Car Air Flow Experiment (Sedan)

 Greetings friends,

As I'm sure many of you who have owned older cars can relate, my E36 no longer has functioning air-conditioning, so I find myself rolling the windows down on warm days to keep cool. I love the breeze on a cool summer evening, and in playing with window combinations to maximize airflow I've noticed that there are a few particular combinations that have unique effects that I wanted to experiment with and share. These results probably only apply to sedans; I'm not sure if they will perfectly translate to coupes or wagons or SUVs, but maybe future posts can address those other body types.

I've printed out diagrams of my car and drawn the airflow that I experience for each window configuration, which will be shown below with each description. I'll start with all windows down, which I feel is the combo most people go for when the car is blazing hot. I've found this configuration to be middle-ground in terms of effectiveness. It does provide a decent breeze along the sides of the car, and everyone in a fully loaded car will benefit from it. It doesn't provide much circulation down the midline of the car, but generally that's not necessary.

The basic setup, can't go wrong with it, but it's not the most efficient.

A configuration I've found to be completely useless is both front or both rear windows open. This doesn't allow any flow down the line of the car, so the result is usually very turbulent air that is more a nuisance than cooling or relaxing. Air needs a reliable path to flow along in order to be smooth.

Front windows open just creates a lot of turbulence in the back.

Next up is one of my favorite combos, rear windows and sunroof open. The best part of this configuration is that the air enters through the sunroof and flows down the back of my neck as it exits the rear windows. This doesn't cause much turbulence in the cabin, and is really comfortable in the evenings. A major drawback during the daytime is depending on your position, the sun may be shining through the sunroof onto your head and neck... not totally ideal.

My fave, perfect for summer evenings!

The most interesting combination I discovered was only having either both left side or both right side windows open. This created an unusual effect of a forwards (from rear to front) draft on the opposite side of the car from the open windows. I've given my best guess at exactly how the air is flowing in the diagram, and I can only assume that it exits the front window and enters the rear window. The benefit of this is that the driver or the passenger can have a breeze without the other having much at all! This doesn't prevent the road noise from disturbing the passenger, so use this method with discretion.

This was surprising, worth looking into further.

I hope these examples will be of interest to some of you, and I'd love feedback on your experiences if you decide to try any of them out. If I gain a meaningful amount of data on the matter, I will likely update with another blog post addressing other vehicle types or window combinations.

Thanks for reading,

Juju

BMW Seat Rail Extensions

Just a quick little post for a fun little project!

Those who know me personally know that I'm always on the search for leg room... As a 6'4" man, my knees generally wind up pushing on the backs of seats in cars, buses, airplanes, etc... Of course, I also run into this issue when sitting behind the wheel.

Tired of my knees constantly hitting the steering wheel of my 3-series, I decided it's time to do something about it. Shocked by the outrageous cost of some custom options, I opted to take care of this job myself.

With the driver seat as far back as possible, my Bimmer still had about 4 inches of room between the back of the seat and the rear passenger seat. Since the seat will still be adjustable post-modification, I figured why not take advantage of all the room I can get?!

A quick trip to Home Depot got me two steel bars, 36" long, 0.25" thick, and 1.5" wide. For only $20, I really can't complain! I knew that my rails would have to be at least 14"+, which is why I opted to get two steel bars instead of just one.

Removing the seat was surpisingly easy, but it uncovered 25 years of gunk! Kidding, it's not like this is the first time the interior has seen a shopvac... But the dust and dirt that accumulates underneath the seat brackets is impossible to reach without removing the seat, so I took the time to get it all cleaned out and nice.

                                   There's crud down there, but it's not too bad...

                                            Just vac it up and it's good as new!

I measured 14" center-to-center between the mounting bolts, which gave me the minimum distance I needed for my brackets. Adding the 4" extra legroom I wanted plus 2 x 0.75" to account for the holes being drilled offset from the end of the brackets, my total required length is 19.5" per bracket. I cut mine to 20", just to give myself a little wiggle room if I needed it.

Cutting the brackets and drilling the holes was a breeze. After very careful measuring and marking, the holes came out nicely centered, and I used a countersink bit to de-burr the edges of the holes. Not perfect, but it definitely did the job.

A little wipe-down with some IPA removed the grease, and the brackets were ready to go! I knocked down any sharp corners with a file. I decided to leave the brackets unpainted to reduce rub-off on the upholstery.

Installing the brackets onto the frame was simple enough, I just used the hardware that was originally used to mount the seat:

The bolts pictured above unfortunately we're not compatible, as the nuts were too large and did not give enough clearance for the seat to slide, so I had to remove the whole assembly again and find new bolts... The best replacement was an allen-head bolt with accompanying washer and nut. 

                                            "We've got clearance, Clarence..."

I used a wrench to hold the bolts in place underneath the rails while I mounted the seat from above. There was not much clearance below the brackets, but luckily the wrench could slide under. This was very effective, and made the installation much easier.

With the seat on top, it was just a matter of screwing the bold into all four bolts! Tightened down, the seat was very rigid, no instability or wiggling of any kind.

Now there's very little space for a backseat passenger when fully pushed back, but the seat will still adjust if needed. Generally I don't carry many passengers, so no issue.

                                       Now that's what I call leg room! Success!

Overall this was a fun and simple project. Aside from the frustration of having the wrong bolts at first, everything came together smoothly!

Thanks for reading,

Juju