What to expect

[coopin87]

I currently have a 1.62:1 alpha one outdrive hooked up to a 5.7 with around 300hp. I am currently at 5500 rpm wide open with a 21 pitch aluminum prop. I have been told to change the upper to a 1.50:1 ratio to match the engine. Im just trying to figure out what I should expect after making the change. The boat is a 95 marada mx3. Top speed right now is around 45 mph and hole shot is decent. WOT range for my motor is supposed to be 4400-4800. Any insight would be appreciated.

 

[Philster]

Re: What to expect

Dang... deleted.

Something doesn't add up. Are you sure of those RPM?

.

 

[coopin87]

Re: What to expect

Dang... deleted.

Something doesn't add up. Are you sure of those RPM?

.

Yes Im sure of the rpms

 

[wca_tim]

Re: What to expect

Agreed that something doesn't add up. Have you got a timing light with a tach on it? you might check to be certain your tach is reading right. IF for example, the little slider on the back was somehow moved from 8 cylinder to 6 cylinder, your numbers would make sense... does it sound like it's wrapped out when you're at wot?

Regarding gear ratios, if you're really at 1.6 now (your numbers could also fit for a 1.98 gear ratio if the rpms and speed are both right...), 1.6 is the one you don't want. you'll be a little faster with 1.8 than 1.5 (after you get it propped right), but both are much stronger than the 1.6 gear set... Let's see if we can figure out why the numbers don't make sense first. Double check the back of the tach if you can see it (or hook an external up), and / or if you're not certain on current gear ratio, take the top cover off the drive and count the teeth on the gears... (those are 12 point 3/8 heads). Hope this is helpful...

 

[coopin87]

Re: What to expect

Agreed that something doesn't add up. Have you got a timing light with a tach on it? you might check to be certain your tach is reading right. IF for example, the little slider on the back was somehow moved from 8 cylinder to 6 cylinder, your numbers would make sense... does it sound like it's wrapped out when you're at wot?

Regarding gear ratios, if you're really at 1.6 now (your numbers could also fit for a 1.98 gear ratio if the rpms and speed are both right...), 1.6 is the one you don't want. you'll be a little faster with 1.8 than 1.5 (after you get it propped right), but both are much stronger than the 1.6 gear set... Let's see if we can figure out why the numbers don't make sense first. Double check the back of the tach if you can see it (or hook an external up), and / or if you're not certain on current gear ratio, take the top cover off the drive and count the teeth on the gears... (those are 12 point 3/8 heads). Hope this is helpful...

I checked the rpm guage with another last week I can check again if need be but it does seem to be accurate. I may need to pull the cover like you sugested to verify what ratio is in it because the previous owner did say it was rebuilt but i kind of chalked that up to bs after finding all the other issues with the boat. At far as being wrapped out im not sure what you mean but there is deffinately way more motor than the outdrive or prop can push right now. Im not sure if that is because of slipping or what. speed is deffinately the variable here ... I didnt have it on the gps :facepalm: just kind of guestimating. I will ask my brother if he remembers what speed he was doing when riding beside me.

If I take the top cover off the drive will I need a new seal or will I be able to reuse the one that is there or is there even a seal.

After I get to about 4000 rpms maybe a bit more it dosnt seem to push the boat any faster but motor will continue to put out more rpms up to about 5500 on the guage maybe a bit more.

 

[Don S]

Re: What to expect

A little background guys, most of the stuff has been covered as to what to do and why the drive is 1.6.
http://forums.iboats.com/showthread.php?t=556141

He wants to know what to expect when he gets the proper gear ratio and proper prop for his engine.

 

[coopin87]

Re: What to expect

A little background guys, most of the stuff has been covered as to what to do and why the drive is 1.6.
http://forums.iboats.com/showthread.php?t=556141

He wants to know what to expect when he gets the proper gear ratio and proper prop for his engine.

Thanks again Don.

