AutoSpeed - Playing Instruments

Last week we looked at the design of different gauges and those used to measure temperature. Now we move on to pressure, air/fuel ratio and the rest!

Pressure Gauges

Oil Pressure

Engine oil pressure is important if you are monitoring oil surge while cornering or accelerating, want to make sure that bearing wear isn't becoming excessive, or - in a worst case scenario - need to confirm that there's in fact oil in the engine!

VDO's "Cockpit Vision" range of four oil pressure gauges take readings from zero to 80, 100, 150 and 400 psi respectively. As an example, the 100 psi gauge sells for $70, the sender is $65 and a T-piece adapter is around $15. An extended feed tube is not needed since these gauges take an electric input. However, compared with a gauge, an oil pressure warning light or buzzer is much more noticeable. A buzzer or a high intensity warning light can be simply wired in parallel with your factory oil pressure warning light for a much more eye (or ear) catching alert. It will sound (or light up) each time that you start the car, though - until oil pressure rises sufficiently.

Fuel Pressure

This 35 psi VDO pressure gauge is ideal for keeping an eye on low (ie carby) fuel pressures - this mechanical gauge retails for $165. EFI cars need to use a fuel pressure gauge rated much higher - especially if a rising rate fuel pressure regulator is used. In that case, a gauge good for 80 psi may be needed, while in more normal EFI systems, 60 psi is sufficient.

Monitoring fuel pressure is a good way of checking the flow of the fuel pump, fuel lines, fuel filter and fuel pressure regulator. A drop in pressure indicates that flow is being restricted. A fuel pressure gauge is also very useful in setting up an aftermarket fuel pressure regulator. For example, when a boosted car needs a little more fuel, you can simply plumb this gauge into the injector rail and watch how the increased fuel pressure affects air-fuel ratios (assuming you have one of these meters as well!).

Mechanical fuel pressure gauges should only be mounted outside of the cockpit, to ensure there's no possibility of a related in-cabin fire. Most people chose to locate them immediately forward of the windscreen. However, an electric gauge is much safer - especially when dealing with EFI system pressures - and can be mounted on the dash.

Turbo Boost

A turbo or supercharged car- especially a modified one - that doesn't have a boost gauge is living life very dangerously. Without doubt, the most important reason for having one of these is to determine if maximum pressure is within safe limits (a cost-effective precaution given the amount of damage over-boosting can cause). In addition, they're absolutely essential in setting up an adjustable boost system. Those boost gauges that show manifold vacuum also double as a useful tool to see if that strange rough running is caused by a vacuum hose that has blown off.

Boost gauges are most commonly available in mechanical forms, although higher priced boost gauges are electric. Electric gauges have advantages in that you don't need to get a hose into the cabin and up to the gauge. If you're mounting the gauge on the A-pillar, for example, it's a lot easier to get thin wires to the gauge rather than a plastic hose. Some electric boost gauges also have a memory recall for max boost, and other useful functions. The downside is that they are a lot more expensive than mechanical gauges.

New A'PEXi electric boost gauges can be bought (at discount prices) through the AutoSpeed Shop from $225 - but there is a cheaper alternative if you don't mind a second-hand mechanical gauge that's normally used in a different application.

In this case, scour secondhand machinery warehouses in search of gauges that have been used with low pressure pneumatic systems. These gauges are normally very accurate, and a white-faced one like this sells for $20 - making them ideal for setting new boost limits and general testing.

Other Types Of Gauges

Air-Fuel Ratio Meter

An air-fuel ratio meter (like a boost gauge) is 100% mandatory in a turbo or supercharged car running increased boost. That's because if you turn up the boost too much, you'll cause detonation and/or lean mixtures. Either way the result is piston damage, which can be extremely costly to replace. But by monitoring the air-fuel ratio under full load (using a factory exhaust gas oxygen sensor), you can decide to reset boost levels, richen the mixture or just simply back off whenever you see the meter in the lean "danger zone". Any of these measures will increase the life of your engine. But not only is an air-fuel ratio meter useful for setting up a high hp engine, it can also be useful in basic fault finding and tuning on everyday engines.

