Canyonfive

Hydra vs Boost Gauge

which one is accurate? lol My boost going up shows the same however the gauge doesnt drop off at the upper rpms the 1 to 1.5psi the hydra shows.

LukeH

Boost leak somewhere? start checking connections.

97montego

Mines always had a 1 psi offset from the gauge at 12 psi.

I've always assumed the gauge was out a bit.

Does it matter?

Faeflora

iTrader: (2)

gauge can be off and also

gauge is relative pressure

hydra is absolute pressure

Faeflora

iTrader: (2)

And. the length of the boost signal line matters. And same with if the gauge line or gauge has a restrictor.

triple88a

iTrader: (2)

Welcome back Fae

albumleaf

iTrader: (7)

Difference in psi between psi and psig is 14.7, not 1-1.5

Wrong, not over the timescale we're talking about here.

Faeflora

iTrader: (2)

No, I am ******* right about the damn boost gauge line and the gauge vs. hydra.

Line affects responsiveness pretty significantly. This is especially important for your MAP sensor.

Now go suck your **** fuckface.

albumleaf

iTrader: (7)

Yeah, definitely on the order of a couple seconds . Pressure is pressure or he has a slight leak on the line. You'd think after being wrong so many times you'd keep your mouth shut.

Aricjm15

The pressure displayed by the Hydra would be accurate if you were at sea level. It is absolute/ converted from kpa like Fae said.

albumleaf

iTrader: (7)

You don't work at UCC do you?

Like I said though, the difference between relative and absolute pressure is an order of magnitude more than the difference he's seeing, something else is the issue.

Aricjm15

No it reads in absolute. And displays in gauge pressure. The difference is because it does not compensate for altitude. If you owned and used a hydra you would probably understand.

triple88a

iTrader: (2)

The difference of absolute vs relative pressure would be seen at idle or even when the car is off. In other words the difference would be there at all times.

Now the OP says his hydra reading drops down while the boost gauge stays stationary and that happens only at the upper rpms, it sounds more like theres a leak somewhere on the boost line going to the hydra.

albumleaf

iTrader: (7)

I know what a pressure reading is. If I see 5psi on my boost gauge I know that's reading 135kPA in my DIYPNP.

Fagflora thinks that somehow the 1-1.5psi difference is coming from the difference in absolute vs relative, when that's simply not the case. Neither the boost gauge nor the MAP sensor in the Hydra compensate for altitude, I'm not sure why you mentioned it.

triple88a

iTrader: (2)

Actually the hydra is reading absolute pressure. It does not compensate for altitude HOWEVER the boost gauge is reading relative pressure. That relative pressure measures the pressure inside the pipe against the pressure it sees outside. The hydra on the other hand uses a standard calibration so unless you calibrate it your self at your current altitude you are using absolute pressure configuration at 0 altitude therefore your altitude will influence the readings.

Faeflora

iTrader: (2)

No I don't fuckign think that. I know the differential is just up top.

I still say it can be the damn boost signal lines. If you want to argue with me about it then you haven't fucked around with tuning boost enough.