340 SUNDANCER THREAD

Strecker25 said:
Interesting stuff. The cocktail cruise comparison is probably the one most open to interpretation. Cocktail cruises for us are literally rides to nowhere (around the bay/lake with no destination except get home) so, speed is irrelevant, and the 6.2 would be slightly more efficient. That being said, these numbers are so close it's almost a wash. The appeal of the big blocks for me is being able to run them at lower RPM and theoretically less wear but who knows if that's even true.

What's hull speed in a 340? I'm guessing the waterline length is like 30' so about 7.5 mph?
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Yes if you are going nowhere...... and just driving for a time period AT THE SAME RPM, then a pair of 6.2s burn exactly 1 gallon LESS per hour then a pair of 8.1s. (and take you 1.9 miles shorter of a distance)

That being said, if you have both boats and where going no where, then you are probably going to stay around the same speed of 7-8mph... and if thats the case you using a speed for a constant, not the RPM... and the 8.1 boat would be at like 1100-1200 rpm, not 1500 like the 6.2.. which would put it burning less fuel, as well.. for the same hull speed.

6.2 is at 3GPH@1500 X 2 === 6GPH = 7.5mph (using cliffs real word numbers)
8.1 at 1000= 2.3GPH X 2 === 4.6GPH = 6.8 mph (using my real world numbers)

so they are 500 rpms off, and only 0.7mph off... so lets say you barley raise the RPM of the 8.1s... to match the speed/cocktail speed of the hull. for the same ride around the bay for nothing but a fun. and your still burning less fuel...

if we think 1100 rpms is enough for 0.7mph thats a 10% raise in RPM, 4.6gph X 10% = 5.06GPH... still less then the 6.2s 6GPH
if we think 1200 rpms is enough for 0.7 mph thats a 20% raise in RPM, 4.6GPH X 20% = 5.52GPH.. still less then the 6.2s 6GPH
if we think 1300 rpms is enough for 0.7 mph thats a 30% raise in RPM, 4.6GPH X 20% = 5.98GPH.. still less then the 6.2s 6GPH
if we think 1400 rpms is enough for 0.7 mph thats a 40% raise in RPM, 4.6GPH X 20% = 6.44GPH.. which is more the 6.2s 6GPH.. but at this point we are way past the 7.5 mph matching speed which was the goal of a similar cruise to no point.


1000rpms=6.8mph
1500rpms=9.4mph
Differecne of 2.4mph
2.4/500 rpms = .48mph per 100 RPMS....so

7.5mph is somewhere between 1100 and 1200 RPMs on a 8.1 boat if we use 1150 (1.5X.48mph = 0.72mph) for it then:

8.1 is 5.29GPH@1150RPMs = 7.5 mph.....which still is less then 7.5mph at 6GPH on the 6.2.
 
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Underwater254 said:
Help!! Looking at a 2001 340 with 8.1s 180hrs. Boat has been under shrink for 2 years. Haven't seen In person yet. Salt water and supposably not closed cooling. What should I look for motor and drive ??? Thanks
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Two years under wraps and only 180 hours total? I assume as mentioned above these may not be original motors. You'll want a merc tech to go through the motors and drives (if IO's?).

I wonder what the inside of this boat is going to look like after 2 years of shrink wrap. Could be a mess in there?
 
Mittens said:
Yes if you are going nowhere...... and just driving for a time period AT THE SAME RPM, then a pair of 6.2s burn exactly 1 gallon LESS per hour then a pair of 8.1s. (and take you 1.9 miles shorter of a distance)
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yep....that is how we boat....for a period of time and not a destination.....I do agree with your math if you use destinations for the calculations.....

and if you do your own maintenance work the 6.2's do offer a little more space in the ER.....

cliff
 
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Strecker25 said:
The appeal of the big blocks for me is being able to run them at lower RPM and theoretically less wear but who knows if that's even true.

What's hull speed in a 340? I'm guessing the waterline length is like 30' so about 7.5 mph?
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the amount of wear on any engine over a period of time depends on things like how it is built and what kind of load it will be subjected to and for how long.....I don't have any data to back this up but IMO I think the amount of wear on either engine is probably not a concern here.....the 6.2 engines are built to rev higher than the 8.1's so there is no extra amount of strain on the 6.2 when it is running at a higher rpm as compared to the 8.1....

I have not calculated the 'theoretical hull speed' but going by the sound of the engines and the wake the boat is making I would think it is around 10 mph.....around 10 mph the boats starts to 'plow' through the water....

cliff
 
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CliffA said:
the amount of wear on any engine over a period of time depends on things like how it is built and what kind of load it will be subjected to and for how long.....I don't have any data to back this up but IMO I think the amount of wear on either engine is probably not a concern here.....the 6.2 engines are built to rev higher than the 8.1's so there is no extra amount of strain on the 6.2 when it is running at a higher rpm as compared to the 8.1....

I have not calculated the 'theoretical hull speed' but going by the sound of the engines and the wake the boat is making I would think it is around 10 mph.....around 10 mph the boats starts to 'plow' through the water....

cliff
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Makes sense. Is your signature pic around 10? That looks like about right on based on the bow wave
 
Strecker25 said:
Makes sense. Is your signature pic around 10? That looks like about right on based on the bow wave
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to be honest I don't remember but most likely that is close......this pic was taken a couple years ago by a friend in another boat.....we had just left our 'swimming hole' and were headed back to the marina and I normally go 8 - 9 mph as normal cruise speed....I do remember it was VERY hot that day....

cliff
 
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CliffA said:
yep....that is how we boat....for a period of time and not a destination.....I do agree with your math if you use destinations for the calculations.....

and if you do your own maintenance work the 6.2's do offer a little more space in the ER.....

cliff
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THe 8.1s are tight in there for sure those impellers where a chore, doing plugs tomorrow, and fuel filters, and oil changes as well.

