There has been a long standing debate in the E46 community about “cold air” and “aftermarket” intakes and their efficacy in our cars.
I wanted to investigate this topic further but instead of looking at temperature, I wanted do look at geometric differences and how geometry would affect the pressure entering the engine.
For my final year engineering undergrad thesis I chose to investigate intake geometry and what effects it has on engine performance. I secretly did this so I can have an excuse to develop an intake for my E46 track car and find out if it's actually doing anything. (Don't tell my supervisor)
I did a lot of research into geometry design, conducted dozens of CFD simulations, and created a 70 page thesis that explained it all... But nobody has time to read a 70 page undergrad thesis. So here is a summary of the important takeaways for E46 owners.
Being that our engines are naturally aspirated, we can only use the pressure available in the atmosphere. For those of you that are boosted, you don’t need to worry about this, but keep reading because I have something for you guys too!
Now that atmospheric pressure isn’t actually what ends up in our combustion chamber. The combination of friction losses, turbulence, changes in cross-sectional area, and air filter restrictions all add up to reduce the useable pressure entering the engine.
METHOD
This leads me to the actual analysis. I got a chance to run a CFD analysis on an OEM air box, i used k-omega SST turbulence models and a mass flow rate of 0.17 kg/s as calculated to be the maximum mass air flow rate of the M54B30 at peak power.
This was a simplified geometry to make the simulation easier. Air filtration was omitted and we are assuming steady state conditions.
RESULTS
I’ll skip over most of the simulation stuff and get to numbers. The difference in inlet pressure and outlet pressure (the amount of pressure lost as the air volume travelled through the air box) was approximately 1800 pascals or 0.3 psi. I’ll be honest when I saw this number I was shocked at how low it seemed. I thought surely this bulky thing with massive resonance chambers would have much higher losses.
But that’s the number I got. So I moved on to a re-designed version of the DINAN fog light air intake. I made this design myself with inspiration from the now discontinued model from DINAN and I was shocked at the pressure drop.
60 pascals was the delta. Which is 0.0087 in freedom units. Effectively (but to remain scientifically accurate, not actually) no pressure loss.
That’s a recovery of 1740 pascals or 1.7%. Which after doing some reading, is incredible improvement.
What does this mean in terms of output power?
Well I can’t directly translate this to output power unless we run some dyno tests.
But if we live in dreamland and assume all 1.7% improvement directly translates to a 1.7% improvement in power for the 225hp M54B30, that is a (idealized) 3-4 horsepower gain!
CONCLUSIONS
This lead me to a few conclusions:
1. If you’re NA there are some power gains to be made from the intake system but they’re not the end all be all.
2. There is more investigations to be made as I made some assumptions in this study, and while they’re not substantial, they can have an effect on the results.
3. Since conducting this study I have been researching more into air system design as part of my final year thesis in school, so I will be coming out with more information soon on better designs.
BOOSTED AND TURBO OWNERS
I am interested in developing custom intake systems for your setups, if you have a car that is boosted I would love to work with you in getting a fully optimized and CFD tested intake in your car!
DISCUSSION
Let me know what you guys think of these results. I have been running that intake since designing it and I honestly love it just for the throttle response improvements and the sound it makes. If you guys are interested in putting this intake on your own personal cars, send me a PM and I’ll happily ship on to you!
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