Just wondering if an old-style compression tester (like the one pictured) screwed into an O2 bung would work to measure exhaust pressure. I guess the one concern I have is the scale on the gauge might go too high to get lower readings accurately enough.
Like you said, the pressure scale is inappropriate.
I use a Harbor Freight vacuum/pressure gauge. I have some fitting I scavenged to thread into an o2 bung, or I'll just drill a very small hole and hold the gauge there, and weld up the hole when I'm done. Had one yesterday, should have taken pix...
I have one of those gauges, too, but the flutter makes it hard to figure out what the actual reading is. I liked that the compression tester has a pressure holding valve (along with a spark plug fitting that fits in the O2 hole), which made consider using it. Perhaps adding a more appropriate psi-ed gauge to the tool would make it work,
Though an appropriate scaled gauge will work I don't like messing with O2 for back pressure tests at all. Reason being they live in very confined spaces, often times very rusty -and breakable - and hot enough to burn you...
An easy alternative to a pressure gauge would be to connect your vacuum gauge to the intake and watch it's needle while rising the rpm gently from idle to medium range/light load and after a snap throttle. A MAP sensor reading/graph will give the same information.
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