So I decided I had enough of taxi drivers and cabbages with a license cutting me off and doing dangerous and stupid things on the road in front of me and nearly taken me out of it too. Seen as mounting a machine gun or ram bars on your car to deal with things the way I would like to is illegal so I figured id at least wake them up a little. So as you would have read from the title of this post, I have fitted a train horn (airhorn) to my F11 530d. It was sold to me as a train horn so that’s what I’m calling it, you can call it an airhorn if you like…..you can call it Sally if you like, I’ve started with train horn so I’m sticking with it.
So this wasn’t something I was in a hurry to get done, which meant this took a really long time to complete and also it was expensive seen as I changed my mind about how to go about it more than once. What I would advise is, if your going to do this then decide if you want a cheap system or not. If cheaper was your option then buy a complete kits from eBay, these will be the red horn ones with a small compressor for 50 quid. I heard these before and I don’t think they had the grunt I was looking for. The expensive option was to design and build one myself which is what I had to do to get the results I wanted.
So here is what I ended up doing. Firstly I purchased a large train horn. The one I chose had a review that said “it makes the Saturn rocket launch sound like a wet !Removed!!” this had me sold. So I bought it. What I was not told was that this will only work as you want it with an reserve air tank. Here is a link to the same kind of horn I purchased Word of warning if you decide to use the same train horn, that reservoir in between the horns makes it sound like a boat horn. This adds a delay at the beginning and at the end of the blast. It kind ruins the surprise. I removed it and put a plug in it and this gave the sudden start and finish to the blast of air.
Next I decided to purchase an air tank. Now seen as the space in a F11 5 series is limited I decided to go with a small 1ltr tank. Which as it turns out was a smart idea. The original idea was to mount this in the engine bay but as I’ll explain later that changed. As I didn’t know when ordering the air tank how many connections I needed on the tank so I just ordered four, then I could block up any I don’t use. I also didn’t know what size connections I was going to have on everything else and the tank comes with G1/2” holes. So a decision needs to be made early as what sizes connections you intend to use and order in plugs and/or reducers for each fittings needs
Next up was an air pump. So I found this great place to supply these brilliant 12v air compressors. They are simple, quite and seems far more durable than the other sh*t I found online. They sell out of these regularly but if you email them they will put you on the list of orders before the next batch goes on sale. They were very helpful and highly recommended. These compressors run up to 120psi and at a max of 10 Amps.
To keep all this in check I decided to buy a pressure switch to turn off the air compressor when it reached 100 psi and then cut in when the horn is used and the pressure drops below 70 psi. Finding a good pressure switch proved a lot harder. The one I went with works but I don’t trust it, so I will change it at a later date for a better one. This seems very Chinese in construction. But for now it works.
The pressure switch would need to be connected to the air tank but also have a supply from the air compressor so a t-fitting was needed. The one I used ended up leaking because it was made of brass. I changed this out for a steel one which solved my air leak. So I would not recommend the brass fittings. I have attached a link but this is just for illustration purposes.
Knowing that I was going to need an inline fuse or two, I made the decision to get them while I thought of it. These ones are really nice feel to them and a good price.
Finally, I found steel braided air lines for the connections between the compressor to the tank and from the tank to the horn. Remember the supply from the compressor to the tank needs a one way check valve in it. This is not necessary for the other line. These ones are really good quality and the shipping from America was way faster than from the stuff from Germany.
Ok so those are the parts I used but how are they assembled? If we think about the plumbing part first. The compressor pumps the air out via the steel braided line with a one way check valve into the air tank. It leaves the air tank via the t-piece where the pressure is monitored by the pressure switch. The pressure switch decides when the compressor runs and shuts off (70-100 psi). The air leaves the t-piece and travels through the second steel braided air line (no one way check valve) to the horns where it is stopped by the solenoid on the train horn. When the solenoid is activated/deactivated it allows the air to pass into the horn or not. In the horn there is a reservoir, I would personally recommend removing this. If not the air will fill the reservoir first and thus creating a small build up on sound as the air exits the horn until the pressure fills the reservoir and then the full air pressure will exit creating a loud blast of air. When the solenoid is disconnected and closes the air no longer passes into the horn and the residual air continues to exit the horn leaving the blast fading out until all pressure is gone. Removing the reservoir and putting in a blank cap gives instantaneous blasts of air directly from the air tank. Below is a picture of the way it was originally connected.
So where on the car did I set this up? I drive an pre LCI F11, which as you know is the estate version of the F10. I have no idea if this will apply to the F10. I did originally plan on putting the horns in the engine bay on the right down at the back very low but as the tank and compressor had to also go in I changed my mind.
