High-flow Intake Mod - Honda CBR500R Forum : CB500F and CB500X Forums
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post #1 of 57 (permalink) Old 07-02-2016, 08:16 AM Thread Starter
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High-flow Intake Mod

Having recently cammed the engine, some feedback from the dyno tuner was that he found it wanting for more air. Running my K&N filter vs no filter through the standard funnel inlet, there was negligable difference, <0.5hp. Completely removing the panel that holds the filter however, returned 3hp gain through the entire mid-range, with 2hp gain in the top end for a total of 57rwhp. His recommendation for me to get those last few ponies from the bike is to modify the intake to allow for a larger inlet and come back for a touch up tune... So here's what I've come up with.

I pulled the stock air filter out of storage for mock-up testing. Though will have to source a different style aftermarket re-usable filter later; as I sure don't want to have to cut up an oem filter every single time it's due for change.

-Tools/Materials needed-
Rotary power tool, Dremel or similar
fibreglass reinforced cutoff wheels for rotary tool
saw cutter wheel for rotary tool
Phillips screw drivers
Eye protection
section of foam large enough to cover back of air filter

The panel you'll be modifying costs $4 (aud) from Honda, if you'd rather hack up a spare.

-Procedure-
Remove seats and battery from bike
Remove back panel of air intake chamber
Separate air filter from panel

Cut out the two layers of flame arrestors (good to have, but in the pursuit of power, they are a restriction)


Remove the foam on the back of the air filter and cut out the back panel section, not much taller than the original hole, and width with sufficient border to allow for sealing later on.


Test fit the air filter to the back panel, mark out the equivalent rectangle and cut that out too.


Source some replacement foam and cut to fit, this will then squash down once the filter is secured back in place.


Re-install filter on back panel, I used the lighter to burn the foam slightly for a cleaner finish.


Reinstall panel in bike.
May require an ecu re-tune after install.
Job done

The original inlet is a 50mm circle = 1,963.5mm2
Modified inlet is 53x69mm rectangle = 3,657mm2
Total change is x1.8 larger inlet.


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Last edited by tothezenith; 07-03-2016 at 01:02 AM.
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post #2 of 57 (permalink) Old 07-02-2016, 08:32 AM
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Good job, but I doubt it will bring too much improvement as I believe your tuner's feedback is totally aligned with the findings of the race prep shop guys - and if thats true the choke point are the velocity stacks. Check your PM for some info.
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post #3 of 57 (permalink) Old 07-02-2016, 08:55 AM
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Good job, but I doubt it will bring too much improvement as I believe your tuner's feedback is totally aligned with the findings of the race prep shop guys - and if thats true the choke point are the velocity stacks. Check your PM for some info.
dammit ... you are making me consider to actually go to see the guys and buy those velocity stacks ... but then it would be good to buy a power commander and have it tuned as i already have an exhaust (running it with the baffle in though), dunno if the stock ecu would be able to handle all the changes ... but if i remember correctly, it should "auto align" after some time, but i may be wrong there ...
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post #4 of 57 (permalink) Old 07-02-2016, 10:15 AM
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dammit ... you are making me consider to actually go to see the guys and buy those velocity stacks ... but then it would be good to buy a power commander and have it tuned as i already have an exhaust (running it with the baffle in though), dunno if the stock ecu would be able to handle all the changes ... but if i remember correctly, it should "auto align" after some time, but i may be wrong there ...
In the closed loop portion of the operation the stock ecu as you said "auto aligns" real time based on the feedback from the 02 sensor. Updating the trim tables takes a bit more time but as per the AFR chart on the dyno table I would not be concerned much.
What abut giving them a call on monday - you guys live a few hundred kilometers from each other and speak the same language - so it should be fairly easy to find out. ;-)
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post #5 of 57 (permalink) Old 07-02-2016, 11:07 AM Thread Starter
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Originally Posted by Oyabun View Post
Good job, but I doubt it will bring too much improvement as I believe your tuner's feedback is totally aligned with the findings of the race prep shop guys - and if thats true the choke point are the velocity stacks. Check your PM for some info.
I do think there's merit to his findings, considering he tested with and without a filter with the standard inlet funnel with negligible difference.
Although we can't really use use 57hp figure with no airbox back panel, as that was run without a filter.

Well it's only an extra $100 for each touch up tune going forward now.
So I reckon I'll get the touch up now that I've done this airbox mod plus exhaust port matching.
And per your PM re the velocity stacks, I think another touch up tune and dyno run will be in order down the track for them as well, to see what net gain can be had ay.

