Any difference in performance??

[146C]

Hi, am I likely to see much of a difference in performance between currently fitted 55hp Chrylser(’72 I think) and 2000 50hp Johnson 2stroke?

Boat is a Haines 14’6C.

Thanks,

Dave

[Steeler]

Yep,your old Chrysler would have been rated at the flywheel whilst the Johno would be rated at the prop.

Would have noticed more again with a Merc of equal HP to the Johno,sorry couldn't help myself.

Steve

[Noelm]

hhmm I guess the biggest difference is the Johnson will more than likely start and get you home again, whereas the Chrysler would be a bit of a lottery now, (when you consider the Chrysler is well over 35 years old) the 50HP Johnson was not exactly a power house performer, but quite a good motor that should see many years of service.

[ozbee]

is the johono the down tuned 3 cyc 70 hp block or two cyc one. big big difference in output.

[Noelm]

I think the 50 of that era is the twin cylinder, but I could be wrong, I often am.

[Jarrah Jack]

As others have said not a lot. Your 50hp is about the minimum you would want on that boat and if its extra performance you are concerned about then get something bigger. Remember a 60 over a 50 is 20% more power. A mate has a 115 on his!

[146C]

is the johono the down tuned 3 cyc 70 hp block or two cyc one. big big difference in output.

Twin cylinder, I presume the 3cyl would be the more desirable of the two.

The chrysler is also a twin cyl and barely got the boat on the plane, might not of been running 100% tho, so was hoping the jonno being newer technology and seemingly larger prop etc would be suitable.

Dave

[FNQCairns]

How is the chrysler proped? you mention it hardly gets the boat onto the plane, it still should outside of another problem concomitant.

Prop it high in the range and you might see some breathing space...just a thought.

cheers fnq

[146C]

How is the chrysler proped? you mention it hardly gets the boat onto the plane, it still should outside of another problem concomitant.

Prop it high in the range and you might see some breathing space...just a thought.

cheers fnq

G'day fnq prop is 10 3/8 x 12.5.

Dave

[FNQCairns]

Did a quick google and found an unconfirmed report of a 1.75:1 gear ratio.

Trusting this with a 12.5p prop you should be seeing at 5500 = 50km/h + a bit possibly...can you go that fast?? What's your top speed by GPS (only GPS)?

Do you know the highest RPM the engine does make on the water?

cheers fnq

[146C]

Did a quick google and found an unconfirmed report of a 1.75:1 gear ratio.

Trusting this with a 12.5p prop you should be seeing at 5500 = 50km/h + a bit possibly...can you go that fast?? What's your top speed by GPS (only GPS)?

Do you know the highest RPM the engine does make on the water?

cheers fnq

Not sure of the rpm.

I know my brothers tinnie does mid 40's kph wot by gps and we were not able to keep up with him.

Dave

[FNQCairns]

Seems that on the surface with nothing else confusing the issue you are over proped, a sick motor will also replicate this hence the importance of an RPM figure. In the absence of one of these if we assume you are at full throttle and not even doing 40km/h the engine was only reving at approximately 4300rpm...hence why you feel the need to change engines.

Consider to beg/borrow a prop with the same diameter but a 10.5 or 11pitch it's very importantant that you keep the diameter the same or very close otherwise the pitch recommendation will also change...with either of the two props above you should just pip your brothers tinny in top speed and do everything else pretty easy but may not be perfect, that will come later.

It is a crystal ball I am looking into but seriously borrow a prop that approximates those above and test it.

cheers fnq

[ozbee]

i had the 3 cyc model was around that year . it was a white one had the grunt of a 70 just a bit slower . the older it got the faster it went . i think they had a baffle in the exhaust . there was a 60 as well was only advertised for a year or two than they went back to the 2 cyc and a lot less cubes.

[Noelm]

the main reason for the 3 cylinder being "re rated" was to do with HP being rated at the prop, not the flywheel, so instead of making more HP, OMC just down rated the HP of the 70, there was no baffle fitted to the 60HP, it was just a 70 with different stickers on the cowling. They were and still are a very successful motor (like the Yamaha 90) very simple, easy to fix, cheap to run and very light weight, not too sure all that many 50HP 3 cylinders were ever made, most were the re rated 55 twin cylinder that was in service for many years in various forms.