Super Jet 760 porting?

[stg5685]

Seems the story with the 760 is that it has no bottom end brap would freestyle porting fix this? compared to a 701 with with porting

 

[OCD Solutions]

Freestyle or Race porting will smarten it right up. I have a race ported 760 that rips off bottom.

 

[Midlake Crisis]

There is so much mixed info on this out there it is hard to know what to think.
Each person's experience depends so much on their individual setup of drivetrain, ignition, & hull that it seems impossible to meaningfully compare to the next guy's experience.
Same thing for the 62T cylinder vs. 61X cylinder; how much difference is there really in a direct comparison on the same setup, or even more significantly on an optimum setup for each?
I am starting to believe that 2 strokes are all black magic.

 

[OCD Solutions]

Power always has and always will be the total sum of all your parts. If you pay attention to the correct details, you can get killer power out of every engine. The trick is knowing what works and what doesn't. If you don't know then you better pay the people that do or expect to spend a lot more finding out for yourself.

Yes, the 760 can be made to rip, even off the bottom. But more guys can make a 701 rip because it has better porting and is more common.

 

[Nuklear6]

Ok so im tired of seeing all the misinformation when it comes to the different between the 61x 701, 62t 701, and the 64x 760 (which is almost same casting as 62t and even is still stamped 62t).

All three cylinder casting measure 4.680 total height, there for i will use the measurement down from the head deck surface to show there isnt NEARLY 5mm difference

Exhaust port measured down from deck:

61x: 1.565"-1.575" (they vary)
62t 701: 1.535" .5mm difference from 61x
64x 760: 1.485" 2mm difference from 61x

Intake ports measured down from deck

61x: 2.167"-2.175" (again they vary)
62t 701: 2.185" Difference from 61x .2-.4mm
64x 760: 2.185" Difference from 61x .2-.4mm

All these measurements were taken from at least 3 of each type cylinder and are accurate to +/- .002"

The 62t and 64x cylinders are very good, mill the bottom of the casting -.030" or run it with out a base gasket, give it some compression and THEY HIT HARD EVEN ON THE BOTTOM!!!! And the 64x can SAFELY measure up to 781cc (85.5mm pistons)

Chuck Palmucci

PS 62t and 64x cylinders are both stamped 62t but the 64x has thicker sleeve skirts and has two extra gussets on the intake side of the casting.

 

[Freakrider]

Ok so im tired of seeing all the misinformation when it comes to the different between the 61x 701, 62t 701, and the 64x 760 (which is almost same casting as 62t and even is still stamped 62t).

All three cylinder casting measure 4.680 total height, there for i will use the measurement down from the head deck surface to show there isnt NEARLY 5mm difference

Exhaust port measured down from deck:

61x: 1.565"-1.575" (they vary)
62t 701: 1.535" .5mm difference from 61x
64x 760: 1.485" 1mm difference from 61x

Intake ports measured down from deck

61x: 2.167"-2.175" (again they vary)
62t 701: 2.185" Difference from 61x .2-.4mm
64x 760: 2.185" Difference from 61x .2-.4mm

All these measurements were taken from at least 3 of each type cylinder and are accurate to +/- .002"

The 62t and 64x cylinders are very good, mill the bottom of the casting -.030" or run it with out a base gasket, give it some compression and THEY HIT HARD EVEN ON THE BOTTOM!!!! And the 64x can SAFELY measure up to 781cc (85.5mm pistons)

Chuck Palmucci

PS 62t and 64x cylinders are both stamped 62t but the 64x has thicker sleeve skirts and has two extra gussets on the intake side of the casting.

For several years on the X it has been written that 2mm was the difference between the 61x and 64x ( Exhaust port measured down from deck)...that's cool you measured it for us.

sj762 has a 64x with the cyl base decked (without removing the sleeves) and special cut domes to compensate...it hit's like a mofo right off throttle...the thing I like about the 62t/64x is the cyl casting is beefier than the 61x...Wavedemon once had 64x sleeves running at 86mm for quite some time even though 85mm is max safe bore...

 

[Nuklear6]

For several years on the X it has been written that 2mm was the difference between the 61x and 64x ( Exhaust port measured down from deck)...that's cool you measured it for us.

sj762 has a 64x with the cyl base decked (without removing the sleeves) and special cut domes to compensate...it hit's like a mofo right off throttle...the thing I like about the 62t/64x is the cyl casting is beefier than the 61x...Wavedemon once had 64x sleeves running at 86mm for quite some time even though 85mm is max safe bore...

