KA-T Idle Vacuum

[Maeda]

Ok at idle my KA-T has always been at -10 vac.

Whats everyone elses look like? I've heard it's SUPPOSED to be around -20 psi.

I tried looking for leaks in my system, and after a couple hours and a full bottle of carb cleaner I can't find diddly. I put my BOV (SSQV) on full tight.

I also tried pressurizing i/c pipes with an air compressor and I hear a hissing sound comming from the rear passenger side of the engine.

The intake manifold is missing a nut on this side aswell...

My wastegate is openning at 2.0 psi... but the spring is set at 4.35

When I step on the gas slowly in Neutral, my vac goes up from -10->-8(1000->2000rpms)and then it starts to go back down to -12 (2000-4000rpms)

Do I indeed have a vac leak, or am I just unique?

:help

[Checkered-Member]

My wastegate is openning at 2.0 psi... but the spring is set at 4.35

When I step on the gas slowly in Neutral, my vac goes up from -10->-8(1000->2000rpms)and then it starts to go back down to -12 (2000-4000rpms)

Do I indeed have a vac leak, or am I just unique?

:help

I think your gauge is hooked up all wrong or its just broken....because you vacuum and psi are off

[erich]

Does the gauge read PSI or mmHg in vacuum? If it really reads PSI then -10PSI is OK. Most gagues read vacuum in mmHg (millimeters of mercury) which is about 28mmHg for -14.7PSI.

[daniel240]

wow, that sounds very wierd. mine idles at about -22psi, and when i step on the gas in neutral, the needle jumps to 0, very quickly, then back to -22. where is your gauge signal coming from, the fpr hose? make sure all those conections are good and tight.

[DriFt3r]

mine idles at 21 psi, hehe

[Maeda]

you guys all sure its PSI?

My boost gauge is off the profec e-01 so its definetly in psi... mabye i'll try and get a different reading?

[erich]

Doh! It inches of mercury, not mm.

[daniel240]

mines psi.

[Jeff240sx]

mines psi.

Once again, are you sure? I had a brain relapse, and just assumed since my boost read in psi, the vacuum would also. Here is the correct thinking:Since psi is pounds of pressure per inch^2, you can't have a negative pressure reading in psi. Also, vacuum would be nearly atmospheric, around -14psi. I read 21inHg, or 10.8psi and have 2 "leaks". If you are reading -24psi of vacuum or whatever.. you have issues.-Jeff

[daniel240]

true, technically you can have neg psi im just going by what the gauge says, and it says its psi, and the needle is a little past the 20 vacuum

[Jeff240sx]

No, you can't have negative pressure. You have vacuum. Measured (by most gauges) in how many inches of mercury is drawn up a standardized tube.There may be a gauge that converts the inHg to psi for ease of use, but I haven't seen one. If yours does indeed make that conversion, please tell me what make and model. If its an autometer like mine, check around the vacuum reading scale for the units.. they're listed as inHg.Also, you simply won't have -20psi of vacuum. -28 inHg is nearly -14psi, which is right on.-Jeff

[tony/ka24de]

what kind of bov are you running? I had that problem when I first put my turbo kit in. In my case I had a bad bov

[Projex240]

umm---the vaccum should jump to zero very quickly and back down again regardless of what the gauge shows it idling at. There is a physical problem most likely with a vac leak. Wherever that hiss is---that seem like the culprit. Theres alot of vaccum ports that could be making that sound on the pass side car rear of the motor.

[C-Kwik]

I've NEVER seen a boost gauge that read vacuum in PSI. EVER. The gauge may be in psi for positive pressure, but below zero, it is on a different scale. I think the exception might be kPA. But I'm not too familiar with that as I've only seen it in pictures and I paid very little attention to it.

[huguetpj]

Yep. All boost gauges that I've seen in PSI use mmHg for vacuum, although rarely do they say mmHg, just PSI. But I'm pretty sure my Autometer gauge reads vacuum in mmHG cause my Blitz SBC says so :pface

[S14tat]

wow mine when its fully warmed up reads 22 inches of hg. and when decelerating in gear it goes all the up to 27 inches!!!

[silviamaniac]

Readings are different with gear in and neutral.

My newly done ka-t has reading at 22-23 at idle, 25-26 with gear in no throttle.

some infohttp://autorepair.about.com/cs...a.htm

[ROB240]

My wastegate is openning at 2.0 psi... but the spring is set at 4.35

I think this is just due to the light spring, at one point Rick told me his tial wastegate would gradually crack open before he hit full boost, and my 38mm tial wastegate (.4bar spring) starts to crack open at around .2 bar.