stainless vs alum=rpm's

[Bcmagna]

just got my motor re-jetted and the timing advanced (running to lean at idle) runs great now all the way around. it's a 1993 evinrude 150 spitfire .The omc mechanic told me that I need to increase the rpms. I have been running a viper 14 1/2 x19 stainless at 5200 rpm's wot. He said to put the original aluminum which is the same 14 1/2 x 19 .I did this and the rpm,s increased to 5600 but the speed stayed the exact same 48.5 mph (gps).I'm wondering if it's all right to keep running the stainless and the slower rpm's. I can not afford to reprop right now (the look from the wife say it all...loudly!!)I just had the stainless trued up and straightened for $150.00 so I have to wait a bit to drop a pitch ,or should I run the aluminum and the higher rpm's? thanks Bill

 

[walleyehed]

Re: stainless vs alum=rpm's

SS is usually more efficent, but is generally cupped more and pulls a little harder, but will run higher trim angles and higher off the transom without ventilation.<br />dhadley is the man to ask for on this....there are many variables (even with one prop) that can be changed to add performance, such as lifting the engine off the transom alittle at a time until you start noticing changes-good or bad. <br />Ask for dhadley...........

 

[Dhadley]

Re: stainless vs alum=rpm's

Walleyehed is correct -- the Viper will run a much higher X dimension than the aluminum prop. Raise the motor. You paid good money for the Viper so take advantage of what you paid for. Besides youre killing the motor at 5200.<br /><br />Good luck!

 

[Bcmagna]

Re: stainless vs alum=rpm's

I know when I had a long shaft motor (20 hp) on a short shaft transom (C -14' Lund ) I needed to raise it 5" and it ran great. What's the processes to raise this motor?or how much to start with? It's on a 18'crestliner pro-am aluminum boat.Thanks for your expertise and advice.Bill

 

[DJ]

Re: stainless vs alum=rpm's

bc,<br /><br />Raise it one notch (bolt holes) and test it.

 

[Bcmagna]

Re: stainless vs alum=rpm's

I RAISED IT 3/4" (ONE NOTCH) AND TESTED IT , NOT MUCH IF ANY CHANGE.ran at 5200rpm's @ wot and 48.5 mph. gps.went back raised it another 3/4" (all the way up)tested again ,this time5500rpm's wot 50.1mph. gps so it helped allot . It seems that allot more spray off the motor and some noise increase but better than before.I still think that there is more in the 150 but not sure what else to try short of re proping. Thanks

 

[DJ]

Re: stainless vs alum=rpm's

BC,<br /><br />5500 will be much healthier for that engine and now you can use that Viper prop.<br /><br />Do you have a water pressure guage? If so, keep an eye on it.