Volvo gear ratio? How do I know?

[Don S]

Re: Volvo gear ratio? How do I know?

Sure it could use a bottom paint....

A dirty bottom will slow the boat down, and kill your WOT rpm.

 

[lyt]

Re: Volvo gear ratio? How do I know?

i wouldnt say its dirty.... but yes the ablative could use a refresh.....


so lets say the bottom was fab.....

would you still look at my #'s and feel the engine is 100%

 

[Maclin]

Re: Volvo gear ratio? How do I know?

lyt,

I responded to a couple of your questions over in the prop section. At that time I held back a feeling that your boat is either way heavier than that, or the engine is not quite as healthy maybe as you think, although a dirty hull can also be a factor.

I think I calced you as a 1.95 ratio but with a 16% slip which is high for a duoprop. You may have something dragging you down. Normal slip for DuoProp is more like 10-11%.

I have a 22 foot Cuddy, and not a light one, not sure of the weight though (trailer and all is close to 6000#), and I can get to 46-48mph @4600rpm with B5's which is about a 23 pitch with ratio of 1.95. I can pitch up to a B7 and still get almost the same rpm and speed goes just over 50mph,it just takes longer to "tach"up. I am usually loaded up and towing and on a smaller lake so I stuck with the B5 set. With no load it can get to top rpm and 46mph speed in 8 seconds or so. Even with a load it jumps up and can hit top rpm's. I am on a much larger lake now and am thinking about going up to a B6 set for more cruising than towing.

 

[lyt]

Re: Volvo gear ratio? How do I know?

This just confirms to me that although I think my numbers are "in the realm of possible" .... I would have to imagine I could use a tune up.

correct me if I am wrong.... but the bottom line is that if I cannot even get to 4600 RPM with a b4 prop, then something is not gellin.

 

[QC]

Re: Volvo gear ratio? How do I know?

correct me if I am wrong.... but the bottom line is that if I cannot even get to 4600 RPM with a b4 prop, then something is not gellin.

If your application is truly comparable as discussed, then probably yes. Point is that the bottom condition, prop condition, weight etc all still matter. And all of that still amounts to not much more than conjecture regarding your engine condition. Yes, may indicate the engine is needing some attention, but all inputs are still required.

 

[Maclin]

Re: Volvo gear ratio? How do I know?

lyt,

Can you confirm the tach reading? It may be worth the time and effort to run it with an independent tachometer just to be sure. Your ear may not be able to tell the diff between 4000 and 4400, just sayin'...

 

[lyt]

Re: Volvo gear ratio? How do I know?

tach is accurate, newly replaced.

 

[Scott Danforth]

Re: Volvo gear ratio? How do I know?

tach is accurate, newly replaced.

New is related to the age of the tach, not the accuracy. have you confirmed the tach reading with a known good high-quality diagnostic tach.

 

[Don S]

Re: Volvo gear ratio? How do I know?

Let's see here.

Not sure tach is accurate,
Not sure what the gear ratio is for sure.
Bottom may be dirty but you want us to assume its "fab".

Yet you want us to tell you what your problem is how to fix it, is that correct?

 

[Don S]

Re: Volvo gear ratio? How do I know?

This is a list of possible causes of low WOT (Wide Open Throttle) rpm.

In no particular order

Engine Won't Reach Operating RPM. Check

1. Fuel condition. Type and Octane possibly old fuel
2. Propeller pitch or diameter, damaged blades
3. Restricted fuel pickup tube or anti siphon valve Fuel System Test
4. Crankcase oil volume, high oil level can cause aerated oil and lifter collapse
5. Marine growth on hull and outdrive
6. Wrong gear ratio in outdrive
7. Restricted carburetor air intake (clogged flame arrestor)
8. Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive
9. Poor cylinder compression Compression Test
10. Carburetor defective, or wrong type.
11. Fuel pump pressure and vacuum
12. Boat overloaded, improperly loaded, or improperly trimmed.
13. Engine Overheating
14. Engine timing and ignition system operation
15. Remote control cables and linkage for proper travel to open throttle plates fully.

 

[lyt]

Re: Volvo gear ratio? How do I know?

No I just want you, to do it, Don

I thought you were the oracle?