Engine

Drivetrain

Misc

Modified MKIs

Intake:

First off, the K&N drop in filters do not give any HP increase whatsoever.  This is where the powermax modification comes in.

The powermax filter setup involves eliminating all of the tubing for the stock air intake system, relocating the MAF higher up, and directly mounting a dual cone filter such as the powermax filter. This gives 5 hp across the board as proven on the dyno. 

So how do you do this mod yourself?  Seeing as this is not a bolt on kit per say, some custom work must be performed by you to make this work.  You will need: 

• a dual cone reusable filter
• a small section of tubing to connect the MAF to the intake
• a way to cover the filter from the rain
• a way to re attach the A/C idle up line (if applicable) 
• a way to bolt the new assembly to the car.

Hooking up the A/C line is an easy one.  At most hardware stores, small brass fittings and nipples are sold, one particular nipple working perfect for this application.  Simply drill a hole into the tubing that is a little smaller than the fitting to be used and screw the fitting in.  Then source a small piece of tubing that will fit on the newly installed nipple and on the old metal fitting for the A/C idle up.

The hardest part of this process is creating a bracket.  This will also vary as the 85/6 cars have different bracket mounting locations vs the 87+ cars.  Some create brackets that will mount to where the MAF was originally located, whereas some will make brackets that will mount onto existing mounting locations higher up in the engine bay.  Many different ways can accomplish the desired goal, a little ingenuity will go a long way.  The web pages below will once again touch on this.

Another problem to face is that once the new filter is in, it will be directly below the left engine vent, thus in the direct path with rain, which will over time destroy the filter.  Once again, with a little ingenuity, one can make a shield of out aluminum sheet that can be purchased from a hardware store, OR can cut a piece of plexy glass to be mounted above the filter.

More info on the Powermax setup found at Dave Aucott's and Rob Sans page: 

IMPORTANT NOTE: When doing this mod, don't touch the screws on the MAF.  The harness on the MAF disconnects with a metal clip on the harness.  If you loosen the screws on the MAF, you will be breaking solder joints in the MAF that will be VERY difficult to fix.

Exhaust:

The good news is that there is a TRD header and many different exhaust systems. The bad news is that the TRD header gives maybe 1-2 extra hp and the exhausts give only about 3-5 hp. The stock exhaust manifold is quite good, and there is not that much HP to be made by replacing it if your overall engine modification level is low. The benefits of the TRD header may be more pronounced if many mods are made to the car, but it does not do much until then. One other note about the TRD header is that if you do buy it, DO NOT use the included gasket, it is very flimsy in comparison to the stock one. Buy a new gasket for the stock manifold, or you will be in about a month after the TRD one breaks. TRD has also said that equipping the MKI NA with an SC exhaust is good for a few hp as it is a less restrictive design.  Once again, like many other modifications that can be made, there are many more headers and exhaust systems that are available in Japan that may be worth the effort for you to try and locate.

As far as exhausts go, these are some of the more common:

• MKI SC: The stock Mr2 SC exhaust can be fitted on the NA to give a somewhat less restrictive exhaust.  While it is not a direct bolt up, it is close.  While you can use a bolt on adapter or weld it on, the easy way to do the install is by modifying the SC exhaust flange.  When you buy the exhaust from Toyota, be sure to order the SC exhaust gasket.  Step 1 is to use a hacksaw to saw off the muffler pipe that extends past the flange.  Step 2 is to grind the bolt holes on the SC flange into slots so that they are just long enough to bolt onto the stock NA cat.  Once these things are done, it will bolt right up.
• HKS: Nice sound, but very little HP increase.  Some reliability concerns.
• ANSA: The dual tips look good, but once again, not much HP gain. This system was also discontinued a LONG time ago. Heavier than stock.
• JANSPEED: Must be imported from the UK. It does away with the CAT, and provides the most HP out of all the exhaust systems. With no cat, it is louder, and will be near impossible to pass emissions if that is something that you have to worry about. The exhaust can be purchased from the large mail Order Outlet Demon Tweaks in the UK, or from Janspeed themselves.
• SUPERTRAPP: A Supertrapp can be bolted right on to the back of the exhaust manifold giving the car a very racecar like sound, it is loud however.
• DYNOMAX: For an few easy hp, a Dynomax can be welded in place of the stock muffler, making a somewhat loud exhaust.
• MONZA (by Pacesetter) Cheap (~$150) and are reported to give a decent sound.  Has dual-tipped chrome outlets and a black exterior

TRD Header Notes
 

SC Pulleys:

