Need to determine best prop for weird setup

jimmbo

jimmbo

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Lpgc said:
Not trying to take the thread off topic, Mercury outboards always had smaller props than Johnson, obviously with different gearing to suit, but which is most efficient at low and high speeds (small prop spinning faster or big prop spinning slower)?
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Not true. Until 1969 almost all of Evinrude/Johnson V4s used tiny 10" diameter low pitch Props spinning very fast(exceptions were the 1958-59 50hp, and later 60hp which was offered with an Heavy Duty Option, using the older 50hp gearcase, and the 66-68 100hp), while Mercury used slower turning, approx 13" diameter higher Pitch Props
 
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Lpgc

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jimmbo said:
Not true. Until 1969 almost all of Evinrude/Johnson V4s used tiny 10" diameter low pitch Props spinning very fast(exceptions were the 1958-59 50hp, and later 60hp which was offered with an Heavy Duty Option, using the older 50hp gearcase, and the 66-68 100hp), while Mercury used slower turning, approx 13" diameter higher Pitch Props
Click to expand...
Why did they change prop sizes in 69?
 
Scott Danforth

Scott Danforth

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The gear ratio change is in the LOWER. The Volvo uppers are the same from 4- cylinders to diesels
 
jimmbo

jimmbo

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Connor0612 said:
1998 Four Winns 180 Horizon RX
1998 4.3GL Volvo Penta 1.51 gear ratio

Hello! I have a boat that’s had its outdrive unit swapped out with one I’m assuming use to be in a v8. As per Google my 4.3gl should have around a 1.80 gear ratio outdrive but I read the tag and it’s a 1.51.

At WOT I’m only getting 35mph at 3800rpm.
Current prop is a quicksilver nemesis 4 blade 14x21 aluminum.

I’ve also tried a 15x17 3 blade Volvo prop with not much difference.

What prop will work best to get more speed and proper rpm at WOT with this setup?

Thanks
Click to expand...
The 1.51 was used with the 5.7. It is what my Motor has

Going from a 21" 4 blade to a 17" 3 blade, should have shown an increase of at least 1000 rpm
Top Speed, would only be a couple of Mph difference
 
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jlh3rd

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Connor0612 said:
1998 Four Winns 180 Horizon RX
1998 4.3GL Volvo Penta 1.51 gear ratio

Hello! I have a boat that’s had its outdrive unit swapped out with one I’m assuming use to be in a v8. As per Google my 4.3gl should have around a 1.80 gear ratio outdrive but I read the tag and it’s a 1.51.

At WOT I’m only getting 35mph at 3800rpm.
Current prop is a quicksilver nemesis 4 blade 14x21 aluminum.

I’ve also tried a 15x17 3 blade Volvo prop with not much difference.

What prop will work best to get more speed and proper rpm at WOT with this setup?

Thanks
Click to expand...

props....
These are readings from my pontoon of 4 different props. 3 different props give the same results.
The 3-16x12 gave me the higher rpm I wanted (6100 +/-) with just me on board so that pulling teenagers on tubes let me stay at the upper 5000 rpms.
Point is, props aren't some magical solution. The 3-16x12 cost me higher end speed. No way around it.
And my motor is a brand new purchase, now 3 years old merc 115hp CT.
So ..your money, your time.....
The engine should be in the upper recommended rpm range, that's not a suggestion.
To get your rpm's where they should be is gonna cost you top end speed.
You want more speed, you need more HP so that you can run a higher pitch and/or diameter prop....or more blades.
or if the motor is weak ,fix the motor....
to me, changing gearcase ratios is basically no different than changing props. Your just "shifting" gears like a manual tranny.....
 

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Scott06

Scott06

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Connor0612 said:
I haven’t verified the tach with a shop tach. The speed I was confirming with gps so I know it’s accurate. I might have a line on another upper Volvo gear housing with a better gear ratio so I’ve temporarily stopped thinking about props until I hear back
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weather you swap uppers or props verify the tach is accurate. Also would do a sanity check on ignition timing and engine tune up (carb/fuel system/ignition components). Check total ignition advance at like 2800 should be 24-28 degrees or so.

Not saying this is the root cause but not getting as many rpm as one would expect going from the 21" to the 17" would have expected higher rpm increase with the 4" pitch change. You may have a couple things going on concurrently

Wouldn't hurt since it is new to you to get a baseline compression test and double check firing order.
 
