VM34 air filters.

toglhot

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I had pods on my 34s and never noticed before, but the actual hole on the rubber grommet on the pods is quite a bit smaller than than VM 34 bell mouth. Seems a bitbsillynto cover the bellmouth with the pod grommet, so, I decided to ditch the pods and make a couple of pancake filters.

I did try fabricating one from sheet aluminium but found punching the centre hole out to make a fitment tube was simply too much of a stretch for the aluminium. So, I bought a 100mm round slab of aluminium, cut it in half and turned it up on the lathe.

I've made the mounting hole in the filter 0.10mm smaller than the bellmouth for a push fit. I was going to slit the fitting hole and run a thread 4mm thread through sideways to tighten the filter on the bell mouth, but am wondering if the push fit would be sufficient??? Alternatively, I could put grub screws through the filter to tighten onto the bel mouth, but again wondering if the 0.10mm push fit would be sufficient.

The back,ofbthebfilterbwill be beaten up from sheet aluminium.
 

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arcticXS

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You should try to machine the largest possible radius from the surface to the bore/ bellmouth. That should help the flow significantly
 

arcticXS

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See attached picture of a dam spillway. Air flow is not quite like liquid flow, since air can expand or compress, but the principle of a rounded entry is still valid for both. Just food for thought, maybe also some inspiration.
 

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arcticXS

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And one more thing for everybody's benefit. The pics of the pod filters are only end view, but it looks like there is chrome at both ends. Genuine K&N filters only have a chrome end cap, or no chrome at all. There used to be some "Mivv" brand pod filters on the market with chrome at the neck end also, and they had just that stupid lip. In fact, on the SRX600 project bike I bought, 2 of those were fitted. To a really nice and expensive pair of TM/RS34 flatslide carbs. Not sure what the plan was, carbs to hopefully add some hp, then some cheap filters to rob an unknown number of hp.
 

toglhot

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I'm aware of all this, as are Mikuni, so, I'm not about to change the shape of the bell mouth??? what I'm interested in, as my post states, is the ftment method.
 
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Grimly

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Here is some hopefully useful info:
Cross-section 11 is the one that worked for me, on the GS850 with the big single SU carb. I discovered that MGB twin SUs had an air intake that was perfectly shaped, incorporated into the air filter housing, but seperable. That, and the suitable sized K&N filter that nicely fits over the flange.
Recovered all the mid-range torque I'd been missing. Goes like shit off a shovel.
 

arcticXS

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I'm aware of all this, as are Mikuni, so, I'm not about to change the shape of the bell mouth??? what I'm interested in, as my post states, is the ftment method.
Well, you could for example turn down that neck to 1 mm wall thickness, make 2 or 4 slits, and use a narrow hose clamp. Like on the Mikuni velocity stacks in the attached PDF. If you want to use grub screws, like you mentioned, the wall thickness needs to stay at minimum 4 mm or so.
Just to avoid any misunderstanding, I did not suggest to do any mods to the carbs, but just point out that there are better shapes than a sharp corner, if you want an improved air flow. With pancake filters, the air needs to turn 90 degrees, in order to enter the carb bellmouth. It is beneficial to make that a smooth, radiused turn, not a sharp corner. In the last scenario, an "invisible choke point" will be created by turbulent air. My impression was that you wanted to improve on the previous poor filter setup, and I just intended to give some input towards that goal.
 

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toglhot

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The VM carb bellmouth is similar to figure 11 in your post, not exactly, but similar, so air is sucked in from all angles. As for sharp corners, they are so slight and so low (about 1mm) that they would make little if any difference.
 

arcticXS

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Ah, I did not see that detail. Some VM carbs have a cylindrical section added, where the filter or hose clamps on to. It seems that your setup will have just a slight corner/ step then. But I think it still would make sense to remove it, and blend it in with the carb bellmouth.
 

toglhot

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Well, I suppose if I wanted to wring every ounce of power out of the bike there are lot of things I could do that would be more benificial than removing 1mm of material from an air cleaner, but I have the bike where I want it, so I'll stick with that.
 

gggGary

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Related and on my "one of these daze" list.
View of "end of the era" carb intakes from a YZF600. Note how the bell extends well into the intake box and separates the slide, bowl, emulsion, vents from the intake stream pulses,
intakea.jpg




intake bell seperation a.jpg


Feel designing a similar bell for our XS era carbs would have benefits.
Just for fun.
Izzat Yoshy's mark on the collar?
I've heard he knew a thing or two......
double velocity stacksa.jpg double velocity stacksb.jpg

Yup
1670503863685.png
 
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