55hp FrankenChryForce Mounting height

[tater76]

Ok folks, so this thread may need to be moved but lets give it a whirl here with the Chrysler Force guys. I have a 1973 55hp Chrysler model 555HF just rebuilt. (Here's the kicker) I changed out the ignition to an 1985 50hp Force stator ign. It runs like new and I am extatic about that. However, having only owned OB's for a few years I am new to the set up, ie.. transom mounting hights, etc. I ran the boat for 3 years as I bought it, no changes at all. As I got tired of 17-20mph I did some research as to possible fixes, and found out here, how to properly set up the Cavitation plate with the hull line. I went out to check/measure, and immeadiately saw that the cav plate was at least 4" below the bottom of the hull. I unbolted the engine, jacked it up to do some measuring. I had it lined up well, but the transom mount clamps are VERY close to the transom cap. My question is, can I get away with cinching it down so close to the top of the transom, or do I need a jackplate/repower? Here are some pics of the situation, and its really not that dirty, the grey stuff is bedliner that the previous owner/gomer applied to the whole topside. But that's another thread Also, when the motor was moved I found two sets of holes. One set was higher than I had been running (about one inch), I just hate to punch holes in a boat if I don't have to, but I will if you guys think It's worth it.

 

[Frank Acampora]

Re: 55hp FrankenChryForce Mounting height



First: very interesting retro for the steering tube.
Second. The engine height now appears to be about right--cav plate lined up even with the vee in the bottom. The clamps are fine that high on the transom as long as the transom is sound. And it does appear to be solid because the P.O. appears the have reinforced it with an aluminum angle. That looks thicker than the standard aluminum trim used on transoms.

If in the future you need to go still higher, make a U out of thin gauge aluminum, bolt through the transom, and fill it with fiberglass. The photos should be self explanatory. The aluminum is about .080 hard sheet, salvaged out of a damaged road sign.

Don't worry about a couple of holes in the transom; you don't want to know how many were in this hull. If you intend to use them again fill them with black silicone RTV until it oozes out on the inside. If you don't intend to use them, soak some house insulation in fiberglass resin and fill them all the way through. House insulation is usually easy to come by in small amounts, it is long stranded, and when hardened, very strong. I used it to raise this transom 2 inches. It is however, a bit difficult to wet out with resin.

 

[tater76]

Re: 55hp FrankenChryForce Mounting height

Thanks Frank, yeah I'm not real sure about the steering setup, but it works well. I will post some results of the lifting later this week I appreciate all the advice.

 

[tater76]

Re: 55hp FrankenChryForce Mounting height

Well, so I remounted the motor as per the pics and ran it last weekend. The motor runs amazing, but the results were exactly the same. In desperation, I tried all three trim pin locations with no changes in speed, just on plane times. It did not seem to matter what I tried it still only pulled 17mph (GPS). I put the wife and kid aboard and it dropped to 16mph. I am beginning to think the motor is just not enough for my heavy old 16ft tri-hull. The boat is rated up to 75hp, so I would think that 55hp should be somewhat ok? This is my first tri-hull, so is the slowness to be expected? I had a 17ft Hydroswift v-hull with a 45hp Gale years ago, and it would do 30mph! Is the hull design my problem? Oh, here are the stats, 1973 55hp chrysler, 10x10 prop, 16ft crestliner tri-hull, 6 gal fuel, almost 400lbs of humans , cooler, fishing gear, partridge in a pear tree, etc...

 

[huskerdaninva]

Re: 55hp FrankenChryForce Mounting height

If it's an old boat, perhaps it's become water logged over the years? The excess weight of the water might account for the motors lack of top end speed...

 

[emoney]

Re: 55hp FrankenChryForce Mounting height

Something is definitely amiss, I think. Seems like you should get better than 17mph, but then again, I have zero knowledge of that boat. I did, however, own a 50hp Chyrsler on a 15' trihull that would do much better. I couldn't imagine there being that much diff in stock weight, but I definitely agree about the possibility of wet foam/rotted wood slowing it down. For the record, the 50 I had (which was a few years newer), pushed my boat 12mph running on one cylinder (don't even ask how I know...lol). Have you done the standard compression check, etc.?

