What's a high vacuum??
 

Ever since I've owned my evo 8 my gauge usually reads around -40 vacuum at idle and I've seen it goes as high as -55 while driving. Is this a high vacuum? If it is, what could cause this. My car is using speed density, so i don't know if I have a vacuum leak as I haven't had time to test it with my work schedule lately. Thanks!

You might want to go ahead and do a boost leak test with that reading. At idle, mine sits between -14/-16. How does it feel when driving it?

verying interesting. I'm having the same trouble too with the high vacuum. My car runs fine. i have the AEM Boost gauge digital. When i'm boosting, it would read what i'm boosting. When it comes to vacuum, it wont read. My gauge used to work just fine, but now vacuum isn't showing anymore. I still have the MR gauge in my car as well, and vacuum reads high like 35 or 40.

The vacuum on the stock MR gauges will seem much higher because in vacuum it reads MMhg.

Vacuum isn't created by a boost leak.

OP - You need to tell us exactly how you're monitoring vacuum. 12-23 is normal for inHg, but from your values I can already tell you you're measuring in something different. You need to assign details to your values.

Sorry I should have clarified. It's the stock MR gauge so it must be reading in CM/HG? I'll try and look up something to convert it over to HG.