But fuel wise and speed wise the 8.1s are the ticket. I really want to try them with 4 blade 18X22 props.... when bottom pain time, pretty sure I will slap a set on.
 
on my engines I found the exhaust manifolds interfered with using a standard spark plug socket on some plugs....the walls of the socket were a little too thick.....I used a standard deep socket and differing lengths of extensions to change the plugs which worked better....

If I enjoyed going fast as it appears you do and getting to destinations as fast as possible I agree the 8.1 engine is the right choice for this boat.....

but if you are just going to normally slow cruise with no real concern about how long it takes you to get somewhere or maybe not even have a set destination I would opt for the 6.2 engines for the slight improvement in fuel consumption and for a small amount of extra space in the ER.....and the boats with 6.2's are a little less expensive.....

as we said before it is all dependent on how you intend to use the boat.....

cliff
 
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I agree with you on boat pricing and the engine room.... but 6.2 is not cheaper on fuel. Math does not lie. Even just riding around at cocktail speed its doing so at a lower RPM, and less fuel burn at the same speed.

anyway I will drop the argument the math speaks for its self. Both great boats, and no problems with either. and Black tops are the best! ha.(I am sure we agree on that!)
 
Mittens said:
I agree with you on boat pricing and the engine room.... but 6.2 is not cheaper on fuel. Math does not lie. Even just riding around at cocktail speed its doing so at a lower RPM, and less fuel burn at the same speed.

anyway I will drop the argument the math speaks for its self. Both great boats, and no problems with either. and Black tops are the best! ha.
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not really arguing but I agree both are fine boats.....each of us makes a purchase decision based on many factors and engine size is just one of those factors....

we love our boat just as it is (as I am sure you do yours) and with all the improvements and mods I have done (and continue to do) our boating experience just gets better and better with time.....

the Admiral loves to decorate the boat with pillows and plants and 'stuff' like that so we are making the boat as 'homey' as possible....if I could go 41 MPH like your boat I would be afraid some of those pillows and plants would fly overboard while running at WOT...... :)

cliff
 
HA I had a argument about pillows with the Girl when I got the boat! and last weekend an argument about some GIANT coffee maker that is to big for a boat.... she does not understand! haha


I just wish I could find a way to easily hot wire the bathroom / head lights to always have power. From what I have found they are on a line going to the front lights and not on a separate hot wire on the back of the switch by the door (for a easy jumper). and this year does not have the light switch by the power vent like the newer hulls do to jumper either.
 
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Mittens said:
I just wish I could find a way to easily hot wire the bathroom / head lights to always have power. From what I have found they are on a line going to the front lights and not on a separate hot wire on the back of the switch by the door (for a easy jumper). and this year does not have the light switch by the power vent like the newer hulls do to jumper either.
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since those lights are so close to the power distribution panel I wonder if you find a constant 12V power source behind the panel to jumper to.....

cliff
 
yea thats a possible shot, but running wires into that small hole on top of the head will be a chore. will look into it though, maybe tag the back side of the cabin lights switch so once thats on the head light works, but not dependent on the main switch on the door as well.

if you have any helpful tips to cutting into the big GPS spot let me know, plan to cut and mount my Lowrance HDS9 today... I have my Dremel tool, Drill, Oscillating saw, and Jig Saw with me today. I know to drill backwards to get through the top layers, but once in in debate about jig saw, or maybe a backwards jigsaw blade...
 
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Mittens said:
if you have any helpful tips to cutting into the big GPS spot let me know, plan to cut and mount my Lowrance HDS9 today... I have my Dremel tool, Drill, Oscillating saw, and Jig Saw with me today. I know to drill backwards to get through the top layers, but once in in debate about jig saw, or maybe a backwards jigsaw blade...
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I'm sure you know this but use a fine tooth blade on any saw to get a cleaner cut.....Dremel makes a side cutting bit that works well to make fine adjustments to the hole....I found that using an angle grinder for the long cuts worked great.....very easy to control the grinder and cut along the template lines......I have not used one but I hear that those 'oscillating' tools have different types of blades and are well suited to jobs like this.....fiberglass is tough and can dull blades quickly....

good luck and post pics.....

cliff
 
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Well Got the hole cut, WOW was that thick. 1.5 inches thick. killed 4 new blades on the Jig saw as well.

BUt its done and insalled, looks clean and is working. Will work on building a NMEA 2000 net work, and adding Smartcraft gateway soon.
 
Mittens said:
Well Got the hole cut, WOW was that thick. 1.5 inches thick. killed 4 new blades on the Jig saw as well.

BUt its done and insalled, looks clean and is working. Will work on building a NMEA 2000 net work, and adding Smartcraft gateway soon.
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without pics it didn't happen....... :)

cliff
 
I tried to upload pics, but the forum gives it red dots saying not uploaded. no matter what size I try.
 
Mittens said:
I tried to upload pics, but the forum gives it red dots saying not uploaded. no matter what size I try.
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you may have to be a sponsor to post pics......not sure though....

cliff
 
Any 340owners, that have replaced their Vacuflush switch, know which model it is?
I thinks 385318032. Was hoping to order and have in hand when I go down to work on the run-on problem this weekend. Already received the duck bills.
 
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