Series 2 On Boost

[Punk72]

gday all

I put a new/more accurate boost gauge in the other day and after taking it for a drive in the country (which was a lot of fun) I found that it comes onto

boost at about 9 psi down low in the rpm, until about a little over 5500 it starts to drop off and gets down to about 7 psi so its loosing about 2 to 3 psi.

Its hard to watch the boost gauge and stay on the road at the same time so these are a little ruff but i do know that there is a fair decrease in boost

high up in rpm and actually feels sluggish at high rpm

After reading a lot of posts on here i am under the impression that the c34 was supposed to have a 2 stage boost setup but mine starts off at 9psi, I have had a look at the boost solenoid and all vacuum hoses and they all look stranded, no cut wires or modifications.

I wouldn't mind so much if it was 1 psi that i was loosing but a couple?!

any ideas

cheers

[mattye]

Hey dude.

The autos came with the 2 stage boost solenoid, and the manuals ran straight 10 psi peak. I'm pretty sure thats what it peaks at.

So sounds a bit off. I'm not quite sure but it could have something to do with the wastegate, or what ever they use instead of a blowoff valve. I belive it would be just plumed back, so there would be a spring that when the preasure built up it would compress it and allow air back past. Same idea as a wastegate

Sounds as though when u peak ur loosing too much preasure so perhaps something is staying open too long. So a spring may have lost its tension.

Anyways just what it seams like to me. Give a mechanic who has experiance on RB25s a call. They might know.

[KiwiRS4T]

Bypass the solenoid and see what happens (possibly faulty but good idea to bypass it anyway). Do a search to find the pics

Instructions courtesy of SK:

This is the 10 minute no cost boost to 0.5 bar rerouting of the vacuum hoses. Disconnect the two vacuum hoses from the solenoid. Then connect the boost feed (from the cross over pipe on the left of the picture) to the standard T piece. Connect one side of the T piece directly to the wastegate actuator (on the right of the picture). The remaining connection on the T piece goes back into the inlet via the BOV return pipe (on the standard fitting). Make sure to put the standard brass restrictor in that vacuum hose to bypass the desired amount back into the turbo inlet. The standard bypass hole of 1.25 mm bypasses enough air flow for 0.5 bar. (See photo)

PS: If you want more boost you can drill out the bypass, 1.5 mm = more boost (around 0.7 bar) 1.75mm = a bit more (around 1.0 bar).

OK, this is the picture of the vacuum hoses. The boost pressure comes out of the intercooler return pipe (that's the big black one on the left) via the standard fitting. It travels down the vacuum hose to the standard T piece.

The right hand side of the T piece goes to the wastegate actuator via another short piece of vacuum hose. It has 2 standard spring clamps on it. So that "some" of the boost pressure goes to the wastegate actuator.

The left hand side of the T piece is connected to another (longer) piece of vacuum hose that goes to the standard fitting on the BOV return pipe. You can't see that fitting in the picture as it is hidden by the (big black) turbo to intercooler pipe. I squeezed the standard restrictor into that vacuum hose, it is tight fit, so be patient and use some lubricant (RP7 in my case).

The restrictor limits the amount of boost pressure that is bled off, so that the "some" pressure that goes to the wastegate actuator is actually less than the boost pressure. This means you get more boost before the wastegate opens at its usual 4-5 psi. How much more depends on the size of the hole in the restrictor, the bigger the hole the more it bypasses and the higher the boost.

The standard hole is ~1.25 mm and gave ~0.5 bar on my Stagea, which has standard everything else (no exhaust, no FMIC, std filter, etc). If you have mods, you may not get the same boost pressure, so you may have to adjust the size of the hole in the restrictor, it is brass so you can easily solder it up and redrill the hole smaller if necessary.

[Punk72]

The autos came with the 2 stage boost solenoid, and the manuals ran straight 10 psi peak. I'm pretty sure thats what it peaks at.

yeah that sounds right, as mine is a manual. thats maybe one part answered, i am maybe thinking its the factory bov

[mattye]

Yeah dude...pretty sure it would be a factory bov plumed back. though was it just dropping under hard throtle? Probs wastgate opening to stop the turbo overboosting and staying open too long.

Maybe. I fix planes not cars so not 100%.

[QWK32]

Still running the stock exhaust? Or even just the stock dump and cat? They can be very restrictive and can cause a slight drop in boost top end.

Another theory is that if standard it only runs 7psi in "high" boost mode, and the stock boost soliniod has been wire/piped open then you may be experiencing a boost spike to 9psi early in the rev range before it settles down to the set 7psi.