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post #6 of 57 (permalink) Old 07-02-2016, 07:25 PM Thread Starter
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@Administrator please move to How-To section. Thank you

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post #7 of 57 (permalink) Old 07-03-2016, 01:35 AM
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In the closed loop portion of the operation the stock ecu as you said "auto aligns" real time based on the feedback from the 02 sensor. Updating the trim tables takes a bit more time but as per the AFR chart on the dyno table I would not be concerned much.
What abut giving them a call on monday - you guys live a few hundred kilometers from each other and speak the same language - so it should be fairly easy to find out. ;-)
Oyabun,
by How much is the stock ECU capable of adjusting its map for different amounts of airflow and fuel requirements? If I have IXIL no-cat Race header pipes, Yoshi muffler, PAIR system removed, and airbox modified with K&N air filter installed - Do you think the stock ECU could cope with these mods, or will I be running dangerously lean fuel mixture? I currently have the O2 sensor removed and bypassed by way of a resistor plug on the loom, but I get the feeling I should install the stock O2 sensor into the IXIL headers to let the ECU read whats going on down there.... Your thoughts and advise please. thank you, Grant.E (NZ)
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post #8 of 57 (permalink) Old 07-03-2016, 04:52 AM Thread Starter
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I'll let Oyabun answer your question on the ECU.

As far as this mod goes though, geez I wish I'd thought of this from the start; even without the touch up tune to suit this, I notice the difference. I've found an aftermarket filter company that makes reusable filters constructed in the same way as the stock ones, so I've place an order for this one from Swift - Sprint Filter P08 Air Filter for Honda CBR500R CB500F CB500X

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post #9 of 57 (permalink) Old 07-03-2016, 06:20 AM
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improving the air flow

The first 'Choke point' in the CBR500 air intake setup appears to me to be the right angle tube that allows air into the airbox. it's not very large, it has a very acute angle bend in it, and it has no ram-air or ducted airflow directly into it, it can only draw in from theair behind the fairing. I am thinking of installing a Naca duct in the right hand side cover panel with some flexible ducting coming from the duct to the air intake pipe. this should increase the volume of air getting into the airbox. the next choke point is the velocity stacks. but there is an aftermarket solution for that, I've seen them on eBay, machined alloy ones. I cant ssem to find them again though. anyone have the link ?
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post #10 of 57 (permalink) Old 07-03-2016, 06:29 AM
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Oyabun,
by How much is the stock ECU capable of adjusting its map for different amounts of airflow and fuel requirements? If I have IXIL no-cat Race header pipes, Yoshi muffler, PAIR system removed, and airbox modified with K&N air filter installed - Do you think the stock ECU could cope with these mods, or will I be running dangerously lean fuel mixture? I currently have the O2 sensor removed and bypassed by way of a resistor plug on the loom, but I get the feeling I should install the stock O2 sensor into the IXIL headers to let the ECU read whats going on down there.... Your thoughts and advise please. thank you, Grant.E (NZ)
Based on what I have seen on the very dynojet graphs which show AFR, and what I've read from tothezenith's dyno feedback the stock ecu runs nicely rich @WOT. However you currently have disabled its auto adjusting capability by cutting/faking feedback to it. An ecu allways looks for a fluctuating signal from the O2 sensor - so a simple resistor ladder will not result in ideal running conditions on the long run.

Before going further it is important to understand how the ecu operates.
In closed loop mode there's no other way, but the O2 feedback have to altered. For this the best method is a WideBand O2 sensor with a controller what has an adjustable simulated NB output. This can properly give real time feedback to the ECU and can be set for your general AFR target.
Open loop can be adjusted by piggyback controllers - as unfortunately the Honda ECUs are well protected - so apart from a few HRC models and earlier ECUs I'm not aware they could be flashed unlike KTM or some Yamaha ones.
Now. The fact is, that if it is a race only bike it will operate in closed loop mode only very briefly anyway so that part is less interesting.

Depending on your budget there are a few options.
Best results can be reached for a competition only bike by buying a piggyback controller and getting a base program during a dyno session. And have a logging capability with an WB O2 sensor to be able to adapt to local conditions if needed (eg. grat elevation changes, humidity, temperature).
Budget option is a stock NB O2 sensor with an acfive EFIE what can offset the 02 signal line towards the ecu to cheat it to a bit richer operation. It does not directly alter open loop operation, but you have use the bike every now and then in a "civilised" mode around the track so the fuel trim tables get populated and adding a bit of an extra fuel to Open loop operations also.

For piggyback units there are three major options;
The Bazzaz ZZ-Fi & Power Commander V are majorly the same, both have logging and self mapping (extra cost) functions, both handle ignition tweakingband allow gear based trimming also. Very advanced stuff but costs an arm and a leg.
EJK from Dobeck unfortunately no self mapping feature (their AFR+ which is a fuel controller linked to a Wideband controller is not available for the 500 series as far as I know), and completely different setup and logic. More like an Electronic Jet Kit (as the name implies) so one can adjust three major areas idle, cruise and WOT and transitions (like float level, main and accel jet in a carb) to alter fueling. No logging, no ignition, but half the price.

I've bought my PCV second hand - it is rare and one needs to wait quite long time for one to drop, but it can be had for significantly less than new. Also Im using a wideband controller what I've built (I'm a recovering electrical engineer, but even I would not build the next one, but buy a second hand WB2 or similar) with a heated bosch 4.9 WB O2 sensor.
I'd recommend the PCV simply because more tuners know it and it has a higher chance to be available used - and as Tothezenith has done some pioneering work - you could use his flash as a baseline.
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