DIY Intake – Key Considerations
June 6, 2025If you’ve realised your intake is a restriction and you want to do a DIY intake, these are the key factors to take into consideration when designing your new setup.
The top priority is zero vacuum at the throttle body/turbo inlet.
Here is an excellent series of articles demonstrating how we can see where and how bad our intake restrictions are.
MAF Sensor Placement
I’d recommend finalising the placement of the MAF sensor before doing anything else. The MAF sensor will dictate the position of everything else.
Bends
It’s essential that there isn’t a bend of any description within 20cm of the sensor. Mounting the MAF directly to the air filter is fine, we just want the air to have a straight path through the sensor.
We don’t have to mount the MAF sensor at the start of the system, we can mount anywhere, as long as there is a straight pipe leading to it.
Diameter
If the existing MAF is a restriction then you need to chose a diameter that will give you the extra flow you need. A pipe area comparer can help you, here’s one.
I would say at a minimum try to keep the rest of the intake pipe diameters within 15-20% of your MAF diameters (pipework diameter being smaller than MAF internal diameter). MAF housings can have a lot of vanes before the sensor to smooth flow over the sensor, these can cause a restriction, so MAF housings tend to have larger internal diameters than intake pipework. Having said all that, I don’t think there is any downside in having all the intake pipework the same diameter as the MAF internal diameter.
It might be possible to go too big with the MAF housing diameter. At idle for example, with a big housing, the air speed over the sensor may be too low to get an accurate reading.
As a general rule, I think it’s fair to say, chose the MAF housing that’s got 10% headroom in power to get the accuracy at idle and full power. We want the smallest housing that isn’t a restriction at full power and also gives good accuracy at idle and low load conditions.
MAF Calibration
If we are putting our MAF sensor in a bigger diameter housing, or perhaps we are changing our MAF sensor completely, then we will need to recalibrate our MAF sensor signal so it gives the engine ECU an accurate picture of the air entering the engine.
We may even need to recalibrate our MAF sensor changed location, perhaps we have put the sensor in a better position than before. This can be done easily with a dedicated product such as MAF CAL.
General DIY Intake Considerations
When we have our MAF placement chosen, we can move on to route and sizing the other pipes.
Diameter Transitions
Most of the time we will have to neck down the diameter of the intake pipes to meet our throttle body or turbo inlet. Try to get the transition to a shallow neck angle (less than 12 degrees) as possible. In other words to make the transition as gradual as possible.
If this isn’t a possibility, fitting a velocity stack to the throttle body/turbo inlet and have the outside diameter of the trumpet/velocity stack the same as the internal diameter of your intake piping.
These are perfect world solutions. Normally we have to compromise here.
Lips
Internal lips, where a silicone joiner connects to a solid pipe, these lips in the pipe can cause turbulence, keep them to a minimum.
MAF sensor housings can have pretty thick walls, say internal diameter 70mm and external 80mm. If we are connecting our air filter to the MAF housing and out air filter neck has an internal diameter of 80mm, we have a 70mm lip inside the pipe which can cause turbulence and possibly a restriction if we are at the limit for our power level.
The factory rubber hose that connects to the MAF housing usually has an internal edge so the transition is smooth from hose to housing. If you can do something similar, that would be beneficial. Easier said than done I know.
Heat Shielding
If we are using alloy pipe and that pipe runs close or over the exhaust manifold (VW/Audi TFSI/TSI motors for example), the metal can get too hot too touch. Adding some cheap aluminium, dimpled heat shielding can reduce the metal temperature massively.
However, having said all that, I wouldn’t expect much of a change in the temperature of the incoming air as it passes through the pipe so quickly. It’s nice to keep the pipes cooler but as long as their not super hot, I personally don’t think its a deal breaker.
Airbox
What we don’t want happening is the intake pulling air from the engine. We should do everything we can to make it as easy as possible for the air filter to pull in air that has the same temperature as outside of the engine bay.
Air Filter Cage
In my experience, any air filter that has some sort of outer metal cage is less than ideal. This cage can get super hot and because the air is passing through (not next it it like in a pipe) it can heat up the intake air.
I choose filter which just have the filter medium visible.
Air Filter Material
From what I’ve read, it is very hard to beat a good paper filter of suitable size. They flow as well as so called “performance” filter materials, they have better dust capacity, which means they will flow more for longer than a performance filter and they also filter out more dirt. And if there may also be a case to be made that says the air, after it passes through a paper filter is more uniform than other filters mediums. If we are mounting our MAF directly to our air filter, this is a plus.
In short, a suitable sized paper filter is my choice. Fortunately we can search for air filters by dimensions on the Mann Filter website here (use the search for filter by dimensions option).
K&N also has a search by size function here. Find the filter you need and then check the “cross-reference” section to find the equivalent paper filter.
Bends
Keeping them to a minimum. It’s surprising how much restriction a bend can have. This is an excellent article on custom intake design. The author test numerous DIY intake setups and measures their respective restriction with different bend angles.
DIY Intake Guide – Summary
That’s pretty much everything, use common sense, mount the intake securely and you should end up with an intake with zero restriction.
MAF Calibration for Custom Intakes
MAF Scaling/Calibration with MAF CAL
Calibrate for MAF sensor and/or MAF housing changes on the fly, without needing a laptop. Permanent or temporary installation. Fast & easy MAF scaling.
MAF CAL by MoviChip
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