zipidachimp wrote on 05/20/24 at 23:56:30:


The good news is you still have your zip at 80!  Ride on!

As a comparison data point, the Honda NC700/CTX700 twin panel filter is a nominal 9"x4".  The Hondas are at about 45hp and don't take quite as large of an instantaneous gulp of air as the single but they are still using a lot more air to make 50% more power (and that is in a pretty mild motor).  

There is a nice bell mouth coming off the end of the connecting tube to the throttle body and the open end sits in free air inside the airbox.  The cover also has a lot of volume and a snorkel.  You can see a parts diagram of one here:

https://www.hondapartshouse.com/oemparts/a/hon/51b92940f87002377498e8d1/air-c...

Some of the K&N filters have a bit of a bell mouth formed into their manifold, but generally putting something right onto the end of the carb is a good way to hurt air flow.  The sides and also the back panel of the filters should be kept at a distance from the bell mouth of the carb/TB.  The Savage has a space problem with getting a decent airbox tucked into the bike so there don't seem to be many good options for addressing the situation.  Looking at what modern dirt bikes do might be worthwhile, they've got limited space but need enough air flow for high power.

Paul, it is a small difference, but measureable.  Here's a good explanation with some illustrations.

https://performancebyie.com/blogs/ie-auto-blog/the-right-bellmouth

cases B and C are basically what you get with the K&N on the carb.  A sharp edge at the outside will probably cause a vena contracta effect as the air enters, reducing flow.

The filter end, if it is a hard surface (as with the K&N) can reflect pressure/acoustic waves that have come out of the carb back into the carb.  I think it was David Vizard that noticed when running an open-carb engine on the dyno there was a cloud of air/fuel "standoff" outside the carb mouth at some RPMs.  He grabbed a sheet of metal and started moving it closer and farther away from the open carb and at some distances he could get the reflected waves to coincide and eliminate the standoff.  But as usual, that distance varies with the RPM (and the engine, and probably cam timing too) so you'd want some sort of auto-adjusting panel in the airbox.  What seems to be more usual is to just make sure that far end is far enough away that any reflected waves are too attenuated to make any difference.  At least then you aren't having to deal with one more data point.

The distance from the valve head to the outer end of the carb will determine the resonant length of the intake tract.  A low RPM bike like the Savage would probably like a much longer intake (but where would you put it then?), where high RPM engines (especially roadrace 2T engines) often can't make the tract as short as they'd like it to be.

You can tune to different harmonics to get a tuned, but different, length, but you may have to pick a harmonic that has less energy than the ideal, and so you get the benefit of the tuned length but not as much due to the lower strength of the harmonic.

So a nice elliptical radius of at least 180* on the end of the bellmouth, standing in free air (so it can pull air from the surrounding area more easily) inside of a large capacity airbox with a low-restriction filter is a good plan.  But wait, the size of the airbox also effects the resonant system (I think you'll find discussion of this as a Helmholz resonator as in this link)

https://www.locostbuilders.co.uk/viewthread.php?tid=149862

While we're talking intakes, my engine builder testedone of those nifty v-stacks with a mesh/grille on them that some people like to use on their bikes when running without a filter.  Flow on the FB and power on the dyno both were reduced, so you might want to avoid them.

A good airbox is a GOOD thing.  The problem can be in finding one and then getting it to fit on the bike.  

cheers,
Michael

The foam sock filters used to come with a spring inside to keep them from collapsing from the suction.  Be sure to use that.

Also, foam does deteriorate with age/use.  I remember at the Suzuki shop I worked at part-time during school they had an MXer on the dyno that wasn't putting out the power.  They finally put a fresh foam filter element on and power was back to where it was supposed to be, and that wasn't a very old filter either.

The spring in the UNI filter is about all it has to hold it's shape.  I'm not an engineer or gear head.  I just want to grab any low hanging fruit and ride.  I read your comment in the right context.  Thanks.

zipidachimp wrote on 05/24/24 at 23:38:56:


10krpm - is that a typo?  Lucky to get 6,000rpm out of the LS650 before upshifting.

I removed the panel out of the fake RAM air intake (hood scoop) on my ‘74 Tran’s Am 400.  I can’t say it made a performance difference, but it sounded badass when you kicked in the 4-barrel.  Never did any real mods on that car, but a freer flowing crossover muffler, different weights in the distributor, a little carb tinkering, and a double roller cam chain added a few ponies and knocked about 1 second off 1/4 mile runs.  Fast enough for my first car at 16 years old.  Saved every nickel I made washing dishes at a Chinese restaurant at age 14-15 that started at $1.35/hour.  If I helped the waitresses by bussing tables when it was busy, I might have cleared $2/hr!

Michael Moore wrote on 05/25/24 at 10:03:11:


No doubt!  I was wondering!  I couldn’t click thru on the link.