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That is likely to vary by the booster and by your personal threshold. The vacuum booster strength is relative to the vacuum it receives, so the more vacuum the more assist.
Your threshold may be different than someone elses
I would say the minimum is likely around 10 - 12 in hg, give or take 2 points, or in the low to mid 30's kpa. But that's a complete guess, I have never had a issue with weak vacuum supply that I measured. I have had one of these new trucks come in with a hard pedal and a failing vacuum pump but he only wanted an oil change so it didn't even come to my side of the shop. I'm used to seeing around 16-18 but qwank said he shows 21, that's probably due to the blower sucking harder on the back of the throttle blade than it would other wise... not positive what these trucks do stock but I can find out tomorrow.
With your cam you should be fine. But check it out and see what you think.
Last edited by 00pooterSS; 01-08-2020 at 09:25 PM.
I will weigh it tomorrow. I just grabbed my bathroom scale and a 5 pound dumbell to see if the scale would read accurate at only 5 pounds. It does.
The dumbell feels slightly heavier than the vacuum pump. There's really nothing to the vacuum pump. The body is tiny and it's aluminum. The pulley is steel but it isn't much of a pulley.
This isn't an end all example or proof of anything. It's just things I am looking at and sharing.
It is all open to discussion for sure, just saying i'm sure if someone starts really digging in they could shoot holes in some of the things I said on film or whatever
Here is a video I took of intake vacuum vs cam timing, unfortunately I cannot control the cam at idle. I can go in a manually advance the cam in the scanner but it makes you run the engine at 2000 rpm and it only allows you to control the cam for 30 seconds and kicks you out. It was hard to get the phone to focus and push buttons and do it all in the time allowed so I just went into data and watched what it does instead.
I deleted my vacuum pump and there is no difference in braking at all. My 2012 Silverado has VVT and DOD and doesn't use a pump. It's got 10in of vacuum at idle and works fine. Also, I think that video posted above is showing crankshaft degrees of retard, not cam advance.
I deleted my vacuum pump and there is no difference in braking at all. My 2012 Silverado has VVT and DOD and doesn't use a pump. It's got 10in of vacuum at idle and works fine. Also, I think that video posted above is showing crankshaft degrees of retard, not cam advance.
Yeah I thought about the previous gen trucks that also had DOD and VVT and wondered what kind of idle vacuum they make since they don't use a vac pump.
I'll have to check out one of those one day on the scanner.
Not sure what you mean by crank retard. Can't advance or retard the crank.
It says Cam CMP angle. CMP is camshaft position so it's cam position angle, crank is CKP. So that would be the position of the cam, and it's reading in positive numbers as you throttle it at low rpm so that would be advancing it. It is from zero, and at zero degrees advance the cam itself may actually be at something other than 0, but it's 0 degrees of advance through the VVT system, in other words at it's default position. I guess lol. I'm not 100% positive how that is factored.
I've never seen what the minimum vacuum was you could have and a booster work okay, if you're making only 10 in/hg and they work great then I guess the minimum is a pretty low number.
Still.. I'm curious as why someone would remove the vac pump. Are y'all taking them off to make room or something?
Last edited by 00pooterSS; 01-13-2020 at 02:34 PM.
I think the main reason people are removing them is on less thing to go wrong. And everybody knows how bad the original pump was. I think I'm going to take mine into the dealership and see if I can just get mine replaced under the recall. If they won't replace the pump I'll just do it myself. But I figure I'll try and get it done for free first.
01-08-2020, 05:42 PM
