Old vs Newer outboard same HP power difference?

[briaineo]

Hi all

I have an old 1974 Mercury 40hp 402, 2-Stroke, the motor has good compression. (the power output is adequate for my boat)

I was wondering if I was to upgrade to a motor that is 10 years old rather than 40+ years old what to expect.

As this is the only outboard I have ever owned other than the small 4hp back-up I have nothing to compare or knowledge to compare!

In current day motors around 2005 ish would a 30hp give the same performance or would I need a 40hp to equal it?

Would there be a major fuel consumption difference? As gas here in Ireland is over 5 bucks a gallon

thanks

 

[enginepower]

I don't remember the year model but older engine HP was rated at the crank. They later started rating them at the prop so yes, newer smaller numbers seemed to have equal or more than older ones but hopefully somebody knows more about this and can chime in for you.

 

[jbcurt00]

Change was in early 80s, IIRC

 

[steelespike]

A healthy older 40 would perform "about" the same as a newer healthy 40 rated at the prop.You would very likely need a gps two tell the difference.
Either one of the motors may be sub par if a bit tired.

 

[hotrod53]

I was told that a modern day 40 would perform as well as my 1977 Merc 500 50 hp.