115 v4 to 115 Johnson four stroke prop ideas

[nashwinter123]

Im just starting the process of repowering my 19' romarine center console and I'm looking for some advice on propping the new engine. On it now is one of the lovely v4 115 evinrudes that they made for centuries. Mid 90's I believe with VRO. One of the few old v4's that still run beutifuly I may add. Pushes the boat around 30 mph. I'm repowering with a Johnson 115 suzuki four stroke from 2006. Should the prop be about the same size for the new motor as the old? I know there's a weight difference of about 120lbs and a 2 stroke generally makes more power. But on the other hand this is a fuel injected low hour engine. Up on size or down?

 

[jimmbo]

Well what are the specs of the 4 stroke, as in WOT rpm range, gear ratio?

 

[nashwinter123]

5000-6000rpms and the gear ratio is 12:25(2.08) on the Johnson 115 4 stroke, no idea on the old evinrude, currently runs around 5200rpms max

 

[jimmbo]

The old engine was 4500 - 5500 and 2:1. I think your old prop is too big by about 3 -4 inches.
The new engine, being a 4 stroke, has to rev higher to makes it power. The torque curves are different but 115hp is 115 hp, and should deliver almost the same top speed(unless one of the engines is not putting out all its power). The gear ratio is close and the boat hasn't changed except for the weight of the engine so to get the revs needed the pitch needs to be lower.
As for fitting, older Suzukies could use the same props as OMC. I don't know if that holds true with the 4 strokes, but see if it fits, and try it out, but as I said, I think you need less pitch to get the revs where they need to be