Prop Pitch vs. Diameter

[Bob197]

I have an old OMC 800 outdrive on my 23 foot Lancer and am currently running a 15 by 17 inch prop which seems perfed tor the poat Chevy 350 ).I now have a chnce to buy a stainless prop with a pitch of 21 inches and diamerer of 131/4 inches.
Are they close enough to take a chance performanewice?

 

[Bondo]

Re: Prop Pitch vs. Diameter

Are they close enough to take a chance performanewice?

Nope........

21"s of Pitch will Kill your motor............

 

[seabasser]

Re: Prop Pitch vs. Diameter

that wheel won't even be close

 

[JUSTINTIME]

Re: Prop Pitch vs. Diameter

no way
what is WOT RPM?

 

[walleyehed]

Re: Prop Pitch vs. Diameter

If that 15X17 is an OMC 391200, it will be hard to beat with a general SS prop. The RPM at which this prop is turning is very important.
and....yes, the 21 will kill the performance if you are at or near the top of your RPM range now.

 

[achris]

Re: Prop Pitch vs. Diameter

The pitch is the number of inches the propeller would move forward in 1 revolution, ignoring slip. As the pitch increases the load on the engine will also increase, as it would have to do more work in the same time. The spec on the 350s is about 4400-4800 rpm at Wide Open Throttle (WOT). The usual is about 400 revs change for each 2" pitch change. So, to go from 15" to 21" will knock about 1200 rpm off the top end, probably more as the engine won't be able to make full horsepower. You must also realise that the extra load imposed on the engine is right across the rev range, not just at WOT. That sort of load will most definitely kill your engine. Look out for holes blown in the pistons, valves burnt, head gaskets blown just as a start. That's even if you never excessed half throttle!

Don't do it!!!

Chris................