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Message started by DragBikeMike on 04/09/18 at 12:41:43

Title: Air Box Performance Tests
Post by DragBikeMike on 04/09/18 at 12:41:43

This is my first post to this section of the forum. I hope some of you find it useful. I have lots of pictures so I may have to make a number of posts to get it all in. Just don't have the skills yet. I wanted to see if the stock airbox performance could be improved without increasing noise levels. I did a series of tests using a rig fabricated from 2" ABS pipe, fittings and rubber couplings with a water manometer attached.

Title: Re: Air Box Performance Tests
Post by DragBikeMike on 04/09/18 at 13:19:35

I'm having difficulty getting the pictures attached so I will forge ahead without them for now. I attached the test rig to the airbox outlet and used a large ShopVac to pull air through the airbox. I measured differential across the airbox with the manometer.

Bone stock: 9.25"

Stock configuration with K&N gauze element: 8.00"

Snorkel removed (loud): 7.75"

Plastic airbox cover & decorative tin removed (too loud): 5.25"

Plastic airbox cover removed, tin replaced (too loud): 5.50"

Snorkel back in, 1.75" hole in plastic airbox cover, tin on (loud): 6.75"

Plastic airbox cover with 1.75" hole and baffle (sounds stock): 7.25"

Oval slot .37" x 2.0" cut in left side of airbox (sounds stock): 7.00"

Two foam blocks removed from underside of seat: 6.5"

Results: the noisy mods (K&N filter, plastic cover removed, tin cover in place) offer the optimum improvement, 3.75" less than a stock configuration, but make what I consider to be too much noise. The quiet mods (K&N filter, hole in plastic cover, baffle, oval slot left side, foam blocks removed from seat) offer a decent improvement, 2.75" less than stock configuration, with no discernable increase in noise.

I will do my best to get pics of the mods posted.

Title: Re: Air Box Performance Tests
Post by DragBikeMike on 04/09/18 at 13:21:52

Here is a picture of the modified air box cover with 1.75" hole.

Title: Re: Air Box Performance Tests
Post by DragBikeMike on 04/09/18 at 13:24:11

Here is a picture of the baffle installation.

Title: Re: Air Box Performance Tests
Post by DragBikeMike on 04/09/18 at 13:29:28

Here is a shot of the oval slot in left side of airbox. It's pretty ugly but I managed to clean it up a bit after I took this shot. You can't tell from the picture but the slot faces downward and the ignition module acts as a baffle. It didn't make any earth shattering improvement but it also didn't make noise. I installed a small mud flap type deflector between the airbox and frame to prevent road grime and water from being slung in from the rear tire.

Title: Re: Air Box Performance Tests
Post by DragBikeMike on 04/09/18 at 13:40:54

Here is a picture of the foam blocks to remove from under the seat. The picture only shows one removed, the one on the opposite side of the seat is still in place. If you go slow, they come off easily and remain in tact so you can reinstall later if you like.

I hope this post provides some useful data for anyone looking for a breath of fresh air.

Oooops! The site just won't let me attach this picture. I guess some of my photos exceed the file size limit (even though when I check the properties of the file it shows less than 2048KB). So let's try a verbal description. There are foam blocks attached to the underside of the seat with double backed adhesive tape. I removed the two blocks running fore & aft that are located just in front of the hard rubber pads that carry the weight of the rider.

Title: Re: Air Box Performance Tests
Post by DragBikeMike on 04/09/18 at 14:01:32

I think I found a way to reduce the file size so let's try again with a pic of the seat bottom.

Title: Re: Air Box Performance Tests
Post by DragBikeMike on 04/09/18 at 14:03:37

OK. That seemed to work. Here is a shot of the rig installed on the airbox. It actually fits quite nicely.

Best regards to all.

Title: Re: Air Box Performance Tests
Post by Dave on 04/10/18 at 06:08:40

I wonder how the flow of the shop vac relates to the flow of the Savage engine - and how the vacuum noise relates to engine intake noise?

Will the improved flow make a noticeable change on a stock....or modified engine? It is my belief that for most operating conditions where the throttle is only partially opened the air box and filter don't provide much of a restriction - but when you are using a lot of throttle and rpm the intake restrictions can make a difference and limit power output.

That is really surprising that the foam seat blocks are restrictive to flow!

Title: Re: Air Box Performance Tests
Post by Fast 650 on 04/10/18 at 08:11:39

Flow is pretty simple to calculate. The equation is Displacement in CID x RPM / 3456. That is assuming 100% volumetric efficiency. For most street engines, about 80% is close. So for a Savage at 6500 rpm that would be 40x6500/3456=75 cfm. 80% of that would be about 60 cfm then.

A typical industrial vacuum like what you would find at a car wash is rated at 100 cfm. So his shop vac test is in line with the airflow of the engine.

