Dangerous power cut/jerks during WOT + high boost

[muffas 180]

Have you checked the rod thats actuates the waste gate? People bend these as a cheap means of more boost.

Michael...

[ARGH34]

Yeah, I have a feeling the bleed valve is dodgy since it was a home chop job by the previous owner. Its been taken in and out before because the car had to pass the pits.

Spoke to a guy at a workshop that I've booked in next week, he says its probably a dodgy piece of vacuum hose and they can replumb it for me, or just take the whole thing out and put it back to factory boost (which isn't a bad idea considering stock internals) so that way I'll at least be able drive past 5000rpm safely. Pretty simple job, but I guess I'll leave it to a pro to fix as I've been quoted about $60 for an hour's work on it plus the cost of a new bit of vacuum hose (although I reckon your average mechanic will probably fix it in 10 minutes).

Will let y'all know how it goes when the car goes into the shop. Thanks for all the help people

[MM2death]

Originally posted by Zahos

- a leak in the line somewhere

Exactly my problem!! Check your vacuum line for leaks!

Scott.

[muffas 180]

A 5min job for an hours labour? I knew i shouldnt have sold my workshop!

Michael...

[Zahos]

ARGH34, just go somewhere else... this guy is trying to rip you! It seriously only a 5 or 10 min job....

[ARGH34]

yeah.. my regular mechanic should know how to do it right? Just a simple bit of plumbing and changing the hoses?

I always had a feeling the "specialist" mod shops in Perth are out to rip you.

[BOoStEr]

I think the mechanic was just quoting his hourly rate not the price of the job. Most workshops have a minimum charge though which also covers the paperwork etc.

[R31Heaven]

THe dills havn,t put it in backwards. My nephew done that on his VL calias and boost went throught the roof :-)

[ARGH34]

All done. Just took out the bleed valve and replaced the vacuum hosing for about $20.

The down side is now the car doesnt feel half as fast as it did before I took the valve out and the boost was going through the roof but I suppose at least my turbo isn't going to blow...

The car is boosting happily away at 0.4 bar now all the way to 7000rpm(?) limiter - which brings me to my next question: my redline is at 8000rpm so why is my limiter kicking in at 7000? it just bounces on 7000 and doesnt want to go any higher. The boost cut is gone however.

is it possible that the redline was lowered with the powerfc previously installed? is this hard to reprogram if so?

If not, does this problem sound like anything else?

[Zahos]

No, your redline should be at 7000 or 73000 rpm? someone else can clarify this...

0.4 bar.... hmmmm, seems a bit low.

Did you not put the bleed valve back in?

[NismoR34]

Sounds like your boost has been returned to the stock output [by way of the vacuum hose replacing it - as you said]. So boost should be approx .55 bar [which = 7.9 psi]. Of course your boost limiter wont be there anymore...it isnt reaching high enough to hit this limiter [which is supposedly 1 bar]. You can probably ignore the factory boost gauge because it isnt accurate and its not in bar or psi anyway [kg/cm2]. Where did you get your figure from [0.4bar]? An aftermarket gauge or what?

Rev limit from factory is somwehre between 7000 - 7200. I know this because I have a stock ECU in my 34 and have recorded on a dyno up to 7100rpm and YES mine cuts out occasionally when I hit this range too.

If your display / rev gauge is not the original nissan one [such as tommy Kaira / Nismo etc] then the actual REDline marking could be anywhere [such as 8000] but the factory rev limiter may still be in operation [at the default value of around 7000].

I am sure the PowerFC would be able to control the rev limit but this is the risk you take when buying a modified 2nd hand car - risk as in, you dont know what your getting or what settings there are. You are asking some questions that are unique to your car and can't be answered by any of us! I hope I have been of some help though!

If you want more power get someone to put a bleed valve in properly or get an EBC [electronic boost controller]...If you are used to your car's power with more boost than stock, of course it is going to be slower now...

[ARGH34]

Zahos: nah, the guy took it out. I figure if I want to increase my boost I might do it later with an EBC of some sort, or at least some sort of in-car adjustable valve.

NismoR34: I got the reading from an Apexi a-pillar boost gauge. It sits on 0.4 all the way to 7000rpm. My dash is the stock Nissan dash and I'm quite sure the redline on the tacho starts at 8000rpm - so does this mean that the redline on the dash isn't really the redline set in the ECU? Does your dash have redline markings from 8000rpm?

