Member Contributer Mohawk Posted April 1, 2015 Member Contributer Share Posted April 1, 2015 Whilst researching variable velocity stacks, I stumbled across Yoshi's dual stacks. Then whilst playing with some spare stacks I had an idea, that I could create something similar. I had previously reduced the standard stacks by 30mm as part of the Big Airbox mod I did last year. So here is the result of my tinkering. Not run the bike yet, but will test tomorrow. This is only possible because I did the Big Airbox mod, which increases the clearance in the box, these stacks would not fit under the standard airfilter position. Upper stack Old & New As above illuminated for effect A full set Enjoy Link to comment Share on other sites More sharing options...
Member Contributer Switchblade Posted April 1, 2015 Member Contributer Share Posted April 1, 2015 It will be interesting the affect on your low rpm range but mid and high should be better . Link to comment Share on other sites More sharing options...
Member Contributer KevCarver Posted April 1, 2015 Member Contributer Share Posted April 1, 2015 You should see the ST1300 airbox. Curved stacks going in all directions! Crazy looking, but I guess they were trying to get length but still have each in it's own quadrant? Link to comment Share on other sites More sharing options...
Member Contributer Switchblade Posted April 1, 2015 Member Contributer Share Posted April 1, 2015 I guess you left the gap at the bottom to help at low rpm . Link to comment Share on other sites More sharing options...
Member Contributer Rush2112 Posted April 2, 2015 Member Contributer Share Posted April 2, 2015 I guess you left the gap at the bottom to help at low rpm . Other way around I think... low rpm air flow through the whole dual stack and the gap at the bottom will allow air flow at high rpm when flow through the dual stack begins to get impeded. ... or are you trying to capitalize on the Bernoulli's principle of pulling additional air in from the sides by the decreased pressure of the fast flowing center air column??? Link to comment Share on other sites More sharing options...
Member Contributer Switchblade Posted April 2, 2015 Member Contributer Share Posted April 2, 2015 I guess you left the gap at the bottom to help at low rpm . Other way around I think... low rpm air flow through the whole dual stack and the gap at the bottom will allow air flow at high rpm when flow through the dual stack begins to get impeded. ... or are you trying to capitalize on the Bernoulli's principle of pulling additional air in from the sides by the decreased pressure of the fast flowing center air column??? Hmmm always thought the longer velocity stack slow down the charge of air at low rpm's. Link to comment Share on other sites More sharing options...
Member Contributer Rush2112 Posted April 2, 2015 Member Contributer Share Posted April 2, 2015 I guess you left the gap at the bottom to help at low rpm . Other way around I think... low rpm air flow through the whole dual stack and the gap at the bottom will allow air flow at high rpm when flow through the dual stack begins to get impeded. ... or are you trying to capitalize on the Bernoulli's principle of pulling additional air in from the sides by the decreased pressure of the fast flowing center air column??? Hmmm always thought the longer velocity stack slow down the charge of air at low rpm's. Everything is a compromise... the shorter the velocity stacks the higher you move the volumetric efficiency (VE) rpm, within reason that is, you can make them too short. Longer velocity stacks improve low end torque by improving the air charge flow at lower velocity, shorter give more top end horsepower... that's one reason why our bikes have the flapper and snorkel; longer snorkel to improve VE at lower rpms and the flapper to shorten the path when the rpms climb... that's part of the theory anyway. Variable length velocity stacks start out long and shorten when the rpms pass a certain threshold... Link to comment Share on other sites More sharing options...
keef Posted April 2, 2015 Share Posted April 2, 2015 Keen to see the results of this. I thought the big air box was brilliant, so looking forward to this next step. Link to comment Share on other sites More sharing options...
Member Contributer Mohawk Posted April 2, 2015 Author Member Contributer Share Posted April 2, 2015 Here's a pic from the KTM forum where I stumbled on the concept. The most impressive part is the midrange gains :) http://www.ktmsmt.com/viewtopic.php?f=13&t=3299 Page 7, page 13, page 17, page 18, page 27, page 33, page 48 Link to comment Share on other sites More sharing options...
Member Contributer Mohawk Posted April 2, 2015 Author Member Contributer Share Posted April 2, 2015 Ran the bike at lunch time & it starts & when warm revs quicker than yesterday, so appears to have improved the torque curve. Revs to the redline pretty quickly. Will try to get out for a run in the next couple of days. Link to comment Share on other sites More sharing options...
Member Contributer zupatun Posted April 2, 2015 Member Contributer Share Posted April 2, 2015 Only way to tell is before and after dyno runs....if you have the luxury of time and cash... Link to comment Share on other sites More sharing options...
Member Contributer Mohawk Posted April 2, 2015 Author Member Contributer Share Posted April 2, 2015 Well I have the luxury of having done dyno runs every year after I have made mods, you will find them posted elsewhere on this site. Power wise its gone from 95hp as std, to 99, to 102, then 107 with my cams & 112 with the big airbox/short stacks mods last year. Hoping the dual stacks & TBR will push it over 120 with no low/mid range loses. Good or bad once I've tweaked the fuelling, I will post a dyno chart with the results. Link to comment Share on other sites More sharing options...
Member Contributer Rush2112 Posted April 2, 2015 Member Contributer Share Posted April 2, 2015 Hey Mohawk, neat work! I've been pondering utilizing the flapper circuitry to actuate some sort of variable length velocity stack... but a fixed version accomplishing the same task would be much preferred. What spacing between the stacks are you using and do you plan to test different spacing to optimize air flow? Link to comment Share on other sites More sharing options...
