cam upgrade! But to low vacuum? experts only! - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

SoguRacing · 10-16-2008, 07:57 AM

Well, I dont know what is normal but as you increase valve overlap you're going to decrease you vacuum at idle. If everything else on your car is fine I wouldn't worry about it as the reason you installed cams is to have more power at top end. Cams with above stock duration and lift will cause lower vacuum readings in lower rpm because you are sacrifcing the low end intake "ram effect" for upper rpm gains. "ram effect" being the velocity of the intake air through the runners as it is sucked into the cylinders. look up "ram effect"

10-16-2008, 07:57 AM	#2
SoguRacing Post Whore! Join Date: Nov 2007 Location: (714) Age: 39 Posts: 2,967 Trader Rating: (23) Rides Gallery: SoguRacing Feedback Score: 23 reviews	Well, I dont know what is normal but as you increase valve overlap you're going to decrease you vacuum at idle. If everything else on your car is fine I wouldn't worry about it as the reason you installed cams is to have more power at top end. Cams with above stock duration and lift will cause lower vacuum readings in lower rpm because you are sacrifcing the low end intake "ram effect" for upper rpm gains. "ram effect" being the velocity of the intake air through the runners as it is sucked into the cylinders. look up "ram effect" __________________ Pre Tune Checkup! Compression,LeakDown,Vacuum Test $80. Cams Install: $180