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EAST APRIL 2018

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76 April 2018 www.thunderpress.net THUNDER PRESS Intelajet redux The intention this month was to show a step-by-step installation of a Thunder Products Intelajet circuit on a Harley CV carb. We'll save that. For now, let's review some reasons you'd want to install one! There are several components that need to be optimal for a true high- performance carbureted Harley street engine. But the "ins and outs" can be tricky for the best of builds. Once you've done your homework regarding heads and cams… they're installed and set. Intake manifolds are what they are… usually not working that much to help, but you defi nitely don't want one that works against you either. Because, again, once installed, intakes are usually a set-and-forget proposition. That leaves exhaust, carb and air cleaner which are out there where you can mess with 'em after they're installed… a process loosely referred to as "tuning." Here's where things get interesting. As far as air cleaners are con- cerned, one would do well to study the design of the Buell Helmholtz type. Ugly as sin but effi cient and quiet. Strip the thing's housing and you see the nucleus (and inspiration) for the elbow-style cleaners so popular today. There's something to be said for a "stack" with a bend in it, because it adds to the inlet tract length… and often helps air straighten out and fl y right… into the carb, at least. Just be sure you're not creating the same issues that plague the intake manifold. (If you're not sure what those are, you'll get some clues in the photo captions hereabouts.) To avoid deal- ing with it at all, simply use one of the many more traditional types… Screamin' Eagle, Ness Big Sucker and other variations of the same theme. As long as there's roughly twice the diameter of the carb bore between the outside edge of the fi lter and the inlet of the carb, it should be fi ne. Not hard to get right and easy to change or mod if you don't. Exhaust systems are so plenti- ful and misunderstood, most folks go with looks and sound. That's too bad, because the right choice can make the build come alive and the wrong one… kill it. The problem, in a nutshell, is res- onance, reverberation, fl uid dynamics and sonic waves if you prefer… and the fact that whatever design you choose, you're stuck with. For a component that affects the results you get from your build as much as this can… you'd think there'd be some form of adjust- ability on almost all exhausts in the When the exhaust valve opens a positive pulse (A) travels to the collector/megaphone/ muffl er, and the vacuum created should also help draw a fresh charge into the chamber. Meanwhile, part of the energy is refl ected back as a negative pulse (B) which should not spoil the fresh charge. This happens in multiple waves… moving so fast that most Harleys are tuned to the fourth wave. Since the pipe "draws and stuffs" both the spent gases and the fresh charge… even a "tuned" exhaust usually only works effi ciently in a band approxi- mately 1500 rpm wide and some even make things worse everywhere else in the rev range, all of which affects carburetion. When Harley fi rst offered Screamin' Eagle intake manifolds, they were for butterfl y carbs. Intake velocity was so slow, there was a spacer about a half-inch thick included in the kit… to give the incoming charge a little extra room (and time) to get moving in the right direction. Since then, manifold designs have slightly improved (a gentler bend on the short side mostly) and factory carbs have increased velocity, especially SE Mikunis! Today these spacers are obsolete… or are they just forgotten? One wonders if any real improvement in Harley's badly-shaped manifold might still come from adding a spacer. These are still available and useful, if you are serious about DIY re-jetting for conditions of temperature and/or altitude. I grew up in the Rocky Mountains and this little slide rule was practically essential for jetting a bike from the Mile-High City to above timberline. It's a solid reminder of how little it takes to upset your "perfect" carburetion and the frequent work of changing jets to keep it right for the conditions at hand. Even then, it's only a rough guide to a fi x. name of tuning. As it is, there are only a couple that come to mind—the vener- able SuperTrapp disc system and Patriot with its "lollipop-on-a-wire" setup. Adjustability is really needed in the header pipes… but if you want to add lollipops to muffl ers or head pipes that came without 'em… Google it. You'll see several ways to do it and there's a YouTube video or two that shows how, as well. Who knows, they might help! Guidelines for head pipes usually start (and stop) with "equal length" and stepped diameters or so-called "anti-reversion" cones. Two-into-one advice, long tube on the back cylinder for torque, merge collector of between 2 ¼" and 2 ½" in exit diameter with megaphone muffl er containing cor- responding large-core baffl e. In my opinion, this still bespeaks the wild west situation that exists for exhausts, where just about the only way to get it right for your specifi c build is "buy it and try it"… no guarantee and no specifi cs. It comes down to word of mouth from those who are happy with

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