Member Contributer Mohawk Posted April 2, 2015 Author Member Contributer Share Posted April 2, 2015 Hey Rush2112, great minds & all that. I started off looking at variable length stacks & I was also planning on using the flapper actuator to control it ! Then I found the KTM site & the Yoshi stacks. So based on the Yoshi design, whch the GSXR guys claim makes more low/mid range torque with no losses up top, I copied that idea. The Yoshi dual stacks inner stack has the same diameter as the outer & its base is flush with the top of the outer stack. So mine are positioned the same. Dyno will tell. With standard stacks, mine made a peak torque of 57.5lb/ft, with the short stacks & big airbox mod, this fell to 54lb/ft, but stayed higher longer to produce more HP. If these stacks can both create more torque and say put the peak back to around 58lb/ft & still hang on at higher revs, then it will improve the HP too. Not to mention the TBR system should help boost high rpm flow as well. I need to raise max rpm torque from the current 48.5 for 112hp, to 50.5 to get 120hp ! I'm hoping the new combined setup will do it. Link to comment Share on other sites More sharing options...
Member Contributer Rush2112 Posted April 2, 2015 Member Contributer Share Posted April 2, 2015 Excellent ideas!!! Do you have a link to the earlier Yoshi work? I tried a search for it and failed... I'd like to read the original work too... Link to comment Share on other sites More sharing options...
Member Contributer Mohawk Posted April 3, 2015 Author Member Contributer Share Posted April 3, 2015 Just do a search for Yoshimura dual stacks Link to comment Share on other sites More sharing options...
Member Contributer Rush2112 Posted April 3, 2015 Member Contributer Share Posted April 3, 2015 Ohhhh!!! I thought you meant our Yoshi... I was looking in the VFRD archives... duh, my bad Link to comment Share on other sites More sharing options...
satariel Posted April 8, 2015 Share Posted April 8, 2015 Yamaha YCC-I in the manual mode LOL Link to comment Share on other sites More sharing options...
Member Contributer Mohawk Posted April 8, 2015 Author Member Contributer Share Posted April 8, 2015 Now that is a neat video, explains so simply how pressure waves work. Pity they simplified it to one pulse, when most bikes are tuned (or not) to the 4th reflection, each one weaker than the previous. This is due to the inlet track length being too short for a 1st or 2nd wave reflection, sometimes the 3rd wave chimes in at lower RPM, but mostly at higher RPM its the 4th wave. Just imagine that Blue wave racing up & down 3 times, with the inlet valve closed & losing intensity then arriving on the 4th reflection as the inlet opens. I've not managed to find anything other than circumstantial info that these work, so will sort my fueling then get a dyno run to compare with previous runs & see what happens. Link to comment Share on other sites More sharing options...
Member Contributer Mohawk Posted May 6, 2015 Author Member Contributer Share Posted May 6, 2015 Still tweaking the fuelling, it was so rich it was crazy. So now almost sorted. Weather crap here at the mo, so will try to get dyno run next week to check the current power curve against the last ones. Will use the same dyno as before. Link to comment Share on other sites More sharing options...
Member Contributer Rush2112 Posted May 7, 2015 Member Contributer Share Posted May 7, 2015 Still tweaking the fuelling, it was so rich it was crazy. So now almost sorted. Weather crap here at the mo, so will try to get dyno run next week to check the current power curve against the last ones. Will use the same dyno as before. Rich?!? We want more air not less... was it a fueling adjustment or related to the dual stacks? Link to comment Share on other sites More sharing options...
Member Contributer Mohawk Posted May 7, 2015 Author Member Contributer Share Posted May 7, 2015 The dyno place I use would not let me run it with my computer attached to map the RB Racing for H&S reasons, no public in the dyno room ;(. So I've fitted a wideband AFR meter, so been manually tuning the fuelling using that. So it does not have a Lambda sensor, so defaults to very rich ECU map, anywhere the Lambda should control fuelling. So below 7Krpm, above that the fuelling is near perfect, though I can't spend much time at high RPM in the higher gears for obvious reasons. So I'm fixing the lower rpm fuelling at the moment.The dyno run will be used to confirm the higher rpm fuelling as well as the whole power curve ! Link to comment Share on other sites More sharing options...
Member Contributer Mohawk Posted May 15, 2015 Author Member Contributer Share Posted May 15, 2015 OK, so got the lowend fuelling reasonable & took the bike for a power run on the same dyno as always, they do racing & race bikes, so the guys know what they are doing, so without further ado here's the results after adding the TBR full system but with my Delkevic mid length silencer & of course with the Yoshi style dual stacks in place.Power & TorqueFuellingAs you can see the power curve smoothed right out with the Yoshi style stacks & peak is up 6hp from the TBR. I may strip the Yoshi stacks out & adjust the fuelling then try again. But a 25% power hike is not to be sniffed at :) Link to comment Share on other sites More sharing options...
Member Contributer Switchblade Posted May 15, 2015 Member Contributer Share Posted May 15, 2015 WOW !! excellent . Link to comment Share on other sites More sharing options...
Member Contributer Rush2112 Posted May 17, 2015 Member Contributer Share Posted May 17, 2015 NICE!!! I'm soooooooooooooooooooooo jealous.... Link to comment Share on other sites More sharing options...
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