What Is Your Vacume Of Your Rb25Det?

[cosworth1971]

What vacume are you seeing with your r33 at idle?

Im trying to work out if i have boost leak that could cause my R33 GTST car to be overboosting to around 13psi with the std actuator.

It was giving me 20psi vacume at idle but after checking some pipes its now 15psi vacume, the serario of boost leak cause overboosting is confussing me but it makes sence if the actuator doesnt get pressure?yet still im confussed lol

Im still learning with turbo cars and pressure turbo systems so please correct my thinking if its wrong?

I have worked out i am hitting boost cut at around 12 psi but what i cant work out is why im boosting that hard, no boost controller(directly hooked up to motor for min boost) Actuator feel free and shuts ok.

It was running ok for one day and held 10psi firm with no issues but now issues back.

I think its boost leak giving me boost creep from 10 to 12-13?

[AngryRB]

boost creep is not to do with boost leaks its to do with the wastegate setup,

if you have a leak in the hose that connects to the wastgate then yes you'll have more boost,

did you hook it up correctly yet???

Edited August 15, 2012 by SliverS2

[cosworth1971]

Not yet as only the std nipples are there(one in incooler pipe before throttle body im currently using and one nipple on bov return line i have blocked off)

im planning to tap the pipe just after the turbo soon as i buy a nipple and some epoxy type stuff..

What is annoying is that it was running ok the other day.

My blitz intercooler uses the std top engine pipes and crosses over under the cooler so top pipes are all still standard.

[Mitcho_7]

You should have a vac hose running from the nipple on the hot side cooler pipe straight to the actuator if you have removed the stock solenoid.

[Moodles2]

20psi of vacuum? yeah right

[89CAL]

You can't really measure vacuum in psi. for what it's worth everyone's vacuum will be different. tune and setup will change vacuum at idle so it will not really help you diagnose this problem

[GTSBoy]

You can't really measure vacuum in psi.

Oh come on! That is not true. You can use any pressure unit you like to measure any positive or sub atmospheric pressure you like. There is no difference. The only argument that you can make is that psi is a stupid pressure unit that we should have stopped using in Australia in 1966 when we adopted the self consistent SI unit system.

[GTSBoy]

Oh, and to the OP, the pressure you were seeing at -20 or -15 "units" was almost certainly not psi. Have a closer look at your guage. The boost side will probably be in psi, but the vacuum side will be in some other unit. FWIW, if your vacuum is only about 15-20 inches of Mercury (another stupid f*kking pressure unit) then you either have a sloppy motor or a leak.

[89CAL]

Oh, and to the OP, the pressure you were seeing at -20 or -15 "units" was almost certainly not psi. Have a closer look at your guage. The boost side will probably be in psi, but the vacuum side will be in some other unit. FWIW, if your vacuum is only about 15-20 inches of Mercury (another stupid f*kking pressure unit) then you either have a sloppy motor or a leak.

This is more what I was getting at. People often put -15psi vacuum, when as far as I'm aware it would be more like a fraction of 1 psi, or a positive measurement in PSIa. I'm not going to start off the whole PSIa vs PSIg argument again. I dont like using -psi because theres not really any manufacturer, aftermarket or OEM that uses it

mmHg or inHg is used because it has a neutral, a positive and a negative. I've used a mmH20 gauge to measure blowby (From memory) on a diesel engine and it works really well, even if it doesnt make sense to alot of people.

Most gauges now are digital anyway, which makes it easier then carrying around a long mmH20 gauge everywhere

But most I've seen will change units when measuring boost vs vacuum. kPa negative, Kgcm^2 positive

Anyway back on topic:

As I said theres not alot of point in comparing setups as its to varied. Mine gauge will sit on -14 in summer and -16 in winter, and adjusting timing I can get it to sit anywhere between -18 and -12. I'm also running 3" Cooler piping which will make some difference

[KiwiRS4T]

Not yet as only the std nipples are there(one in incooler pipe before throttle body im currently using and one nipple on bov return line i have blocked off)

im planning to tap the pipe just after the turbo soon as i buy a nipple and some epoxy type stuff..

What is annoying is that it was running ok the other day.

My blitz intercooler uses the std top engine pipes and crosses over under the cooler so top pipes are all still standard.

Never mind the epoxy just drill and tap the turbo housing.

