QuinnO

Hi everyone.
Any body have the stock port timing #s on a 640?

QuinnO

Exhaust open 113* total Main transfer ports open 122* total. Exhaust port 48mm wide 39.62mm high. This is a 640 unmodified at 75.5 bore.

jetski9010

I wonder if the 770 is close to that. I would measure it when I comes back to me but I just had mine ported. Cant wait to get my project together.

jetski9010

wait are you sure that exhaust opening at 113 degrees is right?

QuinnO

Sorry, I took the wrong # off of the paper I joted them on, it Opens at 91 and stays open 276* buy what I can tell on the *wheel. A 770 should be close to that. I just ported a brand new 644 jug today. The sleve was way off. Up to 35k on some ports. Nice job there Suzuki. I like them but we all see where "Sub Let-Out-Source " components gets you.

jetski9010

compared to the yamaha sleeve/cylinder mismatch the suzuki motor looks like it was built by a pro. I am building my motor for a customs freestyle setup so I am trying to get as much low end power as I can. 91 degree opening isnt bad at all to start with for my build.

QuinnO

Its a Yamaha? Or a TS 770? I don't like multiple cylinders per pipe. The pipe on a 2 stroke is everything. It makes all characteristics of engines power band.
I have compared the Tigershark 640 cast & steel pipes, not a big differance. It is my beleife the signal or preshure wave gets tangled having 2 ports fire into one pipe.

Its 100% wave timing. Its easy to get a single drip into water make a nice clean ripple going one way.
Now add one more drip out of sequence and ripples start overlapping & you get choppy waves going all directions Not good for a sharp tuning on powerband or the best HP that engine is capable of makeing.
Pipes are the KEY in two strokes, thats why all twins and triples have a "chainsaw" like powerband. Why when you can tune the pipes to get a turbo charging style hit like a MX bike.

If you have say 7000 RPM range it should hit hard at 4500 and pull like a rocket into the RPM limmiter.

jetski9010

No its a tigershark motor. I have never hard any good succes from dual pipes but then again I build all my motors to have the best bottom end as I can get.

QuinnO

Hi Jet, Why do you go for low end? Ski's need some, but 500 feet out up on plane, that bottom end is no use. Like building a race car for a Super speedway. It will get a jump right off but the pack will go blowing buy in yards.

I use my ski at 3/4 to W.O.T. 85% of the time. A Montego is 375 pounds & I am light.
With a stock pitch impeller and a pipe tuned to come in at 4500 with more hit & over rev.

Keep in mind it will still have almost the same low it had (good), I think if I don't lose all the hit to cavitation that will be right what I want out of it. I'm also going to use nitrous & 112 octane direct injetion into the case.
That would boost low right off, if I need it. (For when it counts).

If it is on dirt, payment or water a 2 stroke is inherently a screamer. And it should try and pull you're arms out as it rev's up. You can make up the ground you may lose out of the hole by over powering them with high RPM power.

So far it looks like 91* open exhaust and transfers at 116* with a pipes 55 inches long with a max diameter of 8 inches