JackoliciousLegs

I haven't had an rx in a while and I'm about to buy a 90 TII!!! I'm so stoked... new engine with 25k on it. Good body... anyways, i had a couple questions and search couldn't answer.

What units does the stock boost gauge measure boost in? (millimeters mercury?) What does that mean? Where should it read under full throttle? Where should it read at warmed up idle (it seems to be pulling good vacuum)?

Thanks

Jack

NZConvertible

The boost gauge is calibrated in tens of millimeters of mercury (x10 mmHg). 1psi is equal to ~52mmHg. The S5 gauge reads to "45", which is 450mmHg or 8.7psi.

Assuming a healthy engine and turbo, stock max boost for the S5 is 8.3psi (dropping to ~7.5 at redline), so the gauge should go most of the way to the top of the scale under hard acceleration.

The gauge only goes down to -200mmHg, but in normal driving the manifold pressure actually goes much lower than this (around -380mmHg at idle, -500mmHg on high-rpm decelaration), so with anything less than mild acceleration it'll sit pegged down at -200mmHg.

If you plan to do any mods, the very first thing you should do is buy a decent aftermarket boost gauge. The stock one isn't all that accurate, but more importantly it doesn't have nearly enough resolution to tell you exactly what the engine's doing, particularly since the first airflow mod you do will send it off the top of the scale.

Hope that helps.

JackoliciousLegs

G-d I love this forum! Thanks!