Chryco/Force rpm?

[sho305]

Anyone know the best rpm for the chryco stock? I have a '83 85hp 3 cylinder I assume is close or same as 105. It is rated hp at 5500rpm (oops 5K rpm), where should I prop to for speed? It has newer block, runs nice. My inline likes 5700-6K but don't know about this.

I just got a new tach in it and need to check it against my digital clamp on but...it only shows 5200 rpm at 42.6! I used the clamp on before but with two people could not get all the way to full rpm testing...so I figured out what it was at full speed on paper via mph per rpm (using gps at various higher speeds I figured it was hitting 6K at 43mph max) and had the prop done to lower the rpm a little. It ran 43gps before and after prop job, had it thinned on leading edge and slightly more cup.

Guessing the new tach is on or close but will check to be sure before I have prop done again. Other new tachs have been right there so far. I assume it should run at least 5500rpm...but most older OBs seem to like a little extra rpm to go fastest.

[delawarerick]

On the later 120s forces it was 5250 max rpm. We had alot of problems with salt and these motors and they were not around very long. Yet some of the white covered engines are still around. Rick

[sho305]

OH WAIT, I did screw up how did I do that. I have the manual here its 85hp at 5,000rpm, operating range 4500-5500.

75/85/90/100/115hp all same rpm, 140hp lists 5250 rated and 5000-5500 range. 90hp & up are 4 cylinder.

Maybe I am good at 5200? Or should I be top of range at 5500?

Once I had a Merc 80hp I4 that went faster at 6K, much higher than rated at so wondered if that was case here. Hard to find props for this. It has SS mich wheel but at least its SS. Given the boat it can't be all bad for it.

This motor:
http://usera.imagecave.com/sho305/forcemotorbarex.jpg
http://usera.imagecave.com/sho305/baylinerforcepropluxx.jpg

[Tom Smyth]

Cant turn the Chizzlers / Force much more than their rating without doing some tricks inside of them. Would prop it to turn right at the top of the RPM range with a light load and little fuel.


Turned a 73 90HP over 6400 RPM and it was still kicking 10 years later.. but there were a few things fixed inside. wasnt a merc 850 around that would touch it.... and lots of wierd looks on thier faces when they was left looking at the transom...

Smytty

[150aintenuff]

if ya gunna spin one up its gotta be gone though and definatly totally ballanced..... but that only gets ya about 400 more before they go lean and go bang.....

[sho305]

It does make this funny whistling sound when it gets near 5500 or above. Sounds like a horn sort of. I never had one so...:confused: Also tested the overheat horn while working on the tach and found it does not work...:rolleyes: Have to get a new beeper for the dash. I keep mixing 50:1 but then put more in so its about 45:1. Plugs are not light at all, pistons are dark.

Only problem is that it stinks fiercely when you troll with it. It steams and smokes a lot out of the vent holes, I even leaned the idle down far as I could.