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Old 03-11-2015, 02:44 PM   #4 (permalink)
Cyborg ECU
California98Civic's Avatar
Join Date: Mar 2011
Location: Coastal Southern California
Posts: 6,297

Black and Green - '98 Honda Civic DX Coupe
Team Honda
90 day: 66.42 mpg (US)

Black and Red - '00 Nashbar Custom built eBike
90 day: 3671.43 mpg (US)
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Originally Posted by Old Mechanic View Post
You have a 100 mile tall column of air trying to crush you into nothingness. You're worried about a WAI?
More wondering than worrying.

Originally Posted by some_other_dave View Post
Higher vacuum is lower pressure. That is seen as less air, meaning less fuel will be injected. Which is the opposite of what you are talking about.

It is also very unlikely indeed that an air intake would cause more restriction than a mostly-closed throttle plate. At cruise RPMs, it probably isn't enough restriction to even measure.

I see your point about the throttle plate, but I wonder how far I would have to open the throttle for the added restriction from a smaller diameter intake pipe to matter. At some point from closed throttle to WOT the added restriction would start to effect air flow and thus vacuum, since the throttle opening is of greater diameter than my intake airtube. I should be able somehow to calculate where that point is, no? 80% might do it, maybe.

On the injection and vacuum/pressure... maybe I don't understand the intake manifold that well. If vacuum effects both the air and injectors, then would'nt higher than expected vacuum in the manifold increase the effective fuel rail pressure by "pulling" more fuel from the injectors than intended because the vacuum is effectively added to fuel rail pressure?

The car was designed with specific relative vacuum and pressure in mind, and the ECU is monitoring those parameters and adjusting fuel partly based on them, maybe, no?

See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.

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