2003 Volvo Penta 3.0 GSP max speed 25mph

[Vparzial]

Hello,

So I am looking for some ideas on what else to check. I picked up a 2003 Stingray that has a Volvo Penta 3.0 GSP I/O with a SX-M in it and I’ve been doing all the work myself. Originally I would even be able to get this motor above 1600 RPM but after discovering it was a cracked head cylinder I replaced it and now I am able to get it up to about 25 MPH. The manual online says this thing should be able to get to 40ish at full throttle any ideas would be greatly appreciated. I’ll post all work below I’ve done. I believe the max RPMs under load is about 3500ish.

Plugs
Cables
Distributer Cap
Water Pump
Rebuilt Carb
Starter
Throttle Cable
head cylinder (175 On all 4 cylinders)
adjusted timing to 8 degrees BTDC (Manual says 2 ATDC but most forums say the smooth spot is 8 BTDC)
Power Steering Fluid gear
Exhaust rubber boot.
Belt
Fuel Filter
Fuel water separator
oil / oil filter
4 blade prop
Lower gear unit change with new seals

Yes, I know I’ve changed pretty much everything but this thing was a bit neglected and every but the motor was in great shape. Any ideas would be greatly appreciated once again. I’m kinda lost now.

Thanks!

 

[alldodge]

believe the max RPMs under load is about 3500ish
4 blade prop

The prop is most likely your problem.

Everyone wants to put a 4-blade prop figuring it will make it go faster. The reality is, unless you have the HP to turn the prop your wasting money. The next thing that is probably hurting is the prop has to much pitch. Higher pitch and unable to turn it at rpm means over proped

What is the current pitch of the prop?

 

[Vparzial]

The prop is a 14.5 x 17 RH

 

[alldodge]

A 4-blade 17 equals a 3-blade 19

Normally I would believe this would be in range for your boat provided the drive ratio is correct. If you don't know what the ratio is then need to see if a 15 or even 13 pitch 3-blade can be found. This is assuming that current WOT is 3500 rpm. Make sure your tach is accurate

When your setting timing are you using base timing mode?

After setting timing and removing timing shunt what timing is seen?

I'm wanting to know if timing is advancing

 

[Vparzial]

The manual calls for a 3-Blade 19. I did some research and most people say when going from a 3 blade to a 4 blade to drop 2 degrees on the pitch.

I used a timing light @ 1100RPM and set it to 8 degrees BTDC.

I am not sure what timing shunt is.

When accelerating which way should the fire be triggering? towards ATDC or away?

 

[alldodge]

Timing shunt



Having a VP there is no shift interrupter, but the 2 wires are connected together and the one is connected to a 12V source

Timing advance means it goes more toward Before TDC not After

 

[cobalt1999]

VP shunt part number 885163

 

[QBhoy]

It’s not your prop. Must be engine or timing related. Always hard to go from 3 to 4 blades or other way, accurately. Some smaller 4 blades of 2” more pitch than a stainless 3 blade will actually show more rpm !!
has the outdrive been changed from original ? All this would make sense if you have a higher ratio on it now.

 

[Vparzial]

I believe the outdrive is the original. The sticker on the motor says SX-M and the outdrive says the same.

I am not sure if going from a 3 blade to a 4 blade would reduce top end by 20 MPH. I know usually going to a 4 blade hurts top end but didn't think by that much? Should I go back to a 3 blade?

The engine had a lot of issues and is pretty much completely rebuilt as you can tell from the list above. I do maybe believe it is timing related as I've never timed an engine before and not too familiar with the cause and effects of what I am changing.

Originally when I threw the timing light on it, it was showing like 18 degrees BTDC.

I may have someone just come by and check it out as I am good with taking **** apart and putting it back together the way it came apart and following a manual but timing doesn't seem to be my forte.

The image that alldodge posted is for an 8 cylinder, would you still need a shunt for a 4 cylinder?

 

[alldodge]

The image that alldodge posted is for an 8 cylinder, would you still need a shunt for a 4 cylinder?.

Post 6 image shows only 4 spark plugs

 

[alldodge]

Start with the basics
Remove the valve cover and distributor cap and then bump the starter around until the intake on number 1 cylinder closes. Once closed keep going until the notch on the vibration damper points to zero timing

Verify rotor it is pointing toward number 1. Doing this to verify the timing chain was not installed wrong.

If all good, put everything back together and check timing as specified

 

[Vparzial]

My mistake, I was looking at the top right of the screenshot. I'll order the timing shunt and do some youtubing

Yes, the rotor is pointing towards number 1 at zero timing. I had to confirm this when putting the rockers back on at position 1 and position 4.

The timing light I used hooked up to the battery and the number 1 plug.

 

[Vparzial]

I took the boat out today to get some more accurate numbers.

Top Speed 30 MPH at 4200 RPM
There is a rough spot at 1800-2200 RPM where the motor chokes a bit and if I keep the throttle at that spot then it dies. I either need to stay under it or push past it.
Idle is 800/900 RPM

I'm thinking it is timing related but not sure which way I need to turn the distributor. The shunt comes in tomorrow. Any tips for how to time the motor correctly?

 

[alldodge]

 

[Vparzial]

I put the timing shunt on and I was at 8 degrees ATDC when the manual says 2 degrees ATDC. I adjusted it and boom, the motor sounds better then ever. I did not test it on the water yet. I am going to test it this Sunday and come back with the results.

Thank you for all the help. The timing shunt was the difference.