estimated inches of mercury

[ShiftTheDrift]

Can anybody estimate how much vacuum (inches of mercury) I should be getting with an E303 cam, TrickFlow heads and the stock Cobra intake? I hooked up the vacuum gauge yesterday and found 15 inches, steady.

Any ideas?

 

[1105]

My car with TFS heads and stage 1 cam would get 20-21 at idle, and when you let off the throttle 25

 

[ShiftTheDrift]

 

[ShiftTheDrift]

My car with TFS heads and stage 1 cam would get 20-21 at idle, and when you let off the throttle 25

Hmm.. maybe I have a problem here?

My throttle is sticking when I come to a stop and then it slowly returns to idle RPM.

 

[Joes95GT]

I would be more concerned with why you're asking the question. What is the reason for concern?

For what it's worth, my cam, which is much bigger than an E-cam, pulls about 6 inches of vacuum at idle. It's a stick car with full accessories and everything operates very well.

Joe

 

[ShiftTheDrift]

I would be more concerned with why you're asking the question. What is the reason for concern?

The main reason is the throttle sticks when I come to a full stop and after about 2 or 3 seconds, it returns to idle RPM. It seems like one of the symptoms of a vacuum leak. I've gone through the basic routine of cleaning the MAF, IAC and adjusting fuel pressure and so on..

I just remember somebody telling me I should pull between 17-18 inches of mercury at idle. But wouldn't the vacuum numbers depend on what your car idles at anyway? As you can easily tell, I'm shooting in the dark.

 

[v6v8swap]

That sounds pretty normal for our cars to have the "hanging rpm" when stopping with a larger than stock cam. It's mainly the cam that causes this with the 94-95 computer. It sounds pretty much like what mine does and I have the e303 also. Anytime you are rolling the idle comes up, but as soon as you are completely stopped it will come down to normal idle. The computer in our cars just doesn't (in a lot of cases) like the larger than stock cam. I don't know what my car pulls for vacuum, I've never checked it before. Just my $ .02 worth.
Phil

 

[ShiftTheDrift]

I would say that you're absolutely correct.
However, it looks like I've forgot to mention that I have a JMS custom chip installed.

 

[ShiftTheDrift]

Yeah know, I haven't checked the PCV valve. The last time I looked at it, the valve would continuously pop out.

Could this be adding to the problem?

 

[v6v8swap]

That would act like a vacuum leak for sure. Or could at least make the vacuum lower than it should be. I don't know what would cause it to come out by itself though. Excessive blowby? Maybe just a loose grommit in the valve cover? Just guessing.
Phil

 

[mo_dingo]

Your symptoms are very normal. The computer does that for a reason. Have you noticed when you pop the clutch and coast in neutral, the car will remain at a higher rpm, and then shortly after you come to a full stop, the idle lowers.

Very normal. You can get rid of it w/ a tuner.
Scott