MANIFOLD VACUUM AT IDLE.

j.johnson23 · Post by **j.johnson23** » Sun Apr 06, 2014 8:49 pm

Hi all,i`ve just fitted a 14 cux hot wire based injection system to my 3.5 low compression Rover v8 and find that the vacuum at idle is around 10" mercury at around 800 RPM.
The cam is standard (I think) I would have thought that idle vacuum should be around 20" of mercury.
Has anyone got a vacuum gauge on their v8? If so could you let me know what engine size,cam and vacuum you have?
Have to admit that the car drives a lot better than it did on SU`s and that I may be over thinking things a bit.

DEVONMAN · Post by **DEVONMAN** » Mon Apr 07, 2014 7:33 am

Where have you connected the vacuum gauge to on the hot wire set up?

j.johnson23 · Post by **j.johnson23** » Mon Apr 07, 2014 8:13 pm

I have the gauge connected to a pipe coming off the side of the plenum base.
I would have thought that would be the right place as it is downstream of the throttle blade.

Quagmire · Post by **Quagmire** » Tue Apr 08, 2014 5:59 pm

My Megasquirted 3.5 gets a vacuum of 30-32kPa at in idle of 850rpm.

This is an absolute reading, and not a gauge one as engine off is 100kPa, and WOT is the same.

Engine is standard 9.35:1 compression, with 10 bolt heads, standard Rangey 3.5 Efi cam, hotwire inlet manifold, and flapper plenum.

No idea how kPa converts to mercury though!

Quagmire · Post by **Quagmire** » Tue Apr 08, 2014 6:01 pm

...Google says that I am getting around 8.9-9.5 inches of mercury

j.johnson23 · Post by **j.johnson23** » Tue Apr 08, 2014 7:42 pm

Must be the normal vacuum then,cheers mate.