A simple meter working from the factory oh-two sensor is a broad rich/lean indicator - it should not be used to set up programmable management or to set the peak boost limit on a mega-dollar engine. However, it's still damn useful to have! A Mixture Meter kit from Jaycar Electronics (catalog number KC5195) can be bought for just $14.95 - a true tuning bargain! Go here for more details: "Cheaply Monitoring Air/Fuel Ratios".

Tachometer

Only people with cars that don't already have a factory option tacho available should look to an aftermarket item. People with a factory tacho and a dirty big monster tacho are usually just pullin' themselves! The only instances when an aftermarket tacho is justifiable are when you're doing an engine conversion, your modified engine revs beyond the factory scale, you've changed the ignition system, or when the cost of a factory tacho is prohibitive (which is quite rare).

So for those among us that really need a tachometer, VDO sells an assortment that go up to a maximum of 11,000 rpm. Of course, this top-of-the-line Eliminator version also comes with a peak rpm recall window, an output for a shift light or rev limiter and more. A tacho such as this sells for $660, while a more conventional 8000 rpm tacho that just reads revs has a $250 price tag.

Speedometer

Owners of grey market Japanese import cars will love this one. VDO currently sells a 300 km/h speedo with a back-lit LCD screen, which is perfect for replacing the 180 km/h unit. A 300 km/h speedo - now that's serious! It sweeps most of the way around the dial, is numbered in 30 km/h increments and the LCD shows the total and (resettable) trip distance. This unit cost $300, plus the cost of whichever type of sender kit is required to suit your vehicle.

Hourmeter

One gauge that's often used in powerboats to record the running time of an engine is an hourmeter. This is basically a simple timer, which is switched on and off by an electric current. Some of the things you can do with this device includes timing how long an intercooler water spray is running and keeping a running tally of how long you're on boost. For vehicles that are subjected to frequent heavy traffic conditions, it's also a great way to see when your next oil change might be due. You might not be racking up heaps of kilometres but, don't forget, your engine's still ticking over and using the oil. A proper marine hourmeter retails for $180, but shop around at electronics stores and you should be able to find something similar to do the job for much less.

This meter has numerous uses; just let your imagination run wild!

Voltmeters

While many old cars ran voltmeters, these days good batteries and high-current alternators mean that placing a voltmeter on the dash isn't very useful But what about a digital voltmeter that can measure lots of engine management things? In addition to showing normal battery voltage, these meters can also be used to display sensor output voltages such as those from the airflow meter, oxygen sensor - in fact, most engine management sensors. And they're cheap, too!

LCD voltmeter modules are available from electronics shops like Dick Smith, Jaycar and Altronics. However - there's a trick for young players. While most of these meters are happy working from 9-12 volts, not all of them are happy measuring the same voltage source as the supply. This means that you need to confirm that the meter can be powered by the same source as the one that's being measured. In most cases, the voltage measurement can be made to either 200 mV or 20 volts, with the range and decimal point location selected by the addition of two resistors and a wire link. So they'll be a little bit of electronic fiddling, but for about $35 the resulting instrument is cheap and very effective.

Mounting Gauges

First of all, it's important that additional gauges are located in (or near) your line of sight. They must also be positioned where they won't cause injury in the event of an accident. It's also relevant to consider how much forward vision they might obstruct, as well as how visible they are to thieves. You don't want to advertise the availability of all those expensive gauges....

You can mount gauges in your car in a number of ways. For a simple approach, buy an adjustable housing (or a simple clamp bracket), single, dual and triple flat mounting panels, or a moulded pod to fit on the A-pillar. The latter seems to be a bit of a hot-item at the moment - and it's also possible to build your own at near-zero cost (see "Project EXA - Part 2" to find out how). Of course, if you don't really care about cosmetics, you can always just hose clamp a gauge to the steering column... That's an ol' fave!

Oh, and be careful with gauges that need a feed tube run into the cabin (such as most boost gauges). It's very easy to kink the tube (thus restricting flow) or to have it hard up against a sharp edge of the firewall (which is a sure way to put a slice into the hose). Either way it can spell trouble.

Now get out there and fill your car with gauges - Pro Race style!