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Old 11-17-2012, 08:53 PM   #1 (permalink)
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vacuum gauge with WAI...

Hello everyone. I have a 92 VX with 291,000 kms. I've only had it on the road for roughly 3000 kms, after sitting for about 3 years. I recently installed a warm air intake (WAI). Fine and good. My question involves a vacuum gauge used in conjunction with WAI. I want to install a vacuum gauge in lieu of an OBD2 port/scangauge.

But how much do you think the WAI could change the vacuum readings? WAI makes car run leaner, you have to give it slightly more gas, throttle plate opens up a little bit more, less pumping losses but less vacuum too, if throttle plate opens more. I don't know if there is any "scientific" material on this, but wondered if anyone with experience with both at the same time know how much this might throw out the vacuum gauge readings?

Secondly, under the 65+ Efficiency Mods link, one of the mods is a lean-burn led for these type engines. There is a link there but it doesn't work. I would love to have a lean-burn LED light up when the lean-burn engages. Any other working links or info? Or DIY instructions?

Thanks for your time!

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Old 11-17-2012, 11:41 PM   #2 (permalink)
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...vacuum gauge goes AFTER throttle-body (ie: actual intake manifold cavity area), so WAI or CAI variance should be minimal...remember, it's measuring atmospheric pressure depression (ie: vacuum) and not air temperature.
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Old 11-19-2012, 04:46 AM   #3 (permalink)
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You may take a look here:
Monitoring lean burn
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Quote:
Gerhard Plattner: "The best attitude is to consider fuel saving a kind of sport. Everybody who has enough money for a strong car, can drive fast and hit the pedal. But saving fuel requires concentration, self-control and cleverness. It's a challenge with the nice effect of saving you money that you can use for other more important things."
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Old 11-19-2012, 10:49 PM   #4 (permalink)
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AndrzejM: thanks, I'll go over it. Circuitry is not my forte, unfortunately. I was hoping for a ready-made kit or something easy!

Old Tele Man, thanks for the reply, but I know the vacuum gauge measures vacuum and not temperature! Also where it goes. :/ The connection is that warmer intake air leans out a mixture, which means one needs to open the throttle plate up just a hair more under normal operation, which reduces vacuum throughout the vacuum system, by how much I am uncertain. See where I'm coming from now? I wondered if anyone actually knew how much the vacuum was reduced, if such a thing has been measured before. This would help me compensate the readings if they are thrown off a bit.

take care.
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Old 11-20-2012, 02:12 AM   #5 (permalink)
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Hi VxonFumes,
That's an interesting thought.
Baa runs a warm air intake, with a vacuum gauge and the vacuum readings have always seemed low at higher engine loads when compared to my previous car (also a 1.8L 4 cylinder).
Unfortunately, I bought the car like this and don't have the original bits to change it back to a cold air intake to compare the two.

I doubt the previous owner intended it as a WAI of course, I think he replaced the original panel filter and box with a pod filter "cause it sounds cool at WOT"
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Old 11-20-2012, 09:22 AM   #6 (permalink)
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...the answer to your question then boils down to simply looking up (in a physics book) the table listings of air-density vs. temperature. And, as I vaguely recall, just such a hand-drawn graph was posted here somewhere in the past.
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Old 11-20-2012, 11:11 AM   #7 (permalink)
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Old Tele Man, thanks, but I don't think it's quite as simple as you're saying. If the throttle plate didn't open up more with warm air temps then what you say would hold more merit. However, since leaning out mixtures due to warmer air temps means less power and a consequent opening up of the throttle plate to compensate, that changes things. A throttle plate opened up more means less vacuum in the system, irregardless of air tempterature and/or air density. It's that variability I'm trying to account for.

I understand I may appear to be a "fastidious nitpicker" here, but I want to be more accurate with readings...you know...strictly emperical and all that.
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Old 11-20-2012, 03:05 PM   #8 (permalink)
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Air density is 25% lower at 212 Farenheit than at 32, 100 centigrade and 0. Air density also is about 50% at 18k feet as it is at sea level.

regards
Mech

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