1984 85hp Chrysler

[guitar_picker85]

Hey guys, just wanted to say first of all, that it is good to see at least a few people that still like these motors. I get sooo tired of hearing about how pretty that anchor is on the back of my boat My quesetion is, I have an '84 85 hp that runs pretty good and reliably, but I would like to see if I can get anymore performance out of her. I basically have an entire parts motor that could donate parts to be modded, worked, etc. to get more hp out of her. Thanks for any replies in advance

 

[jerryjerry05]

Re: 1984 85hp Chrysler

My opinion!!! Leave it stock.
Unload your boat.
If anyone makes remarks about my boat/motors I leave them at the dock.
I did that one day.The guy kept making smart remarks and i warned him.
Back to the motor.
Need to know what the rpm's are at WOT.
Should be about 5500.
What boat? Make size,weight??Prop?? Size?
The load makes a difference.If there is something you don't use leave it at the dock.
Smaller cooler,fewer people.Don't need 5 passengers to ski??
Post the results of the WOT test. and we can go from there.

Then the next step is buy a 125 Force.It will bolt right up to the same holes.Just make sure they are the same length.J

 

[stubtail]

Re: 1984 85hp Chrysler

If you want to get adventurous, go back a few months worth of posts in this forum and look for a post by Frank A. that has to do with squeezing more from an 85 hp (i think).

Anyway, Frank has done some serious work there; more than most would even dream of, but it is definitely worth a look!

 

[guitar_picker85]

Re: 1984 85hp Chrysler

I don't think weight is my problem. It is on the back of a Skeeter SS-1 bass boat (15', around 850lbs. empty) with me and fishing gear, it runs *around* 40-42 mph, by running with boats with gps. If my tach is correct, the last time I had her out, she was turning 5800-6000 RPMs. Prop is a stainless 13x19. I am going to put a jackplate on it, if only to free up more space on the back deck. Would that help me, or hurt me performance wise? Thanks again

 

[Frank Acampora]

Re: 1984 85hp Chrysler

Unless your engine has the 1.7 to 1 gear ratio lower unit there are no bolt-on modifications to increase horsepower, although some guys swear by aftermarket reeds. IF your engine does have the 1.7 to 1 ratio lower, then you can swap on a 2 to 1 ratio lower. Increase prop pitch to 21 and it should yeild somewhere around 3-5 MPH increase in top speed.

If you do install the jack plate, it will set back the engine into cleaner water and (if you can visualize it) higher water. (water coming off the transom rises. Thus, you will be able to run the engine higher. You may need to re-prop to a higher pitch.

5800-6000 is higher than the factory specs of 5000-5500 but will not harm the engine. You may, however see an increase in top speed by switching to a Ballistic 13 X 19 while the rpm will drop some. It is a great prop. Again, however, you may need to modify the prop thrust washer and nut to allow it to fit on your lower unit. I did it a while back with a 21 pitch and it has so much rake that it hit the exhaust snout.

If you don't mind working on your parts engine you can square the ports for a significant increase in ponies.---on the order of 5 per cylinder.

All these things have been discussed in depth in previous posts by me so use the search function when the forum allows you to again view photos.

 

[guitar_picker85]

Re: 1984 85hp Chrysler

Okay, as far as the prop is concerned, I don't think that I can go with a larger dia. prop. The 13x19 is only probably 3/8" from the bottom of the cavitation plate now. I don't know that much about 2-strokes, but would shaving the head help?

 

[jason32038]

Re: 1984 85hp Chrysler

You will have to get a 12 5/8x21. Easy to find Piranha has one.

 

[guitar_picker85]

Re: 1984 85hp Chrysler

You will have to get a 12 5/8x21. Easy to find Piranha has one.

Does anyone on here have any feedback about the Piranha props? I didn't think that there were any manufacturers from whom I could get a "performance" prop vs. the one I have now. The interchangeable blade idea sounds neat, but I am curious about longterm reliability. Sorry for all of my ignorant ?'s guys.

 

[maverick974]

Re: 1984 85hp Chrysler

Does anyone on here have any feedback about the Piranha props? I didn't think that there were any manufacturers from whom I could get a "performance" prop vs. the one I have now. The interchangeable blade idea sounds neat, but I am curious about longterm reliability. Sorry for all of my ignorant ?'s guys.

I can't speak about the Piranha props but I have the exact same engine as yours. 1984 Force. 85 hp. A couple of years ago I bought a Comprop. 4 blade 13x19 and I loved it. The hole shot was a little slower but the top speed more than made up for it. It was very smooth and the boat handled better with the 4 blade prop. They have several choices for your engine as well.
Unfortunately, my brother borrowed my boat a few weeks later and got into some shallow water and busted the blades but the prop did exactly what it was supposed to. The blades broke off and saved the gearcase.
They aren't expensive and I would buy another except I got a different boat. They run about 90 dollars or so.

 

[jason32038]

Re: 1984 85hp Chrysler

Piranha doesnt make performance props. They make replacement props and the hub is solid. The blades are meant to break..the blades are made out of a composite material called vertex (i think) and has the same strength or greater than aluminium. The piranha props stand with the competition of similar props. Ofcourse stainless steel props are in a league of their own. Instead of replacing an entire prop due to damage or having your prop "serviced" due to a spun hub you can replace only the blades that you need. They also have an exchange program where you can experiment with different pitched blades so you can get the performance you want out of it. I'm getting one very soon. The feedback and comparison tests vs. other props can be found on their website.

 

[Frank Acampora]

Re: 1984 85hp Chrysler

Horsepower is basically set by port size and timing. Milling the head for higher compression will indeed raise the BMEP of the engine but not enough to make a drastic difference.It is the combination of modifications that results in noticeable power gains.

All internal combustion engines have a pressure curve called the Base Mean Effective Pressure. This is the working pressure that the burning gases exert against the piston. When you raise compression, although the BMEP curve remains the same, you raise this curve on the graph and so, horsepower increases. However, you also increase the need for high octane fuel. And, since carbs are at almost their maximum venturi cross section there is nothing to be gained there. Enlarging ports for better airflow and pumping efficiency will give the most bang for the buck. But, you must be willing to disassemble the engine and do the work.

 

[guitar_picker85]

Re: 1984 85hp Chrysler

Okay, I just thought that, with the other motor, I couldmaybe do some easy bolt on mods, but I don't have accesss to the machining equip to modify the ports, etc. Thanks for the input, guys.

 

[Frank Acampora]

Re: 1984 85hp Chrysler

Ports can be squared by hand with a Dremel tool and carbide bits. It takes about an hour per cylinder.