[GTSBoy]

This is more what I was getting at. People often put -15psi vacuum, when as far as I'm aware it would be more like a fraction of 1 psi, or a positive measurement in PSIa. I'm not going to start off the whole PSIa vs PSIg argument again. I dont like using -psi because theres not really any manufacturer, aftermarket or OEM that uses it

mmHg or inHg is used because it has a neutral, a positive and a negative. I've used a mmH20 gauge to measure blowby (From memory) on a diesel engine and it works really well, even if it doesnt make sense to alot of people.

Have you ever stopped to wonder what happens to "mm of arbitrary liquid" pressure units when the local gravity field is not 9.807 m/s^2 ?

There is only one pressure unit that we should be using. That is the Pascal, and its SI multiples and fractions.

[89CAL]

I'm not arguing what we should and shouldnt use. I'm just saying what I have seen

Shouldn't have opened up that can of worms.

I'm not turning this into an argument, especially seen as I gave up physics years ago.

It's all good

think OP has disappeared anyway

[pipster11]

Have you ever stopped to wonder what happens to "mm of arbitrary liquid" pressure units when the local gravity field is not 9.807 m/s^2 ?

There is only one pressure unit that we should be using. That is the Pascal, and its SI multiples and fractions.

i hope you also take into account change in local barometric pressure then if your getting that accurate

pretty sure most boost guages also work in psi or bar for positive pressure and mm/inHg for negative (mm/inches of mercury)

pretty sure most of the cars i've had have been around 10-15 inHg at idle

you are also not likely to detect a boost leak at idle as the silicone joiners that usually leak will be under vacuum and seal themselves against the pipe

but i have heard of people spraying start-ya-bastard on the joiners as you can head the engine pickup if some spray gets in

[GTSBoy]

i hope you also take into account change in local barometric pressure then if your getting that accurate

pretty sure most boost guages also work in psi or bar for positive pressure and mm/inHg for negative (mm/inches of mercury)

Some people design equipment that gets used outside the Earth's local environment. If they were so backward as to use units of pressure that relied on the height of a column of liquid, then there was be at least 2 ways that they could have spectacular calculational failures. Just like when the Mars probe smacked into Mars instead of landing on it because one group of engineers was using SI units and the other was using US customary units. It is 2012. Time to give up on shithouse units. All I'm saying.

As to me correcting for local barrometric pressure....yes, in fact, when I am doing pitot measurements of air flows in industrial equipment (and various related exercises) I do in fact calculate the actual air density based on the actual local pressure (and elevation) and temperature. Of course I do. Anyone who doesn't is just being lazy.

[89CAL]

This (not talking pressure, but similar subject):

[pipster11]

Some people design equipment that gets used outside the Earth's local environment. If they were so backward as to use units of pressure that relied on the height of a column of liquid, then there was be at least 2 ways that they could have spectacular calculational failures. Just like when the Mars probe smacked into Mars instead of landing on it because one group of engineers was using SI units and the other was using US customary units. It is 2012. Time to give up on shithouse units. All I'm saying.

As to me correcting for local barrometric pressure....yes, in fact, when I am doing pitot measurements of air flows in industrial equipment (and various related exercises) I do in fact calculate the actual air density based on the actual local pressure (and elevation) and temperature. Of course I do. Anyone who doesn't is just being lazy.

fair enough if its something important and a variance in pressure is actually a big deal

i thought we were talking about boost gauges

i still don't get why jap boost gauges come in american units too

i'm all for metric units, it makes my life a lot easier

[cosworth1971]

Hey guys, yeah i was not think right and yeah it's obvious now i think about it, boost pressure is way more than vacume would ever be,

The whole reason i was asking about vacume was seeing if it could be a diagnosis for boost leak, well good story today as i think my fmic was leaking.

One $4 clamp and no more overboost, coil pack type missfire feeling.

My car has actually never felt so crisp or fast, it boost well to around 9psi.

Before my car had a very soft but loud feeling, it would boost fast but i think it was free boosting?, with the air leak the power was very on or off, it felt sluggish and the exhaust was loud.

Anyway thankyou everyone for your input, ive now learned about the mercury system lol,hope my car cotinues to run well but fnger crossed.

I plead to everyone to check there car for air leaks, your car might be lagging and you dont even realise it, i thought my issue was coilpacks but now im thinking it wasnt even electrical.

If we do a forum catch up ,beers on me

Edited August 16, 2012 by cosworth1971

[AngryRB]

good to hear its fixed, but i would of thought the boost would of gone even higher after a boost leak was fixed...

when i fixed my boost leak it didnt drop in boost.

you sure you didnt just find a hidden boost controller or somthing??

Edited August 17, 2012 by SliverS2