J6renm Johnson 6hp 1992 question?

R

robert53a

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Hi I have a 1992 Johnson 6hp short shaft motor that is one of my favorites. This is one of the quietest smoothest motors Johnson ever made. My question is one of difference between that years 6 and 8 hp engines. It appears that both engine are identical part for part(according to the BRP website.) The high speed jet and or reed valves usually are what determines the hp. But in this case it appears only the back decals are different. Does anybody know where the horse power difference is at? Thanks.....Robert
 
JB

JB

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Re: J6renm Johnson 6hp 1992 question?

In engines of similar blocks it is usually the port timing, carb throat diameter, compression ratio and/or displacement that make the differences in power output, Robert. Reed stop settings, ignition timing and link 'n' synch are often different.

Jet sizes in a carb are matched to the venturi and barometrics and usually cannot increase HP unless the venturi is enlarged. Reed thickness and material can change HP.

Now, all that said, I do not know what differences result in the different outputs in the 1992 6 and 8HP engines. I am just going on my experience modifying 2 stroke engines.
 
nwcove

nwcove

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Re: J6renm Johnson 6hp 1992 question?

i do believe your 6hp is a de-tuned 8hp i had a 6 and an 8....both a couple years older than yours, and the only difference i could find in any specs was 500 extra rpms for the 8. ( how the extra rpms were gotten could be carb, could be exhaust, could be timing, could be a combo)
 
Tim Frank

Tim Frank

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Re: J6renm Johnson 6hp 1992 question?

My OEM manual also shows a 3+ LB. weight difference.
 
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Haffiman

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Re: J6renm Johnson 6hp 1992 question?

Depending on suffix number/letter there are differences in intake manifolds, carb throat diameters, leaf plates and in some cases ports.
You may have to pull down and measure/check what is what on your engine.
 
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robert53a

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Re: J6renm Johnson 6hp 1992 question?

Thanks for all the impute. This was just a curiosity and I have no intention of modifying this motor. The engineered difference are many and subtle. This motor runs too good to monkey with modification. I also have a 8hp that's a little newer and i was just doing a little side by side comparison and head scratching. Thanks again.....Robert
 
Tim Frank

Tim Frank

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Re: J6renm Johnson 6hp 1992 question?

I have a '74 6 HP and a '92 8 HP (E'rudes) but only use them on one boat.
The 6 HP is such a better runner that the 8HP hasn't been in the water in 2 years.... :)
 
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