gsl-se addict

iTrader: (3)

Yes, you should see about 20 inHg of vac in your 12A, depending on the porting. My stock GSL-SE (13B engine) sees about 22inHg. If the engine is ported, the vacuum will less. So it depends on the engine for what vacuum is normal. Like how trochoid's bridge port produces only 8" Hg. You can't say the engine is bad because of the low vac in that case. It is probably about normal for a BP. It is just a byproduct of the porting. The same thing happens in piston engines with longer lift/duration cams. The vacuum is decreased. Vaccum can also be used to tune idle. The stronger the vacuum at the same throttle position, the better running the engine is. Timing, mixture, throttle position, etc all influence the amount of vac.