 

[Philster]

Re: What to expect

A 1.5 strains the engine a wee bit more, so should knock RPM down a little. I actually typed the exact numbers before and deleted them when I doubted them.

Should knock the RPM down to around 5000 +/-. It might have more impact than sheer numbers on paper would indicate. Expect what I posted; test it and then you will be able to stay propped as is or make a small change.

 

[Tail_Gunner]

Re: What to expect

I currently have a 1.62:1 alpha one outdrive hooked up to a 5.7 with around 300hp. I am currently at 5500 rpm wide open with a 21 pitch aluminum prop. I have been told to change the upper to a 1.50:1 ratio to match the engine. Im just trying to figure out what I should expect after making the change. The boat is a 95 marada mx3. Top speed right now is around 45 mph and hole shot is decent. WOT range for my motor is supposed to be 4400-4800. Any insight would be appreciated.

Before your spend any money you need to get a handle on what you have goping on here.
1. Verify the tach with a independent tach from 1000 to 5000 dont ake anything for granted
2. post your gps speed's along with correct tach reading's take your time
3. changine gears will only be a finer point do not expect any big gain if any
4. Is the bottome of your boat squeaky clean
5. Borrow a 23 p prop and lets pull that engine down a tad

 

[coopin87]

Re: What to expect

Yes bottom is squeaky clean
Gunna put a 23p SS on this weekend at least for now to try and get the rpm's down so I dont kill it
I will take the gps with me this weekend and extra known good tach and report results back

 

[wca_tim]

Re: What to expect

Yes bottom is squeaky clean
Gunna put a 23p SS on this weekend at least for now to try and get the rpm's down so I dont kill it
I will take the gps with me this weekend and extra known good tach and report results back

Perfect! btw, you understand that what we're doing is looking at your numbers and doing some calculations. IF you're running a 21" prop at 5500 rpms with a 1.6 gear ratio, you should be flying a lot faster than you are now (like 15 mph or so more), In other words, there is either something wrong with your information, OR there is a problem with your current prop, etc... that lets it slip like mad as you go faster. without verified gps speed and rpms, or riding in it, we're just guessing.

Are you playing with the trim on the drive? does it change your speed a lot? What kind of a prop do you have on there now (as in manufacture, diameter, etc...)? what kind of shape is it in? too many variables to list, but if your numbers are correct (I would suspect something there first without seeing it run), then something else is definitely very wrong. If there is any doubt about the gear ratio, I would pull the cap and count teeth just to definitively eliminate one of the variables. I would also check the tach - if it is the setting on the back of the guage, it'll be consistently off by 4/3 all the way up. by wrapped out, I meant does it sound like it's running over redline, screaming, etc... a stock 350 might start to sound a little strained at 5500 rpms... if as you mention it doesn't increase in speed much as the engine rpms increase, something else is the problem... no matter what tour gear ratio is, you can get it propped to run fine, but I would be very comfortable running either 1.5 or 1.8 gears behind a small block in that boat. the difference in pitch to make the two run the same rpms is not absurd and there are a lot of decent props around that would work for the 1.8 even though 1.5 would be the norm for that engine. imho... and just my two cents...

 

[coopin87]

Re: What to expect

Numbers on the front of the prop looking around the hub while mounted read 48-78122-21
Numbers on the side of the prop in between fins reads 4878122 A40 21P

It is a used aluminum prop that the mechanic put on there when I took it from the shop. Previously had a 19P michigan SS prop he was woried rpm's would be to high. The used aluminum prop has a few small nicks on it but its not horible. Could the hub be spinning once it gets to a certain speed (thought that if they spin off hub the go completely had to ask as i dont know)

Playing with trim does not do much for me there is a slight difference but its nothing extravagant.

Not sure on brand of prop.

At 5500 rpm it does not sound like it is screaming but it is getting close. If it were pushed a bit further say 200rpm or so I would imagine it would redline. Its not quite a stock 350.

I will check the back of the tach after dinner and let you know where it is set.

