Post by ossapioneer on Mar 7, 2018 22:26:47 GMT -7
Can you comment on why the valve seems to open so little as engine speed increases? I was expecting to see the valve swing open noticeably and in direct proportion to increasing revs. It doesn't really seem to do that though.
The EXUP valve helps evening out the power output Curve by regulalting exhaust pressure, simply put it controls the counterpressure when the intake and exhaust valves are in overlap, it helps controlling fluctuations in the powercurve.
Post by ossapioneer on Mar 13, 2018 15:03:30 GMT -7
Wow, thank you very much mrharwood! I have opened the link that you provided, and... . I haven't done much more yet than just skim, but I am looking forward to reading it fully. Wow, Yamaha's own summary of the development and concept of the EXUP valve. I'll probably have a comment once I've fully read the link. Thanks again. OSSA Pioneer
Post by ossapioneer on Mar 23, 2018 0:25:45 GMT -7
Riders- Try the official Yamaha website that the above link will connect you to; the site is called yamahapart.com. I never knew of it myself until now. The site is quite amazing. You can read not just Yamaha's own account of how the EXUP valve was developed, you can also read Yamaha's own account of how any of their major engineering and technical innovations were developed, from the 1950's right on up. For example, there is an explanation of Crossplane engine theory that is interestingly and comprehensively detailed, although to me I must say still comprehensively difficult to understand. yamahapart.com provides a huge amount of technical and historical info about Yamahas. You can also order OEM parts through yamahapart.com,, and for lots of their classic bikes. For example Yamaha has plenty of parts listed on the website and apparently available for sale now, for the DT series dirt bikes of the late '60's. Pretty amazing. Thanks to mrcdharwood for providing the link. OSSA Pioneer
Post by gsxwetodddid on Jun 28, 2018 4:41:55 GMT -7
i am looking into doing a custom dual exhaust and i want to keep the EXUP valve so that i don't bother my neighbors at 6 am everyday, are there other external external control cables going under the seat from the valve other than the electrical? or is it all located down at the valve?
also if anyone still has their EXUP valve and would be willing to part with it im interested!!
There are two steel cables which are controlled by the EXUP control motor under the seat, these cables mechanically open and close the valve in the exhaust flow downstream from the catalytic converter. There are no electrical wires running down to the EXUP valve.
Back when EXUP first came out to the public ( from moto gp) it was engineered to balance power curves, though in the last decade or so they're primarily for noise emmisions. Not a lot of change in power from keeping the flap open. There is some, but not much. I personally keep it open with my rigged stock exhaust, and later on I'll get a full system. No one can argue that that much of a restriction in flow does have an impact when it is in the fully closed position, but in modern exhausts with these collector boxes power change isn't the engineered function. Others chime in, I'm not claiming to be infaulable.
There is the Graves 3/4 system that does just that, it has it's own exhaust valves and uses the oem cables. I've always wondered if they engineered the system for power gains in the low end from the valve, but it is for sure openly stated on their site it is at the least for not angering your neighbors.
As for removing it, you'd have to cut the section of pipe out, you can't simply remove the valve. The screws that hold the flap to the spindle are tack welded in, and the spindle has what I think are brass bushings. I've considered a custom cat eliminator that uses the exup valve section, I've butched 2 fz10 exhaust boxes and 1 R1 box. Let me tell ya, simply gutting the cats with no kind of tune is a bad idea, lol. Massive losses in low end power. Better off with a decat y pipe if a person wants more volume without investing in a tune. Or just take the slip on off and replace it with a auto store exhaust tip and keep the flap straight by repositioning the spring. And removing the cables. That's my current setup. Sounds just like a V8.
I was also expecting a more linear behavior of the valve, but it remains closed even at elevated rpm, unless the throttle is opened quite a bit. Very interesting. That's why the diameter of the muffler doesn't really matter. It's huge, by the way. It looks like the same diameter of my 3.5L twin turbo engine. Without the valve, it needs to be quite a bit smaller. Yamaha knows what they're doing, so not concerned about the valve, but it's amazing the bike can make so much power with only a small fraction of the valve open. Need to read the other link when I have time too.
Last Edit: Oct 31, 2018 18:52:13 GMT -7 by elptxjc