760 Ported VS 701 Ported my opinon

What would you do with your 760...

  • Put it in my Waveblaster

    Votes: 5 33.3%

  • Find someone to get more power out of it

    Votes: 3 20.0%

  • Use if for TEAM SCREAM rebuilt

    Votes: 7 46.7%
  • Total voters
    15
  • Poll closed .
orangefinger

orangefinger

Location
Reno,NV
Hi ,

I have now come to the conclusion that...( please proof me wrong :) Or let me know what your opinion is

The 701 61x/61x Ported hits harder than 760 62t ported, after numerous tests with almost identical setups ada girdled head, pipe, msd enhancer, same intake, scoop, impeller, hence single 44SBN to dual 44SBN and other stuff it seems that I am more please with a snappy 701 than the 760.

And therefor would like to hear final opinions on

- putting the 760 in my Waveblaster
- finding someone who can meke the 760 fly
- And having another engine built by TEAM SCREAM
 
DAG

DAG

Yes, my balls tickled from that landing
Location
Charlotte, NC
i had a ported 61x @ 81.75 blew it up and went with a ported 62t @ 84.5mm and it hits alot harder and i still dont have this top end tuned worth a crap. But if i were to do it again i think i'm swinging towards the true BB 61x re-sleeved at 84mm, but at the time i cound not afford it. i'd recommend the ported 62t to anyone on a budget as its half as much cash

my ..02 from my experiences
 
dajnglst

dajnglst

Glass Happens
Location
Charleston SC
Without having access to an oxygen sensor or sniffing equipment to fit in the combustion chamber i think it would be hard to snuff out why the 701 hits better over the 760. It may be possible that the return wave of spent exhaust gas that is rebounded into the chamber does not allow enough fresh intake charge to wipe out the combustion chamber of the spent gases. 760 bore being a little larger may not wipe out as well as 701. Better effective wiping out of cylinder from a 701 bore compared to 760.Then again how many companies out there made chambers specifically matched for 760/785 engines.I would imagine most people just use a 701 bolt on performance exhaust and not one formulated to work with larger bore. Simple theory I have never effectively been able to measure with the means that I have. Kenny Roberts group back in the day was about the only place in the United States that would have had the means to make such a measurement with a 2 stroke engine.

Let's just say as far as combustion efficiency goes in a well tuned 2 stroke engine displacements of 80-150CC reap the largest HP #'s for displacement.

500cc GP machines being based on what was a 4 cylinder 125cc displacement per cylinder. Aprilia attempted a large bore twin and Kenny Roberts developed a triple. None of which reaped any massive benefit or gains over the multi cylinder 125cc designs of HonYamSuz. They could be easier to ride in tighter tracks where throttle response was crucial to exiting the corner, but they did not spin up as fast as 4 cylinder screamers.

You may also find that the OEM crankcase volume of 760 is the same as 701.
(I have never measured it) Having larger surface area underneath piston should provide better primary compression, but if the overall volume is too large it may not be as effective. More volume better top end revs, less volume better low and mid but restricting piston speed when returning to BDC. Is it getting the proper squeeze beneath the piston ?

I have always considered making a full rounded crankshaft for the superjet engines. Placing a plastic insert attached to crank web surrounding the connecting rod where there is nothing taking up that volume. Same as found on a lot of GP and motocross bikes. Once again have never made the measurement to see if that is what it needs.

Jet pump design being what it is we are limited in the revs these large displacement PWC engines will turn.

The 760 should be capable of doing more work, but obviously providing more torque does not equal the desired throttle response.

Measuring combustion dynamics/ ensuring enough fresh charge has entered the chamber for the best possible burn is beyond my abilities.

Many ways to formulate what would work best.

Just some idea r's for you.

What exactly are you looking for, more snap quick pop pulls or screaming top end? Ask your engine builder what they did in the bottom end and what it measured out to be.

Dual 44's with water injection works nice, but single carb intake around 46mm with and reed spacer on the 62 T set up should work better for throttle response. Back off timing and look for more compression if more snap is desired.
 
Last edited:
Matt_E

Matt_E

steals hub caps from cars
Site Supporter
Location
at peace
LOL.

Dude.

The porting is different, more geared towards higher RPM power.
That's all.
 
K

Kennay

Squarenose for the _____
Location
Myrtle Beach, SC
Crammit's Superstock is a freaking animal.

It's a Jetworks ported 62t/64x cylinder. It's badass. I want one. When the power came on, it was harder to hang onto at first than his 6mil stroker was. His has bottom end, I don't know about what you have, though.
 
Matt_E

Matt_E

steals hub caps from cars
Site Supporter
Location
at peace
dajnglst said:
So the port timing on the 760 is higher than 701 ?
(Wouldn't know).

I've got one hanging out around here I'll have to check it out.
Click to expand...


The transfer duration is longer, blowdown is different, exhaust ports are higher.

However, the roofs are angled, so when it's bored up a bit, timing gets closer to stock 61X specs.
 
Mouthfulloflake

Mouthfulloflake

ISJWTA member #2
Location
NW Arkansas
I really hate to hear that, since im building ( still) a 64x760 cylinder based engine.

But, I can also say, im not impressed with the power output of a 61x/61x engine configured as yours are ( ada head, B pipe, msd timing, light flywheel)

perhaps our methods of testing ( simply by riding for me) are far too subjective to be helpful?

can you ad enough compression, and timing advance to the 760 to make it survive a few seasons, and get that snap?

can you pitch the impeller lower, and move the " bottom end snap" slightly further up the engines RPM range?
 
orangefinger

orangefinger

Location
Reno,NV
Thank you for all the great comments and suggestions....

Too answer some questions

The 760 was ported for freestyle as the 701 was too.

The 760 came out of a Blaster II so I guess would be 62t/64x .

I am looking for low end power not high end.

Any suggestions on settings or changes to be made for the 760 ?
I like the way it feels when you ride it but it just is not so snappy and I just cant get over the fact that I might be missing out on something...but what ??
 
WaveDemon

WaveDemon

Not Dead - Notable Member
Location
Hell, Florida
it won't have good snap if it wasn't ported properly or tuned right.

either way (without knowing who built your motor) it won't have the snap of a team scream built motor.
 
Big Kahuna

Big Kahuna

Administrator
Location
Tuscaloosa, AL
orangefinger said:
Thank you for all the great comments and suggestions....

Too answer some questions

The 760 was ported for freestyle as the 701 was too.

The 760 came out of a Blaster II so I guess would be 62t/64x .

I am looking for low end power not high end.

Any suggestions on settings or changes to be made for the 760 ?
I like the way it feels when you ride it but it just is not so snappy and I just cant get over the fact that I might be missing out on something...but what ??
Click to expand...

If your motor is tuned properly it should be making good power, just not where you want it to be. You could try getting a lower pitch prop to try and make the hit come on sooner.
 
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