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> Intake Modifications , improving the Normally Aspirated intake tract of the Elantra engine, from filter to cylinder head
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Intake Modifications

  • The internal combustion engine is basically an air pump, so anything you can do to improve the flow of air in (and exhaust out) has the potential to improve efficiency... try breathing through a straw as opposed to an open mouth
  • Much like your lungs, a Normally Aspirated (NA) intake system relies on negative pressure (vacuum) in the cylinders to literally "suck' the air in
  • It is also important to know that cold air is denser than warm air... the molecules are closer together. This translates to the fact that a given volume of cold air carries more oxygen than the same volume of warm air. Oxygen is a vital part of the combustion process... more oxygen plus fuel means more "bang for your buck". This is why you will see folks with bags of ice on the Intake Manifold at drag races or other performance events... also why cars with Forced Induction (FI) Turbo or Supercharger benefit from an inter-cooler; as increased pressure heats the air
  • The ideal intake tract provides a smooth laminar flow of air to the engine with minimal twist and turns
  • Improved efficiency can be realised as either increased power OR increased fuel economy... depending on how you drive
  • The basic family car, stock from the factory, is designed as a compromise leaning towards fuel efficiency and comfort which includes low noise levels... this can leave room to shift that compromise towards power which also often increases engine noise
  • The stock intake is long and tortuous with resonator boxes designed to keep the intake quiet and also to draw in engine-warmed under-hood air, so clearly there is some room for improvement
  • Realistically though, unless you force more air under pressure into the engine (Forced Induction = Turbo or Supercharger) there are only minimal efficiency gains to be had on a modern engine by improving the intake air flow... you can open you mouth as wide as you like but your lungs will only suck in as much air as they need

Basic Care and Feeding

Although strictly speaking NOT a modification, it is still important to keep your air filter clean and replace it at least as per the maintenance schedule. A dirty air filter can have a significantly negative effect on your engine's efficiency leading to poor performance and bad fuel economy. Use a new Original Equipment Manufacturer (OEM = stock) or good equivalent panel filter. You might also consider cleaning out the Throttle Body on a regular basis as the stock emissions system sends unburnt oil fumes into the intake to be burnt in the engine... this can result in an oily buildup throughout the intake tract.

Simplest Intake Modification

Upgrading your stock panel filter to a free-flowing panel filter such as made by K&N can allow more air into the engine

Types of Free-Flowing filters

NOTE: Some have a concern that these types of filters in allowing free-flowing air also allow more dust and other small particles into the engine and this author has read articles which show that is in fact the case... however those same articles do not show any damage to the engine as a result of the extra dust and these filters are widely used in the tuner and performance market.
  • Oiled cotton-gauze on a wire fame such as made by K&N or AEM not only allow increased air flow but they can be cleaned, re-oiled and reused for practically the life of the car. In this way the higher initial outlay is offset by never having to buy another air filter. When re-oiling one of these filters, avoid over-oiling as it may be possible to damage the MAF sensor. Important Information: These filters are "rechargeable" but must be properly cleaned and re-oiled. This page... from K&N details the proper technique to do so.
  • Dry Flow as made by AEM improve air flow... they can also be cleaned and re-used multiple times without any need for re-oiling

Easy Intake Modification

As described in this Do It Yourself (DIY) project... you can improve air flow by removing or bypassing the stock resonator which is in the wheel-well. In doing so you shorten the intake tract and allow air to flow more easily into the engine, while still maintaining the stock air-box. You have the option to remove the whole resonator assembly but leave some piping down into the wheel-well in order to draw in cooler outside air. Or by disconnecting the resonator (and either leaving it in place or removing it) allowing the stock air box to continue drawing in warmed under-hood air.

MAP versus MAF

Prior to late 2003 the XD/XD2 used a Manifold Absolute Pressure(MAP) sensor and an Intake Air Temperature(IAT) sensor in the IM to calculate air density and temperature for determining the engine's air mass flow rate, which in turn is used to calculate the appropriate fuel flow. From late 2003 onwards the XD/XD2 (and HD?) uses a Mass Air Flow (MAF) sensor inline in the intake tubing to replace both these sensors.
This makes it easier to fabricate an SRI, CAI or LRI in the earlier models as a straight run of tubing can be used. To accommodate the MAF the tubing must be cut and additional couplers are required. NOTE: it is recommended to keep the MAF in the same relative position (distance to TB) as stock.

Short Ram Intake (SRI)

An example of an SRI on an Elantra without a MAF sensor

  • Easier install
  • Good engine response
  • Louder engine noise
  • Looks cool
  • Easy to clean filter
  • No chance of hydrolock*
  • May increase high end power

  • Louder engine noise (extremely loud cold start sucking noise)
  • Sucking engine heat instead of outside ambient air (some people fight this off with Heat Shields and hood spacers)
  • May reduce low end torque

Cold Air Intake (CAI)

  • Less engine noise than SRI
  • Sucking cool ambient air instead of engine heat-soaked air
  • Looks cool
  • May increase high end power without loss of low end torque

  • Harder install than SRI
  • Risk of hydrolock* (which can be mitigated with a bypass valve)
  • Harder to access and clean filter
  • Some complain of a humming sound with a CAI that can be removed by using the stock black tubing from TB to MAF as in the above picture
  • 94-97 Honda Accord 4-cyl 2-piece CAI's are a direct fit for the 01-03 XD without MAF. sells theirs in the stock T/B size of 2.75" and comes with a filter of good quality.

