MAF Mod

The "MAF mod" sometimes referred to as "CAP's MAF mod" is a mod first engineered by "Cap Weir" - a user on Spyderchat. The mod creates a ignition timing advance resulting in an increase of about 10bhp and 10ft-lbs of torque for most of the rev range, up to about 6000rpm. Peak power is also reached sooner, at 6200rpm instead of 6400.

Whlist the maximum output is untouched, this mod allows you to access more power most of the time, but especially in lower gears or at lower speeds, significantly impacting acceleration. Fuel effeciency is effected positively also.

Technical Details

The mod in short consists of 3 elements:

• The removal of MAF calibration vains
• Elevating the MAF by 0.25 inches/6.25mm
• Replacing the stock injectors with 2ZZ injectors

The changes to the MAF housing and positioning cause the MAF to read consistently lower than it typically would. This alone creates an issue - the MAF is critical for the ECU to determine how much fuel should be injected into the engine. This is especially true in open loop, where the o2 sensors aren't used. With the MAF reading low, the ECU will command less fuel be injected, which will result in lean running - a potentially engine failure causing situation.

That is where the 2ZZ injectors come in - with higher flow compared to 1ZZ injectors, but the exact same fit, they can easily be installed and would make a typical 1ZZ run extremely rich. This makes them an ideal candidate for solving this issue - Cap experimented with various MAF spacings until he found the ideal spacing to make the engine run normally (in AFR terms) with 2ZZ injectors fitted - this spacing turned out to be about 0.25 inches, or 6.25mm.

Most users using this spacing report the engine still runs slightly rich, with long term fuel trims of about -5 to -7.5%. My vehicle reports -6%. This isn't outside of the %10 to -10% range most consider to be safe, nor is it especially abnormal given the cars age and the tendency for japanese cars to run slightly rich. Getting -5% on a stock 1ZZ wouldn't be abnormal.

Application

Install

The installation process is a simple one that consists of only a handful of steps. It can relatively easily be done within an hour, although accessing the injectors is fiddly. You will need:

• A set of 2ZZ injectors, preferably made by Denso
• A MAF sensor - they can be 3D printed. ABS is advisable
• Something grabby - like a good pair of pliers
• New injector gaskets (optional)

The injector swap is exactly the same as any other, since the 2ZZ injectors fit perfectly into the 1ZZ ports.

The hard part is removing the calibration vains from the intake. Just before the MAF sensor, in the pipe in the Airbox, there is an insert with 2 vains on it. You essentially need to use brute force to remove the insert.

Then, place the spacer onto the MAF. You generally need to remove the gasket (this will not cause a leak) - now is a good time to clean it also. Then simply reinstall the MAF - the stock screws should reach.

Finally, finish by resetting the ECU. Remove the EFI-1 fuse from the engine bay fuse box for at least 30 seconds. This resets the ECU without also deleting other things like your radio settings.

Compatibility with intakes

Aftermarket intakes often cause issues with MAF readings by placing the MAF into a pipe that does not match the original. The same applies when you want to do the MAF mod, if you don't use a matching intake pipe - 2.75" ID with no vains - where the MAF is inserted, it could have adverse effects.

The most commonly reported form of this is the MAF being placed into a 3" housing. This causes the air to slow down, decreasing the reading, and making the engine run lean.

However, if you use a MAF housing that matches what you end up with after the MAF mod, the intake will work fine, retaining the effects of the mod whilst also adding the mods of the intake system. The best way to do this is to use a 2.75" 45 degree connection to the TB, followed by a 3D printed ABS MAF housing using a design by superhero, finishing with a 3" filter - I recommend PRORAM.

This is not only easy to create, but it also places the filter in the best location for peak power. A slight increase in diameter going from the TB to the filter is shown to increase power.

Effect

A lowered MAF reading combined with a matching amount of overfueling leaves you with the ECU beleiving the engine is under less load than it actually is. In response to that, the ignition is advanced.

The real world effect of that is slightly improved effeciency and a significant power increase throughout most of the rev range, although peak power is not increased.

Notes

• 21/08/2025 - Page populated

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