Pros & Cons - 701 61x vs 701 62t vs 760 64u

Y

Yamer-Jammer

Location
Mesa, AZ - Flagstaff, AZ - Covington, WA
Sounds like a lot of work... you would either have to remove the sleeves or cut the "skirts" off in order to mill the base of the cylinder body. I guess if one is resleeving a cylinder, that is the prime time to do that mod! Also, I would think that the domes/ head would need more clearance for the piston travel if the cyl body is lowered.

If someone has done this I would love to hear about it as well.
 
Polish jet pilot

Polish jet pilot

4aces4aces4aces4aces4aces
Location
Warsaw, Poland
We have a 727cc, a 760cc and 845cc motors.

727cc: is a ported 61x cyl with enlarged exhaust ports, and cleaned up transfers. 33cc domes, about 210 psi compression. Has epic, Bpipe, single 48BJ.

760cc: ported 64x cyl, ported, compression around 185psi, dual 44mm, MSD TL.

845cc: maxx sleeves, cr500 pistons, rest of setup as above for the 760cc.

Comparison:

responsiveness feels very goon on all skis, however there is a considerable difference from the 727cc to 760cc. The 845 feels a bit stroneger that the 760, but only by a small bit (probably more torque, not power as such).

To make this fair, I must say the epic was not fine tuned, and the 727cc has oem flywheel, the other setups use the power and weight of the MSD wheel and system.

To be honest, if I port the cases and fine tune the ignition and water and pump I can get close to the 760 power range. That said a 760 seems to be the best in terms of power/cost. Later go big at least 900-1000cc range. The 727-845 cc are super reliable except the crappy MSD switches and connecteros that take in moisture and cause problems.
 
GIL

GIL

Power In The Hands Of Few
Location
Cullman AL
SUPERTUNE said:
The 760 stock cylinder porting is designed to run the 760 huge volume exhaust pipe and no way can you fit it in the Superjet. The more aggressive 760 cylinder is more like a heavy ported 61X cylinder for closed course racing, a loss in bottom end and big increase in mid to top power.
If you build the 760 like a race setup then the more aggressive porting will make really good power even for freestyle, but most don't want total loss ignitions, race gas compression, expensive custom race carbs and so on...
The port location is a little different and SHOULD be port matched to be correct, bolt pattern is the same, but the 760's use the 10mm bolts instead of 8mm bolts to support the huge stock exhaust from the 760 engine.
No big deal there, as you just screw in 8mm X 1.25 helicoils into the threaded holes as they are the same 1.25 thread pitch.
As far as sleeve's go...yes you have about .080 more in bore size with the stock 760 sleeves.
Click to expand...


Race carbs................... LOL
 
ItsRixter

ItsRixter

SoCal Wav Jumping shiznit
Location
Sunny Diego
Another thing I've learned about the 760 (64U) motor: pulling one of these out of a stock couch like a WB2, waveventure, GP760, etc is that the stock setup is not ideal for SJ or B1. The head is weird and is set to give the two cyliders each different compression. Also, the electronics (stator, fly wheel and ebox) are set with dual timing. Yamaha did this so the motor would not twist and break the crank under a 155mm (couch) pump load. This not a concern for SJ or B1's. So ideally with a 760 (64U) setup you should use a flywheel, stator and ebox from either a 61x or 62t. That makes upgrading to 760 motor almost the same as just taking a 701 (62T or 61x) and just swapping out the cylinder (with the added port work mentioned on this thread). A 760 needs new electronics while the 701 would just be switching cylinders & pistons. Both need new heads and carbs reworked.
I know Chuck mention something about the 760 cases have a 2nd pulse line but I can't remember if that is good or bad.
 
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C

Conrad

Location
Russia
Hi All. I have been alreade going to bore my std 62T into new 84mm (ProX) but the local mechanic told that it will be VERY unlelible job becouse of thiny skirt with mentioned by #0 grooves on the sleeves... I have bought already MSD, B-Pipe, Reeds and impeller for better performance. Coud you pls say me based on your mass statistic my real risk and limitationof use (more or less of cource). I use ski only as amature freestyler on flatwater no more than 20 times per season. I want it be strong in low end and have resource for two upcoming season and reach it now with no huge expences anymore. I would apreciate if smb provide me with DIY links or manuals for porting and epoxy of the engine.
 
KTM434

KTM434

Jamie FN Hickey
Location
Palm Coast FL
Without knowledge of airflow characteristics, port timing, angles, shapes, and area for a given engine setup then you can lose power. It's not about going in there with a big carbide bit and making everything bigger. Your engine needs good flowing carbs and exhaust to benefit from bigger port area and by making the ports and cases too large for a given engine size you will lose crankcase pressure and air velocity. Small adjustments to port timing and angles make a big difference on power. If you are asking a vague question like "how do I port my engine myself" Have a professional do it.
 
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