85 Amberjack 255 re-power & Modifications

[CAGE RATTLER]

Ive replied about what im doing in other threads and have started threads asking questions but thought i would start a thread to update what im doing and to post pics of my projects in one spot as i go.

I bought the boat in may of 09 and had to replace the transom assembly and have the transom rebuilt due to soft wood around the I/O cutout. Wound up putting over 100 hours on the boat in 09 mainly fishing the chesapeake bay and the 03 350 MAG MPI ran great all season untill she overheated and injested water on my last trip of the season thanksgiving morning.

During the fall of 09 I had a custom hardtop made from Atlantic Towers and installed it this spring. Im haveing an enclosure made for it now.

Here is a few pics i took of the hardtop that I also posted in another thread.

I also wound up purchasing a new 2010 496 MAG MPI engine for it. I pulled the 350 mag out a couple weeks ago and between working alot of OT and working 2-10 on normal days, I havent been able to find the time to get much work done on it.

The new engine has been sitting in the back of my pick up in the garage for over a week now. I knew i wanted to get the boat ready before the 4th of july weekend so i took this week off to get some work done on it.

Over this weekend and monday & tuesday I was able to do the work in the engine compartment i wanted to get done before dropping the engine in. I cut out a section of the stringer on an angle to be able to pull the starter off easier if need be in the future.

I also filled alot of screw holes, did a little patch work, moved & cleaned up alot of wiring and got the bilge & engine compartment painted. I used some of the black wire loom around alot of the wiring and it looks so much better than the mess of spagetti it used to be.

Finished everything up today and was able to get the motor dropped in before it got dark ..... barely. It took alot longer than i expected to drop it in there and it was a VERY VERY tight fit!! I only had a chance to get the back mounts tight and lower the front mounts down on the stringers

Even with the wide open cockpit & 10 foot beam of the amberjack, I wound up haveing to lower it in sideways and attempt to turn it once it was low enough in the engine compartment. I had to remove the steering actuator to get it in as well but managed to get it in there. I just hope it wont be to difficult to get that back on there now.

When i was done for the night I put the engine cover on and put the hatches on and at the front of the engine the hatch only clears the top cover by less than a 1/2 inch. Its also very tight at the front of the engine. looks like only 1 inch clearance from my raw water washdown sea cock to the sea water pump pulley.

Ive been rushing to get this done so unfortunately I didnt get any pics of the work so far but will start taking some now that the hard part is finally done.

We've had record heat the past few days as well and thank god I have a pool. My fiancee has been helping me and also took the week off. We've been working as long as we can stand it and then hopping in the pool to cool off. She's been working on the teak for me while ive been working in the engine compartment. She put the 1st coat of cetol natural teak on today and it looks great!!

Cant wait to get her splashed and hoping to test out the new engine on friday but i also want to make sure everything is OK.

 

[KRB64]

Sounds like you are having fun! Will be worth it.

Will the enclosure snap from the inside edge of the top to the winshield? What level tint is that?

Good luck with the finish.

Looking forward to more pictures!

 

[Big Island Lifer]

you have made some great progress. Good Luck!:smt038

 

[CAGE RATTLER]

Sounds like you are having fun! Will be worth it.

Will the enclosure snap from the inside edge of the top to the winshield? What level tint is that?

Good luck with the finish.

Looking forward to more pictures!

Snaps on the outside. Same snaps that was used for the bimini.
I think the rain would pour in if it snapped on the inside.
Front & side panels are on right now.

Not sure about the tint. Pics do make it look darker though.

 

[KRB64]

I meant the inside edge of the hard top to the out side (like normal) of the windshield. Was wondering how you were getting around/incorporating the metal top supports.

 

[CAGE RATTLER]

ooops ........... Yes they are using snaps on the inside of the tubing and used a track across the front. Right now they just have lil half moon cutouts on the sides where the roof supports are. The sides arent finished and they havent started on the back yet and we're trying to figure out the best way to deal with the bracing on the back support.

 

[CAGE RATTLER]

I wanted to update this thread each night but in order to get it ready by the 4th of july weekend I wound up putting in some long hours getting everything done. Thursday & friday night I wound up working on it till 4 AM.

