This tester is great if you're by yourself and don't have someone to turn the key for you or you want to log your compression at certain intervals.

Things you'll need:

1. Data acquisition unit
available from www.dataq.com (http://www.dataq.com)
P/N: DI-194RS
$24.95 plus tax & shipping; total $30.02

2. Pressure transducer
available fromwww.grainger.com (http://www.grainger.com)
P/N: 1X742 @ $103.05 plus tax & shipping; total $117.04

3. Misc.
avaliable from Radio Shack
16-gauge 2-conductor wire with one red and one black jacket, battery clips, fuse holder & fuse, and shrink tubing assortment for about $30 +/-

4. Flex hose with connector from previous compression tester – free

leave it to ozzy to come up with a "build-ur-own" compression tester.

unfortunately the transducer is a discontinued item and can't be ordered online, and causing in store quantities to be limited or depleted. but i'm sure it can be found else where.

as for the need to have someone turn the key, i've made my own remote starter button.

more info on the transducer type so you can track down an equivalent. I think you can still get it from the mfr so here is that p/n too:

Industrial Pressure Transducer, Pressure Range 0 to 200 PSI, LVDT Type, 1-5 Volts Output

Grainger Item: 1X742
Price (ea) : $103.05
Manufacturer: US GAUGE
Mfg. Model#: P207
Ship Weight (lbs): 0.3
Ship Qty : 1
Sell Qty (Will-Call) : 1
Usually Ships : Discontinued
Catalog 396 Page: N/A

I may have a source for the transducer! Im waiting for a call back from the guy, he comes into my RadioShack all the time and knows his shit.

www.digikey.com has TONS of pressure sensors.

They don't have anything with 1-5V output.

But here's a part for $62 with 500 psi range:
MSP6858-ND
The datasheet gives you a circuit that will convert it to a 3V range.
http://rocky.digikey.com/WebLib/Measurement Specialties Inc/Web Data/Model 85 Ultra Stable.pdf

1/4" NPT so it should be easy to mount.