The 'E' Type Forum

Slightly off topic. Sorry.

I have an MGB and I'm fitting a supercharger to it.

Can I take vacuum for the brake booster from the inlet manifold?

Hi Andrew

Surely you need to take vacuum from supercharger inlet/carb outlet. Inlet manifold on engine will be positive pressure.

Yes, you can.

As long as you retain a butterfly throttle you'll still have -ve depression in the inlet manifold during some parts of the engine's operational curve which you can harness.

You could add a vacuum reservoir as Jaguar did on the E type to increase the volume of vacuum in reserve.

Or you could look at what other manufacturers have done in the same situation. Audi initially substituted a hydraulic servo assistance. Nice and compact but expensive and dropped it later to return to vacuum.

Diesels have the ultimate problem since they have no restriction on inlet flow and no possibility of generating vacuum. In my limited experience they substitute mechanically driven vacuum pumps so you could add one of those if you find in practice you're not generating enough vacuum for your braking needs or I'm sure an electric equivalent is available.

By way of example:
https://vi.aliexpress.com/item/10050062 ... ry_from%3A

Thanks John for the detailed reply.

There are small vacuum pumps that are often used by muscle cars with big cams.

I've just bought one.

https://www.ebay.com.au/itm/315933698085

Every day is a school day. So I was wrong about there being vacuum at supercharger inlet. Must do some more research to understand because that seems odd.

Enjoy your supercharged B Andrew!

The supercharger can see vacuum, it depends where it is in the inlet configuration.

If it's after the throttle butterfly, Bentley blower style, then it will see partial vacuum at some parts of the engine's operations such as at idle or over-run.

The supercharger can only pressurise air that's fed to it so if at a moment in time it's inlet is a partial vacuum it's output will be similar since there's no air for it to compress.