Title: Re: Air Box Performance Tests
Post by justin_o_guy2 on 04/10/18 at 08:54:40

Remember the flow in operation is pulsed. You're dealing with pressure waves. The volume of air between filter and carb need to be equal or greater than the volume of the cylinder.
There are articles about intake design theory.

Title: Re: Air Box Performance Tests
Post by batman on 04/10/18 at 09:21:36

Peak EV for any motor only occurs at peak torque (3400 rpm for a stock LS650) .Before 3400 you have reversion in the intake ,after peak torque not all the exhaust gases leave the cylinder.

652x3400 /3456=641

641/652=98.27% EV (in a perfect world)

Title: Re: Air Box Performance Tests
Post by Fast 650 on 04/10/18 at 09:29:32

I think he is just testing for airflow differences with different filters and airbox mods, so in that case pulsing won't matter. All he needs to see is overall flow to determine if combination A flows better than combination B. And as long as his final results flow as much as the engine can use he should be golden.

Making major changes to the airbox shape and size would open up a can of worms though, and he would have to account for the pulses then.

Title: Re: Air Box Performance Tests
Post by DragBikeMike on 04/10/18 at 12:42:25

Regarding Dave's comment: wonder how vacuum noise relates to engine intake noise. I'm not sure I understand the question but I will try to provide an explanation. My comments regarding noise were based on the noise level I heard with the engine running, not the vacuum cleaner. I would install the mod and run the engine. It was strictly my opinion based on what I heard with my ears. I wish I had some sort of sound measuring instrument. If it was hands down louder I defined the result as "loud", if it was obnoxious I defined it as "too loud", if it was a close call I would do several iterations with and without the mod until I felt comfortable with my final opinion of the sound level.

Regarding Dave's comment about the seat foam: I could actually watch the column drop in the manometer as I lifted the seat off with the test in progress. The foam blocks form a channel that guides the air in from the rear of the seat down to the snorkel. I'm pretty sure they are for noise mitigation. Taking those two out didn't seem to affect noise much. The rear foam blocks are a bit larger, but I didn't mess with them because I was able to achieve a reduction equal to total seat removal by just taking out the forward foam blocks.

Regarding comments on the ShopVac cfm: I used a 5.5 Hp vacuum rated at 140 cfm so I knew it would be a torture test. To amp it up a bit more, I removed the vacuum cleaner's filter so it was probably capable of moving more that 140 cfm.

Regarding justin O guy 2 comment about airbox volume: I don't believe I changed the airbox volume appreciably.

Regarding comments about resonance, reversion, etc. Fast650 has it exactly right, I was simply doing a comparison. I deem these modifications successful. The stock airbox restriction to flow has been significantly reduced without any noticeable increase in noise. This modified airbox will support higher airflows required by other mods like increased displacement, better exhaust systems, better flowing carburetors, head mods, etc. Will it fully support any and all mods? Don't know, but it will definitely do better than the stock box.

The testing I performed provides some concrete data. I know it's not very sophisticated but it's good solid data. To me, it's better than making a change and going for a ride to see if it works. Of course, the proof is always in the pudding. It's a beautiful sunny day here on Oahu. Perfect conditions for a little test-n-tune. I will let you all know how it works.

Title: Re: Air Box Performance Tests
Post by Dave on 04/10/18 at 13:19:29

I didn't realize the sound test was engine noise......not the vacuum cleaner noise.

Title: Re: Air Box Performance Tests
Post by DragBikeMike on 04/10/18 at 23:53:59

Test & tune went well. On the initial ride the bike felt very good. It started right up, no enricher needed, and settled into a nice idle. I drove straight off with no hiccups, surging, or afterfire. Roll-ons on the surface streets around my house were smooth and strong. A quick run up the freeway to the next exit went well but at speeds above 55 it felt a little light on fuel. Seat-o-the-pants test but it felt light on fuel by my standards.

Changed main jet from 145 to 147.5. Went for a long freeway ride into Honolulu. Strong headwinds made the little single work for it's dinner. The entire round trip included long downhill freeway grades, long uphill freeway grades, city streets, stop & go, and suburban surface streets. Carburetion felt spot on for the entire trip (about 1 hour total). Very good power on surface street roll-ons from about 20 mph and up, 3rd & 4th gear. Decent passing power on freeway. No hesitation or flat spots. Noise level equal to stock under all but WOT conditions. WOT up hill may be slightly louder than stock but hard to tell with wind noise and helmet. Not a hint of ping or knock. Only one afterfire on the entire trip and that was when the engine was in warm-up mode.

I am satisfied with the results.