 

[coopin87]

Re: What to expect

Prop Pictures

 

[coopin87]

Re: What to expect

Back of tach ... I think it is in the correct position

 

[wca_tim]

Re: What to expect

Sorry, didn't mean to sounds like I was talking down to you - just hard to tell how much folks know or have a feel for rpms and what things sound like. Sounds like you're on the money with the rpms and tach. while it's still a good idea to check your tach, I'm betting based on your posts above that it's not that far off. how about the gear ratio? feel like pulling the cap off the drive to remove that variable?

 

[coopin87]

Re: What to expect

Sorry, didn't mean to sounds like I was talking down to you - just hard to tell how much folks know or have a feel for rpms and what things sound like. Sounds like you're on the money with the rpms and tach. while it's still a good idea to check your tach, I'm betting based on your posts above that it's not that far off. how about the gear ratio? feel like pulling the cap off the drive to remove that variable?

Is there a gasket that I would need to replace. If so I will order it and pull it tonight or tomorrow and let you know the count. If no gasket is needed I will pull the cap off tonight and let you know.

No worries about how you sound lol I have tough skin ... Just need it straight. Im with this stuff but by far no expert. You guys are teaching me more and more each day.

 

[coopin87]

Re: What to expect

Can you partially spin a prop hub? I put on my new to me 23' prop last night and when I pulled off the above pictured aluminum prop the rubber hub looked quite odd. Like it was partially twisted. I have had a spun hub before but never anything that looked like this. Im just wondering if it is possible that it slips once it gets to a certain speed which is why i was at 5500 rpm's.

 

[wca_tim]

Re: What to expect

no gasket, only a thin rubber oring, just be sure it goes back in and you're good to go... Sorry for the delay, been playing, etc... Not sure on the partially spun hub thing... I had a coupler that acter a little like that for a short time once, but it went the rest of the way pretty quickly. I wouldn't be surprised if you were slipping a lot and your prop[ is just catching air.. that's if you really are picking up a lot of rpms and not making any difference in speed. another thing to have a look at is to be sure the drive is running straight through the water... first check the gear ratio and see how another prop (pretty much any other prop) works... Hope this is helpful and also that the boating weather there is as gorgeous as it has been here today!

 

[coopin87]

Re: What to expect

no gasket, only a thin rubber oring, just be sure it goes back in and you're good to go... Sorry for the delay, been playing, etc... Not sure on the partially spun hub thing... I had a coupler that acter a little like that for a short time once, but it went the rest of the way pretty quickly. I wouldn't be surprised if you were slipping a lot and your prop[ is just catching air.. that's if you really are picking up a lot of rpms and not making any difference in speed. another thing to have a look at is to be sure the drive is running straight through the water... first check the gear ratio and see how another prop (pretty much any other prop) works... Hope this is helpful and also that the boating weather there is as gorgeous as it has been here today!

Well I put on a 23' prop this weekend and gave it a shot. Did extreemely well but with 4 adults and two kids in the boat it will only turn 4000 rpms ... with just me and my daughter it was right at 4800 give or take a little bit. We put the other prop on a similar boat with less hp but roughly the same size weight and hull design. It was doing the same thing ... not as drastically but after you got a certain speed with it there were still rpms to go but would not go any faster. I have never herd or seen anything like this but im guessing the prop is just messed up or was reworked in the past and is just junk (any ideas?)

Anyway Im fairly happy with the 23' prop it actually jumps out of the water fairly quick and does not seem to slip much.

As for the rpm's when loaded should they really drop that much when you add an aditional 500lbs or so? (droped about 800 give or take)

Will the smart tabs that I add (as soon as I get them in) increase the rpm's at WOT loaded?

Or should I try a 21' SS prop and see how it does?

 

[coopin87]

Re: What to expect

BTW sorry for no gps speeds but as we were loading the boat at the dock to head out I handed my wife the gps and Bloop she dropped it in the water :facepalm: Needless to say it does not work anymore and Im in the market for a new one.