idle to 3000rpm missfire

flyingcircus68 · Post by **flyingcircus68** » Sat Sep 18, 2004 7:42 am

I've also been thinking about air box tuning for some time. I've Frankenstein-ed my air box by adding on a newer, larger snorkel and filter element from a %%WORD23%u0 on my 87 1000 and I am happy with the result. I've also done some mental excercise on how to make an air box with variable tuning to reap benefits over a broader rpm band. I've thought about making a snorkel with adjustable cross sectional area/ length. I've also thought about making twin snorkels and shutting one off with a butterfly plate. Another method that I've considered is based on the high performance subaru svx. This is a 6 cylinder boxer engine that has two separate induction systems in parallel. Each has a plenum and runners to feed half the engine. between the two plenums is a butterfly valve that opens above a certain rpm. What this does is it either isolates both halves, or allows them to cross talk. It's not really a matter of exchanging air flow, it has to do with the forcing frequency. When the halves are isolated, they only see half the pulses that the engine is producing. Opening the butterfly allows them to see all the pulses. So, the clever Japanese engineers make the butterfly open when the intake pulse frequency is equal to the resonant frequency of the plenum/runners. They close the valve when the rpm increases and the pulse frequency of the engine is twice that of the plenum/runners. When the butterfly valve is closed, each half is isolated and sees only half the pulse frequency and the plenum/runners start to resonate again. To apply this concept to the air box, you would need to split the air box in two and have two smaller snorkels. You would need to have a butterfly valve on the divider wall that you could control with a motor, or bellows. Since I've bored you guys this far, I might as well continue with the following 'neat' concept that I read about in an industry mag. BMW has been developing an intake system that has variable tuning. It consists of a plenum and variable length runners. The runner length is changed by rotating a drum to different positions. This drum is not a full cylinder, but has a portion cut away ( looks like half a pie when you view it lengthwise). It has grooves on its OD that look like half a pipe. These grooves mate up with the grooves in the plenum where the runners enter. When the drum rotates, its grooves mate up with the grooves in the plenum and form an extension to the runners that are permanently cast in. The cut away portion of the drum defines the end of the intake runners. The rotation is controlled by a servo motor hooked up to the ECU. This is a very clever concept for which the krauts deserve applause.<img src=http://img.photobucket.com/albums/v209/ ... Cheers.gif ALT=":cheers">

cvhjkdis · Post by **cvhjkdis** » Sat Sep 18, 2004 5:58 pm

I wasn't up on the Subaru, but the BMW manifold was something I've had in mind for awhile, I had heard BMW was working on variable length runners, but I didn't know that was the format. Yes, they do deserve the clever award. ( apparently, Ferrari does have a full variable runner setup ) I just have to say this though, at least I'm not the only one staying up way to late at night thinking this stuff up! The Dual manifold set-up kind'a reminds off some mid '80s Yamaha's I remember, with the YICS system. Remember that? Iv'e seen it on the 550 Vision's and various different Seca's. Thank God they found a better acronym, Otherwise we 'coulda been the YICS brotherhood <img src=http://www.ezboard.com/images/emoticons/laugh.gif ALT=":lol"> I'm still planning to do some more pipe and jet tuning on my bike, and it'll probably stay that way, But I do wonder how much weight could have been saved if a workable airbox had been devised instead of the EXUP valve. I'll keep the neurons engaged just in case. Bob. I approved this message

flyingcircus68 · Post by **flyingcircus68** » Mon Sep 27, 2004 7:40 pm

Getting back to John's question on improving hp. There are two ways that you can go about increasing the output: 1. fatten the torque curve (head work, possibly higher compression, supercharging) 2. shift the torque curve higher up the rpm range (i.e. new R1) You mentioned that your bike seems to go flat on top. Was this after you put in the big bore kit? That would make sense, since the increase in displacement would cause the torque peak to be lower and cause the bike to reach the limits of it's breathing ability at a lower rpm. It's also possible that your jetting could be off, or that adequate fuel is not being supplied. You could have a plugged up vent within your gas cap, plugged filter, or a pump that is going south. if you're looking for hp, you need to help it breath better. Chuck pointed out that in his earlier postings that head work is where the hp is hidden, and what will make you go broke. I'm not advocating going broke by paying someone to restructure your ports, I'm talking about something simpler. Have you considered a competition valve job? This is where additional machining is done to remove material on the valve and seat that shrouds flow at low lifts. Since valves spend the majority of their open time at some value other than max lift, the gain to be had is sizable. I have this done on mine and the angles on the seat inserts have been blended into a radius that terminates at the seat contact point. An excellent book on head modification and on constructing your own flow bench is 'How to Build and Modify Chevrolet Small Block Cylinder Heads' by Motorbooks International. Although this book is dedicated to the chevy engine, the theory is very much universal. Another way to fatten the torque curve is to help the engine ingest cooler air. You could create a baffle out of some temp resistant foam to keep the hot air from the coolant tubes and engine from rising up to the intake area. McMaster Carr has a good selection of foam materials and they have an online catalog. You could also try to degree your cams. This would fit in category 2 listed above. In essence, degreeing cams synchronizes the valve motion with the tuning of the exhaust pipe and intake system. The point at which they are synchronized together is where the torque output reaches it's peak(s). My practical experience with degreeing cams is with small block chevies, so I can't offer you favorable values for the positions of your lobe centers. This type of information is obtained by exhaustive amounts of analysis and is not normally given away for free. I believe that Chuck has a fair amount of practical experience with this and might be gracious enough to offer some wisdom on this matter. lastly, the air box does present a restriction at max output and modifying it as described earlier could be beneficial (If you succeed in jetting it correctly). You could try to remove it as Bob has, or you could try to construct one that has greater cross sectional area to make it less restrictive and bring the resonant point higher up the rpm range. Fiberglass would be a great material to construct it from and you could use the original as a plug. Make sure that you use mold release. A great book on fiberglass construction is 'Composite Construction for Homebuilt Aircraft' by Jack Lambie. I bought my copy at Borders Books. The big bore kit seems to be a popular mod. Anyone else want to chime in on their experiences? <img src=http://www.ezboard.com/images/emoticons/smokin.gif ALT=":smokin">

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idle to 3000rpm missfire

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