Size of Engine

[chrishowden]

I have an Avon Adventure 450 with a 40hp Honda and looking to upgrade to a bigger engine and want a bit more top speed but still reasonably economically. Any Suggestions.

[9D280]

When you say economically do you mean fuel consumption or the cost of the upgrade?

Bottom line is if you are running at WOT all the time (implied by the "more speed") there's going to be naff all difference in consumption for a given horsepower.

The upgrade cost is a bit of a cost vs risk decision. You can either pay handsomely for a new engine with guarantees etc etc, or you could spend £400 on an unknown. It will either last indefinetley or go the way mine did & expire spectacularly. Assuming worst case, ballpark budgets are say £100 per piston, say a couple of hudred for a rebore and another £100-150 for gaskets, oil seals & all the other bits you wil lhave to / might as well replace while it's a kit of parts. That all assumes you have facilities & time to dis & re assemble it yourself.

Other relatively cheap option (if your transom allows) might be to find another 40 & move the one you got over a bit....... Then you know you have at least one of known history even if the "new" one packs up.

I'm sure the trade bods can give you a ballpark for trade- in type deals.

[chrishowden]

Doesn't have space for 2 outboards so will have to a bigger outboard

[Locozodiac]

Originally Posted by chrishowden

Doesn't have space for 2 outboards so will have to a bigger outboard

If in pursuit for max top speed, put a induction tacho to your motor and make a wot test, check max wot rpm achieved, factory outboards usually comes with medium pitched props so you can play a bit with different -, + size pitches for different applications.

Example: If your motor works between 5 to 6 k rpm and you are achieving lets say 5.5 k with current prop at wot, placing a less size pitch prop will rise about 250 more rpm. Install the prop that gives nearest rpm reading to match 6 k at wot. Will lose best hole shot but will gain slight more final speed. Check props sizes, tacho brands market available. If final speed does not suits you, go for a larger engine.