Handheld Digital Manometer

 

Over the years we’ve covered in many articles the measuring of pressure variations. By using a gauge with an appropriate sensitivity, you can easily work out how well your intake system flows, whether the throttle body is restrictive, and – of course – measure boost and exhaust back pressures. But the more sensitive of these measurements – for example, those measuring intake snorkel or air filter restriction – have always required a special instrument. That instrument doesn’t have to be expensive (it can be as cheap as a bucket of water and some clear plastic tubing) but most often we’ve used a variety of Magnehelic gauges - special low pressure measurement devices. In short, to measure all the pressures you might want to see (and we’ve forgotten in this short list to mention aerodynamic pressures over the bodywork of the car!), you’ve previously needed a bunch of different gauges.

Well, now you don’t. Instead, you can do nearly all of them with a single digital instrument. Not only does it measure positive, negative and differential pressures to 30 psi, but it can also express those pressures in nearly any units you care to name, has a peak hold facility, and is light, convenient and accurate. And it’s cheap as well!

The Instrument

Firstly, how much does it cost? Well, we bought it on eBay for AUD$124.95 and at the time, it was also available as a Buy it Now for $129.95. However, the company that is selling the AHJ-8230 instrument lists it at its website of www.gastools.com.au at a price of $225. So we figure if you twist their arm you should be able to get the instrument for well under that $225 price.

For the dollars you get the handheld instrument, a case, instruction booklet and two short lengths of coloured hose. The instrument works off an internal 9V battery or an external supply. (The battery is supplied but the external mains supply is not.)

In addition to a two-line LCD there are also six buttons and two pressure ports (circled).

Pressures can be displayed in no less than eleven different units. These are: bar, mm hg, oz in2, kg cm2, psi, in H2O, kPa, ft H2O, in Hg, cm H2O, m bar. That’s a huge bonus because it means you can immediately correlate your measurements with nearly any other gauge – including some factory boost gauges that work in millimetres of mercury (mm Hg). You can also use the units which are most familiar to you – for example, here at AutoSpeed we usually measure boost in psi or Bar and intake restriction in inches of water.

Each of these units is displayed to a very high resolution – for example, psi is displayed to two even decimal places (eg 4.02 psi) and inches of water to 0.5 of an inch of water. This resolution is very useful, not only in taking specific measurements but also in seeing trends. For example, we were interested in seeing exactly when a turbo started developing positive pressure - being able to see the boost shown to such a fine resolution (far better than any analog gauge) showed this clearly.

Maximum and minimum values can be held, with the in-built clock showing how long after activation these measurements were recorded. Differential pressure measurements can also be made. When measuring single-ended pressures (eg boost), the pressure sensing hose would normally be connected to the ‘+’ input port and the ‘-‘ port left open to the atmosphere. However, the difference in pressure between the two ports can also be measured. For example, connecting a hose to either side of the air filter and pressing the Diff button will immediately show the pressure drop across the filter! Doing the same across the throttle body will show how restrictive the throttle is – and, unlike a normal manometer, you won’t overload the instrument when the throttle is closed.

The digital manometer normally shuts down 20 minutes after first being switched on. However, this ‘sleep mode’ can be disabled by the user, allowing the monitoring of pressure for as long as the battery (or external supply) maintains power. The meter also incorporates a backlight that stays on for 30 seconds after the appropriate button is pressed.

Manual calibration is possible and the meter’s display can be zero’d easily and quickly. Accuracy is quoted at 0.3 per cent of full scale.

An optional RS232 data logging package is also available.

In Use

The instrument doesn’t have the feel of a super high quality design. It’s not encased in a protective rubber holster (although one normally used for a multimeter could be easily sourced) and it’s light and a bit ‘plasticy’. However, that said, we dropped ours pretty hard on a bitumen surface and it still works fine!

The update rate of the display is commendably quick at 0.5 seconds and we found the instrument easy to use. In comparison with other analog gauges, its accuracy appears fine, although we didn’t compare it with a true reference standard.

Conclusion

This is a must-have instrument for anyone seriously into car modification. In one instrument it combines perhaps $500 of Magnehelic gauges, boost gauges and vacuum gauges. (About the only on-car pressure readings it can’t do are fuel and brake pressures.) Add to that the digital accuracy and resolution, and ability to hold minimum and maximum readings, and you’re talking an absolute bargain.

Contact:

AHJ Systems 02 99381886 www.gastools.com.au

The digital manometer was purchased for this review.