Had some trouble hooking up the exhaust and also getting the engine aligned. I had to use some wet exhaust hose to go from the y-pipe to the elbows. 4 inch was to big and 3.5 inch was very tight. wound up putting the 7 inch pieces of hose in boiling water to soften it up to get them on there. Worked out pretty good too.

My Fiancee was a huge help. She finished the teak and also sanded and painted the bottom for me & re-installed the side panels i had removed to mount the hard top and to also get to the deck fills i replaced. She also washed and waxed the boat for me. I think i found a good one!!! I really need to get a windlass for her. The anchor on this boat is really to heavy for her :smt043

I got the engine aligned the best i could and then took it to the shop where i bought the engine to see if they could do better. We wound up cranking the front mounts almost all the way down which worries me and even then the alignment tool would not go all the way in easily.

Theres double wound lock washers that were on the rear mounts from the other engine but my new engine installation manual said they need to be removed if the new engine coupler had knurled bottom edges at the coupler mounting points. Im starting to wonder if I should have left them in there?

The outdrive was a little tight going on but it went on and after my 1st test run, i thought everything was ok. (more on that later)

By the way, I managed to meet my goal of getting it launched in time for the fireworks display at middle river. dropped it in at cox's point and cruised around the river a little to check everything out and then cruised over to see the fireworks and once again, their show didnt disapoint!!

I was however a little disapointed with the performance i was seeing out of the new motor. For break in purposes, Im supposed to run the engine no lower than 1500 rpms and no higher than 3/4 throttle which i figured to be around 3700 rpms. well that was a problem because i had to run the engine to 4000 rpms to just get it on plane. Once on plane i kept trying to lower the rpms but she would fall off plane everytime.

On the way back in I tried a WOT test and it jumped to 5000 rpms and i had plenty of throttle left so right away i knew it was under propped with the 14.5 x 19P prop.

The next day i picked up a 14 x 23P prop to try and was really hoping it would make a big difference in performance. The good news is i think i have it pretty close on the WOT test but unfortunately the performance was about the same.

I can barely hold plane at 3500 RPM's unless i drop the tabs down and my top speed was no better than what i had with the 350 MAG. I guess the added weight of the hardtop and the big block itself is really hurting performance more than i thought it would.

Hopefully it will get better when she's broken in more. :huh:

I do still have an alignment problem. Im getting a knocking sound when i go over 3/4 turn in either direction on the steering wheel. I guess it still needs some tweaking. Before i pull it out of the water & pull the outdrive off, Im going to try to raise and lower the front mounts a little bit at a time to see if that goes away. Im sure if i leave it this way it will damage the coupler eventually so I need to correct this. The coupler on the new engine has a tube extension that looks to go into the transom assembly with not much room around it and i think the knocking im hearing is the extension just being to close to the opening.

I did manage to have a nice time at the fireworks show and then monday gave the new prop a good test by heading over to belly button beach to meet my nephew and some friends that spent the night over there. My nephew just picked up a nice 92 290 sundancer and his buddy has a gorgeous 96 400 express cruiser. That thing is huge!!

Once again Im sorry i didnt get any pics. It has just been to hectic trying to get everything done in time. I planned on getting some pics monday at the beach but unfortunately left the camera in the truck :smt013. She looked great in the water too. All nice and clean. I really wish i would have goten some pics before launching her. That fresh bottom paint really made it look great. I went with a multi season ablative that was a darker blue than was originally on there.

 

[out-n-aboat]

What was the top speed difference between the two engines? What is the horse power and torque diffrences? What is the estimated weight differences? I would think the big block should have way more torque.

 

[EricW]

Do you know what gear ratio is in your Bravo I drive? Most of them are 1.5:1. If you are able to turn 5000 rpm with the 19" pitch prop, and nearly that much with the 23" prop, your boat should be really flying!!!

What model props have you been trying? Are they Aluminum or SS?

