Hey everyone, I am hoping that someone can help me understand some of the components of the vacuum system on our cars. I've looked at the parts diagrams and understand that there are 5 basic systems tied back to the intake manifold - SAI, flapper valve, fuel pressure regulator, brake booster, and AOS. I'm not looking so much for plumbing diagrams as I am trying to conceptually understand these parts and their use of the "vacuum". (Sorry for the quotation marks there, the term really bothers me since it's not a vacuum at all but just a source of lower than atmospheric pressure) Here's where I am with my knowledge, can anyone fill in the holes and correct my errors? I'm sure there are plenty!
SAI - Creates positive pressure for injection into cylinder heads. As a positive pressure system, does it actually rely on a vacuum source for function? It seems more like the changeover valves are there to actually isolate the system from the "vacuum" when the pump is not in use.
Vacuum resivoir - why? I get the idea of why a low pressure resivoir would be helpful, but by the diagrams it looks like it really is primarily plumbed to the SAI system. Is that true? Or does it also play a role with the flapper valve? Does anyone know if this is on the ROW vehicles which had no SAI system?
Fuel pressure regulator - not so much why but how? Does this provide a "backstop" to prevent unrestricted flow from the fuel rails to the return lines? If that is the case, do the returnless rails not have this feature? Most importantly, what does the "vacuum" source actually provide to the valve to operate? Is the function of the valve dependent on and proportional to the intake pressure or does it simply need a pressure differential to function properly?
Brake booster - this one I understand. Where does it plumb back to the intake? Has anyone experienced braking in our cars without the booster functioning (not broken, just disconnected from the "vacuum"). I'm curious to know if it would simply take a bit of a heavier foot (although this would certainly make heel toe shifting more challenging) or if it would be downright undriveable.
AOS - effff this confounded contraption. I think the only interesting thing about this part is the fact that it is the closest thing our cars actually have to a PCV valve, although it seems to me that this is actually a NEGATIVE crankcase pressure ventilation system. Has anyone ever run their motor with the AOS vented to atmosphere instead of vented to intake? I saw one post here where a guy did this and blew oil out of cracked spark plug tubes, and I have seen comments regarding the piston rings needing a "vacuum" to seat properly, but it seems rather wild to me that such a modest difference in pressure could have such a profound effect on the workings of a machine designed to literally contain the force of tens of thousands explosions a minute
Sorry for the stupid long post. I'm a tinkerer by nature and as my confidence has grown working on this car, so too has my desire to pursue the enemy of good (better!) And to me it seems like the vacuum system is one area where some significant simplifications might be possible (especially that piece of crap AOS).
Thanks!
Ike
Btw, I should get a post up in the next week or two about an intake modification I'm working out. I'm sure that plenty of people will find it ludacris (it involves a Corvette intake!) But it should be very interesting either way.
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