Here is a intresting issue

[Kern O]

The YZ60's just ran stronger than everything else out there. It was one of those combinations that just plain worked. Are you off on technologies? That's tough to say. I like my big block Camino because I can see all 8 plugs and swap the manifold in an hour. I have newer things where you cannot even see the plug wires. But you also never have to fix 'em........

[Drifter]

Originally Posted by glassman

A friend of mine just repowered his kencraft he went from a 150 yam.hpdi to a 150 yam 4 stroke.

question 1:
Is it the horse power to weight ratio? The HPDI does not weigh as much as the 4 stroke.

According to Yamaha's 2004 catalog, the 150 HPDI actually weighs 9 lbs more than the F150. Thus, transom weight should be a non-issue.

Gear ratio is different between the two engines, so the props that worked on the Z150's might not be optimal for the F150's.

Just because a prop reaches max rpm range does not mean that it's the best prop. Several props will likely provide the correct rpm's, but not all will provide the same performance.

As for comparing previous and current performance, were the loads of the boat the same during the tests? Amount of fuel, people, gear, ice, water (in livewell or washdown system), etc can have an impact on performance.

I would keep searching for an answer, as I don't think the performance difference should be that much.

Good luck.

[Prodigal Son]

This isn't going to help, but I'll just comment on the YZ60 vs XR80 thing...I had a 400EX 4 wheeler, bored to 440cc, etc.

Raced my 80lb cousin down a dirt road with her on her KX85...guess who won?

Won't me

[surfncnow]

2s will out do most 4s any day.

My father got me a 200X 3 wheeler that was fast. I jetted the carb and put an over sized cam in it for performance. The problem was kick starting the darn thing cause it had so much compression. I used to call 4s the long stroke.

[Kern O]

I don't think that anyone will ever argue about the power to weight ratio of 2S vs 4S. One fires twice as often as the other, so it has twice the effective displacement. Two strokes are also easy to tune so they make a huge power peak without loosing too much elsewhere. But even with twice the firing strokes, they still have less than twice the power because of the cross breathing and exhaust dilution. Their emissions characteristics are not great, but they do their job well. I like 'em, but realize that they are not going to rule the outboard market again in the foreseeable future. We first saw large four strokes in 2001/2002. Now, they own the market.

[glassman]

talking about the dirt bikes my son who is 13 just rode my rm125 for the first time this last sat and had a ball (NO FEAR) fun to watch he has been riding since he was 5.

Back to the ken craft jonh told me that they tried 7 different props he did get about 1.5 mph back but that is it. and yes the conditions are the same

[Inspector62]

Listen to Glen. The right prop can make a huge difference. I gained about 6 mph with the same prop pitch, just a smaller diameter.

I do like the Yamaha black steel props. They seem thinner and lighter than the silver colored steel props.