All this could be purely academic if the engine shouldn't really be revving past 7000 anyway, regardless of where the markings on the dash are - I realise that. But I'm just curious why it cuts out at 7000 when the redline on the dash is at 8000.

And one last thing, 0.7 bar the figure I'm getting to be the safe boost level for stock internals/turbo on an R34 for street use - can you guys confirm this?

And yes Nismo/Zahos you guys have been a big help and its much appreciated

[Zahos]

Originally posted by ARGH34

And yes Nismo/Zahos you guys have been a big help and its much appreciated

No worries....

Yeah, 0.7 should be quite safe. You could probably run a little higher for street use (squirst here and there), but 0.7 should be just fine.

Zahos

[NismoR34]

No my markings start at 7000 which is a broken red line [- - - -] and then the unbroken red line [----] starts at either 7500 or 8000 approx and goes all the way to the end of the tacho @ 9000rpm!

*brainstorm* With the vaccum hose that now sits in place of your previous boost valve, did they put any restrictors in there? I am guessing they havent! The standard hose has 2 metal restrictors inserted at either end of this hose, when I removed these 2 restrictors the boost dropped! This sounds like what you now have. Which is less boost than standard. I dont know where you could get restrictors from so I would suggest getting a boost controller in ASAP!

[ARGH34]

Yep. Just spoke to my mechanic, he says boost is pretty low at the moment (0.4 bar or around 6 pound) and that he regularly sets up customer cars up to 1 bar boost on stock turbo/internals safely (although he'll have to dyno it to test and make sure nothings going to blow up). I plan to get some EBC or dual stage boost controller. Mechanic said the cheapest way is to go the bleed valve/boost cut defender option and stick it up to 1 bar or thereabouts.

For the moment, the boost is going to have to wait - my alignment is out, and the wheel alignments were out by varying degrees on the left and right sides of my car - suggesting an accident and the need to use a chassis alignment rig (*sighs at buying cheap accident repaired japanese import*) to stop the car pulling to the left on a flat road

[ARGH34]

Oh as for the redline, my mechanic said that theres not much point going over 7000 anyway because the car drops right off its power/torque band at around 6600, so I really should be changing gears about then anyhoo.

I'll have to go home and double check my dashboard redline.

[NismoR34]

Your redline will be the same as mine - unless u have got an undercover GTR

I just remembered an ultra-cheap way to increase boost a little - use a cable tie to crimp [restrict] the hose a little bit. The other cheap way is to do what I did, fit a bleed valve. I fitted mine myself and it cost me like $25 total. Check for sale section or post a thread in WTB there may be some for sale around this place.

If I were you I would only increase the boost up to around 10psi or 12 psi at the most [1 bar is 14.5 psi]. HPI's r34 GTT project car had their turbo blow up at just .85 bar whilst flogging it around the track. You may not take yours on the track but do you wanna risk it for the sake of a bit more power now?

Most sensible people in the "turbo car" industry agree that 2-3 psi above standard is okay for stock turbo's / engines. Standard being approx 8psi. Its up to you though!

Hey mine pulls a bit to the right, but not too badly.

Dyno testing can be very helpful in finding out your cars power, boost setting, air/fuel ratios, state of tune, problems - like detonation etc...I had mine dyno'd and power was peaking at 7100rpm's when the rev limit kicked in so changing gears earlier on mine is not optimal especially in drag racing...Nissan quote 6400rpm as peak power on a standard car, which most of ours are not...

[ARGH34]

um, just checked my dash and the redline definately starts at 8000rpm. Is this not normal?

[NismoR34]

:confused: now you have made me wanna go and check mine...though I am already 99% sure it starts at 7k...

...another brainstorm, instead of going out to the garage which is all of 10 metres away I will sift through a hundred odd photo's on my pc cause I am sure I have got a pic of my dash here somewhere...*goes and browses*

...hours later []...

ah ha, in fact I posted a pic on SAU before...now I just got to find that link...

aahh there it is

See 7000rpm redline! If your dash doesnt look like that then it isnt the stock nissan one [for a 34GTT].

[ARGH34]

I'll take a piccy of mine on the weekend and post it. Then you tell me what kind of a dash I have :