out drive ratio selection help?

212rowboat

so... choices... 

my 'lil 4.3LX is rated @ 190HP and pushes through a 1.81:1 ratio to a 19p/14.124" five blade prop.... i can hit somewhere around 4500RPM and at 45mph representing a respectable high six low seven slip rate.  I'm sure the engine is tired, and I'm certain it would once have pushed that prop through that ratio to at least 4800RPM. 

My inbound engine is a SBC rated @ 260HP... I hope to twirl that prop @ 4800 max RPM... I'm also buying a replacement outdrive, but I'm dropping the parachute until I figure out the ratio equation...  So... My question to you guys is:

1.62:1 out drive ratio or 1.47:1?  Will the v8 provide enough TQ to swallow the difference in leverage and run the 1.47:1, or, should I consider the 1.62:1 better suited? 

212rowboat

somewhat of an educated estimation to better explain my concerns:

1.81 will bury the tach... but it will make the boat a stump puller and it will allow for slower blade RPM at idle speed, which equals great dock handling.  will likely NOT decrease the prop slip, but rather increase it a bit.. will NOT lug engine even a little bit at any speed or range.

1.61 will split the difference.  a little faster mph at docking speed, a little faster top speed, a little slower out of the hole, a little more work for the engine (load).

1.47 will twirl that 19p maybe closer to a max rpm between 4400 and 4600, and will spin the boat up to likely 55 or so mph- but it will load the engine... it will lose it's sure footedness around the dock and in slow speed handling situations and slower out of the hole- but if the engine isn't loading too much, it will provide a faster speed/ per RPM...  

of course this is all working around an existing prop... but it's the only consistency I have right now, so I leave it in the conversation... removing it from the topic will mean a 1.47 using a 17p and a 23p on the 1.81 will net near the same results... but I don't want to go there yet... this will get confusing quick w/o that prop as the consistency. 

212rowboat

oh.. by the way... the 19p is the average 'blade' angle, but it behaves more like a 20.5' pitch. 

Handymans342

I think Al can only answer that

Michael T

I'm thinking 1.47

212rowboat

yes sir- votec heads... I'll aim for 5k, but I think I'll need that 1.62 to hit it... 

the prop is a ron hill pleasure five, 14 1/8 19p but it behaves much more like a 20~21p 3 bladed turbo geometry on the top end and a michigan wheel 17p 14" four blade out of the hole... 

that can be said as I've ran those exact set-ups for comparison.  that mysterious fifth blade and an overlapping blade does something weird... the blades are much wider across the face than a high five, and both cupping and the dramatic alteration of pitch is apparent with the naked eye... the rake is a little more swept than vertical... it's truly an amazing piece of work.   there are no issues with reverse with this prop... I think likely because how wide the blades are and the diameter compared to the highfive, and maybe something to do with the overlapping blades.... it's durn near like turning an unbroken inclining plane through the water... 

212rowboat

oh.. and thank you, sir. 

halifax212

The  set up in my 212......5.7 mag, 1.47 alpha 2, 19p 4 blade Merc revolution prop, wot @4500rpm. Works very well for me getting on plane and 55mph top end. No complaints.

212rowboat

thank you, sir halifax (yes, I just knighted you)... that is a valuable piece of information...

all things being equal, that's 3061 twists the prop makes @4500RPM at that ratio... the same prop spin w/ 1.62:1 would be 4950RPM... which means that is dead center mass of where I would like to be.  

more evidence I need a 1.62/1 instead of a 1.47/1... and I was really close to yanking the trigger on a 1.47 earlier today... they have a 1/62... and so will I, soon.. 

Michael T

Is there any chance that you might "breathe" on that 260 HP a bit, moving it towards 300HP? If you do a 1.62 will probably leave you having to compensate using a propeller change, not the best scenario, IMO. To further explain my thoughts, I have up-graded a number of engine/drive packages in my own and friends' boats over the years. A couple of times we have not up-graded our drives enough and had to go back to the well for a more solid drive or one with taller gears. I'd hate to see you want to take your project to the next step and be limited by your drive. 

212rowboat

so- big question.....

what are the forum's thoughts on SEI replacement drives?  I can buy one of those w/o paying shipping for about $800 less than I can the reconditioned 100 hour mercruiser.... SEI116 in 1.61 shipped to door w/ install kit and shower for $1600... Mercruiser for $2.4k+shipping... One new; one used/reconditioned...

thoughts?  

Handymans342

Sometimes reconditioned is better than new sometimes not. What's the warranties?

212rowboat

no warranty on the merc, three year no fault no questions on the SEI, which I read from people who've actually used it is outstanding.  

Handymans342

SEI. No brainer

212rowboat

caveat: SEI comes with the gears unlashed, which requires a break in period that will require me to operate under planing speed for 10 hours- pretty much standard break in such as cars who regear face- fluctuating speeds, no hard launches, ect.... but couple that with the nee engine, all is well- I'll be out on the water every afternoon for a couple weeks tweaking timing, breaking in gears, ect- so... the unlashed gears aren't a big deal... 

Dream_Inn

I've heard SEI does a decent job with their outdrives.

212rowboat

it's a done deal now... we'll see!!!

Handymans342

Spend that money Drew!

212rowboat

Awesome, Sir!! me be feelin' mucho better about it with your endorsement... I was thinking it was worth the risk based off of experiences with the warranty... and now I have one inbound.... 

I'm going to package up the 4.3LX and the 1.81(or maybe it's 1.84) upper and lower, turn key, and sell it as a package.... I'll cut you a deal, Al, if you or one of your customers need one.  they both (engine and drive) run fine, and likely just need a tune up and service (which I will do before I advertise it)....