Fitting a Boost Gauge

What is a Boost Gauge and why do I need one?

On cars fitted with a turbo, the air flowing into the engine for combustion is compressed rather than being allowed to flow in naturally (as in a normally aspirated engine). The advantage is that compression means more air can be forced into the cylinders, and a combined with higher fuelling rate, results in an increase in power output from the engine. The pressure of the air (commonly referred to as ‘boost’) is measured in standard units (PSI or BAR) and can be checked using a boost gauge. Boost gauges are useful for troubleshooting if the car is running lower boost than expected and can also be employed as preventative measure: i.e. if you suddenly see the boost drop when driving you know something is wrong.

This guide will give a brief set of instructions on fitting a boost gauge using a few pictures I have from when I fitted one on my 306 DTurbo.

What you need

– Boost Gauge
I used a standard 52mm diameter mechanical gauge for my install. Having a mechanical one means running a section of tubing from the engine bay into the car to measure the pressure. The alternative is an electrical gauge which requires a wire rather than the tubing. In either case, there will also be a few wires to connect to +12V and GND for illumination.

– For the mechanical solution, you should get with the gauge, a fitting kit consisting of a T-Piece, some tubing and maybe other fittings. If you didn’t, then any DIY store should have these things quite cheap. Also, get some jubilee clips to secure the fittings.

– Somewhere to mount the gauge
I got hold of some A-pillar mounts for my gauges but a common place is in the dash itself if you are prepared to do some retrofitting.

In the Engine Bay

The first thing you need to do is locate the boost pipe. In the case of the 306, it is connecting the intercooler to the fuel pump. The pipe itself is quite thick, but the internal diameter isn’t so make sure you get a suitable t-piece. The plan is to split this pipe in half and fix the t-piece in the middle and take a feed to the boost gauge. The image shows the approximate location of the pipe circled red (ignore the orange pipe bit; the picture was taken after I fitted the t-piece and that was added to lengthen the existing pipe):

Fit the T-piece, either using an extra bit of piping like I did, or cut your existing pipe and fit it between the two halves. Secure each joint with a metal jubilee clip to ensure a tight seal so no air can escape.

The above photo was taken from below the joining section looking up – just in case you were confused by the perspective.

You can now connect the boost gauge pipe to the T-piece as shown in the picture, again securing it with a jubilee clip. This now needs to be fed around the engine block and through the bulkhead, into the car. I used the hole and grommet I had already made when wiring my amplifier so this was straightforward – it’s likely there will be an existing one you can use so look around. Try not to make any kinks or sharp bends with the tube, as this will impede air flow and give an inaccurate reading on your gauge.

Inside the Car

Now that you have fed the boost pipe into the car, it needs to be routed to wherever you are planning on mounting the gauge. In my case, it was on the driver side A-pillar.

Once there, it should simply be a case of connecting into the inlet on the back of the gauge. At this point, connect up the electrical connections on the gauge as well. On mine there were +12V, GND and LIGHT leads. Obviously connect +12V to a fused live wire (disconnect batter before playing around with power cables!) and GND to a chassis point or GND wire. The LIGHT lead, when switched on, will activate the illumination on the gauge face. You can connect this to your headlight switch for it to come on automatically when you turn your lights on, or as I did, to a custom switch panel so it can be controlled independently.

In the image above, the top one is the boost gauge, the bottom one is an oil pressure gauge (see a different article for that one). The gauges I used are black when off, and illuminated backlight red and white when on. The pillar pods were made for a 306 and fit flush with the pillar. I mounted the switches below the gauges – to the right of the steering wheel so they are out of the way but easily accessible.

Final Words

As always, this guide is based on my own experiences and I’m NOT responsible if you mess something up. Feel free to comment here if you have any questions or if you have any specific issues, use the forum and I can try and give you a hand.

Leonard