Need some performance numbers

S

sabrejocky

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Joined
Sep 11, 2003
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12195
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I was wondering if anyone can give me some help.Trying to sort out a 1993 350 aft cabin with volvo-penta 740 engines and transmissions.
These engines are 80 and 480 hours old with new mercruiser style manifolds and ricers, also the problematic Holleys have been replace by custom blue printed 800cfm rochester carbs.

I like to get some performance numbers, rpm verse knots, cruise speed and top speed. prop specs would be nice too.

So far testing this boat we where getting only 3200 port side and 3400 starboard with 22 knots on the gps.
My thinking is that we should be getting like 4500 although the top speed should be close as is?

Before we pull the props to have them reworked I really like to have some comparison numbers from other owners.

Cor
 
do you know why the rpms are so low?? Has all the other stuff been done, clean bottom etc?
 
Yes everything is clean and the engines have been gone through. I have a feeling the props are wrong that is why I am asking for experiences from other owner.
 
While I don't know for sure what the Volvo max rpm specs are I know you should at the very minimum be getting at least 4200 out of the motors.

How are you checking rpm? Is this on the original tachs? Have you confirmed that the tachs are correct?

I am at 32/3300 pushing about 20/21 mph and at 4400 right at 32/33 mph for full throttle in a slightly heavier boat with a wider beam running 7.4 454 Crusaders at 350 H.P. a side.
 
+1 with 370 motor yacht's assessment. Go to volvo's web site for gas motors and pull up the specs. If the tachs are in working order it may be the following.

Worst case you have low compression in some cylinders on each engine.
Questions to ask, why 80 hours on one motor and 480 on the other?
Why did you have to replace carbs for both engines?
Why do you have different risers and when were they replaced?
Did the motors ever ingest water.
Do the motors start to misfire at 3200-3400?
Coils, wires or plugs could be bad.
Water in fuel
Props are the wrong pitch.

They just some of the things to check. Need more info.
 
1) Was the timing checked, correctly?

2) Blueprinted carb? Ok, been doing this for a long time; what is a blueprinted carb? Holleys were a problem? Huh? Generally, it's the other way around. FWIW - quadrajets use about 50 different sets of metering rods for various applications. How do you know these blueprinted carbs are blueprinted carbs for your engines that came with Holleys?

If the timing is right, my next step would be to go back to OEM carbs. 800 cfm at 4200 rpm seems a bit overkill, since you can run a na 600 hp engine at 5500 rpm with a 750.
 
Ok, here are some answers to the questions posted.
480 hours is on the original starboard engine. The port engine had to be replace after water had gotten into the tanks do to the very crummy badly corroded fuel fills. Between the than owner and boatyard the port engine was destroyed after a piston shrapneled and was beyond saving.
The holleys had been butchered by that same boatyard and had water damage. These particular Holleys do not have a very good track record, they are known to be problematic to keep a steady idle and are inefficient. We got a pair of remanufactured Rochesters that we send out to Cliff Ruggles who blue printed them with a custom set up.
The manifolds and risers where replaced because the original volvo ones where shot. The volvo manifold and risers are very expensive so the decision was made to convert to the mercruiser style, all in all about a 1/4 of the cost.
The ignition has all new spark plugs, cables, cap and rotor and is working just fine. The timing was set and advance checked using a digital timing light.
All compressions where checked with in the last 4 months and are perfect.

No water in the fuel, checked the racors.

I have done some research today and all seems to be pointing to a fuel supply problem. These engines have electric inline fuel pumps that could have very well gotten damaged with all the water in the fuel troubles. We are looking to replace them with better holley marine fuel pumps as suggested by Chiff.

Going back to the holley carbs is not an option as they beyond fixing and never allowed the engines to go over 2500 rpm or would go haywire, to much damage to those.

Before you guys ask, all the water problems and the bad boatyard was all before we got our hands on it. Not going to bash the yard here openly but if anyone is in need of a yard in Fort Meyers,FL contact me and I will tell you who to stay away from, you would not believe the stupid and and down right bordering on criminal workmanship we have uncovered on this boat.
 
