1994 Evinrude 120...max safe rpm?

[Digdug]

Hey does anyone know the maximum safe RPM for this engine? With a 13X19 stainless OMC prop it will turn 6000 with engine trimmed up. I usually do not run it over 5000 but occasionally another v-4 comes scootin by and its on!

 

[lakerunner]

Re: 1994 Evinrude 120...max safe rpm?

I'm not sure what the safe RPM limit is; but depending on the year of your engine the revive limit is set at 6200 or 6700 RPM'S.

 

[omctech]

Re: 1994 Evinrude 120...max safe rpm?

Max RPM is 6000. You need to go up 2" in pitch to get your best performance.

 

[Dhadley]

Re: 1994 Evinrude 120...max safe rpm?

An interesting question. As the guys have stated the first thing that limits RPM is the limiter. If we are taliking strictly from a stock V4 looper engine standpoint, it concerns me to turn a stock (cast) piston over 6700. It's been done but it makes a real mess if it comes apart. The looper reeds are good into the low 7000 range. <br /><br />If we go above 6700, we use forged pistons and Boyesen reeds. With stock port timing we have turned 8200. On a ported and modified V4 looper we have turned 9500 to 9600. The light rods did not like life above 9300 so we went back to the heavy rods on that motor.<br /><br />Keep in mind these were race boats. Your particular set up will depend on a lot of things, but 6000 is a good start. <br /><br />Good luck!

 

[Digdug]

Re: 1994 Evinrude 120...max safe rpm?

Thanks for the information. My engine is a stock loop charged 120 hp. I think I'll keep her under 6000 rpms and keep her in one piece (Dhadley 9600!!!). Motor runs strong for a stock engine. My boat is a 17'9" stratos bass boat and It will run 50+ (speed ometer shows about 56 mph).<br /> <br />Omctech, I have been thinking about trying a 21 pitch but I havent found the right deal yet (looking for a omc raker). If I went to a 21 I'm thinking the boat might be sluggish getting on plane (3 batteries and full tank of gas and 2 passangers). Are there any other prop tricks I might try that will add a little top end but still but still get out ok?

 

[Dhadley]

Re: 1994 Evinrude 120...max safe rpm?

How high is your motor mounted now? Do you have a jack plate? The 21 will drop your RPM but you may be able to raise the motor (watch the water pressure gauge) to gain some back and get even more speed.<br /><br />Good luck!

 

[Digdug]

Re: 1994 Evinrude 120...max safe rpm?

I do not have a jack plate. I think the motor is about as high as I can get it because I already have to trim down to accelerate. Also not able to turn very sharp unless motor is all the way down. Will a jack plate give me a better hole shot? If so I should definately be able to handle the 21 pitch. I guess cables will need to be 6-8 inches longer with a jack plate??

 

[Dhadley]

Re: 1994 Evinrude 120...max safe rpm?

In a way, yes it will help. A jack plate with the set back will allow you to set the boat up with a "better" propeller. Sounds like you have optimized your set up for your current propeller. Now to gain effeciency we will go to a propeller with more technology. <br /><br />Your prop is ventalating so we move to a prop with more "bite". With more "bite" you can run the prop higher. If you are running an SST you can go to a Raker or Stilleto of higher pitch (21) and because of the way they are built, you can raise the motor (increase the X dimension) without venting or "breaking loose". Anytime you are able to run the motor higher, you reduce gearcase drag which means faster top end. They have lots of "lift" so you are reducing the wetted surface or hull drag. <br /><br />Props are a lot of fun and you have a good boat that will respond well.<br /><br />Good luck!

 

[Digdug]

Re: 1994 Evinrude 120...max safe rpm?

Dhadley, thanks for your interest in my post. I stayed up late last night and have read a lot of your posts from way back. Seems like you are heavy into outboard racing. Will you help me optimize my boat/motor? Here are some specifics on my boat. 1994 Stratos 270 (17'9")(Turbo Vee Hull Design)(max 150hp). Transom goes down 17" then insets 10" then drops another 7" to bottom of hull. Motor is a 1994 Evinrude 120hp (model# E120TLERC). Motor mount is 1" above trasom with room to be raised about another 3/4". Cavitation plate is 3" above bottom of hull and 3.5" below the inset. Transom seems to slant backwards a bit (lots of negative trim when motor is all the way down). I did the cavitation plate measurements with the engine trimmed so that the cavitation plate is parallel with bottom of boat. Putting a yard stick on bottom of hull and extending to motor only 2.5 of the 4 water intake ports are under water when boat is on plane and motor is level with bottom of boat. Water pressure is great (25+ psi at 5000 rpm). I can start hearing my exhaust at 1/3 trim. Prop is the stainless steel prop (has factory black paint) that came with the motor when purchased new in 1994. Boat will run 55 mph on speedometer with engine approaching 5900 to 6000 rpm (engine exhaust is loud and motor kicking up spray). It makes me nervous to run that many rpms (engine is singing). What should I do first to get the most bang for my buck (new prop or jack plate)? I know you like stilletto and raker but I found a performance prop called a "Rapture" on sale brand new for $209? What is your opinion on the Rapture prop?

 

[Dhadley]

Re: 1994 Evinrude 120...max safe rpm?

I've sold several props that replaced the Rapture but that doesn't mean it won't work on your boat. A good rule of thumb, especially in props, is you get what you pay for. I expect a Raker, Stiletto or Turbo to perform better than an SST but certianly not as good as a Mazco. <br /><br />Anyway, you still have some vertical adjustment left, so the prop would probably come first. However, at some point I would suggest a manual jack plate for two reasons. The 5" set back will move the center of gravity back and will give you the ability to change the X dimension in minutes without a hoist. I prefer the ones from Bobs Machine, manual or hydraulic.<br /><br />You've got great water pressure. Keep an eye on that throught out this process. Oh, and your motor is singing because it's happy. <br /><br />If you decide to try the Rapture, let me know how you make out. If you decide to go with a Stiletto or Turbo, I can get those for you. If you like, you can e-mail me at dhadley50@aol.com. Have you ever thought about a 4 blade? Or are you pretty set on a 3 blade?<br /><br />Let me know! Good luck!

 

[Digdug]

Re: 1994 Evinrude 120...max safe rpm?

Dhadley, I tried a 13.25X20 today. It made a big difference. The whole boat seemed to ride different. Max rpm now 5800 and max speed now 58mph (per my speedometer) (just me in boat). Prop grips the water much better...can maker sharper turns without trimming down. The only negative was the boat is a little slower out of the hole and midrange acceleration not as good. Motor seems to be much quieter. Thinking about lifting motor one notch to see what happens. Wanted to say thanks for the help! Here is picture of new prop (if it works). There was a definate difference as compared to the 13X19 SST.<br />