BTW, I had already gone through the carb prior to the airbox testing & mod. I think if this airbox had been used with a bone stock carburetor it would have probably run pretty ragged . The low speed circuits on the stock carb setup are so lean that the additional air would have made things worse. Best as I can tell, most everyone on this forum has or is planning to go through their carb. These mods work good with a properly setup stock carb. I intend to do a separate post on my stock carb modifications. They're slightly different from what I have seen here on the forum so I hope you find it interesting.

Title: Re: Air Box Performance Tests
Post by batman on 04/11/18 at 08:28:12

Taking out the foam blocks on the side of the seat, changes the path of air flow, and may be a mistake. The normal path of air from the rear of the seat to the inlet "snorkel" provides a flow across the voltage regulator fins for needed cooling.

Title: Re: Air Box Performance Tests
Post by Eegore on 04/11/18 at 10:58:10

Is "bone" stock the same as stock?

Title: Re: Air Box Performance Tests
Post by DragBikeMike on 04/11/18 at 12:57:10

That is an excellent observation Batman. I am embarrassed to admit that I totally missed it. I think maybe I need to reevaluate removal of those foam blocks. Back to the drawing board on that part of the mod.

Title: Re: Air Box Performance Tests
Post by DragBikeMike on 04/11/18 at 13:08:11

Regarding Eegore's question about "bone stock" vs "stock". My use of the term "bone stock" means the airbox was completely stock with an OEM air filter element. I would consider an airbox with a direct replacement filter element as "stock" since it doesn't have an OEM element but rather has a direct replacement, supposedly equivalent to the OEM element. I would consider an airbox with a K&N element to be "modified" since the K&N is a performance element superior to the OEM element.

Title: Re: Air Box Performance Tests
Post by DragBikeMike on 04/11/18 at 13:42:17

I have attached a photo of the regulator orientation. Note that the cooling fins run right and left, not fore & aft. I would expect the factory to orient these fins fore & aft if the designers were taking advantage of induction air to cool the regulator. Also note that the picture shows two large electrical connectors just forward of the regulator, one on the right side and one on the left side. There is a relatively large space between the connectors. That large space could be intended for air flow....but.....if you go back and look at the photo of the underside of the seat, you will notice a hard rubber pad support at the rear. I believe that pad sits right between those electrical connectors. That would effectively block off any cooling air. I think I'm going to try and test this system to see what effect it has on regulator temp.

Title: Re: Air Box Performance Tests
Post by batman on 04/11/18 at 14:19:12

D B M ,guess your right about the orientation ,wasn't aware ,I moved mine years ago along with the stock seat and rear fender.

Title: Re: Air Box Performance Tests
Post by DragBikeMike on 05/23/18 at 01:53:05

Hey Batz, I finally got around to checking the temp on the rectifier. After a twenty minute ride I popped the seat and shot the rectifier with a thermometer. It was 145 degrees. I don't know if that's OK or not. Anybody know what the temperature threshold is for one of these rectifiers?

Title: Re: Air Box Performance Tests
Post by DragBikeMike on 12/02/18 at 20:41:35

I’m unearthing this old post because I want to try testing the airbox with my budget flow bench. The simple manometer readings indicate improvements, but the readings don’t really quantify the improvements. In other words, the simple manometer readings may show that a configuration is better, but better could be anything from 1 CFM to 50 CFM. That’s because there’s no way to correlate a 1” H2O change to CFM. Using the flow bench with the inclined manometer and orifice will allow an estimate of actual flow and will also permit comparison in percent of flow from one configuration to another.

If I can achieve a test pressure of at least 5” H2O, I will be able to use the flow bench conversion tables to convert to anticipated flow at other test pressures. If I can’t achieve at least 5” H2O test pressure, then at least each configuration can be tested at the same pressure, and the data will be expressed in %, which IMO is more meaningful.

Fast 650 shared a formula for estimating maximum horsepower potential based on flow through the intake tract at 10” H2O. I found the same formula in one of my old books. The formula is .43 x (cfm at 10” test pressure). The cfm value is obtained from a complete intake system (head, manifold, carb and air cleaner assembly). So, if you want to build an engine with a target HP of 45, you need about 105 cfm through the entire intake system. To achieve that much flow, I assume the air filter assembly (airbox, filter, connector hose, etc.) must flow at least 105 cfm. Since their will be compounding losses of differential pressure as the air travels downstream through the carburetor, port, and valves, the airbox probably should flow more than 105 cfm @ 10” H2O. Having the capacity to flow more than 105 cfm at 10” H20 will maintain the highest differential possible across the downstream components.

You must start somewhere, and that starting place is the airbox. All the tests were performed with a 209-cfm orifice.

Here’s a shot of the budget bench installed on the bike.

Title: Re: Air Box Performance Tests
Post by DragBikeMike on 12/02/18 at 20:42:27

Here’s a shot of the connection at the airbox.

Title: Re: Air Box Performance Tests
Post by DragBikeMike on 12/02/18 at 20:49:46

Everything fit nicely, and the hookup was a breeze.