Some thing to add, I have seen some mentions in anther treads about anti syphon valves in the fuel supply lines. If so where are they, can they go bad and are they easy to replace.
I have inspected the tanks and they are spotless, they where totally cleaned out after the water problems.

All is pointing to fuel supply problems with engine surging and running out of power at +/_ 3300 rpm. No misfires but surging with a couple of times one of the engines totally dyeing but able to restart right away.
 
There should be anti syphon valves on the fuel pick up. It's a simple Ball and spring deal but at 20 years and a fuel history they could use some cleaning

Has the boat been weighted at haul out? Could it b heavy due to water saturation? Waterline where it should be?

You mentioned Racors, how about a secondary at the carb inlet?

Why don't you call carver and ask what the stick prop set up was and start there?
 
Now thatwe know the boat is new to you with unknown history I agree it is a good idea to call Carver or any good prop shop and get an idea what the basic props should be. Then have the current props measured. The stamped numbers may not be accurate.

People have been known to overprop in a mistaken attempt to get better fuel economy.

Michegan wheel can also give you some info

http://www.miwheel.com/propellers/prop-it-right/
 
Last year when we hauled it it was 21000lbs with water, fuel and gear on board which seems about right. The waterline is where it should be.
I called Carver to ask them about performance numbers and props yesterday. They said they do not have that info on this boat but looking at a couple of years newer 355 it should get up to 30-35 miles/hour and 22x22 props.
The survey report shows 22x21 props.
Yes there are filters in the carb inlet and that is all brand new, this was the first time running it with the new carbs but the surging problem also showed up with the old holleys.
I think I will start by inspecting and or replaying the anti syphon valves. Anyone have any info in these, where are they, who makes them, where to get new ones?

Cor

Ps pascal you have seen this boat, it is the same one when I met you at the sandbar the last time.
 
I remember ...

So the new carbs didnt solve the problem. I d double double check the ignition just i case, keep in mind NEW stands for Never Ever Worked.
Try to measure temperature under way and loaded with an IR gun. Either at the plugs or exhaust. That would tell you if a jug is not firing

The anti syphon valves are at the top of the pick up tube on the tank. Pull the tube and disassemble then clean. Also, check the screen on the pick up as well as cracks or air leaks in the tube.

If you run out of ideas, I v had god luck with anchor marine on the river. Volvo dealer among others. Mike the owner is an old fashioned no non sense guy who knows his stuff (cash only, doesn't bother with plastic) Not cheap but good work. He sorted out an old Volvo with stern drive some mechanics had screwed up (that was 20 years ago..), Since then I ve used him on the Maxum I had after that and recently on Charmer s Northern Light gennies for an injection pump leak.
 
This is going to be fun as I do not think it is possible to pull those tubes without having to cut access holes in the floor, does not look like carver ever figured on having to do this.
I think it could very well be the anti syphon valves as i already had a problem not being able to run the genny of the port tank because of fuel starvation.
I did a quick search online and found that these valve are really not that expensive, so if I can get to them I will just replace them with new ones regardless.
 
I missed the surging. That is normally fuel but can be eletrical. Two tanks and lines or one shared?

Two independent fuel systems would be unlikly to have identical problems. A lazy engine will prevent the other from reaching full rpm because it is over loaded. Are both surging or just the slow one??
 
Two tanks separate lines, but the surging is intermittent on both engines.
When I ran the boat sunday, on first throttle up the port engine ran up to about 3000 and started dropping off, backed down to idle and tried again about 10 minutes later. This time both engines ran up and held at 3200 and 3400 for about 5 minutes when they started to surge, backed down to idle for the rest of the way. On the return on throttle up the starboard engine surged and died twice, so gave up and just ran at about 1800. I have had this kind of surging/ dying in rough seas even at low rpms (1500-1800) with the old carbs.
I am pretty sure it is a fuel supply problem, those valves or pumps or both but at this point I am leaning to replace them all that and hope to be done with that.
 
Sounds like fuel... Syphon valves, fuel pick up, air leak on suction side. Check the seals on the Racors too
 
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