90 or 70 hp 4 stroke motor for 170cc

[JETPILOT]

How do you find the difference between the 15 pitch and the 17.
Is the 15 stronger out of the hole and how mutch top speed do you loose.

Cheer Paul

[jebsr50]

I bought my 01 logic 17dc in 2002 from a tournament fisherman who had a 90hp yamaha on it. He needed more room and a larger livewell ect for the redfish. He fished it one season and sold it to me. The 90 he had on it ran great but I put a 60hp on. Now the 60 is much lighter and plenty of power for my type of fishing in the flats, for anything more I could understand more power would be necessary. I find the 60 to be an advantage in the flats because of weight it's a 2 stroke.

[wpschaef]

I have a 75 HP 4stroke on my 170CC and it gets up and dances. Top speed around 43 on the speedo. Haven't tried to time the "up on plane" time but I am certainly not unhappy with it. Dinged my alum prop and am shopping for a stainless with just a bit more pitch to keep below max RPM at WOT.

[RPK513]

I have a Yamaha 2 stroke on my 06 170cc. Top speed is 38 when by myself and around 35 with passengers. Great fuel economy and adequate power to pull a skier.

[ILLOGICAL GGC]

The 15 Turns 200 Rpms On Average Faster Than The 17 Thereby Helping You On The Bottom End Get On Plane ,however It Will Use More Fuel And Cause The Motor Work Harder On The Top End. The 17 Will Allow You To Go Faster At Lower Rpms Once On Plane But Is Less Responsive From Still To Plane

[bluecrab]

I have a 60 hp Suzuki 4 stroke that weighs 357 lbs pretty heavy.
Purrs like a kitten and very low emissions. Actually mine has California Emissions so it may have a restrictor plate of sorts. Still trying to figure it out.
It goes plenty fast for me.
I am a newbie boat owner though.

blue

[BarryB]

Hi All,

My 170CC has a 70Hp 2 stroke Yamaha. I like the 2 stroke for its simplicity and ease of maintenance. It's also the lightest engine for the 170 at 228lbs. Since I like to fish and dive, I have less water jumping over the transom during moderate seas.

The motor started with a 13 1/2 X 15 prop. This gave me a better "hole shot", however, I lost some top end, my fuel economy was off and my max RPM was about 6,000. Although Yamaha states the operating RPM is between 5,000 and 6,000, keeping it at the high end just wears out the engine faster.

I switched to a 13 1/4 X 17 and top speed increased to about 38MPH while RPM dropped to 5,500. The stated 70HP is at 5,500 RPM according to the dyno reports. So, I get a little better top end, the fuel economy increases and there is less wear on the motor because I'm turning less RPM.

I've checked out the Yamaha performance bulletin on both the 70 2 stroke and 75 4 stroke. The 4 stroke gets about 1.2 MPG better than the 2 stroke at certain RPM's, however, at 4,000 (the best fuel economy for the 2 stroke) the 4 only gets about .7 MPG better. I'll live with the 2 stroke.