The modifications and testing I previously did examine various combinations and their associated drop in U-Tube manometer vacuum. I reviewed all the various configurations and decided I would test five. Based on the intended application, I consider these five combinations to be typical choices. For the flow tests, I only had two elements, stock & K&N. I don’t have a spare filter frame to use with the poly-fil material. If I acquire a frame later, I will test with the poly-fil filter media and post the results. I gave each combination a name meant to be descriptive of the application. The prior entries to this post provide pictures and details of the various mods.

Stock Configuration

Stock configuration is all the components of the airbox assembly exactly as delivered by the OEM except for the air filter element.

Street Modified – Quiet

1.75” hole in the airbox cover, the baffle in the airbox cover, the oval slot cut in the left-hand side of the airbox, the foam blocks removed from the seat bottom, the decorative tin installed over the airbox cover, and either filter (Stock or K&N).

Street Modified – Semi Quiet

1.75” hole in the airbox cover, no baffle, the oval slot cut in the left-hand side of the airbox, the foam blocks removed from the seat bottom, the snorkel removed, the decorative tin installed over the airbox cover, and either filter (Stock or K&N).

Street Modified – Maximum

no airbox cover, the oval slot cut in the left-hand side of the airbox, the foam blocks removed from the seat bottom, the snorkel removed, the decorative tin installed over the airbox opening, and either filter (stock or K&N).

Maximum Modified

no airbox cover, the oval slot cut in the left-hand side of the airbox, the foam blocks removed from the seat bottom, the snorkel removed, no decorative tin installed, and either filter (stock or K&N).

Title: Re: Air Box Performance Tests
Post by DragBikeMike on 12/02/18 at 20:52:21

As mentioned above, I wanted to test at a minimum of 5” H2O so I could use conversion tables to predict what the flow would be at other test pressures. With some of the configurations, I was not able to achieve 5” H2O. The flow restriction was reduced to a point where my little bench just couldn’t pull anymore flow. All the bleed valves were closed and there wasn’t any more left.

Here are the results of the tests.

Stock Configuration
Stock filter: 45% @ 5” H2O (converts to 133 cfm @ 10” H2O)
K&N filter: 51% @ 5” H2O (converts to 151 cfm @ 10” H2O)

Quiet Street Modified
Stock filter: 51% @ 5” H2O (converts to 151 cfm @ 10” H2O)
K&N filter: 58% @ 5” H2O (converts to 171 cfm @ 10” H2O)

Semi-Quiet Street Modified
Stock filter: 54% @ 5” H2O (converts to 160 cfm @ 10” H2O)
K&N filter: 61% @ 5” H2O (converts to 180 cfm @ 10” H2O)

Max Street Modified
Stock filter: 57% @ 5” H2O (converts to 168 cfm @ 10” H2O)
K&N filter: 60% @ 4.75” H2O (no conversion, max depression <5”)

Max Modified
Stock filter: 59% @ 5” H2O (converts to 174 cfm @ 10” H2O)
K&N filter: 62% @ 4.25” H2O (no conversion, max depression <5”)

Title: Re: Air Box Performance Tests
Post by DragBikeMike on 12/02/18 at 20:58:26

You can see from the test data that even with the stock airbox, the 105 cfm threshold for 45 horsepower can be exceeded. It appears as if downstream losses like the carburetor, intake port, and valves will be the limiting factor. But using real world experience, most of us know that even with a stock engine, modifications to the airbox yield substantial improvements in performance. You can feel the improvement. So there is obviously more to it than meets the eye.

It looks to me like it’s a compounding problem. The airbox drops the pressure as the air flows through, which then reduces the differential across the carburetor, which then drops the pressure as the air flows through, and so on. Ultimately, the test needs to be performed with all the major players connected (airbox, carburetor and cylinder head).

You also see that if the stock airbox becomes the limiting factor, it would be very easy to modify the airbox to achieve large improvements in flow. Using the stock filter, flow can be improved about 41 cfm. If the K&N is installed, it looks like flow could be improved at least 47 cfm, and most likely more (no flow data for the Max Street Modified and Max Modified configurations).

My little bench isn’t calibrated, so the data contained in this post can’t be considered dead-nuts accurate, but its probably close, and the changes in flow resulting from the modifications most likely reflect the actual change in flow.

It looks to me like there’s plenty of juice to be had by playing around with your airbox, regardless of which filter you use.

Title: Re: Air Box Performance Tests
Post by VortecCPI on 05/21/19 at 09:02:10

After reading through all this I decided to put the right-side airbox cover back on. The engine is noisy without it and it does prevent rain from entering the airbox.

And... Judging by the numbers such a drastic change in pressure drop would likely require a larger main jet...

Very good read by Lonn here: http://thunderproducts.com/your-airbox-friend-or-foe