Ported or Manifold Vacuum?

[MPO]

Is the STD TVR Plenum Vacuum classed as a ported or manifold system?

Also, if the plenum is opened up to 72mm does this have an impact on the functionality of the vacuum?



MPO

[davep]

The vacuum take off is located near the throttle plate, so I'd say ported.

[Boosted LS1]

It depends on whether the suction is applied behind or in front of the throttle plate ie sucking all the time or only when the throttle's been closed. I can't remember exactly where the pipe is on the rover relative to the throttle. I wouldn't have thought a slightly larger throttle would effect ported vacuum as that's determined by the engine itself and there's an inlet restrictor in the rocker cover. If things were to change you would be able to tweak things.

Edited by Boosted LS1 on Sunday 10th April 10:39

[MPO]

Thanks for your reply Guys

Here are some pictures I just took of a spare 1992 plenum.

The first picture clearly shows the tiny vacuum is the AFM side of the butterfly when completely closed:-



This second picture shows the butterfly slightly open (probably not enogh to maintain tick over!) and the tiny vacuum hole is directly under the butterfly:-



So, would we class this as a Ported or Manifold Vacuum?

Cheers

MPO

[NZ fan]

It's ported vacuum. With throttle closed tick over is taken care of by the stepper/throttle bypass. Max vacuum signal is at part open throttle I.e. Cruise for improved fuel economy. There is almost no vacuum at this port when the throttle is closed.

[ChilliWhizz]

I've learned something new today... despite over 45 years of messing with cars this is the first time I've ever heard of ported and manifold vacuum... I bloody love it when I learn something new. especially if it's connected to a subject close to my heart

So, a big thank you to the OP....

Being an enquiring kind of chap I had to research this to try and gain an understanding... Went on a few websites, but this short vid on Youtube is brilliant, I'd say for technical content (if you're patient), but also because it's made by a self confessed redneck It's both educational and entertaining....

https://www.youtube.com/watch?v=fQmO2H6Pbas&no...

Thanks again to the OP

[blitzracing]

I can confirm the vacuum drop off completely as the throttle plate is shut. If it did not do this you would end up with about 20' of advance at idle as vacuum advance is added on top of static advance, and that's far too much.

[Sardonicus]

This is pretty much how almost all old school dizzy vacuum advance systems are plumbed in, its only the late 70's onwards carb systems fitted to Japanese cars prior to EFI that throw a spanner in the works with their dual capsule advance & retard systems

[Boosted LS1]

Sardonicus said:

with their dual capsule advance & retard systems

Crikey, you've lost me there. I'm all in a tizzy now. Bedtime for me, I need sleep without nightmares, lol.

[Sardonicus]

Boosted LS1 said:

Crikey, you've lost me there. I'm all in a Dizzy now. Bedtime for me, I need sleep without nightmares, lol.

ETA

[MPO]

Guys, thanks for all your responses

So, can anyone confirm that the vacuum still works when the plenum is opened up to 72mm?

Love the video, I hope the guys Mrs didn’t see the carburettor on the kitchen table!

Cheers

MPO

[blitzracing]

cant see why it should not work- you are not altering the angle of the throttle plate or the position of the hole.

[Boosted LS1]

Vacuum is vacuum. When the throttles closed there will be vacuum, a lot of it regardless of throttle size.

[Sardonicus]

I think the OP'er is wondering that when modded for the bigger butterfly the advance take-off will still be the right side of the throttle plate of course the answer is yes providing the butterfly is set correctly after the machining work