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Old 05-07-2008, 09:21 AM   #1
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Hi all,

Ive been a lurker here on MT for a while and decided it was about time to contribute something. So here goes....

It started off as a bit of day dreaming stuck behind my desk at work but the more I thought about it the more sense it made. "Doesn't that long vaccume line between the manifold and MS cause some lag?"

So I got out my slide rule and pencil and did a "back of a beer mat calculation"

As I understand the wavefront from the manifold to the MAP should move at the speed of sound (assuming that the transition is from full vaccum to WOT) at sealevel. Approx = 340 m/s

Most people use about 5 feet of vaccum hose = 1.52 meters

Speed = Distance/Time Time = Distance/Speed

1.52/340 = 0.00447.......... round up to 0.005 seconds or 5 milliseconds.

Doesn't seem like much but when MS is sensitive to 1ms values for things like injector opening time it starts to sound significant.

Would mounting the MAP in the engine bay as close to the manifold as possible reduce that lag and make using MAP based acceleration enrichments more accurate for a nice crisp throttle responce?

Has anyone tried it? Would anyone be interested in trying it? My MS is still in bits at the suppliers (coz I aint ordered it yet ) but as soon as I have it I'll give it a go.

PS Im very sorry if this has been asked before but I did have a search and a read before posting. Honest SamNavy!!!
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Old 05-07-2008, 09:45 AM   #2
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Which is why we have acceleration enrichment. I think you're worrying over nothing.
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Old 05-07-2008, 10:08 AM   #3
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I wasn't really worrying, MS obviously works fine with the long vac line coz so damn many of you get such damn fine results . But if you think about it there are 5ms after the throttle being opened before any extra fuel is added (+any time taken for MS to do its thing) Time for some more beer mat math..

4000 rpm = 66.6 rps = 0.015 seconds per revolution.

2 cylinders fill per revolution

time for one cylinder to fill 0.0075s or 7.5ms

so 5ms of being lean would affect at least one of the cylinders power causing slight hesitation upon acceleration?

Just more harmless ideas
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Old 05-07-2008, 11:09 AM   #4
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Listen to Ben. We have TPS based accel enrichment. Its all electric.
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Old 05-07-2008, 12:19 PM   #5
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D'oh! forgot about the TPS option.

Dont suppose theres any 1.6 owners out there without a proper TPS who have problems with MAP based enrichment?
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Old 05-07-2008, 12:21 PM   #6
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MAP based enrichment works well, I played with it for a little while. You should look into getting a variable TPS though. The added response is great.
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Old 05-07-2008, 07:40 PM   #7
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I have it externally, 1bar GM MAP sensor mounted on the strut tower brace, then a 5" vaccum line to a nipple on the intake manifold. Works great and I don't have to worry about tracking down leaks or restrictions (ie a bent line).

Jim
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