Talk Morgan Forums Morgan Sports Cars Morgan Plus Four, Supersport & Plus Six (CX & CXV Generation Vehicles) unstressed which will last longer.

Driving back on the motorway last night about 1650 revs doing 70 mph nearly tickover. Just bought a new suzuki140 hp outboard and been carefully running it in at recommended various revs. Over 5000 revs to get on the plane scale back to 4300revs gives nearly 20 knots I wonder which one lasts the longest.

It's all about the oil. Sufficient volume of the right viscosity delivered at the right pressure at the right temperature with the right level of filtration.

A car engine doing 1650 rpm is doing 99k revs per hour, say 100k for easy sums. That gets you 70 miles. A reasonable life span for a car engine is 180k miles, so a total of 257 million rotations of the crankshaft in that life time. Of course, a lot of the time you're going to be doing higher revs in lower gears so let's round this up to 300million rotations, which represents in the order of 2,500 hours of driving. Of course, average speed for a car is more like 35 mph so it's more likely to take 5,000 hours to do the 180k miles.

Outboard motors can't be measured in miles but in time. To get 300 million revolutions out of an engine that spends its time at 4500 rpm on average is less than 1200 hours of service, which if Google is to be trusted is well within the expected life span of an outboard motor, which is around 4,000 hours.

So somewhat surprisingly, I'd expect your outboard to last comparatively longer than the car!

I didn't bother doing the maths I just looked at the country of origin of the engine manufacturer and went with Japan and Suzuki, and their experience in high revving engine applications and the design was for a more extreme marine environment.

The Suzuki will be in a bin in 15 years time also the raw sea water cooling taking its toll. I hope the b58 will still be chugging along. Surprising stats all the same. Em

The American marine industry posted some remarkable figures a few years back, (prior to the universal rise of four stroke outboards) The average lifetime of the OMC -as was and Mercury outboards was 60 hours ! Yes that is right prior to the Japanese takeover and Four stroke outboards -, most outboards in salt water at least corroded away rather than wore out , also stale two stroke pre mix took its toll with carbs gumming up etc etc. Of course the relatively small number of commercial users got good hours running them hard (like courier vans). Now with lightweight efficient four strokes and Diesel outboards for the commercial market the whole scene has changed for the better. I have a Suzuki 20hp with self powered electronic fuel injection on one of my boats and it is a marvel of economy, especially when I recall a V6 200hp two stroke Evinrude I owned in 1978 that my friends used to say one gallon two gallon three every couple of minutes, luckily petrol was cheap then!

I've never been much involved with any form of boating (comes from living 70 miles inland I suppose) but one thing I remember from when I was a young lad was one of my father's boat-owning friends telling him that the horsepower of an outboard motor gave a guide to its fuel consumption, a 10hp motor using 1 gallon per hour and so on. This would have been around 1968-1970 or so.

Was this a mis-remember? Was it true back then? Is it still true today?

Your not far off one gallon for every ten horses but that would be more or less flat out and carbe'd two strokes. Things have changed dramatically in the outboard world with the introduction of the four stroke. However having said that engines have got so much bigger in horsepower and many new boats are totally over powered .People generally have no concept of fuel usage on a boat I still shock myself sometimes and that 's after 60 years . Go to any Marina in the country and many twin engined petrols v8s never go out they can run to 40 gals an hour. Em

Blimey!

Thanks for the info, very interesting.

Can be more can be less depends on hull size and that was at WOT.

Yes these things are all relative , a friends launch that I was away on at Christmas can run at full throttle 400L per hour a side in Diesel -we dont run that fast very often.