[ssshonky]

What boost controller are you running?( sorry I admit I am slack and didnt read the entire thread )

Sounds like it might be your boost controller letting you down. You would do well to stick it on a dyno so you can get an accurate reading of your boost levels ( and AFR etc )

I ditched the standard boost controller and got a TURBOTECH boost T . They use a spring and ball arrangement to build boost as fast as possible. Warning though they are very fiddly to adjust - but having said that they are cheap enough so give it a shot.

the guy who took lotty out on the AHD track day said our stag felt a bit quicker than the others. so I wonder if the boost controller had anything to do with that?

http://cgi.ebay.com.au/Turbotech-manual-tu...A1%7C240%3A1308

[RBPOWA-(TJ)]

mines running 10psi full 3inch

[pork hunt drifting]

mine seems to hold same boost right through rev range, going by standard boost gauge (right on line between 0 and 7) but yeah its hard to go flat out and watch road and gauge.

ild hate to think its runing 10 pound stock, cause i want more out of it now im used to it. can anyone confirm 100% rs4s does.

oah and my mods are only pod and rear muffler replaced with pipe.

[Punk72]

every thing is factory except 3inch cat back, the cat was replace for importing so i might rip it off and have a look to see what diameter the opening is.

I went out and bought a bov today ( gfb gt hybrid ) but doesn't get it till Friday, I can hear a slight hissing noise coming from around the bov area when the car is running and when you turn the engine off it keeps hissing for a second, Not sure if thats supposed to happen, guessing not!

probably should have checked all these things before posting, But where would be the fun in that

cheers

[Punk72]

mine seems to hold same boost right through rev range, going by standard boost gauge (right on line between 0 and 7) but yeah its hard to go flat out and watch road and gauge.

ild hate to think its runing 10 pound stock, cause i want more out of it now im used to it. can anyone confirm 100% rs4s does.

oah and my mods are only pod and rear muffler replaced with pipe.

yeah my stranded boost gauge said i was running 7psi and holding all the way through, Its a different story with a accurate gauge.

[Jezboosted]

I have noticed a very similar thing in my rs4s. It goes up to 12psi, then once it gets to roughly 5000rpm, tapers down to 10psi. I fitted an autometer boost gauge to get more accurate readings.

At first i thought it was from having std dump pipe on the 3"catback, so i got the JJ stainless dump, and it's still there.

I am running a Turbosmart Manual bleed and from what i have read, nothing short of an EBC will sort it out. I am currently looking into the jaycar kit.

Hope i am on the right path !

[Punk72]

I have noticed a very similar thing in my rs4s. It goes up to 12psi, then once it gets to roughly 5000rpm, tapers down to 10psi. I fitted an autometer boost gauge to get more accurate readings.

At first i thought it was from having std dump pipe on the 3"catback, so i got the JJ stainless dump, and it's still there.

I am running a Turbosmart Manual bleed and from what i have read, nothing short of an EBC will sort it out. I am currently looking into the jaycar kit.

Hope i am on the right path !

yeah sounds about right, I am not running as much boost but yes, I am pretty confident that it isnt the exhaust being to restrictive. Are you running

stranded bov?

Strange question but are you located in Hobart?

[Jezboosted]

Running a hks super sequential plumb back and located QLD.

[BKC34]

you said earlier that you can hear a hissing sound? is it like a high pitched whine ( sorta like a supercharger) or like someone blowing on a gum leaf? how many kms on your car? does the sound come on as soon as you accelerate? if its over 100 000 kms it could be your exhaust manifold gasket...

not a fun experiment, i've just got my turbo and exhaust manifold off as well as my old dump and cat (got the jjr stainless one and x force cat )

it could also be your turbo however, im getting mine checked tomorrow by a pro to be sure

[Punk72]

you said earlier that you can hear a hissing sound? is it like a high pitched whine ( sorta like a supercharger) or like someone blowing on a gum leaf? how many kms on your car? does the sound come on as soon as you accelerate? if its over 100 000 kms it could be your exhaust manifold gasket...

not a fun experiment, i've just got my turbo and exhaust manifold off as well as my old dump and cat (got the jjr stainless one and x force cat )

it could also be your turbo however, im getting mine checked tomorrow by a pro to be sure

only 54000km and it sounds like a vacuum leak but from a small hole so fairly high in sound, had another look last night but couldn't find it.

Doesn't do it when car is cold and you can only hear it when idling

[mattye]

correction not 10 psi. 7. Or half a bar

[mosquitocoils]

Hey guys, sorry to bring up an old thread, but I'm having related issues with my boost solenoid... When talking about the boost restrictor (remembering that the sizes involved are very small), do you think that the size of the vacuum hose would change anything?

I'm running 4mm hose for everything around there (to and from solenoid, to actuator, to BOV return line etc) and I'm not getting the extra 2psi bleed off.

[KiwiRS4T]

By-pass the solenoid (instructions elsewhere) and then regulate the bleed to get the desired max boost.

Then save up for an electronic boost controller.

[dirtyRS4]

By-pass the solenoid (instructions elsewhere) and then regulate the bleed to get the desired max boost.

Then save up for an electronic boost controller.

Yeah what he said - but go a dual solenoid electronic boost controller.

I think chefstagea has one going for cheap.