Tune up of Johnson 90 hp v-4 1982

[baiwan]

What are the max RPM? Can I go at higher RPM for a couple of minutes for propeller selection without trouble?
Is it possible to tune up a Johnson 90 hp v-4 to 115 hp.
Generally the motors are the same; what is the difference:

 

[tashasdaddy]

Re: Tune up of Johnson 90 hp v-4 1982

alot of stuff, porting, exhaust, not being an expert mech, you can screw up a good motor, real easy.

 

[ezeke]

Re: Tune up of Johnson 90 hp v-4 1982

The full throttle operating range for your specific model is 4500 to 5500?; instructions used to be to prop WOT in the top half of that range.

Technicians now recommend to prop above the range, generally up to 5800 RPM.

There is still considerable debate on this subject, but the engine is less likely to lug at the higher RPM.

?.See page 1-13, 1982 OMC Service Manual # 392790, or your OMC Owner's Manual specification sheet.

 

[Chinewalker]

Re: Tune up of Johnson 90 hp v-4 1982

Is it possible to upgrade it to a 115? Yes. Easy? No. Intake and exhaust ports are considerably larger on the 115 and would require full disassembly and machining. Also need larger carburetors to match.

- Scott

 

[emdsapmgr]

Re: Tune up of Johnson 90 hp v-4 1982

That engine is going to run out of breathing capability and torque over 5800, so why twist over 5800 for no gain. The 115 that year had a different block but used the same heads as the 90. They got the added hp from larger carbs that flow more fuel and the intake filler blocks. If you don't want to get into machining-I'd probably move right up to the 140 carbs and rejet them for your block, install a set of 140 heads, add the intake fillers and a set of composite reeds. If you want more, you can always tear it down an port it.

 

[baiwan]

Re: Tune up of Johnson 90 hp v-4 1982

I wonder wheather to overhaul the engine now or next season and want to gather more information on the motor before my final decision. I've always wanted this engine but couldn't find a newer one; this one is the first one offered here and I took it without hesitation. I'm reinforcing my boat now, then I'll do a test run - one season - about 50 hours and then I will decide whether to try to tune up or overhaul it.
It all depends on the performance.
Thanks for the attention, I've received lots of hints to consider
I'll be in touch