Frank's definitely your man. If anybody knows these motors, he does! He'll chime in with some real information I'm sure.

 

[NYBo]

Re: 55hp FrankenChryForce Mounting height

Any idea how many RPMs the motor is turning at wide open throttle? I think you may be under-propped.

 

[Frank Acampora]

Re: 55hp FrankenChryForce Mounting height

Even on a 16 it does appear that you are underpropped. Yes, a big heavy 16 foot tri-hull is a lot for that engine but I think you might try a 10X 11 1/2 or 10X 12 1/2. I was running a 10 X 13 1/2 on my 15 foot Glastron V153 and reached 27 MPH with driver only, 23-25 with passengers. I would expect that yopu could get 20-22 MPH top speed

 

[tater76]

Re: 55hp FrankenChryForce Mounting height

Well the hull is dry, as is the transom, ( I replaced the floor, foam, etc.. stringers were clean and dry. Now, as for RPM's you have a point, I am currently looking for a 20 pole tach to add. It sounds like it is WOT, and I ran it with the cowel off to see if it was fully advanced (it was on the carb). I know without a tach I am in the dark. I have two 10x10 props, tried them both with the same result, and a 8x10 that is alot slower but could pull a truck out of the mud. I just rebuilt the motor, and it has 140-145psi on both cylinders, excellent spark, etc.. This is why I am thinking it may be the boat or setup? Although, I am questioning the timing now. My manual was difficult to understand, and remember, I now have the 1985 force 50 ignition. I took from the manual, and research from here to set the timing. I have it set at 30 degrees btdc. As I am writing this I think this may be the issue. Anyone have a clear cut step by step idiots guide to setting the timing on the force 50 ignition? Just to weed out the possibility As for being underpropped I don't think so, as it takes the boat 10-15 seconds to get on plane (feels like forever). However, the 8x10 I mentioned earlier barely gets the boat on plane, but at low speeds could pull anything.

 

[tater76]

Re: 55hp FrankenChryForce Mounting height

Wouldn't a taller prop cause more stress on the engine? Acceleration already seems to be too slow with the 10x10? Frank, do you still have any extra props?

 

[Frank Acampora]

Re: 55hp FrankenChryForce Mounting height

You have a 16 foot boat rated for at least 75 HP with a 55. That is like a four cylinder truck with a high rear end gear. Don't expect blazing acceleration and if you do prop for acceleration, don't expect good top end. There is just so much two cylinders can do. Forget about waterskiing with any prop. Wakeboarding, maybe and tubing is ok but it just will not have the power or acceleration to pull up anything except a little kid on baby skis.

I'll give you an example: I have a three cylinder 90 on my 15 foot V153. it tops out at 45. I also have a four cylinder 105 which also really only delivers 90 HP. (that's it in the avatar) It also tops out at 45 on the same boat. BUT because of the extra cylinder and torque, and because of the different horsepower curve, it gets there much faster than the three cylinder.

As with any combo, dialing it in requires a tach. If the higher pitched prop still lets the engine rev to within its operating range, then there is no added stress. trying to reprop without a tach is hit or miss--like trying to set temperature on a refridgerator without a thermometer. Sure, you may eventually get it cold enough but is it too cold and wasting money or just on the edge of safe?

Do I have props--yes, I do but I don't know which ones are good and on some I'm not sure of the pitch. I'll send you a private message later.

 

[tater76]

Re: 55hp FrankenChryForce Mounting height

Thanks Frank, I am a realist, so no, I don't expect much from my setup. I just want reliability and an average speed of above 20mph, as we have some long resivoir's here If it takes me a good 30 seconds to plane out to 25mph I'm good with that. I found a rebuilt prop 10x11 for $75 at a local marine shop, is that reasonable?

 

[tater76]

Re: 55hp FrankenChryForce Mounting height

On another note, I did find a tach from a maxim boat aboard when I first bought it. It was just hanging way behind the dash , I had to dig for it? It has 1-4 setting on the back, and a sticker stating 4cyl-#2, 6CYL#3, 8CYL #4. The PO had it hooked up and it did function, but it was set at the #1. I don't know how reliable it is?