How To Read Your Factory Boost Gauge

[96GTS25Tii]

Hey dudes I finally found out how to read the factory skyline gauge (if you like me haven't installed a better aftermarket one)

Anyway based off a useful article in the members section of SDU (The Sky is the Limit) which had the formulas needed. The skyline gauge is a measurement of millimeters of mecury as follows:

760mm HG (mecury) = 1 Bar = 14.6PSI

So I complied the following list so I could decipher my gauge and I though it might be useful for other people who don't have a proper boost gauge yet.

Sky(7) is the gauge in increments of 7 (i.e 0 to 7)
Sky(1) is the same gauge but in increments of a whole (i.e 0 to Full)

PSI -------- BAR ------ Sky(7) ---- Sky(1)
0.000 ----- 0.000 ----- 0.000 ----- 0.000
1.000 ----- 0.068 ----- 0.522 ----- 0.075
2.000 ----- 0.137 ----- 1.045 ----- 0.149
3.000 ----- 0.205 ----- 1.567 ----- 0.224
3.360 ----- 0.230 ----- 1.755 ----- 0.251
4.000 ----- 0.274 ----- 2.090 ----- 0.299
5.000 ----- 0.342 ----- 2.612 ----- 0.373
6.000 ----- 0.411 ----- 3.134 ----- 0.448
6.720 ----- 0.460 ----- 3.510 ----- 0.501
7.000 ----- 0.479 ----- 3.657 ----- 0.522
7.300 ----- 0.500 ----- 3.813 ----- 0.545
8.000 ----- 0.548 ----- 4.179 ----- 0.597
8.760 ----- 0.600 ----- 4.576 ----- 0.654
9.000 ----- 0.616 ----- 4.701 ----- 0.672
10.000 ---- 0.685 ----- 5.224 ----- 0.746
10.100 ---- 0.692 ----- 5.276 ----- 0.754
11.000 ---- 0.753 ----- 5.746 ----- 0.821
11.500 ---- 0.788 ----- 6.007 ----- 0.858
12.000 ---- 0.822 ----- 6.269 ----- 0.896
13.000 ---- 0.890 ----- 6.791 ----- 0.970
13.400 ---- 0.918 ----- 7.000 ----- 1.000
14.000 ---- 0.959 ----- 7.313 ----- 1.045
14.600 ---- 1.000 ----- 7.627 ----- 1.090

So thats it, I hope its helpful
Ajay

[GTR-80Y]

wahhh!! just found out last week that the mmHG was torr.
wat should it reach from factory..?? That is a series 1 r33 gts25-t?? mine does just under halfway...(nearly 3.5???)

[96GTS25Tii]

Hey Man,

I have a 96 GTS25T Series 2,
It was stock standard when I got it - it ran about .5 Bar which is around 7psi or around halfway on the factory gauge.

After getting a full 3inch exhaust from the turbo, the boost actually decreased slightly (note I am using the factory boost still) this is because the computer retards the boost if it thinks it is overboosting.

So to solve this I am getting a turbosmart boost controller in the weekend. Hopefully should be safe to run 10-11 psi.

Ajay

[GTR-80Y]

decreased?? did it make you much slower? gettin a full 3 inch sys too..i thought i would be quicker....such crap boost from factory though! i got a series 1. where abouts you get your exhaust done?

[96GTS25Tii]

It decreased because I am still using the factory boost, and the computer senses that it is overboosting so it then retards the boost to the saftey boost level which is about .5 .

Once I get the the turbosmart boost controller all will be good!

The place where I got my exhaust done is awesome, really on to it people.

Please note it is not the exhaust that has retarded the boost - it is the factory boost controller sensing overboost.

Ajay

[mincemeat]

Originally posted by 96GTS25Tii
So to solve this I am getting a turbosmart boost controller in the weekend. Hopefully should be safe to run 10-11 psi.

Make sure you bypass the factory boost control solenoid altogether or strange things will happen with boost spikes, etc.

Cheap and effective, those things...

[flupstar]

Ok Im really peeved today, Im on the verge of blowing $300 on a pretty apexi boost guage.

I have a blitz turbo timer which doubles as an electronic/digital boost guage. I am aware that the R33's factory boost guage may be a couple of psi inaccurate but my two guages are ridiculously different. Where the electronic guage (which I assumed would be accurate) shows 1 bar, the factory guage is displaying around 5.6 mmHg which is only some 7.something bar. I have had temporary overboosts where the guage burst to 7mmHg and didnt detect any detonation (but got a nice gutful of power and I have a feeling that this factory guage may be the more accurate of the two.

Also.. where the factory guage stays constant throughout the rev range, the electronic one is less consistant, initially boosting high and then dropping off.

If anyone has any suggestions as to how I could work out how much boost Im really running or as to why these guages are different.. please speak up! I might order one of those pretty backlit apexi things anyway... if I have the money. Time to go online banking! DD

[mincemeat]

Any boost gauge should be connected from a vaccum source tapped from the manifold. Check your Blitz item first?

[OzGTR97V]

Warning on the STD boost gauge in GTR's and GTS's, they are not an accurate readout of what you are boosting too, especially if you get up above 10 LB or .7 Bar under the bonnet.
When I first started to increase the boost on my GTR, and I thought I was boosting up to .7Bar, which I thought, was safe. I drove on that setting for about 2 weeks until I went to my mate's performance shop. I took him for a drive and he said there was no way a stock GTR should hammer like that on 10Lb, so we checked it against his workshop HKS gauge which he gets checked once a month. I was actually running 1.2 Bar, thank god I had the steel shaft and wheels upgraded on the turbo's, other wise bang!!!!!!
I personally don't have an after market one installed in the car but anyone who does not want to destroy their Turbo's or engine should be using an aftermarket gauge to tune the boost and also have it checked against a workshop one.

P.S. on a GTR if your stock gauge gets up to .7 on the dial, you are running anywhere from 1Bar to 1.2 Bar.

[GTR-80Y]

Hey where did you get your exhaust done 96GTS25?? really need to get one on in the next 2 weeks!?

[96GTS25Tii]

Hey GTR-80Y

Got my exhaust done at Midas in Porirua, NZ - Awesome job. But this won't help you if you are in Australia

Also BTW, found out my boost went down cos actuator arm got stuck , freed it up and installed a turbosmart boost controller valve - its all good now. Running bout 10psi

I got a bolt on 3" system (no cat) from the turbo back.
I am also getting a custom built ProMuff Stainless muffler installed on saturday - I found that the straight through barrel type was way to loud (for me) so I got Promuff to custom build me a stainless oval one which will be quiet but still maximise flow. The cost for the muffler is $NZ480

Hope this helps

[mincemeat]

96GTS25Tii,

When Midas did your exhaust did they recommend two straight-through mufflers fitted in series?

[96GTS25Tii]

Yes,

I resonator up front, then the straight through rps stainless muffler, but that was too loud, so another resonator was added, but again it was still too loud.

So I am getting an offset muffler custom built by promuff, so should be much better

[Nemesis]

Midas Porirua do an awesome job, I would very highly recomend them if your looking to play around with ya exhaust system.

Ant:alien:

[EDS33T]

GTR-80Y
I had my exhaust done at liverpool exhausts, they done an excellent job. For a full 3" from the turbo to the 5"tip in stainless steel with a high flow cat, resonator, and straight through muffler it cost $1500 all up.