Quote:
Originally Posted by CajunChristian
The tohatsu is a 2 stroke direct injected motor, the 40hp has a restrictor plate on the intake. Just like the 4 cylinder 4 stroke Merc and the 50hp 4 cylinder, 4 stroke merc has a restrictor plate in the intake. Intake restrictors is an old trick used by manufacturers for 25 years  Some even use exhaust restrictor plates. Just a small steel plate with a hole drilled in the center, the plate was inserted into the exhaust pipe on some outboards.
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thanks, im always looking for more power if I can get it. I have direct fuel injection and no sign of any restrictor plates I can remove
Quote:
Originally Posted by CajunChristian
Then you need to play with props. The 3 cylinder, EFI, 4 stroke 40hp Merc has a 2/1 gear ratio. I propped mine to run loaded, it will bang the rev limiter empty. BUT, it pushes an 1844 Alweld marsh tunnel with 3 men, dog, and hunting gear 30 mph. Gets on plane in about 15 feet distance loaded. I run loaded 90% of the time, so I don't care how fast it runs empty.
For my 1556 with the 4 cylinder, 4 stroke Merc, I run 4 different props. I run a 14 pitch 4 blade prop in the marsh, gets on plane in the length of the boat, then hits the rev limiter in about 50 feet. In the river, I run a highly modified, pitched up 16 pitch Yamaha semi cleaver, average pitch is 18.
Just for giggles and dares, I run my old short course race prop, a 12" diameter, 20 pitch Quicksilver cleaver. Takes 30 yards to get on plane, then put the cat outside and hang on.
First thing to get is a tach, otherwise you are guessing.
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I have a tach and a gps for speed and ran some tests.
on take off it seams to have too much bow lift making the stern dig in yet everything I could find says I have the right prop on it now and even the powertech props tech support suggested the SRD3R13P (which is what I have) is the right prop but he just suggested I could buy the 4 blade version of the same prop SRD4R12P and that could help lift the stern and give better hole shot.
that makes no sense to me since the 3 blade prop tends to dig in on take off so I don't see how a 4 blade of the exact same shape and design would do any different just by adding a blade and dropping 1 pitch size. to me that seams to negate each other and bring me right back to where I started. if the blade design is exactly the same (which he said it was) wouldn't a 4 blade prop give the exact same bow lift and stern digging in that the 3 blade does if not worse?
I am thinking I need a prop with less bow lift and more stern lift but because of the Suzuki gear ratio no one is willing to take the prop back if they recommend anything that doesnt work. that's the key, im not willing to spend $300-$500 buying props until I luck into one that works well or maybe spend that and still not find one.
the prop I am using right now is a PowerTech
SRD3R13P SS and my Suzuki lower unit has a gear ratio of 2.27:1 and im getting 28 mph top end
here are the speed and rpm numbers I have for the boat:
first test condition:
fully loaded boat with 2 batteries (one in bow storage), one full 6 gallon plastic portable gas tank, two tackle boxes and 4 rods, one ice chest and a 25lb. bag of ice, 2 people weighing 450 lbs. with one of them sitting on the bow deck to balance the load. test was done from idle on smooth protected saltwater (1" ripples no chop).
from idle:
rpm - mph
1000 - 2.8
1500 - 4.5
2000 - 5.6
2500 - 6.5
3000 - 7.6
3100-3200 started to lift out of water, took 3500 rpms to finally reach true plane and loses plane below 3500 rpm
3500 - 14.6
4000 - 17.9
4500 - 22.3
5000 - 25.1
5500 - 27.6
5600 - 27.8
second test condition:
unloaded boat with 2 batteries (one in bow storage), one full 6 gallon plastic portable gas tank, 1 person weighing 230 lbs. in protected freshwater canal (no ripples no chop).
from idle:
rpm - mph
1000 - 3.1
1500 - 4.6
2000 - 5.6
2500 - 6.5
3000 - 7.9
3050-3100 started to lift out of water, still took 3500 rpms to finally reach true plane and loses plane below 3500 rpm
3500 - 16.5
4000 - 20.5
4500 - 23.5
5000 - 26.0
5500 - 28.0
5600 - 28.6
you will notice that in both tests, the numbers for rpms 1500-3000 are close to the same for the loaded and unloaded conditions (given a small margin of error) because its hard trying to judge the needle position to determine exact rpms since i don't have a digital tach.