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Connor0612

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Scott Danforth said:
The gear ratio change is in the LOWER. The Volvo uppers are the same from 4- cylinders to diesels
Click to expand...
Thats news to me! Thanks for pointing that out before I go in blind with someone telling me its in the upper and all the lowers are standard rotation
 
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Connor0612

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Scott06 said:
weather you swap uppers or props verify the tach is accurate. Also would do a sanity check on ignition timing and engine tune up (carb/fuel system/ignition components). Check total ignition advance at like 2800 should be 24-28 degrees or so.

Not saying this is the root cause but not getting as many rpm as one would expect going from the 21" to the 17" would have expected higher rpm increase with the 4" pitch change. You may have a couple things going on concurrently

Wouldn't hurt since it is new to you to get a baseline compression test and double check firing order.
Click to expand...
OK your probably right, something else might be going on. 17" 3 blade 4000rpm. 21" 4 blade 3600rpm. I agree should have seen more change than that based on the 200rpm per inch of pitch rule.

I havent checked ignition timing in that depth before so im not sure how. Ive only ever gotten cylinder 1 to top dead and lined up the mark of the rotor.

what shop tachs are people running to double check rpm?
 
Scott06

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Connor0612 said:
OK your probably right, something else might be going on. 17" 3 blade 4000rpm. 21" 4 blade 3600rpm. I agree should have seen more change than that based on the 200rpm per inch of pitch rule.

I havent checked ignition timing in that depth before so im not sure how. Ive only ever gotten cylinder 1 to top dead and lined up the mark of the rotor.

what shop tachs are people running to double check rpm?
Click to expand...
You will need an advance timing light. I have an old Craftsman with a dial on it, you can put in the advance on the dial and it should time with the TDC mark on the balancer. Just looking for total degrees of advance, with out advance engine will not make power

Some more modern timing lights have a tach in them, I have this ignition analyzer that measures Kilo Volts of ingtion spark as well as RPM.


You can also use a cheap spark gap tester to see how far the spark jumps

 
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Connor0612

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Scott06 said:
You will need an advance timing light. I have an old Craftsman with a dial on it, you can put in the advance on the dial and it should time with the TDC mark on the balancer. Just looking for total degrees of advance, with out advance engine will not make power

Some more modern timing lights have a tach in them, I have this ignition analyzer that measures Kilo Volts of ingtion spark as well as RPM.


You can also use a cheap spark gap tester to see how far the spark jumps

Click to expand...
Now that ignition analyzer that doesnt do timing as well right? if i get a modern timing light with a tach also on it that will suffice?

like this one for example?


then i can verify the rpm and the timing?
 
Scott06

Scott06

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Connor0612 said:
Now that ignition analyzer that doesnt do timing as well right? if i get a modern timing light with a tach also on it that will suffice?

like this one for example?


then i can verify the rpm and the timing?
Click to expand...
Yes the Innova timing light will do both tach and timing functions.

This goes over checking total advance

total timing is at 6:53
 
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Connor0612

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Scott06 said:
Yes the Innova timing light will do both tach and timing functions.

This goes over checking total advance

total timing is at 6:53
Click to expand...
Thanks for the link! So I double checked in the manual and it only says for the 4.3gl a/b/c/d that the Idle timing should be 1° BTDC. In theory if I have it set to that degree at idle should it be correct when it’s advanced at 2800rpm? Let’s just say that it’s not around 25°, should I change the timing even tho the idle timing is right ?
 
Scott Danforth

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follow the manual for setting base timing. put the timing shunt in and set to 1 degree BTDC

then CHECK full advance at 2800 RPM. is it within spec? Yes, or No.
 
Scott06

Scott06

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Connor0612 said:
Thanks for the link! So I double checked in the manual and it only says for the 4.3gl a/b/c/d that the Idle timing should be 1° BTDC. In theory if I have it set to that degree at idle should it be correct when it’s advanced at 2800rpm? Let’s just say that it’s not around 25°, should I change the timing even tho the idle timing is right ?
Click to expand...
In theory, as danforth points out with the timing shunt in to lock it in base mode should be at 1 deg BTDC, with shunt out it will be around 10 at idle, at 2800 or so should go up to 25 or 28 total. you just want to confirm it is advancing. if it doesn’t advance could be bad module or base timing has moved. Just something to rule out, if off yes you can advance it but only would do that if the module is advancing it as you move through rpm. On the other hand if it is 10 at idle and advances only a little I’d look to replace the module .

again just rule it out as a sanity check , otherwise you’ll end up running an11” prop pitch …
 
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