I think the props you are using may be too small of a diameter for the weight of your boat and the power of your engine. You may not have enough blade area, and are experiencing a lot of prop slip. Maybe you can try a larger prop with at least a 15" diameter, like a Mirage Plus. Or, maybe a big four blade prop will slip less and move the boat better.

Congrats on getting back out on the water. I hope to see you again on the river.

 

[keokie]

Play with the props and trim. The torque difference of the 496 vs 350 should far more than offset the additional weight of the motor and hard top.

 

[CAGE RATTLER]

What was the top speed difference between the two engines? What is the horse power and torque diffrences? What is the estimated weight differences? I would think the big block should have way more torque.

No difference at all as of yet in the top speed. Both are right near 33 MPH.

The new engine has 75 more HP and around 100 more in torque.

The hardtop is probably between 150 & 200 lbs.
The engine about 250 lbs more.

 

[CAGE RATTLER]

Do you know what gear ratio is in your Bravo I drive? Most of them are 1.5:1. If you are able to turn 5000 rpm with the 19" pitch prop, and nearly that much with the 23" prop, your boat should be really flying!!!

What model props have you been trying? Are they Aluminum or SS?

I think the props you are using may be too small of a diameter for the weight of your boat and the power of your engine. You may not have enough blade area, and are experiencing a lot of prop slip. Maybe you can try a larger prop with at least a 15" diameter, like a Mirage Plus. Or, maybe a big four blade prop will slip less and move the boat better.

Congrats on getting back out on the water. I hope to see you again on the river.

The bravo 1 is 1.5 gear ratio. Both props so far have been Black Diamond aluminum 3 blades. When i get it dialed in i might go with SS. Been wondering what differences i would see with a 4 blade. And im not sure what the largest diameter fits a bravo 1 but i dont think its very big.

 

[EricW]

Max prop diameter on Bravo I is 16". Even though its only 1" or 1.5", I think there's a good chance for significant improvement going from 14" diameter to 15.5". The blade surface area is quite a bit more on the larger prop. A 4 bladed prop can help too.

Also, I think a SS prop will help since you have a big boat and big power, and Aluminum blades flex quite a bit under large loads. The Merc Mirage Plus prop should be a perfect fit for your boat. Its made to move heavy boats with lots of power.

 

[out-n-aboat]

Like someone said I would try a bigger prop. At least it should get up on plane quick and hold it there with less spped.

 

[kybishop]

Once you get everything dialed in it will be interesting to see what your fuel consumption and cruising RPM's are with the 496 as compared to the 350.

Nice job and nice project.

 

[CAGE RATTLER]

No clue what the fuel mileage was with the 350 mag.

I was hoping the 496 mag would do better on fuel at cruising speeds.

 

[CAGE RATTLER]

So Im assuming i should go with the largest diameter (16") 4 blade SS prop to get the best performance??

Im open for suggestions!!

I looked at the mirage plus but the ones i looked at where all under 15" diameter.

Another thought ......... If prop diameter makes that big of a differrence, would i be better off with a bravo 2 drive??

 

[keokie]

In theory, the smallerthe diameter prop the higher the top speed, the larger the diameter the better the bite and acceleration.

Cage, something is amiss here. I have experiance with a number of small block to big block conversions. The 496 should eat that 350's lunch. You should see an 8 to 12 mph gain in top speed, and the same cruise speeds for 700 to 1000 rpm less. Your hard top should hardly affect this.

 

[CAGE RATTLER]

Cage, something is amiss here. I have experiance with a number of small block to big block conversions. The 496 should eat that 350's lunch. You should see an 8 to 12 mph gain in top speed, and the same cruise speeds for 700 to 1000 rpm less. Your hard top should hardly affect this.

Thats exactly what I was hoping for.

 

[EricW]

The 19" pitch Mirage Plus has a 15.25 diameter. Although its only 1.25" more than a 14x19 aluminum, it has a lot more total blade area and is a lot more efficient on heavy big block powered boats.

On lighter boats, smaller diameter props give the best top speed. I think with your heavy boat, a larger prop will help all areas of performance.

The Bravo 2 or Bravo 3 are likely better choices for your application. However, I still think you can get great performance with the Bravo I once the prop is dialed in.