Where's the power from?

[bonsy17]

Alright @Jakobi86 and I have been tossing around where the power difference comes from in these two setups and are wondering what you guys think is the single most contributing factor?

Ski #1
Shortened SN hull (5" off the back and 4" off the front)
JM Ported 718 61x/61x
Single 44mm carb
MSD Enhancer
Boyesen dual stage reeds
ADA head w/35cc domes
B Pipe Mod Chamber
stock water box
9/15 hooker prop
stubby pump cone

Ski #2
Stock SN hull
701 - 6m6/61x Frankenstein motor
Dual 38's on what I believe is an R&D mani
MSD Enhancer
Protec Recreation Head (~150 psi per hole currently)
Protec pipe
Stock Water box
Solas SS Prop... Stock Pitch (maybe 14.7/18.5?)

Based on the weights of a bare stock sn hull we have and the bare weight of the shortened hull in Ski #1 is that Ski #1 is about 30 lbs lighter.

Ski #1 has SIGNIFICANTLY more low end snap than ski #2. To put this in perspective I have a stock 650 sn and would occasionally ride Ski #2. The power difference from the stock 650 to Ski #2 is probably comparable to the power difference from Ski #2 to Ski #1.

My thoughts are that most of this is coming from the porting and impeller.

What are your thoughts?

 

[SmittySX]

I would say because of the porting and the hooker. That prop is probably the biggest difference.

 

[OCD Solutions]

I agree, the impeller will make a significant difference. Start there and then work towards porting and getting the compression up around 185. The rest will come from tuning.

 

[IS0LD0UT]

Porting. Jm motors have some serious snap.

 

[schicks]

i think short hulls feel like they have more power because the nose comes out of the water so fast. But those two props listed will have a pretty big gap in performance. Prop #2 is designed for all around performance where the hooker is geared more towards low end response. I say the biggest difference is due to 1. the hulls and 2. the props.

 

[Blue]

The Porting of course...... thats why i port them the way i do..... But in all seriousness the smaller pitch prop does help the engine get on the powerband quicker and the big hub helps increase the pressure as the water is forced from the leading edge to the trailing edge of the prop all so it can ripp ur arms off.

 

[SXIPro]

Hooker

 

[waxhead]

The pump is the biggest difference.
6m6 cases on one killing the power big time on ski 2
Lower compression in ski 2
there is way to many factors here to even try and make a definitive answer

 

[bonsy17]

I understand that there's a multitude of factors that contribute. Sounds like a good, cheaper starting point is a prop...then a ported top end kit.

 

[waxhead]

yes prop and get rid of the 650 cases,

 

[MADMAT]

I hated a 14.5 18.5 prop on numerous set ups I tried. I think I chucked it in the garbage years ago!

 

[Jakobi86]

I thought there was barely a difference between 61x and 6m6 cases? Btw, I'm the guy with ski no2


Sent from my iPhone using Tapatalk

 

[waxhead]

The 650 has lot smaller reeds. It will never go as well

 

[CRJ]

ski 1 you have
single carb = better low end
9/15 = better low end
ported and bored = more power
cutback/rockered = lighter
b-pipe = more power
pump cone = more thrust.

i bet its night and day difference.

The 650 has lot smaller reeds. It will never go as well

untrue, reed cage is almost exactly the same size, and uses 3 larger reeds vs 4 smaller reeds in the 61x.

 

[waxhead]

ski 1 you have
single carb = better low end
9/15 = better low end
ported and bored = more power
cutback/rockered = lighter
b-pipe = more power
pump cone = more thrust.

i bet its night and day difference.


untrue, reed cage is almost exactly the same size, and uses 3 larger reeds vs 4 smaller reeds in the 61x.

Makes you wonder why yamaha bother to make the change

 

[CRJ]

Makes you wonder why yamaha bother to make the change

If i had to guess, i would say smaller reeds can be thinner material, which will flex more allowing for more airflow. i could measure each and see what the changes are.

 

[bored&stroked]

Makes you wonder why yamaha bother to make the change

Because going from single to dual carbs netted a large peak HP increase, needed when competing with kawi in advertisments and racing.

 

[waxhead]

Because going from single to dual carbs netted a large peak HP increase, needed when competing with kawi in advertisments and racing.

I'm talking about the difference between 61x and 6m6

 

[Jakobi86]

Well ended up adding a 9/15 and while there is definitely a difference, the major difference is from the motor/porting. That's the thing I do t have done and bonsy17's ski is night and day different than mine


Sent from my iPhone using Tapatalk

 

[Roseand]

You have 180+ psi and a ported cylinder. I'd sure as hell hope yours hits harder. Porting makes one hell of a difference, and so does 30+ extra psi.