Long Ram Intake (LRI)

A compromise between SRI and CAI, the filter in the LRI sits just behind the headlight where the battery normally is. This can be accomplished by either repositioning the battery (to the trunk for example) or by using a smaller lightweight battery such as the Odyssey PC680... This can further be improved by routing tubing from the front of the air dam (near foglight) up through the hole from the wheel-well to ensure a constant supply of cooler air as the car drives forward. An even better modification would be to build an air-box around this corner of the engine bay.
  • Less engine noise than SRI
  • Sucking cool ambient air instead of engine heat-soaked air
  • Looks cool
  • Easy to clean filter
  • No chance of hydrolock*

  • Harder install than SRI

K&N Apollo CIS (closed intake system)

As you can see in this thread..., this system has advantages from all of the above: the filter is in an air-box to minimise the engine-heat effect, it is protected from tire spray but has the benefits of a CAI by virtue of the tubing leading down into the wheel-well. In case of deep-standing water it is even possible to disconnect the tubing and drive on through the same as an SRI. It is K&N part number: RC-5052AB. Here's a link to another thread on the Apollo showing a different way of routing the flexible cold air tubing.

*Hydrolock : air is compressible but water is not, so if your air filter is submerged and sucks water instead of air into the engine cylinder(s), on the next compression stroke the engine block will tend to burst at any weak point. This should not occur as a result of the air filter just getting splashed but rather driving through deep puddles. You are advised not to drive through standing water that comes over the wheels anyway. To quote Bobzilla, "If you are stupid enough to drive through water 12" or more deep at [Wide Open Throttle] WOT, you DESERVE to have the engine blow up. The top of my filter is just over the center line of my wheel, meaning it's about 12" off the ground. To hydrolock, you'd need to completely submerge the filter with the throttle open. I don't know about you, but my tires can't handle more than 4" of standing water without hydroplaning."

Throttle Body coolant bypass

As described in this Do It Yourself (DIY) project..., "When Hyundai builds cars, they build them to be sold anywhere. To keep the butterflies from freezing open while driving in extremely cold weather, they flow engine coolant through the throttle body. This keeps the throttle body warm, which also warms up your intake air." As discussed above, colder air is better and several forum members (including this author) have survived 2, 3, 4 or more Canadian Winters with this modification and no issues of the TB butterfly freezing.

Knife-edged TB Butterfly

The TB butterfly is a circular piece of yellow metal pivoted across the mouth of the TB to control air flow as you modulate the accelerator/throttle pedal. It is about 1mm thick and square on the edges which can interrupt and disrupt the air flow over those edges. This can result in vortices at both the leading and trailing edges of the butterfly, not just at WOT but at any open throttle position. By carefully filing or grinding those edges to a knife-edge you can further improve air-flow towards our smooth laminar ideal.

Phenolic Spacer

Phenolic is a plastic resin which for our purposes acts as an insulator. Placing one of these between the IM and the cylinder head helps to keep the IM cooler... and as we already know... cooler intake air is better. They can be purchased at: Compact Divisions... or Shark Racing. Shaped like the IM gasket they are about 1/4" thick.

Ported And Polished Intake Manifold

Again in the quest to provide the engine with a smooth laminar airflow... there is nothing to be harmed by porting and/or polishing your IM. However, it may not give you much performance benefits on our 2.0L beta. The increase in airflow and speed does not seem to affect the performance numbers significantly. The most likely effect is smoothing the torque curve: as above the SRI may impair low end torque but adding a P&P IM may help to regain that torque.

Seems like there ought to be a big benefit from this but as we have determined, the real problem with these motors is in the intake chamber in the head.

This head was ported and polished by member JPJR and is running on OIML8's vehicle. You can view his Dynojet dyno sheets in the Timeslips section under the Features tab. The first sheet was before the porting and polishing and the second one was after.

JPJR ported and polished this IM with a variety of attachments on a Dremmel. He had some extra long ones so he could get all the way into the head. This is uncommon unless you get it "extrude honed". Extrude Honed is a process where a abrasive paste is pushed through the entire IM under pressure and both ports and polishes at the same time. Additional porting can be handled with a grinder to get exact openings.

Port matching is a process that matches the port openings of both the TM and IM, and the IM ports to the head ports.

Last update: Jun 12 2011, 02:08 PM by elantragt    Created: Nov 29 2007, 09:52 AM by fgummett    Edits: 155    Views: 13,388
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