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Author Topic:   Maximum RPM - Evinrude 70 HP
Buckda posted 09-09-2002 05:05 PM ET (US)   Profile for Buckda   Send Email to Buckda  
First, I do not have the manual for my 1995 70 HP Evinrude - any advice as to where I can purchase one?

Second - Took my boat out this weekend on Lake Michigan (Beautiful weekend) and at full throttle, the Tach indicated 6100 RPM....I think this is high (?) and am concerned that (1) I need more prop and/or (2) my tachometer is wrong

Currently there is a 13.75x15 prop (slightly "chewed" by the previous owner).

Any suggestions / recommendations as to new propeller design/measurements and what the max RPM should be? I'd like to be able to run WOT and NOT max out the engine on RPMs...just hit the max power band.

Boat is an '89 15' Sport -GLS. I carry 18 gallons of fuel aboard behind the aft thwart (12 gal Tempo and 6 gal reserve) along with a battery and VRO tank.

Buckda posted 09-09-2002 05:09 PM ET (US)     Profile for Buckda  Send Email to Buckda     
Oh...the reason I think the Tach may not be accurate, besides the high reading, is that when the engine is off, it rests just above 1000 RPM...and when at Idle, it hovers around 1,000 too...
jimh posted 09-09-2002 06:16 PM ET (US)     Profile for jimh  Send Email to jimh     
It is typical for the pointer on an analogue Tachometer gauge to read upscale when the engine is off. Mine does it, too.
Peter posted 09-09-2002 07:47 PM ET (US)     Profile for Peter  Send Email to Peter     
The tachometer for the 1987 150 Johnson on my 18 Outrage rested at about 1000 with the ignition off. Seems to me that the 70 on a 15' GLS should be able to turn at least a 17" pitch propeller.
djahncke posted 09-09-2002 09:47 PM ET (US)     Profile for djahncke  Send Email to djahncke     
My 1978 15 Sport with a 1978 70hp Evinrude has been turning a 12 7/8" x 21" prop since I bought it new.
Buckda posted 09-10-2002 09:17 AM ET (US)     Profile for Buckda  Send Email to Buckda     
Thanks for the responses everyone. I guess the Tach may be more accurate than I suspected. So, did I over-rev the engine last weekend?

I had planned to order a new propeller (13x19) and would use the existing one as a reserve, but I'm still concerned about redline on this engine...

How high is too high? As I said, I want to be able to maximize the engine's potential without damaging it. I would prefer that WOT be just below redline and that I have a proper setup.

Cicada posted 09-10-2002 09:26 AM ET (US)     Profile for Cicada  Send Email to Cicada     
78 15' sport 70hp Johnson.
The original prop that I have I think is a 13.25 X 17 - no markings. Alone in the boat the rpm hits close to 5900 rpm. One additional passenger about 5600 and above that stays within rated range. Gets up on plane real well.

When I switch to a 13 X 19 prop the boat becomes difficult to plane. By myself I can get it up ok. With a passenger, have to send the passenger forward or it takes forever. Max rpm alone about 4800, with passenger 4600.

With either prop maximum speed that I've been able to get is about 38 mph GPS. Typically carry 9 gals of fuel. With the 17 pitch the boat has pulled me up on a wakeboard with one adult, two kids and two large dogs, wouldn't even consider it with the 19 pitch.

Question - Are boats faster in salt water vs. fresh water?

Cicada posted 09-10-2002 09:29 AM ET (US)     Profile for Cicada  Send Email to Cicada     
Rated range on that motor is 5000 to 5500 rpm. Owners manuals should be readily available. Marine dealer here has them for a 78.
where2 posted 09-10-2002 01:13 PM ET (US)     Profile for where2  Send Email to where2     
'85 15' Sport with an '85 70Hp Johnson. Running a 13-1/4"x17" aluminum with extra cupping for pulling up slalom skiers. For running flat out I can up the prop to a 13-1/4"x19" Stainless with cupping.

I would suspect your 13-1/4"x15" is a minimum of 2" under-pitched. You probably have awesome hole-shot with any load configuration, but watch the max RPM's. With the 17" pitch, I get 6100rpm without a skier for extra drag...

Bigshot posted 09-10-2002 01:43 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Actually since 1986 70 PMC's are 5000-6000. My 15' with a 13x19 double cupped to a 20" would turn 5900 and spin 48.3 on the GPS. Holeshot would pin you to the seat but I think to ski, you would want a 19" w/o the double cup. 15" is WaY too small.
Buckda posted 09-10-2002 02:20 PM ET (US)     Profile for Buckda  Send Email to Buckda     
You're right...the holeshot will dump you onto the floor behind the aft thwart if you're not careful (thank heaven for the kill switch)..When fully trimmed she'll jump up out of the water at what must be an angle through 65 degrees.

So I shouldn't be too worried about the RPM being around 5500-6000 (the engine is a '95)?

Bigshot posted 09-10-2002 04:15 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
No problem with 6k, that is redline for a 86-2002. But I would get a 13x19 on it. Like I said that 15" is too small. Plus landing on the gas tank can hurt:)

Not good running a chewed prop also.

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