New Guy. I came for the knowledge! And y'all have some sweet boats!

[Flex]

Hey fellas, new guy here. Been on the water my whole life. Owned some outboards but never did much too them. Been running and fixing up inboard ski boats the last several years.

I just rebuilt an older aluminum semi v, and am trying to squeeze more performance out of it, because going fast is awesome!

It's a 16.5 mod v, sea nymph bass attacker, have a 1975 70 Evinrude with an old cmc manual jack plate. Built as light as possible to run fast and skinny! Trying to learn about props and the jack plate setup to squeeze more speed out! Right now only hitting 35 but I think I should be close to 50 set up right.

[NICE PAIR]

"Howdy" and Welcome :thumbsup:

[Krazymaan]

You would need to weld a pad under it so it "slides" across the surface. A V will just keep cutting and creating drag.
Looks like you could bolt two motors back there. :D

[Flex]

It is only a modified V up front to cut the chop. The back of the hull is almost completely flat.

[Flex]

Also, does anybody have tips for the "optimum" jack plate setting? Currently have motor with cav plate about 1.5" above bottom of hull.

[home made tunnel]

You can go way higher... The prop shaft centerline can be a couple inches below the hull. Forget about the cavitation plate... that's for nancies. This site normally refers to the prop shaft. Get that higher, and a couple inches below the bottom of boat.
This obviously will put your cavitation plate way higher than the bottom of transom. That's ok.

Your biggest problem is probably the 2.4:1 gearcase ratio.

[Stoker1]

You've got to start with a baseline. I'd want to know:

- Current RPM
- Current Prop

Raise engine 1/4 to 1/2" at a time, run, check #'s. Not sure how high you can raise it without going low water pickup. Your cheapest investment is going to be a good prop.

[Flex]

Thank you guys! Awesome. I am from South Louisiana, but in Central Tx now. So not a lot of people around that know anything about going fast and skinny!

I will experiment raising the motor higher this weekend and post pictures and results. I ordered a tach yesterday. I know I need that in order to make sure I get the prop perfect. I will also check and see what prop is on there. I know its got to be a "power prop" Boat launches up on plane with no effort.

Do my speed expectations seem reasonable? I know it wont scream 60+. But I just think it has to have at least mid 40s in it. Motor had 125 compression on all 3 cylinders. And we tested right after the first time it had been cranked in years.

[H2OPERF]

Put a water pressure gage in too, more important than any other gage if your going to play with raising the engine. Dave

[home made tunnel]

Put a water pressure gage in too, more important than any other gage if your going to play with raising the engine. Dave
^ This is important ! If you're going cheap and easy, get a simple water pressure guage at an automotive store (O'Reilly's / Pep boys / AutoZone etc). Every motor usually has an NPT fitting somewhere on the block to put a nipple on.

Tractor gearing ratios like 2.4:1 will help you launch and pop out of the water very easily... but are tough to go fast. Need like a 30 pitch prop to do it.
I have a 19pitch prop on my Force 90hp, and it launches easy, but tached out @ 45mph. (red boat in my signature). More prop and better low end gear will get you more speed.

Good news is your lower unit came with x2 ratios. 2.4 and a lower one like 2.07 or 2.1:1

picture your car stuck in 3rd gear trying to go 100mph... just doesn't spin fast enough.

[NICE PAIR]

Water pressure is your friend. :thumbsup:

Don't fry your motor. :nonod:

[Flex]

Just checked it out. That's a unique build! I know I'm not building a raceboat. And a normal guy would probably be content running 36 in an old tin boat. But the Cajun DNA just says it needs to be faster! If I can reach mid to upper 40's I will be stoked!

[Krazymaan]

Upper 40s in that boat will feel like 70mph

[delawarerick]

Upper 40s in that boat will feel like 70mph:thumbsup:I agree that will be ripping and fun welcome this is the place. Rick

[Krazymaan]

From the shore it will look like a moped cruising down a blacktop road. From in the boat it's going to feel like your conquering the great rapids of the Colorado river with that aluminum bottom slapping the waves at 40+. Now I know why you want to do it. :cheers:

[Flex]

From the shore it will look like a moped cruising down a blacktop road. From in the boat it's going to feel like your conquering the great rapids of the Colorado river with that aluminum bottom slapping the waves at 40+. Now I know why you want to do it. :cheers:

This is exactly why I want to do it! You have not lived until you have gone 40+ on your bare feet and 40+ in a tin can!

[transomstand]

You have not lived until you have gone 40+ on your bare feet and 40+ in a tin can!

Naaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa:nonod:



You ain't lived......:nonod::nonod::nonod:


Until you go 90+ with a bunny
http://i221.photobucket.com/albums/dd58/transomstand/Romp%202016/romp21.jpg (http://s221.photobucket.com/user/transomstand/media/Romp%202016/romp21.jpg.html)

[Flex]

Naaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa:nonod:



You ain't lived......:nonod::nonod::nonod:


Until you go 90+ with a bunny
http://i221.photobucket.com/albums/dd58/transomstand/Romp%202016/romp21.jpg (http://s221.photobucket.com/user/transomstand/media/Romp%202016/romp21.jpg.html)

I think I have a new hero.

[Flex]

Ok, so put in new spark plugs. Trying gapped just a hair over .030. Old plugs that came in the motor weren't the correct plugs. And they were all gapped between .05-.06!

Also looked at my prop, 13 3/4 by 15. This is a torque or power prop I think? 371217371217371218371219

[Flex]

By the way, the motor is a 1975 70 Evinrude. Manual tilt. 125 Compression all 3. Motor was sitting in storage for years. Looks in great shape. Runs very strong so far.

[tunnelmike]

The shape will determine the purpose of the prop. Torque props will usually have larger rounder blades. Post a pic of it. Mike