Engine Rpm vs. Prop pitch

[Andrew Leigh]

Hi,<br /><br />I don't know where to post this one but here goes with some questions.<br /><br />a) Am I correct in assuming that if I get 5400 Rpm out of my 1998 115hp V4 Evinrude with a 17" prop that I am correctly "propped"?<br /><br />b) If holeshot performance is not important would it not extend the engine life were I to go for a 19" prop and consequently reducing the rpm?<br /><br />b) Would the 19" prop give better top speed or would I run out of torque owing to the fact that I will running lower down on the torque curve?<br /><br />Cheers<br />Andrew

 

[JB]

Re: Engine Rpm vs. Prop pitch

Good questions, Andrew, and some that many boaters don't understand.<br /><br />1. Yes. If you are getting 5400 at WOT you are probably using a correct pitch for your rig.<br /><br />2. No. Going to a longer pitch will probably not allow your engine into its best operating range and shorten, not lengthen its life. <br /><br />3. The 19" prop would probably reduce your top speed as well as your WOT rpm.<br /><br />Your engine would have to work harder to reach WOT rpm with the 19" prop, resulting in greater strain on your engine, not less, and it may not have enough torque to reach the same top speed.<br /><br />Depending on how you use your boat, some might even recommend a shorter pitch than the 17", looking for a WOT rpm closer to 6,000rpm.<br /><br />I am going to move this to General Outboard, where propping questions get more attention.<br /><br />Good luck.

 

[Andrew Leigh]

Re: Engine Rpm vs. Prop pitch

Thanks JB.<br /><br />Cheers

 

[ZmOz]

Re: Engine Rpm vs. Prop pitch

Yeah, you need to find out exactly what RPM range the manufacturer recommends, and get a prop that lets you do that. Outboards are very picky about their WOT RPM, and they like to be around 6k.

 

[seahorse5]

Re: Engine Rpm vs. Prop pitch

If you have the 115 FICHT Evinrude, it will run and perform better with one size smaller prop up in the 5800 rpm range.<br /><br />If you have the carbureted 115, either 60 degree looper or the 90 degree crossflow, then you are propped right near the recommended upper part of the rpm range of 5500 rpm.

 

[walleyehed]

Re: Engine Rpm vs. Prop pitch

My 2 cents....Prop for 5800-6000RPM, light load with the 90 deg, crossflow.....It likes it there. <br /> You might take a look at the mounting position of your outboard, as well. is it "setting" directly on the transom (Top hole), or is it raised slightly-2nd, or 3rd hole????<br />I'm talking about the bolts holding the engine to the transom, not tilt-pin position.

 

[Andrew Leigh]

Re: Engine Rpm vs. Prop pitch

Thanks for the replies.<br /><br />ZmOz and Seahorse, I have been trying to find out which motor I have but a internet search only confuses as I seem to have odd model and serial numbers. I was on www.marineengine.com. I am unable to establish exactly which one it is can anyone be of assistance.<br /><br />Model F115 TSI ECM<br />F = ??? perhaps ficht<br />115 obviously the hp<br />T = Trim and tilt with electric start<br />S = ???<br />I = ???<br />EC = '98 year of manufacture<br />M = ???<br /><br />The motor layout looks like a 60 deg with carbs. It is the one with the engine cover that when viewed from directly above has the shape of a rattlesnakes head.<br /><br />Serial No. G 0449 1432<br /><br />Walleyehed, I have four mounting holes it is in the second from the top i.e. the one further from the water.<br /><br />As a matter of interest I live at 5600ft above sealevel. This has a marked effect on performance as the effect of altitude can cause up to a 20% loss in power due to the rarified atmosphere. It may be possible that I will not be able to get up to 6000rpm?? Any comments?<br /><br />Thanks for the help. <br /><br />Cheers<br />Andrew

 

[Andrew Leigh]

Re: Engine Rpm vs. Prop pitch

Correction to above post.<br /><br />Model E 115 TS L EC M<br />E = Evinrude<br />115 obviously the hp<br />T = Trim and tilt with electric start<br />S = ???<br />L = Long shaft (20")<br />EC = '98 year of manufacture<br />M = Model run which I understand is not relavant<br /><br />The bottom line of printed dots on the model was very light hence mistaking the E for an F and the I for an L. Have not idea why companies use dot matrix printers for printing critical information like this. I am unable to make out any of the smaller print like weight, oil type etc.<br /><br />Cheers<br />Andrew

 

[seahorse5]

Re: Engine Rpm vs. Prop pitch

Your 115TSLECM is a crossflow 90 degree motor. The trim switch is on the stb. side of the motor pan.<br /><br />Be sure you use Champion QL82C plugs gapped at .030" for best results. If you are getting 5400 rpm at 5600' elevation, you are doing good. The factory redline for that engine is 5500rpm.

 

[Andrew Leigh]

Re: Engine Rpm vs. Prop pitch

Thanks Seahorse,<br /><br />will check out the plugs and gaps.<br /><br />Cheers<br />Andrew

 

[walleyehed]

Re: Engine Rpm vs. Prop pitch

Andrew, if you want to set that up for your altitude, here's the list....Go .003 smaller (3 steps) leaner on main jets, go .005 larger (richer) on idle circut, and if you DO NOT have the OIS ignition system (Big black cover over flywheel and components) advance max timing 3 degrees. <br />With this set up, you will gain about 300RPM at 5000ft MSL (above sea level).<br />Average power loss is 3% per 1000ft...16-17% at 5600ft.<br /><br />EDIT: If your getting 5400RPM at that elevation with a 17" prop, you've either got a very light 16-17ft boat, or some jetting has already been done.

 

[Andrew Leigh]

Re: Engine Rpm vs. Prop pitch

Hi Walleyehed,<br /><br />Thanks for the jetting low down. You are spot on. It's a 17' shallow V hull bowrider.<br /><br />I would not be sure if the boat as been jetted correctly so to change jet sizes may not be prudent at this point. Will first need to establish what the original jets were.<br /><br />Am I correct in assuming that all motors are initially jetted for sea level?<br /><br />I have done some extensive google searches but have been unable to come up with any spec sheet / brochure etc for the motor. Could you point me in the right direction until I purchase a manual?<br /><br />Thanks again for the help.<br /><br />Cheers<br />Andrew

 

[walleyehed]

Re: Engine Rpm vs. Prop pitch

They come from the factory with sea level jets....what the dealer may have done is anyones guess. I'll head back to shop and see what jets were std. and we can go from there. I'm guessing 68C, but we'll see. I'll get back to ya later.