I need a refresher course.....

[MADMAT]

in octane and compression.

I can run my b piped 180psi 701 on 94 octane, right?

Now. Can I run a b piped 760 with 175psi on 94 octane?

 

[sflsurfrider]

yes and yes.

 

[SUPERJET-113]

Does the 760 still have the staggered compression like OEM?

 

[MADMAT]

Does the 760 still have the staggered compression like OEM?

i dunno. i'm new to the 760.

 

[Matt_E]

Not entirely sure....but 170psi on pumpgas on the 84mm bore sounds a bit risky. Especially with a stock or enhancer ignition.
Dome shape and squish band plays into it, too.

 

[MADMAT]

Nikad recommended I swap heads when it gets here. That will put me down to 165psi on the 760 and 175psi on my 701 sj.

I just wanted to be sure. I didn't realize you could not run a 760 @ 175 on 94 octane.

I am pretty stoked to get the motor though!.

 

[MADMAT]

Or I start keepin some race gaz up in here:Banane01:

 

[Matt_E]

Like I said, I am not 100% sure. You might be fine.

 

[MADMAT]

Does sea level have anything to do with it?

Does anyone near me run a 760 with 175psi and 94 octane?

 

[sflsurfrider]

theres that much diff between the two? is it due to the higher exhaust ports???

 

[guiness92]

hmm i run a 760 with 180 on 94 octane now you got me wondering.

 

[MADMAT]

hmm i run a 760 with 180 on 94 octane now you got me wondering.

Does it rip? Ever tore the head off to inspect?

 

[norcal ex]

Every 760 i have used i have built it at 175PSI and used 91 octane. They were all fine. my first one was sooo good that when i took it all apart, it looked like someone just cleaned my B-pipe manifold and the pistons... they were sooo clean! (i know this has other factors also)

 

[SUPERJET-113]

If i remember correctly, the OEM 760 ran hotter in the rear cylinder so Yamaha made it with 10 psi less. I think its like 160 front/150 rear in virgin stock form.

 

[MADMAT]

If i remember correctly, the OEM 760 ran hotter in the rear cylinder so Yamaha made it with 10 psi less. I think its like 160 front/150 rear in virgin stock form.

:bigeyes: trippy.

 

[#ZERO]

I run an 84mm bore, 195 lbs of compression with 3 degrees advance and MSD enhancer.

Full throttle runs across the lake have yet to kill it on 93 octane.

 

[#ZERO]

If i remember correctly, the OEM 760 ran hotter in the rear cylinder so Yamaha made it with 10 psi less. I think its like 160 front/150 rear in virgin stock form.

I think the compression is the same front and rear on the Yamaha 760, it's the main jetting that is different.

Dual 44's OEM Stock Jetting for Yamaha 760

Front
115 Pilot Jet
135 Main Jet
1.5 Needle & Seat
115 Gram - Gold Spring

Rear
115 Pilot Jet
137.5 Main Jet
1.5 Needle & Seat
115 Gram - Gold Spring

 

[Mile9c1]

The 760's from Yamaha came with lower psi on the rear cylinder. But they were designed for a sitdown... sitdowns that dumbasses beat the piss out of. I think you'd be plenty safe with 175psi on a 760 and 94 octane.

 

[Matt_E]

Theoretically, the octane requirements at equal compression goes up as bore size goes up.

That said, several people here have stated that it's fine. So, just run it.

 

[MADMAT]

Yee haw!! This thing should rip then!!

I'll still use Sunoco Ultra 94 though.