Most everything i do anymore is off the 62t/64x casting. Like you said due to the casting being beefier a girdled head isnt even needed. Also like you said (and i forgot to mention above) the domes need to have the squish relief cut when the cylinder is lowered.

I also have seen 64x at 86mm and running fine. Even pulled a motor apart that was 64x w/ 86.5mm pistons, however the reason i pulled it apart for yamacrazed was because the pistons ripped the sleeve down from the transfers like a can opener. ALL because they were paper thin. He bought the whole motor from a guy who told him it was a 760 on stock bore!!! HAHAHAH

 

[Foximus]

so if you dont deck the bottom of the cylinder, and just run without a gasket.... would you just use threebond 1211 instead? I'm interested in trying this with a new 62t motor I'm building... Perhaps use my non girdled Riva head on it with the 35cc domes...

 

[Oshweeken]

Bump!!

 

[chriselmore_1]

What exactly are you bumping?

 

[iangdesign]

I would imagine the question of using 1211 to seal the cylinder to case instead of a base gasket. I was curious about that as well.

 

[jd91t]

I measured them as well and got 1.550" for 61x roof of exh to deck, and 1.480 for the 760 stamped 62t. For a .070" difference. 2mm is .080" so its close to 2mm according to my mic.
The intake distance on both my X and T cyls were identical @ 2.185"
Now the exh roof difference equates to about 10 deg more exhaust duration on the T cyl.
Opening the exh valve 5deg sooner as well as closing it 5 deg later, and starting compression later.
So opening the exh valve 5deg/1mm sooner is good to evacuate the cyl of exh better, but it you also loose that same 5deg of blowdown forcing the piston down.
Closing it later in the up stroke may help wash out any remaining exh gases, but also hurts compression building (easily fixed with head mods
I have my x cases bored and was 90% done with a port job on my 760 cyl when I gave up on this build due to too many nay sayers
Telling me it would be fast mph wise, but laaate.

I had planned to bore it to 85mm for 771cc. I figured a freshie fully ported/polished 771 would be a nice power up from my 61x, but all I kept hearing was its a waste of time and money. X cyl will out accelerate it every time. 2 very trusted professional yam pwc engine builders talked me out of a 760cyl based eng. Saying if you want cc's the x cyl CAN do cc's for instance jetworks can do 771 and 828cc BB X cyl!
Anyway I'm not saying the 760 casting cant have low end grunt/freestyle power bc I DONT know. "black magic" or whatever..
Kina mad at my self for not just finishing it, and making an opinion based on my own experience. (sigh)
So I'm doing an 83mm X cyl instead since we all KNOW that works..

 

[kevbo]

Keep in mind that there is only two out of the box impellers that are low enough for a high port cylinder, they even need a bored nozzle. Custom low port cylinders will pull everyones pump where the high port will not. I think you could have had acceptable response with the right pump setup.

 

[550/440]

For several years on the X it has been written that 2mm was the difference between the 61x and 64x ( Exhaust port measured down from deck)...that's cool you measured it for us.

sj762 has a 64x with the cyl base decked (without removing the sleeves) and special cut domes to compensate...it hit's like a mofo right off throttle...the thing I like about the 62t/64x is the cyl casting is beefier than the 61x...Wavedemon once had 64x sleeves running at 86mm for quite some time even though 85mm is max safe bore...

Do you know who did the base decking without removing the sleeves? I have a 62t that I'd like to get some work done to for my ski.

 

[waxhead]

I love the 760 cylinders I just wish you guys wouldnt stop the rumour they are so bad. Its making them more expensive

 

[Freakrider]

Do you know who did the base decking without removing the sleeves? I have a 62t that I'd like to get some work done to for my ski.

X SCREAM Chuck did some magic on his 62t 760 cyl with said decking.

 

[oside-tanner]

So what's the verdict with using 1211 to seal between the cases and the cylinder, are there any down sides to running the 1211 and not the gasket. I've need had a problem with a gasket giving me a problem in this location. Does 1211 last just as long

 

[waxhead]

It works just fine. It will not give you grief at all

 

[orangefinger]

we had a 64X Cylinder freestyle ported in our superjet by Paul and it was amazing, I loved the linear never ending power..and that with oem 84mm pistons....just sayin

 

[River Rat]

Anybody ever stroke a 760 cyl?say to 4-6 mm? Is it worth it? Was always told to stroke n not big bore since u loose some transfer volume but f what I know all I do is take mixed information in about these cylinders. Would love to know if anyone has one of these cyl stroked!