Help me get full boost earlier

[Lith]

Hi guys,

Sorry, this question applies to a Skyline - but its worth a shot

I'm bound to have spoken to some of you about this issue I have been fighting for a while but now I feel compelled to try and really get it nutted out, the lack of lower-midrange torque is starting to frustrate.

Anyway, the short of it is that my internally gated GT3076R (yeah yeah I know...) opens starts to open wastegate before it reaches the desired boost level - which induces a reasonable amount of lag any time I step on the throttle. Here is the best way I can demonstrate how it behaves when I am targetting 15psi:


Obviously I would much prefer it to hit and hold 15psi instead of pissing around from 11psi to 15psi. I have tried an AVC-R and a bleed valve as different kinds of boost control which help SLIGHTLY but definitely don't fix it, and I am currently trialling a dual-port actuator which so far does the exact same thing. Today I decided that to rule out the possibility that the reason it spools lazily is a boost leak or some other issue elsewhere, I'd do a quick run to 3500rpm with the actuator hose removed to see how much it builds and my result is:


So clearly the turbo and setup is capable of building 1+bar well before the 5000ish rpm I am stuck with at the moment, but the trick is making it do so without free boosting. Any one have any ideas? It may help reduce some stress here

Cheers!

[strx7]

put a pressure regulator/relief before the wastegate so it wont let any air thru until it hits say 1.5 or 2psi before the boost pressure you want to run

[Lith]

Cheers, yeah meant to put in the OP that I was pondering using a Norgren valve - might do the "Autospeed boost control" trick

[Bazda]

Yep do that, I have the same issue with my electronic boost controller. Going back to my manual tap in a closed loop setup.

[Lith]

Yeah a couple others have mentioned that - almost tempted to actually try just getting a ball valve to bring it up to 14psi quickly, and using the AVC-R for the control from that point. Sound silly? I have the AVC-R anyway...

[gasman]

What computer have you got? Aftermarket? If so then why don’t you grab a solenoid valve and plug it into the wastegate and vent the other end and set up the solenoid to be up until 15 psi or so then close. That way the wastegate will always be fully closed until u want it to open, and still keep the avcr to control boost.
If not aftermarket then go buy a voltage switch from jaycar and tap that into your map sensor, and set it to close the solenoid at 15psi.

[Crampy]

might do the "Autospeed boost control" trick

I was reading throgh that the other day. Seemed to work quite well. I might try something similar on my Levin.

[MAGN1T]

You probably just need a stronger spring on the wastegate. What PSI does it start to open at? The exhaust pressure might be blowing it open enough to make a leak.
Another opti n is that you might have a leak between the exhaust manifold and the head but only leaking when on boost, due to the exhaust manifold being warped.

Steve

[flygt4]

consider if forced traction control?

[Lith]

You probably just need a stronger spring on the wastegate. What PSI does it start to open at? The exhaust pressure might be blowing it open enough to make a leak.
Another opti n is that you might have a leak between the exhaust manifold and the head but only leaking when on boost, due to the exhaust manifold being warped.

Hi

Yeah I agree, a stronger wastegate is the obvious - so far the best price on a suitable one I have found in NZ is $450! I'd rather avoid that if necessary, currently unemployed.

Did you see the pic I posted of when I did a free boost run (actuator on, but boost feed removed) up to 1.1kg/cm2 to rule out leaks etc? Hit 1.1bar by 3600rpm on a 530hp turbo on a 2.5litre, pretty sure its all pretty tight... its just when I try and control the boost where the problems arise.

consider if forced traction control?

Haha well thats kindof nice, but it'll be nice to have the option

[MAGN1T]

Just go to the hardware shop, get a pull type coil spring and hook it in parallel to your wastegate...you'll figure it out. Give it a test with an air compressor & pressure gauge.

One of Steve's many $3 mods.

Steve

[iOnic]

Isn't it common for those turbo's to be pretty laggy with internal wastegate setups?

[Lith]

Cheers Steve I am actually looking at grabbing a pressure relief valve to trick it some.

Ionic - there shouldn't be any reason for an internal wastegate to be laggier if it is set up right, I'm trying to not blame my tools

[Dell'Orto]

Just swap da hosez bei







Actually, how is it plumbed up?

[BlakeNZ]

is the boost source that opens the wastegate taken from the inlet plenum, or from the turbo side of the car?

[Lith]

^^ Now look what you've made me do, I've had to go and play with Paint!

Hopefully this explains what and how I've been trying to achieve things:

[gasman]

going from your diagram, you would want the avcr to be pulsing quite quickly to keep the valve closed then open up after boost case come on then slowly close up again as it gets up to the top of the rev range to compensate for the turbo starting to boost outside its preferred limits. And going from what has been said previously about the avcr you can only set the target boost level and not the duty cycle of the solenoid directly.
Thus u need some kind of way to set the avcr to pulse quckly from once it hits boost until it boosts upto 15psi then pulse slower to open up the wastegate.
Or find another hack to make it work

[fivebob]

How about plumbing it so that both sides are connected to the boost signal, and the AVC-R solenoid bleeds boost off the lower side when it reaches target boost, i.e. it vents to atmosphere.

That should make the wastegate open slower, though it's also possible that, depending on the size of the hoses, the wastegate may not open at all if the pressures equalise. In which case I'd try a smaller hose going to the lower side.

[Lith]

How about plumbing it so that both sides are connected to the boost signal, and the AVC-R solenoid bleeds boost off the lower side when it reaches target boost, i.e. it vents to atmosphere.

Thats how its plumbed.... unless I have read you wrong?

[fivebob]

Like this?