in the past with outboards). But the 19p 4 blade should be good right? they have 20p, but very limited options.

 

[jkust]

so what you guys might be saying is my engine might be undersized for the deckboat? Is this a known issue with Tahoe cause they put the 4.3 in them often. It's only a 21.5 footer about 3,500 to 4,000lbs. Yeah I guess I need to get better numbers and report back (and yes I guess I'll take the hydrofoil off, but I had good success with them in the past with outboards). But the 19p 4 blade should be good right? they have 20p, but very limited options.

Your boat is specking out at 3425 dry weight. A bit heavier than some bowriders of that size but deck boats are heavier. It just needed to be ordered with the upgraded engine but presumably the package was sold on price. Regardless, if your tach is correct, the engine should be operating at its max rpms and your suggested props don't garner an extra 600 rpms to get you there. I'd say your dry weight is right on the edge of needing a bigger engine to get satisfying performance but none the less, it should be WOT at 4800 rpms. Sea Ray is notorious for underpowering their larger Bowriders and Sundecks. They get ordered with the 5.0 MPI in them when they need a 5.7 or larger. Tahoe I can see as they are a budget brand but Sea Ray...I just don't get why. My boat is 200lbs heavier dry weight and has a 350 Mag MPI in it which is a night and day difference than a v6 but for only a couple hundred lbs difference. Hard to compare hull to hull but at least on its face, you seem to be underpowered but with an underlying issue you need to investigate. You should get 46ish out of that engine.

 

[shackle101]

Yeah my tach could be off and the speed certainly could be off. Any suggestions on a backup method to try? I've tried the spark plug tach gauges and I don't think they are very accurate. I assume my Hydrodoil and lower unit tilt might be coming into play here too. ( I tilited all the way down cause hole shot was pretty bad.)

According to this article they used the 190hp non MPI and it seems to have enough power (mine should be pushing 220hp):
http://www.boattest.com/oem/444/boat.../0/off/640x360

 

[shackle101]

Anyone happen to know what size Props these come with on the 4.3 engine? It could be the prop was replaced as well I bought it used, and the prop wasn't in rough shape as all just missing a little paint.

 

[jkust]

Gps for speed check and the tach requires a separate tach to test. Hydrofoil is a big drag and I'd yank it off. Your boat may or may not need trim tabs but a hydrofoil is just not done. They are more of an outboard application and even then not looked kindly on. If you are trimming way down with a foil, that would kill your performance. I'd yank the foil, and work the trim with the prop you have and do some baseline testing. The v6 is a fantastic engine, one of the best I think but at a certain point pushing a heavy boat with a tank of gas and gear and a couple people is just going to slow it down and you have to work the trim to offset some of that.
My last boat had a v6 and was about 3000lbs dry...it was great except that it was the third smallest engine offered and you cold tell with a heavy load. I'd say that at least you have the MPI engine so that's good.

 

[shackle101]

Called Tahoe and they told be the stock is 14 1/4 x 21 so it is propped right. I'll let you guys know how my testing goes with hydrofoil off and trim adjusted for top speed.

Anyone happen to know what size Props these come with on the 4.3 engine? It could be the prop was replaced as well I bought it used, and the prop wasn't in rough shape as all just missing a little paint.

 

[jkust]

That is generally the stock Black Max that you might see on there. The thing is, boats are rigged at the dealer so a dealer can put anything on for a prop. A lot of times you will see a 23" prop used for published test results because of course you get higher top speed. That prop you mentioned is the prop my 4.3 came with that I mentioned I used to have. I got decent top speed but you couldn't trim it up as high and it blew out in corners more than some of the aftermarkets I had. Of course again....can't compare hulls.

 

[shackle101]

Thanks! As far as the 4 blade I already went with do you think that was a good choice? Generally they say go down 1 pitch, but I wanted the Solas Rubex 4 which worked well for another boat I had. The 20 pitch options are very limited, and I figure there will be times this boat will have 8+ people. I guess if it stays under 4600 rpm I should be fine right?

That is generally the stock Black Max that you might see on there. The thing is, boats are rigged at the dealer so a dealer can put anything on for a prop. A lot of times you will see a 23" prop used for published test results because of course you get higher top speed. That prop you mentioned is the prop my 4.3 came with that I mentioned I used to have. I got decent top speed but you couldn't trim it up as high and it blew out in corners more than some of the aftermarkets I had. Of course again....can't compare hulls.

 

[steelespike]

220 hp is plenty.I've seen lots of 3.0s that were over 3000 lbs.and were performing within their rpm range and speed.
I think a healhy setup at 220 should be at least be high 40s.

 

[jkust]

Thanks! As far as the 4 blade I already went with do you think that was a good choice? Generally they say go down 1 pitch, but I wanted the Solas Rubex 4 which worked well for another boat I had. The 20 pitch options are very limited, and I figure there will be times this boat will have 8+ people. I guess if it stays under 4600 rpm I should be fine right?

You want to be right at 4800 at WOT. Not under and not over to harness all the available HP as that is how boat engines are designed to be used....lugging an engine is actually not good for it. One inch of prop pitch generally equates to 200rpms...not always but nothing is ever set in stone with boats. What I discovered about having a 4.3 in a boat that was optioned available all the way up to a 5.0 MPI V8 (this was an 18 foot boat so 270HP is a lot of juice) is with a lot of people in it, you get very poor out of the hole and planning and then once the initial excitement of the boat wears off in a couple year, that's when it hits you that you either got adequate power or not. The fact is the 4.3 has an amazing amount of torque which of course nobody talks about and Mercruiser and Volvo don't publish.
When I got fancy with my props, I realized there just wasn't enough umph there to utilize the features of the prop such as a bit of cupping and I lost RPM's and speed. Now add on to all of that that I got the previous boat in my early 30's and now am in my early 40's and I go wot for maybe 2 seconds and pull back so top speed isn't a concern any longer though my kids are always asking me to floor it. It's nice to get out of the hole fast but when I want speed, I jump on one of our supercharged waverunners and go faster than most boat can ever achieve and use more gas than most boats can ever use.