4psi at plenum, 2psi on manifold!?!
Turbo Mini Forums

Hi guys,

I had my boost gauge plumbed inline with the actuator off the plenum and I got a consistent reading of 4 psi when on boost. I changed it today to the take off for brake servo ( before the one way valve) and it now reads 2 psi when on boost. The car doesn't feel any slower so is this normal??

Which boost figure is accurate??

Don't take offs for servos have a one way valve to stop the servo getting boost?

Are the gauges accurate at boost levels that low?

It's before the oneway valve so shouldn't make a difference and it read 4 consistently up until I swapped the position!

I would expect that. You should really take the tap off for your boost gauge from the inlet manifold between the head and carb butterfly. Fitted this way you will see vacuum on idle

Own the day

The takeoff is on the inlet manifold! I drilled and tapped a hole in the top of the bolt that secures the banjo connection to the servo. I see vacuum on idle just not as much boost as I did this morning when it was off the plenum.

a carbs always going tpo drop a little pressure due to having a venturi,

Is this with full throttle?

Yeah full throttle it only ever shows a max of 2 psi. I plan to fit a bleed valve and increase pressure to 7 but is it safe to take the reading from the manifold when I know actual plenum pressures is higher ??

yep, take it from the manifold, this is what the engine is actually getting.

Excellent! My question now would be...
If the STD metro turbo ran 4/7 psi measured at the plenum then is 7 psi at the manifold still safe to run on a STD 9.4 cr engine?

yes

Sweet cheers fella!

Also if you dont have the blled solenoid and computer fitted you will get very little boost as the waste gate actuator see plenum chamber pressure and start to open the moment you start to produce boost thus very low boost figure.

Own the day

The standard Metro surely ran 7psi at the manifold.

you could run 15psi on 9.4:1 with a good setup and an intercooler.

Edited by wil_h on 18th Sep, 2011.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

I was confused as the actuator is set to allow 4 psi and without a bleed valve this is what I measured at the plenum. I seems 4 is actually 2 and 7 is

Sorry stuPid I phone... And 7 is more like 5 ish?

Maybe not explained the best but what I'm getting at is ... Did the metro turbo actually only run 5 as measured at the manifold?

It runs at 4 psi at the turbo outlet without the boost solenoid (assuming it is still plumbed up as per the factory install). With the solenoid fitted the boost will increase to 7 psi at the plenum. If you have no intercooler fitted, turbo outlet and plenum are virtually the same anyway.

With the restrictor in the plenum,what press drop would you expect between plenum and manifold?Presumably depends on airflow.

'Where does the engine go?'