Ian Sutton

Finally managed to get my boost gauge fitted and working(even though Lavender Hill Subaru insisted that it was broken).Can any one tell me the correct vacuum reading at idle and what the max boost reading should be when going for it???

I own a STI 5 with SS DP and back box and decat'd Magnex midsection.

...Ian

Trout

iTrader: (1)

0.35-0.4 bar...

...on overrun I get 0.12 bar which is very good vacuum!

IWatkins

Rannoch,

Was the 0.12 bar a typo ? Should it not be around 1.2 bar ?

Totally unrelated, but on my GT4 I get approx. -20 psi (warm idle) and up to -25 psi on overrun.

Cheers

Ian

jase cooper

1.1bar on boost- sometimes a fraction higher
-0.5 at idle
-0.7 on overrun

Is that normal? (Sti5)

jase.

Trout

iTrader: (1)

Ian,

if your car is boosting 1.2 bar on overrun then fine

Mine goes down to Row 1 (correctly) and gives a very good vacuum at 0.12bar - not typo. Best vacuum comes when the car is at high revs and there is zero load (i.e. overrun).

It's is useful to know, as a car with very good vacuum is aslo not going to blow past the rings on boost. Basically the piston is sealing efficiently.

I am not sure how good mechanical boost guages are at this level of vacuum - I am getting much more accurate readings from the MAP sensor and datalogging.

R

[This message has been edited by Rannoch (edited 04 September 2000).]

Trout

iTrader: (1)

I thought about this - best vacuum is not actually at zero load - but actually significantly negative load - overrun/engine braking...

Ian Sutton

Hi thanks for the replies,
I seem to get a reading of between 15 and 20 on the vacuum and the boost shoots to nearly 2 and holds just above 1.

Does all this sound okay, these gauges must have differing numerals/measurement on the vacuum side.Mines made by Autometer if that makes any difference??

...Ian

Bob Rawle

Rannoch is absolutely correct in his statement and is refering to absolute bar, 0.12 is -0.88 bar vac which is indeed very good for the car.

Blackscooby

So is peak boost 17PSI and -14PSI reasonable on UK MY94 ?

Ta

Mark.

Richie

I get +14psi, sometimes 15 when I go from 3rd to 4th and then plant it. Drops to about 12ish when at high revs.

-18/19 on tick over, and -24 ish on overrun.

This is on a 5k miles MY00.

Richie.

Bob Rawle

Mark, if standard with no tweaks 17 psi is a touch high for the My94, 13 psi is the spec.

Just to clear a point ... boost guages come with a variety of dial markings, psi and bar usually for boost, vac can be in bar, psi, mm of Hg (mercury) or inches of water ... all very confusing so when quoting vac figures try and also quote the unit of measure (marked on the guage usually) and then a correct comparison can be made.

Blackscooby

Bob,

Yep its "tweaked", I was more concerned about the negative boost that was being discussed in terms of getting blow past.

Boost is now down from 23~25PSI, but I damaged a piston resulting in a rebuild
But with Cosworth pistons so they can take it .
But the gearbox can't

Mark.