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manifold vacuum on a turbo ???
Posted 08 August 2004 - 12:55 PM
I need to ask if the intake manifold has vacuum (as on a N/A engine )at lower speed , I know it is pressurized when you are on it, but where is the vacuum for options and stuff .
Mainly interested in the selective 4wd on my 86 xt turbo , I see the vac source tube on the manifold to the selonoids and to the selector diaphram, but how can it operate if the manifold is full of pressure instead of a vacuum ?
Is there something else to it ?
Is there vacuum at lower RPM ??
Thanks for any help
Posted 08 August 2004 - 01:01 PM
most of the time it operates in a vacume just like any other motor.
all you need is a check valve to a vacume canister to get a good constaint vacume source.
Posted 08 August 2004 - 01:03 PM
you dont use brakes when your uner boost, so thats all the same. and you never shift into 4x when under boost.
its got vac just like a regular car, cept when your boostin.
Posted 08 August 2004 - 04:22 PM
Posted 08 August 2004 - 10:08 PM
Yeah ive got an 86 gl turbo coupe. When im on the gas the boost guage reads +6-7 but when i let off it creats about 20psi of vacuum.
Holy ****!! 20 psi of vacuum?!!>>
to the original poster. on the EA82 cars, there is a little white canister on the passenger side behind the strut tower. Thats what th eheater controls and the 4wd(or difflock) controls run off of. Not only does it keep a small reserve built up in the canister, it has a check valve built into the feed line to stop it from going in to positive pressure.
Posted 08 August 2004 - 10:16 PM
Posted 09 August 2004 - 01:31 AM
the only engines I know of that don't create intake manifold vacuum are diesel engines being as they don't have a throttle plate. Or a forced injection engine(turbo, supercharged) under boost.
Posted 09 August 2004 - 01:56 AM
Inches of mercury. One inch Hg is the pressure exerted by a column of mercury one inch high.
Posted 09 August 2004 - 07:49 AM
Posted 09 August 2004 - 08:18 AM
No. first off, in/hg does not equal psi
Now if it didn't have the turbo and the vacume stayed the same, than wouldn't the turbo be creating 31 psi in order to bring it from 25in/hg to 7psi boost?Does this make sence to anyone?
Second, on an N/A ca, when accelerating, manifold vacuum reaches ~0 in/hg. Thus to reach 7psi, your turbo must put out ~7psi (not accounting for boost leaks or boost drop due to IC or anything like that)
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