Anyone who has used a K&N type filter will know that to properly clean, dry and oil the filter it will take a minimum of 2 hours (or more if done thoroughly) if its an oil-less type dry element filter like AEM it will take atleast 1 hour to clean and properly air dry (not blow dry) the filter. Time is money and authorised service centers can't afford to waste for 1 to 2 hours for cleaning and re-installing air filters in customer cars when they have to deliver 10 to 20 cars at a minimum on an average day! Not to mention if the oiling wasn't perfect the customer is either going to come back or ruin his engine!! Too risky for the manufacturer and the dealers!
So the hunt for a freer flowing air intake begins to replace the stock paper filter and the stock airbox, and this hunt lead me to buy one of the best air filter systems out there the BMC OTA. While i do like my BMC OTA carbon fiber airbox with the cold air feed for the performance it delivers at the top end of the RPM range i wish it was a bit easier to clean. It requires the complete removal of the airbox from the vehicle and further unscrewing of 4 small little screws to take out the filter element. Its not that it needs cleaning every month or even every 6 months and the filter is good to go without cleaning for atleast 5000KMs in light to moderate dusty conditions, but the thought of taking the filter assembly out to clean the air filter element is tiring. Yes, looks like I'm beginning to appreciate convenience these days. With the factory airbox you undo two clips take out the filter and you clean or replace it and shut the airbox. That's it! Done! How easy?!
So this got me thinking, i needed the convenience of the stock airbox but with more power and better airflow than what a stock factory airbox would allow. Is it possible, can the stock airbox be improved?
If you open the stock airbox and look inside you will find lot of plastic moulded ribs inside, both in the pre-filtered and post-filtered area. You will be wondering how these would influence airflow inside the box, I don't think it enhances the airflow, these should hurt the smoother airflow. In 4 Stroke Performance Tuning by Graham Bell it is mentioned that the job of these ribs are for sound suppression! Yes! That could be it! I remember when this model was launched Suzuki has claimed lower Noise Vibration and Harshness (NVH) for the new generation Swift and yes the engine sound refined compared to the previous model K-Series Swift (my cousin has one) with the 1.2 engine which had an airbox with smoother insides. I don't mind slightly higher NVH if it could get the engine breathing better all around. So, time to do some cutting and grinding with my Dremel Fortiflex.
What Mr. Bell said
The photos below with before and after comparisons so that you can see what exactly has been done to the stock Suzuki airbox.
Pre air filter side of the airbox
Post air filter side of the airbox
While doing this i decided to seal off the resonator hole in the intake pipe too. I used a bit of 3M aluminium tape for this and it sticks really well to plastic. This helps.
Impressions
Honestly I did not expect much improvement in drive-ability before i embarked on this airbox smoothing job. I was expecting an improvement in breathing at the higher RPM band. When i took it for a drive after the smoothed out and resonator sealed airbox was installed there was a very noticeable improvement in the throttle response and torque from just past 1500RPM to a much noticeable improvement from 2000 RPM upwards, much like a mild rush! At higher RPM near the redline it is considerably better than stock with the engine feeling eager to revv out. When the car is running on headers in place of the stock cat-con exhaust the stock airbox wasn't able to keep up with the airflow demands and it used to hit a brickwall near 5000 RPM, so the BMC OTA was the only option when i had the exhaust headers installed. With this smoothed out setup the engine goes clean till the redline. What this means is that the smoothed out box is flowing well enough to support the headers! All this with the stock paper filter! I'll try out the K&N stock replacement filter in this airbox and let you know how it goes.
NVH
Yes, as expected the engine noise is slightly on higher side, but not too intrusive. There is a light booming sound at about 4500RPM, i think its cool :) Anyway the stereo should help drown that out!
Improving it further
Another interesting bit about air intakes in Bell's book, 4 Stroke Performance Tuning, the author states that most of the factory airboxes have a smaller air inlet opening to minimise the intake suction noise. The author further suggests that the airbox's air inlet opening should be of the same size as that of exit on the throttle body side. The Swift's stock airbox has a rubber funnel at the tip of the airbox inlet pipe, this funnel instead of flaring out like a bellmouth, reduces in diameter before opening up slightly.
I bought a length of 60mm ID air inlet duct from ebay and installed it at the end of air box after taking off the (now sealed) resonator section. A larger bellmouth, which i got with BMC OTA, is installed on the other end of this duct and the duct is then routed to the opening just behind the front grill section. The airbox now gets air from outside of the engine compartment at all times, the BMC bellmouth helps direct the air into the duct efficiently.
Here is how it looks. The duct you see in the photos is a 70mm ID an outer duct over the 60mm ID duct inside. The outer duct offers a bit of heat insulation and abrasion resistance. The gold reflective tape was applied as the part of heat management within engine bay. I will make a post about it soon.
Impressions
Honestly I did not expect much improvement in drive-ability before i embarked on this airbox smoothing job. I was expecting an improvement in breathing at the higher RPM band. When i took it for a drive after the smoothed out and resonator sealed airbox was installed there was a very noticeable improvement in the throttle response and torque from just past 1500RPM to a much noticeable improvement from 2000 RPM upwards, much like a mild rush! At higher RPM near the redline it is considerably better than stock with the engine feeling eager to revv out. When the car is running on headers in place of the stock cat-con exhaust the stock airbox wasn't able to keep up with the airflow demands and it used to hit a brickwall near 5000 RPM, so the BMC OTA was the only option when i had the exhaust headers installed. With this smoothed out setup the engine goes clean till the redline. What this means is that the smoothed out box is flowing well enough to support the headers! All this with the stock paper filter! I'll try out the K&N stock replacement filter in this airbox and let you know how it goes.
NVH
Yes, as expected the engine noise is slightly on higher side, but not too intrusive. There is a light booming sound at about 4500RPM, i think its cool :) Anyway the stereo should help drown that out!
Improving it further
Another interesting bit about air intakes in Bell's book, 4 Stroke Performance Tuning, the author states that most of the factory airboxes have a smaller air inlet opening to minimise the intake suction noise. The author further suggests that the airbox's air inlet opening should be of the same size as that of exit on the throttle body side. The Swift's stock airbox has a rubber funnel at the tip of the airbox inlet pipe, this funnel instead of flaring out like a bellmouth, reduces in diameter before opening up slightly.
I bought a length of 60mm ID air inlet duct from ebay and installed it at the end of air box after taking off the (now sealed) resonator section. A larger bellmouth, which i got with BMC OTA, is installed on the other end of this duct and the duct is then routed to the opening just behind the front grill section. The airbox now gets air from outside of the engine compartment at all times, the BMC bellmouth helps direct the air into the duct efficiently.
Here is how it looks. The duct you see in the photos is a 70mm ID an outer duct over the 60mm ID duct inside. The outer duct offers a bit of heat insulation and abrasion resistance. The gold reflective tape was applied as the part of heat management within engine bay. I will make a post about it soon.
Apart from having a larger air inlet opening, less restrictive breathing, a possible ram effect at higher speeds an additional advantage with this setup is that now engine gets its airfeed from outside of the engine bay directly, that means cooler air. IAT reading confirms that.
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