This F11 is a single side dual exit exhaust on the left. Underneath in the center is a black plastic box which houses the air compressor for the rear air suspension (yes I did think about connecting to that and no it will not work). On the right hand side is another black plastic box which is empty and probably just to aerodynamically fill the hole left behind from the non-use of the dual exhaust system. This is where I intended to fit the system. The box is held in by a few screws and plastic tabs. In the picture of the plumbing you can see the layout of the box. Note* inside the boot of the f11 on the right is a storage compartment with space for two bottles. This compartment hangs down directly into the area I planned on using for the train horn system. Hence the gap between the compressor and the air tank. You can probably see in the background where I cut a small part of a bracket out to make it the horns fit in, this may not be necessary for you depending on your layout. I changed my tank set up a little which made this unnecessary. I will weld back in the brace later.
Some advice. When you decide where to locate the set up and have it all plumbed together, check for leaks. Power up the compressor and fill it with air. I jerry rigged the electrics to do this. You can use a drill battery or a 9v square battery to power the horn solenoid. I’m glad I did. Because I found that the brass t-piece was a weak point and leaked like a cheap plumbers job on a Friday evening. I replaced the t-piece with a steel one and used tread lock on all the treads. Do not use Teflon tape as it will leak and give the thread lock a few hours to set before testing. To test for leaks, get a spray bottle filled with water and a small drop of washing up liquid. Spray it on all the joints and fill the system with air.
The top picture shows the t-piece leaking and the bottom one shows the jerry rigging of the electrics just to get the compressor to pump air into the system. Like me, its ugly but it works. PS. Note the sound deadening under the compressor.
Now we have to talk about the ugly bit of electrics. There are a number of different ways to wire this up but here is how I did it. Firstly, I would like to point out that if you are wiring up anything with 20-30+ amps you really should use a relay to switch the power. As the compressor I am using only draws a maximum of 10amps, I decided that it may not be necessary. So this is the method I used.
Also you will note from the diagram that there are two inline fuses on the positive supply from the battery. The car battery is already grounded but the compressor and solenoid need to be grounded to the body or frame. I used the grounds in the boot behind the right rear light cluster. Good electrical wire is important here and be sure all connections are clean and strong. I used male and female connectors and put heat shrink over the connections to protect them and stop them from coming apart. This also adds the ability to disconnect anything without cutting any wires by just removing the heat shrink. Ideally the use of color coded wires would be ideal. As I had a huge reel of only blue wire, this is what I used.
I installed a simple momentary switch on the dash above the small compartment by your right knee and ran the two wires through the cabin of the car along the drivers side door sills to the rear right of the boot. One of these wires was connected to the battery with an inline fuse installed in it. The other wire was connected to the terminal on the solenoid. Either side is fine but the opposite must be to ground. For the compressor power source I connected the compressor directly to the pressure switch and then from the pressure switch via a fuse to the back of the 12v power socket in the right rear panel in the boot. This was a pain because it took a lot of hidden bolts to remove the panel to access the socket. I’ve attached a picture of the rear of the socket to show it’s not as easy as unclipping the socket only unfortunately.
So now all the wiring is connected and its technically ready to go. If you were to follow the way I did it then you still have to make it all fit into that small empty area under the rear bumper. This was quite awkward to do but it is do-able. I originally had my air tank held by two pipe fittings found in a hardware shop but as this had a lip around it which stuck out, it was enough to stop the fitting so I took it off and replaced it with some large heavy duty cable ties which worked very well. Sorry I don’t have a picture of that but here is how it was as I connected it up and about to install it. You can see the pipe fittings holding the tank with the large lip around the outer part.
If you plan on using a relay here is a useful link to some information you might want on setting one up. Relay Wiring Manual.pdf
Ok, so after having it on the car for some time, here are my thoughts. I will revisit this to change a few minor things. I will change the pressure switch for a better one with a higher pressure rating. Maybe 100-120 PSI. I am quite happy with the incredibly loud blast from this monster horn but it is capable of the higher psi, so why not? The compressor is still audible from inside the car but not really loud and it only runs for approx. 10 seconds after a good blast and if completely emptied the tank (this would take a good 8-9 second blast) it takes about 35 seconds to refill, so I’m very happy with that. I could increase the capacity of the tank but after using it for a while I think it doesn’t need it.
Removing the reservoir that came with the train horns was a great idea. Its crap with it installed and without it’s as sudden as an erection in the Playboy mansion.
So would I recommend installing one? Well, it’s a lot of work and its quite expensive (my one was) but I enjoyed making it and I enjoy startling people with it (especially taxi drivers!) so yes I’m glad I have it. And in case you are wondering about the law moaning about it. It cant be seen on the car and the original horn works as usual so if the boys in blue say anything then I can say it wasn’t me!
And finally a video of how it sounds. Gotta say my phone does not do this justice.