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74 airbox dimensions and design.

cbrianroll

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My bike came with pods...not a fan...I cant find a decent used airbox so I wanna make one. Problem is I don't know what the inside looks like to replicate it. Any help with dimensions and pics of the inside would be awesome. Thanks
 
Been looking, I'm cheap....not diggin the prices and I'm a gluton for punishment lol. I think a copper one would look good....unless I fail miserably.
 
Yeah I guess you do like punishment. lol The amount of hours its gonna take to make it look good and seal correctly you will have been able to buy 3 or 4 air boxes. I am all for hand made parts though.
 
https://www.ebay.com/itm/HONDA-CB75...noa=1&pg=2047675&_trksid=p2047675.c100623.m-1

If you can't come up with one after looking there at the construction you are not able to do it. You can pull out a small measuring tape and closely copy the distances on the screen pics to copy it well enough to work.

The most important part is the length and ID of the rear rubbers that extends back inside the box that you can't see. That rubber is part of the overall intake ram length and needs to be there to best work right. You can measure an OEM rear rubber to get an ID and then measure those pics on your monitor screen to get approximate measurements of the top half of the box, which is really what matters, the bottom half merely waterproofs the filter element. Important to have enough room for air to curve to enter the rubbers as to where the back wall of the box ends up.

The SOHC uses direct lift carbs unlike the DOHC, the DOHC as a result of the CV carbs is super b-tchy about wanting the stock airbox as the internal volume impacts the slight rise of vacuum in the box as the paper filter restricts slightly, that rise makes the carbs open slides faster and fuller, something the SOHC has zero trouble with. The SOHC is plenty happy to run with zero vacuum in the airbox and why pods can work well on them. The DOHC is so picky it even requires different rubber configuration inside the airbox based on the engine size even though they all use the exact same basic carb body casting.

I have pods on my 550F and it runs like gangbusters with no problems at all. Again, the direct lift carbs are why.

I actually at one point ran around on my DOHC with the bottom of the airbox cut off (they aren't split two piece like SOHC is) to simulate using just the top portion like Honda designed the SOHC airbox. I fitted the top up to hold the paper filter in place on the bottom. Like an open air element round air cleaner on a car V-8. The CV carbs ran perfect, the filter element being the restriction there. I did the same on S series Kawasaki triples, the back part of the box simply came off to again expose a round paper filter and I ran that all the time with the rear cover off, it's mainly there to prevent massive water getting in and for noise reduction. All of those bikes ran great.
 
Thank for the info sir. I was thinking backwards about sohc and dohc. I have the factory rubber pieces, read somewhere they are important! I'm In Washington so I want a waterproof box. Gonna mess around designing today, not sure how to make a big box sexy lol.
 
Just so you know, waterproof is nice but not absolutely 100% necessary except in the case of a rock solid gully washer as we call them here in Texas. I've run open pods in so much rain I can't say and only one time did it ever rain enough to affect them and that one was raining so hard I could not literally see at all to be moving while driving anyway. All the rest I had to have the bike running as I had no car for many years, bike only, so I drove in the rain and countless times. The Kawasakis I rode in downpours and no effect on the open paper element. And at a facing up at 45 degree angle. On pods, the foam ones if not dry of oil will repel water far better than K&N type gauze, the cel openings on the gauze are too big (run one to draw the oil down and hold it up to the sunlight to see all the open pores in it). The K&N are also relatively thin too and why you see those holes, foam (UNI type) is more convoluted and much thicker and why they do better in rain. They also trap dirt much better than K&N do. If oiled correctly the foam simply shunts the water to the bottom of filter by gravity and the water then drips off the bottom. I never ever ran into water ingress issues except for that one time and that I note was K&N type filter. By far a worse problem on the DOHC was water during hard rain running down the inside of the front fuel tank notch at frame to then stack up enough to wet the coils out to try to drop spark. By experimenting I found that if you dropped speed to 50 mph the water stackup rate would slow down to not do it, any time I sped up the coils would then short until I slowed back down. Weird, huh? The Kaws did the exact same thing to shock you through the clutch cable lever as the engines were newly designed with rubber mounting, but on them I found that if you ran a dedicated ground wire from engine to frame the issue stopped 100%. Kawasaki found it too, the next years had the harness modded to do the exact same thing. The UNI podded CB550F I have has had no water issues at all but I don't drive in rain like I used to either. I blocked off the rear filter case (two big pieces, front and rear, on a 550) on that one to make a waterproof glove box of sorts to hold things. The DOHC with open lower OEM filter showed no water issues at all due to the modded filter. The filter just gets dirtier faster.

90% of my bike riding time the bike was stored outside in all rain, so there's that. They had to start and run correctly right then or problems. For some reason I never end up where there is garage space for a bike. Even now the 550 is out in the open.

A couple points. On a UNI foam filtered bike with pods you can shove them forward to squeeze out excess water before cranking bike up. I used to practice that if coming out from work to an all day rain soaked bike. Try that on K&Ns. And one thing you must have running them or any other modded open air cleaner element. There must be a full length rear fender front section to keep throwoff water from tire from literally flooding the air cleaner area, that disappears on lots of custom bikes and you will flood engine out with water not having it in place as a deflector.

Food for thought, yours and do as you will...........
 
Great info, thanks. I had thought about running unis, thought breadbox type box might look neat, we'll see lol. Washington has some terrific rain and it goes everywhere, pods on my previous bike was awful in the rain so I figured I should do my best to keep dry. Interesting about the coil issue, fun to hear about things.like that.
 
You would know far more about Pacific NW low pressure systems than I. Here we don't get drowned sasquatches floating down the river. More like jackalopes and rattlesnakes. I parked my Bridgestone (before they dropped bikes to go to tires only) once in the late '60s to stand and reach out to get a hand flooded with rain, yet I was bone dry 2 feet away, the rain literally formed a line where it was and wasn't. Very surreal, like out of a Fortean picture book.

Texas...............I would love to see the density of your deep woods up there, I used to go off in woods in the northeast US, be gone all day long. Communing with all wild things.
 
Lol, curtains of rain are cool, dont happen alot here. Last month it was raining in my front yard but not the rear.....neat. oh the wokds are glorious here especially hiking in the national forests, HUGE trees and just endless it seems. I have 5 acres but am surrounded by timber, until they log it it is pretty cool, except it has lots of undergrowth, pretty easy to get turned around....
 
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