stratman

Hi

Just fitted a boost gauge (HKS) but could someone advise me as to what I should expect to see on the gauge with a healthy MY96 UK car?

I hits 0.9/1.0 bar, which I understand from reading other threads, is what should be expected, but this a peak and does not hold for long. In fact the gauge shows a vacuum a lot of the time....on the move not just at idle.

Is this normal?

Denis

AlexM

Denis,

This is perfectly normal...

Boost levels sound quite good for a MY96UK c1.0bar.

The reason you see vacuum at idle and on the move is because the pistons are trying to fill the cylinders during the induction stroke, and the throttle is causing a restriction in the inlet tract when partially closed as it is at cruise or idle.
This drops the pressure in the inlet manifold below atmospheric.

Cheers,

Alex

Gizmo555

MY00

At idle and on run down ~ -10psi
Any small throttle and goes +ve
Peaks at ~15psi (~1 bar) and then drops to ~13psi quite quickly and then to ~10psi as red line approaches.
Won't see this in first gear cause turbo can't spin up fast enough

Tim Taylor

Hi Denis

Sorry to hijack your tread but I fitted my boost gauge today - running -18psi normal, peaking at 15psi then falling to 13-14 psi. Does my vacuum figure sound right, it seems low?

Tim

rroberrto

Hi Gizmo,

Can you explain why can't i achieve full boost in first gear? I'm asking this since i always thought the turbo's speed is governed by the amount of exhaust gas, which in turn by load and RPM and not speed or gear. Or is this ECU related protection thing like in some SAABs(automatics) where max power is reduced by certain ammount at first gear, supposedly for reduction of torque steer?

Roberto

stratman

Gizzmo
Thanks for that info. Mine is almost identical to what you describe, so thats reassuring.

Tim
My gauge shows -0.7bar (-10psi) on idle, on over run, and on cruise.

1.0bar peak dropping to 0.7/0.8bar on hard acceleration.

This is more or less what Gizzmo has confirmed, so yes, -18psi sounds a bit low by comparison.

Denis


[This message has been edited by stratman (edited 08 April 2001).]

[This message has been edited by stratman (edited 08 April 2001).]

pat

Tim,

running minus 18 PSI is impossible, that's beyond absolute vacuum... if you mean it's overboosting to 18 then faslling back, that's a bit more than usual, but not catastrophic.

FWIW, my boost I'm still mapping, running between -0.8 and -0.7 bar at idle... these cars really "suck" LOL

Cheers,

Pat.

Tim Taylor

Hi Pat

Just been out and checked my reading, they are:

-22psi on idle
+14psi peak
+13psi held

This is on a MY99 with full decat exhaust. The vacuum figure does not sound right but the peak and held figures seem OK.

Any thoughts on this?

Tim

bigdog

Hi Tim Taylor and all.

You may well find your answer at the end of this thread.

Gizmo555

Rroberrto

No idea, just remember reading it somewhere. Also too scared to look at A pillar boost gauge under hard acceleration in 1st for fear of crashing, everythings happening too fast

Gizmo

Clarey

This might explain:



The unit of measurement for vacuum values is in.Hg not PSI (dont know what the conversion is though)
My vacuum reading is also around 22 in.Hg and boost holds around 15 and try's to peak over 18 in certain gears but can't

Phil.

Tim Taylor

Oh I see...didn't look that close at my gauge!!

Now lets find the conversion chart...

Tim

Neil F

I've just fitted a boost gauge which reads Bar and was wondering what I should expect from my STi4.
I get 500hg/mm on idle vaccum (more on overrun) and 1.2bar (+ a bit) peak boost and 1.1 held.

Is this normal doctor?

Neil.

Steve vRS

1 psi = 2.036024 inHg

1 psi = 0.068948 Bar

1 inHg = 0.491153 psi

1 bar = 14.50377 psi

1bar = 10 000 Pascals

1 Pascal = 1 N/m2

Vaccum is zero pressure when the units are absolute pressure or -1 bar (-14.5psa etc) when the units are gauge pressure (ie atmospheric pressure is zero psi).

Steve

James_Harvey

All sounds OK....

My MY98 vacuums around 20 in Hg (whatever that is).

Boost is only 12PSI, but the car is restricted... thats why a went out and bought an HKS EVC IV. That reads vacuum of -0.6 Bar on idle.

James.

Stelios

in Hg = height in inches of Mercury (Hg)Ancient pressure units based on Barometer Column Height ,I think 760 mm Hg = 1 atm
(love being a smat@ss)

Tim Taylor

Cheers Steve

That makes my vacuum 10.8 psi - about normal.



Tim

GREEN SCOOBY

1st gear 0.8 bar peak
2nd gear 0.85 bar peak
3rd gear 0.85/0.9 bar peak
4th gear 0.9/1 bar peak
4th gear 1 bar peak
holds boost good in gear after peak
Does this sound alright for a uk my 97 car ???????????

Jza

Ive got a uk MY01 WRX - and ive noticed that if you floor it from low revs in 2nd or 3rd i get 0.9 bar, but if im already at say 5000 rpm i only get 0.7 bar!

And this seems to vary - i know it sounds daft but i get less bosst when its raining!!!

Is that a normal subaru trait?

Jza