Hi guys, Silly question: I have a 612 engine that I am using in a project car (https://www.facebook.com/minottocars) and I am wiring up my own engine management for it. The variable intake manifold is operated by that black cylinder with a piston in it at the front top of the engine, and based on throttle position and rpm either has the short or the long intake track. I've found the rpms and throttle thresholds on the web, but not what position of the lever is long and what is short. I could take the thing apart and figure out, but I'd rather leave things in place. And so to any 612 owner: When your car is idling, is the cylinder pulling the lever, or does it leave it in the same place as it is when the engine is off? A big THANK YOU! Hans Image Unavailable, Please Login
I have the same cylinder on my 550, although it is located at the rear of the intake. I have played with this vacuum cylinder during my reassembly process. As near as I can tell, the cylinder pulls at idle from the generated intake vacuum to the cylinder port. The free setting of the pull/push rod is with the throttle plates in the open position. Seems wrong, but that is neutral position and how I set mine up. Interestingly enough, there is very little info on this cylinder on F-Chat. or online. All we know is that it improves drivability. http://performancetrends.com/Definitions/Idle-Vacuum.htm
I have taken the stuff apart and took as many notes as I saw fit, but forgot to note if there was any electrically operated solenoid controlling the valve. Or is it just vacuum operated, period? In other words: if there is vacuum the cylinder contracts, and at higher power settings the absence of a strong vacuum sort of lets the cylinder release automatically? Thanks Hans
The 550 system (and probably all the others) has a vacuum storage canister tucked up under the battery, and the variable intake system probably uses stored energy from that to open the secondary butterflies at high RPM, where normally there would be little or no vacuum in the system.
That shouldn't be needed. The default setting of the butterflies is open, and vacuum is used to close them. Open = the engine sees short intake runners, used for high rpm/power settings. Closed = long intake runners, used for low/mid rpm/power settings. So vacuum is needed when it is available, and not needed when it is not.
