Low WOT rpm on Santego 3467

[BarryK]

Hi all,

I'm not getting full rpm at wide open throttle, both engines. I will troubleshoot but I want to make sure that the propeller size is in the ballpark,

1990 Santego 3467
454 Crusaders
Warner transmissions with 1:1 ratio
Walter V-drives RV-36 with 2.09 ratio
propellers 20x21, 3 blade

I'm seeing about 3500 rpm port and 3800 starboard. This is on the ocean at about 70 deg. air temp, calm seas.

I've only had the boat for a few months and have been going through everything. So much to check! I think it made better rpm and speed on the sea trial back in December. Compression was OK on the inspection at that time, both engines.

The engines sound fine, coolant temps are OK, Oil pressure OK port (40), a bit high starboard (70). Both run smoothly. I made about a 25 mile run yesterday mainly at low rpm (1500) and everything was fine.

I'm getting more exhaust steam from the port than the starboard at full throttle but it returns to normal at a bout 3000 rpm. Coolant levels are fine and I am not loosing any coolant from the heat exchangers. Port stays at 160 deg at WOT, starboard rises to 170 deg. I recently treated port with Rydlyme; I will treat the starboard very soon. Raw water pumps are newly rebuilt on both (new bearings, impellers, etc).

Engines have about 1000 hours. Exhaust manifolds and risers are about 1 year old.

I recently had both carbs rebuilt. They are original marine Quadrajets. I can't guarantee that the job was done correctly.
I recently set timing on port to specs.
Fuel filters have not been changed yet.

Is it possible that the props have too much pitch? What top speed should I expect with this boat? It weighed about 18,000 lbs at haul-out. WOT rpm is supposed to be 4000-4400 based on Crusader shop manual.

Thanks,
Barry

[bud37]

Source of the post
I've only had the boat for a few months and have been going through everything. So much to check! I think it made better rpm and speed on the sea trial back in December.

Considering that, was the bottom clean on the sea trial ?....it has now been a while and I'm guessing you are on salt, if so could just be growth on the bottom and running gear. That will really slow things down, also you have probably added quite a bit of gear ( weight ).

Just a couple things to cross off the list before you get to the props etc.

[ColRon]

Have you done a tune up on the engines? New plugs, wires, points, caps and rotors can make a world of difference. I had a 3067 that seemed to run fine when I bought her with the exception that roughly 3000 rpm was WOT. After I did a tune up on the engines, she ran up to 4400 with out a problem.

[BarryK]

No tune up yet. I will get to that soon!

Bottom is cleaned regularly but could be a problem. Yes, salt water.

Yes we added weight and water, fuel tanks were all full.

I should add that I get about 15 knots at 3000 rpm.

I adjusted the throttle cables a few weeks ago so I will check that the throttle plates on primaries and secondaries are able to open fully.

Thanks!

[buster53]

When you say the bottom is cleaned regularly, how often is regular?
My 356 with 8.1 Crusaders will top out at 35 mph. Right now, I can barely hit 20. Barnacles grow fast and can kill performance in a very short amount of time.

[BarryK]

The diver cleans it at least once per month. It was hauled out for new bottom paint in December. I will have it cleaned and then run it full throttle right after that.

I confirmed that secondaries on carb are fully open when throttle levers are fully forward today.

[Cooler]

Three things to consider:
1. Accuracy of tachs. 2. Condition of fuel, any ethanol in gas can degrade in tank in a relatively short time. 3. What is the prop size supposed to be? Call Carver, with your hull # in hand, and ask them what size props were on the vessel when it was built. My feeble memory tells me the standard prop was 19X19, but like I said, my memory is good but short. 1" in prop size or pitch will cost you 200 rpm of top end. Any of, or a combination of the above, can result in those types of WOT RPM's. When the sea trial was done, did the engines get to that 4400 range? Unless you need to run full throttle all the time, I wouldn't get too worried. You're only going to gain a small increase in speed beyond that 3800 RPM anyway, but burn a lot more fuel. I get 19 MPH at 3000 - 3100 RPM with my 5.7 Crusaders, but I am about 2500 lbs. lighter. er

[BarryK]

I ran it at WOT briefly the other day. This time the seas were calmer and the wind was behind me. I had full tanks of fuel and water tank 3/4 full, so I was pretty heavy. I let it go a bit longer and starboard got to over 4000 and port to about 3800. They might have gone higher but I cut the throttles. So, I think the props are correct and the problem is not too bad. I will change the plugs and distrib. caps soon and see how it goes.

Thanks again,
Barry

[BarryK]

I also found the original manual for the boat and these are the original equipment propellers for the gas inboard option.

[Viper]

Seems there are still a few regular maintenance items you need to get done before going any further such as complete ignition tune-ups and fuel filters. What process did you follow to set timing?

Why did you mention that you can't guaranty the carbs were rebuilt correctly? Was it not done by a trained technician? Also always best to send to a shop that can measure flow rates.