Recommended WOT RPM for 70 hp?

[TDmanager]

I have worn my eyeballs out looking for information that will verify the correct WOT RPM for my 1979 model motor.

I read in one place that the older (1979) motors had a lower (5000 rpm) WOT RPM rating than newer (5500-5900 rpm) models. I read in another place that they all 70hp Evinrudes are the same.

Could someone please tell me the correct WOT RPM for my motor (1979)?

Thanks!

 

[jtexas]

Re: Recommended WOT RPM for 70 hp?

According to my 1979 OEM service manual, WOT is 4600-5000 RPM. I run mine at 5200-5300. That's about 34-36 mph on a vintage 15' kingfisher tri-hull.

 

[TDmanager]

Re: Recommended WOT RPM for 70 hp?

Thanks! That is exactly the information I was looking for.

My boat should be about the same size. Right now I have a 17 OMC stainless that turns the motor to 5600 about 34 mph. I'm considering going to a 19 SST or a 20 Raker to get the rpm down a little. I have access to both. What pitch prop do you run to get to 5200-5300?

I'm only interested in cruising about 20-25 mph. Pulling a tube or skier is not a consideration. I don't want to lug the engine but I don't want to keep the old motor winding high all the time either. Would you recommend a 19 or 20 pitch?

 

[jtexas]

Re: Recommended WOT RPM for 70 hp?

I never have been able to find identifying marks on the prop -- but I know it's stainless steel and 13 diameter which makes it 19" pitch (assuming its the original evinrude prop which I believe it is, on account of all the previous owners were friends of my dad's and I just don't see any of them spending money on a prop).

I have manual trim (power tilt, manual trim), it's in the second hole. Hole shot's never been a problem.

I don't know much about different props, but if you post a question over on the "Prop" forum you'll get lots of opinions.

Your gear ratio is 29/12:1, by the way (about 2.4:1).

 

[Boss Hawg]

Re: Recommended WOT RPM for 70 hp?

Thanks! That is exactly the information I was looking for.

My boat should be about the same size. Right now I have a 17 OMC stainless that turns the motor to 5600 about 34 mph. I'm considering going to a 19 SST or a 20 Raker to get the rpm down a little. I have access to both. What pitch prop do you run to get to 5200-5300?

I'm only interested in cruising about 20-25 mph. Pulling a tube or skier is not a consideration. I don't want to lug the engine but I don't want to keep the old motor winding high all the time either. Would you recommend a 19 or 20 pitch?

Don't know if it helps but i have a 1987 70hp behind my 16' fiberglass bassboat & i went from a 13 3/8x17 pitch to a 14x19 & am now running about 5500 at 40mph @ WOT

 

[TDmanager]

Re: Recommended WOT RPM for 70 hp?

Thanks for the info. I appreciate it!

 

[jtexas]

Re: Recommended WOT RPM for 70 hp?

Don't know if it helps but i have a 1987 70hp behind my 16' fiberglass bassboat & i went from a 13 3/8x17 pitch to a 14x19 & am now running about 5500 at 40mph @ WOT

isn't that 70hp at the propshaft (as opposed to at the powerhead with the older motors)?

what were you getting with the 17" prop?

 

[Boss Hawg]

Re: Recommended WOT RPM for 70 hp?

isn't that 70hp at the propshaft (as opposed to at the powerhead with the older motors)?

what were you getting with the 17" prop?

Sorry, not smart enough to know the difference
With my chewed up 17 i was turning about 5800 at 36-38 (GPS) mph
I thought that was too much RPM & not quite enough speed & got a deal on the 19 so thought i'd try it
Think i did right?

 

[TDmanager]

Re: Recommended WOT RPM for 70 hp?

I just tried the 20 pitch Raker prop on my Ebbtide with 70hp Evinrude. With one person, and a normal load, it turned 4900 at 35 mph at WOT. That is 1 mph faster than the 17 stainless prop turning 5600 rpm.

It was good but not great coming out of the hole but it acceptable to me. I gained 1 mph but the biggest improvement was it was so smooth and quite. The Raker holds the bow slightly higher and the spray is coming off the hull further back than before so I feel it may be running through the water easier. (I don't have tilt/trim)

At cruising speed with the the same throttle setting where it was doing 25 mph at 4150 rpm with the 17 pitch stainless, now I'm going 27 mph at 3600 rpm.

I will try the 19 pitch stainless when I get a chance but I'm very happy with the 20 Raker. I like the lower sound when cruising and it handles great.

The boat is used mainly for cruising at about 25 mph My next question is: does anyone think the 20 Raker and lower rpm will hurt the motor?

Thanks for all the input!

 

[jay_merrill]

Re: Recommended WOT RPM for 70 hp?

I never have been able to find identifying marks on the prop -- but I know it's stainless steel and 13 diameter which makes it 19" pitch (assuming its the original evinrude prop which I believe it is, on account of all the previous owners were friends of my dad's and I just don't see any of them spending money on a prop).

Why would being a 13" diameter SS prop "make it" a 19" pitch model?