Because the pulley on the SC has an integrated clutch, a small replacement pulley to increase the boost cannot be easily made. As a result, the aftermarket has instead reversed the problem and created larger crank pulleys. Here are some of the more common:

• HKS: The was first pulley on the market that was introduced years ago.  Gives 10 psi of boost.
• Blitz: This pulley will give up to 12 psi.  There have been some corners about reliability with this pulley.  One owner has reported the pulley itself broke.
• Cusco: The ultimate in pulleys, the Japanese manufacturer Cusco sells a pulley larger than both of the above that will max out the SC giving around 13-14 psi on a stock head.  This pulley will spin the supercharger close to its limits. As a result of this high pressure increase and because of the low efficiency of roots blowers, intake temperatures will be very high.  Be careful using this pulley in areas that have high ambient temperatures, and/or cities that don't have 93 octane gasoline.  Colder spark plugs are recommended with this pulley.

For more SC info and performance upgrades, please read the SC Notes.
 

Cams and Cam sprockets:

In the search for more power for your MR2, cams are a somewhat good place to start. The stock cams are (as in most toyotas) very mild, and the engine could benefit greatly from larger lobes. However once new cams are put in, it can be difficult to get the correct of fuel metered in.

There are currently 3 different manufactures of cams for the MKI NA. Both HKS, TRD and Web make cams that can be used in both the SC and the NA. Although the cams from the 4A-GE can be used in the 4A-GZE, there are custom cams made just for the 4A-GZE. 

HKS makes many different cams that vary in both lift and duration. They also make adjustable cam sprockets to be able to fine tune the cams to exactly how you want them.

The TRD cams are also well known and once again come in a variety of choices from mild to wild.

Web also makes 2 camshafts for the MKI, those being the #294 and the #101. The Web cams are a less expensive alternative to the HKS cams, while still being of high quality. Dave Aucott offers the following on the Web cams:

WEB Cams, #101 and #294 Grinds

Web now offers a 3rd grind, called the #577.  It fits between the #101 and the #294 as far as lift and duration goes.

While often working well out of the box, it has usually been shown that another 5-15 HP can be found with adjustable cam sprockets.   These will let you adjust the torque curve to find the best compromise of high rpm HP to low rpm torque.  And while seat of the pants tuning may let you find what you think is more HP,  the best results are far more often found when using a dyno to tune.  This is another costly piece of the puzzle that will have to be taken into consideration.  All this however is true usually only on aftermarket cams.  Little will be gained on the stock cams with adj cam gears.
 

EFI tuning:

Once many engine modifications are made, it is a natural choice to upgrade to an adjustable EFI. A custom EFI will give the user greater control over new injectors or a higher flow fuel pump to handle the engines new found ability to inhale gasoline. Because of the way the Toyota EFI system is designed, there is no easy way to swap out chips to give added fuel. The only way to "chip" or add an adjustable fuel system to the factory EFI is to piggyback the new system on. This is accomplished by the new component reading, along with the factory ECU, input signals, and after they come out of the stock ECU, it will modify them to the specifications put in by the user.

G-Force engineering offers the only adjustable piggyback system for the MKI that I know of.  It will change fuel, timing, rev limit, TVIS point, plus more.  It however can only be set by the shop doing the reprogramming.  There are a few shops throughout the US that offer this upgrade.  This is a good option if you plan to mod your car to a certain extent and then stop.  For those whose car's are in a constant state of flux, a fully adjustable EFI might be a better choice.

Simco also has made a chip for the car. Please look at Jorn Inset's web page to find out more about the Simco chip:

Simco Chip
 

TRD:

Back when TRD was heavily involved with modification for the MR2, they had printed up their upgrade recommendations for the MKI. It included showing their different products, along with other valuable MKI info.

Dave McCristall from the Toyota Mods list had sent the following:

TRD AW11 Engine/Suspension Prep Guide

Also, for those that want more than just the regular old mods, check out the specs for the TRD Atlantic engine, and see if you can deduct for yourself that it won't work too good on the street. ;)

Atlantic 4A-GE Engine specs
 

Fuel Mods:

This is old trick that comes courtesy of the classic, but sometimes incorrect book called "Toyota Performance Handbook" (ISBN: 0-87938-320-8) is the A/F Ratio mod, along with the MAF mod to help the engine rev more freely. Please be careful when making these mods, as the A/F ratio mod doesn't really help if you have not done anything to you car, also, the MAF mod is not overly significant either. 

Jorn Innset's edited version of the article:  A/F ratio and MAF Mod