One of the first modifications done to the Skyline is to fit an induction kit to rid the engine of the restrictive stock air box, which helps the engine breathe more easily. This is a very simple modification, and there are many different induction kits available. The next question is, "Which one is best?". This article relates to the 4 most popular kits available, being HKS, Apexi, Blitz and K & N.
What are the benefits of an Induction Kit?
The primary function
of an Induction Kit is to clean the air before it enters the engine, but also
to provide better air flow to improve the engines power output. The power output
of an engine is proportional to the volume of air it can ingest at any given
time, assuming that the fuelling is also set up correctly. The most minute restriction
in the air induction system will cause an engine's optimum power output to drop.
Maintaining optimum, unrestricted air flow becomes a problem when the air must
pass through a filter element. There are many different designs of filters on
the market, and each manufacturer will make claims that their design is more
effective than their competitors. Generally, the greater the air flow restriction,
the greater the power loss. Therefore, the ultimate acheivement is to choose
as filter that will flow as much air as possible, witthout sacrificing filtration
efficiency.
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Blitz Sus Filter |
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Blitz Claim:"The Blitz air filter is by far the best performing and best looking automotive air filter money can buy..." |
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HKS Mega Flow Filters |
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HKS Claim:"The ultimate in both air filtration and air flow for maximum engine performance..." |
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Apexi Power Intake Filter |
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The Apexi dual funnel Power Intake has evolved from the Apexi Super Intake filter with some subtle refinements in the design and filter element. According to Apexi, this resulted in a 10% reduction in pressure drop by utilizing an upper and lower funnel. The Power Intake reduces air turbulence within the filter and creates smooth air flow into the throttle body. Maintenance is kept to a minimum as this filter is a dry-type air filter and will alleviate the problem of filter oil from "wet" air cleaners, interfering with the air-flow meter. Apexi Claim:"Accept No Imitations..." |
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K & N Filtercharger |
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K & N Claim:"...Doubles the air flow...adds up to 15 extra horsepower..." |
How
they were tested.
The filters were tested on the quality of the filtration, simulated by using
a vacuum cleaner and millions of microscopic dirt particles. The particles that
penetrated the air filter, were collected on a secondary paper filter, so that
a fair comparison could be performed, and the results could be compared like
for like. As well as the fine particle test, the performance gains were also
measured using each of the induction kits in the test. Therefore, in the quest
to find the ultimate induction kit, the filters must not only filter the particles
out efficiently, but must maximize the amount of clean air flow, through the
filter. The winner would be the induction kit that filters the most dirt particles,
whilst acheiving the maxmimum power output of the vehicle.
Filter Type | Filtration | Maintenance | BHP Gains | Cost | |
Blitz Sus |
Dry Metallic Mesh Type Filter |
Poor |
Zero Maintenance - Lifetime Use. | 13.9 bhp | £200.00 |
HKS Mega Flow |
Wet, Foam type filter. |
Very Poor |
Throw away. Change Filter every 10,000 Miles. | 13 bhp | Replacement filters cost around £25. £200.00 |
Apexi Power Intake |
Dry, Mesh type filter. |
Excellent |
Zero Maintenance - Lifetime Use. | 14 bhp | £200.00 |
K & N Filtercharger | ![]() Wet, Mesh type filter. |
Good |
Lifetime Usage - Inspect every 30,000 Miles or 12 Months - Clean and re-oil, if appropriate. | 13 bhp | £200.00 |
Conclusion
The comparison clearly shows that the Apexi Power Intake filter wins the test, not only on filtration but also by providing the maximum power gains, with K & N, Blitz and HKS coming in second, third and last, respectively. From a filtration point of view, the photographic evidence shows that various induction kits had poor filtration properties, leaving high levels of dirt and carbon on the paper filters. Any deposits that are allowed through the filters, can potentially cause problems with the Air Flow Meters on the car, which are attached to the ends of the induction pipes. It is a fairly common fault with the Skyline, to 'blow' an A.F.M, and a large amount of carbon can be found coating the sensor in the A.F.M.
It is questionable how accurate the original source of data is, as HKS are proven to sell more induction kits than any one of the others featured in the test, and yet there induction kit rates as the worst kit in the test. This suggests that either HKS rely upon their brand name to sell their 'poorly' manufactured air filters, or that the original Japanese test was nothing more than a PR stunt to promote the lesser known equipment. HKS and Blitz continue to be the best selling induction kits in the UK, and are used by Middlehursts, Hiteq and Abbey Motorsport as their first choice when the induction kit modification is carried out.
One thing that does stand out is the fact that all the induction kits seem to offer similar performance gains, of around 13 - 14 bhp. This would seem consistant with actual power gains that have been confirmed by using a rolling road.
So the question still stands, "Which Induction Kit is the best?". Well, if you can trust the original source of data, then the clear winner is the Apexi Power Intake. For those of you that are more sceptical, the choice is probably more to do with the cosmetic looks of the induction kit, as the performance gains are very much the same.
Important Notes regarding the comparison:
- Extracts of this
article have been transcribed from a Japanese article featured in Revspeed Magazine,
August 1999.
- The original test was based upon the results found when using filters specifically
made to fit the Toyota Supra. However, the filtration is unlikely to differ,
as all the filtration materials used are the same for every model of car.
- The cost given for the filters are based on a the kit for an R33 Skyline GTR,
except the K & N kit which only currently exists for a Skyline GTS, and
are inclusive of VAT.