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Old July 30th, 2020, 11:52 PM   #7
DannoXYZ
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Name: AKA JacRyann
Location: Mesa, AZ
Join Date: Dec 2011

Motorcycle(s): CB125T CBR250R-MC19 CBR250RR-MC22 NSR350R-MC21 VF500F CBR600RR SFV650 VFR750F R1M ST1300PA Valkyrie-F6C

Posts: A lot.
MOTY - 2018, MOTM - Nov '17
Now there's some truth to this "automatically rip out airbox and install pods with giant jets" idea. It really had to do with early days of sport bikes way back in '60s before age of computers and CFD software. With Honda's breakthrough CB750, suddenly bikes took a huge jump in displacement and engine size. None of manufacturers had built anything so monstrous before and there was no database of engineering data on how to build huge bike engines.

And being short on time with insufficient R&D, they just scrambled to get a big bike out to market to compete with Honda. Result was lots of bigger bike engines were built with of-the-shelf small-bike parts in haste. You ended up with tiny carbs and airboxes being grafted onto engines much larger than they were originally designed for.

So of course this new generation of big bkes ran poorly in factory trim. Tuners and aftermarket suppliers came up with ways to unchoke these monster machines being forced to breath through straws. So yes, on big 750-1500cc machines breathing through shoebox-sized airboxes and sandwich-sized air-filters, removing them and giving each carb their own filters does improve breathing and gets more air into engine and more petrol is needed.

However, by the '80s, bike makers had figured out how to match airboxes, filters and carbs to engine-sizes. CV carbs became extremely precise mechanical computers that can meter exact amounts of petrol needed in large variety of operating conditions from idle all way to WOT @ redline. Pretty much any bike from '80s onwards has no need in factory trim for any changes to intake system.

Tuners still had ways to improve on factory designs because they're not constrained by needing 100k-mile durability, cheap manufacturing or emission regulations. So as with autos decades earlier, factory engines were ripped apart and larger higher compression pistons were installed. On one particular EX500 engine I saw, there was enough room between new big-bore cylinders and factory pistons to fit an entire finger through! They had bored out EX500 engine to 600cc! So of course intake needed more breathing than factory airbox and fi!ter allowed. And custom cams and custom spun valves were needed to flow that extra air. So jet-kits were designed with these kinds of air-flow increasing mods in mind.

Check out Bruce's, Garth285 and RacerX's builds for flow-improving mods. Big-bore pistons and turbos increase amount of oxygen going into engine and jet-kits are way to match petrol-flow to new air-flow patterns. Yeah, A LOT of dyno-tuning time is required to dial in these beasts with double factory air-flow and double power! Note that tuning with jet-kits come after air-flow increasing mods. It's mods that come first, and tuning with jet-kits is done as last step to tie all previous mods together.

Wth modern computer-designed engines and dyno-tuned carbs, there's really no simple way to improve them. But decades-old tuning ideas still hang around.
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