[DML] SuperCharger and Engine Vacuum
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[DML] SuperCharger and Engine Vacuum

Hi Martin and David,

Thanks for the help. 
I was in a huge rush last time i posted and did not explain it at 
all properly. 
The situation is that i started this project about a year ago 
stripped all the accessiores, manifold, water pump etc etc. The 
whole block was cleaned and the manifold and rocker covers 
powdercoated, a new water pump, supercharger mounted and re 
assembled and put back in a freshly blasted and powdercoated frame. 
That is were it has sat under a sheet for the past year.
My memory has faded on how all the systems worked that i had 
previously studied before removal. As i was removing the K jetronic 
anyway alot of the components that i removed would never be re-
installed. (i do have a workshop manual also)

The brass tube that you mention below is the one i was talking about 
and with the EFI system i dont require a cold start value or an idle 
speed motor (the GM throttle body i am using has one). I was 
addiment that that port was connected to all 6 intake ports (as i re-
installed the manifold) but the reason for my question was the guy 
doing the supercharger pumbing for me thought that the Volov's went 
right through into the valley and i did not want to remove the 
manifold to prove my point. 

>The big long one with the cold start injector on the
>end serves to apply engine vacuum to the oil filler, to the charcoal
>cannister, and connects directly to the centre of all siz intake 
>so is connected to the idlespeed motor, and the cold start injector.

I asked this same question some time ago (a year) and one of the 
responces i recieved was that the crankcase was under constant 
vacuum. I coulnt see how that was the case and from the responces 
this time i see that it is not.

>I would install a non-return valve in it through so you 
>end up pressurising the crank case too much to the point of blowing 
>out through the main seals. However the Renault ones don't have the
>vacuum feed, just the breather. The cap is clipped on and the 
>has a catch tank that feeds back to the sump.

That was my other thought. To have an alloy tank made that the oil 
cap breaths into and have that feeding back into the sump. 

The root of all my questions really was: If i have no Idle speed 
motor, char.canister, or cold start value, do i require this long 
brass tube especially if it will be under preasure most of the time 
and not vacuum. And if i dont have it and capp it off at the 
manifold what do i need to do with the small tube coming off the oil 
filler cap??? Capp it off or re-direct it to another source?? If i 
figure this out then i can move forward.....

>A blow-off valve (dump valve over here) is there to vent boost when 
>throttles shut and is actuated with vacuum downstream of the 
>It doesn't do anything at idle.

The value i was having installed is a Bosch unit that at idle it 
opens to re-circutale the boost back into the intake before the 
throttle, been a belt driven supercharger with no magnetic clutch it 
will be spinning and boosting (although not much) at idle. This 
simply acts to reduce the load on the motor at idle so it is not 
permantly under boost preasure. Once the throttle opens the valve 

When car is running i will decide on weather to fitt a dump valve 
depending on boost preasures. The supercharger pulley was machined 
to a diameter that should not over boost and on decelleration this 
bosch valve will open also and act simular to a dump valve.

Thanks for the advice.

Cheers, Nick

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