whats causing my decreasing boost curve

[frankiman]

so i've been thinking about this issue since last year

first have a look at my last dyno chart;


so my problem is i'm loosing too much boost throughout the rev range
i'm still making good max power, but only at ~16psi
i'd rather have 17,5psi @ max power, but because of my declining curve, i'd have to set my boost 1,7psi higher and alsmot hit 20psi @ peak

in a perfect world, i want to set it at 17,5 and simply flatline there till the rev limiter

now is the part where i'd like to speculate on whats causing the issue

heres a quick list of my power-related mods;
HKS fuel pump
Sard 720cc injectors
Nismo FPR
Splitfire coilpacks
NGK copper racing plug
R34 GTR N1 turbos
R34 GTR dump pipes
Nismo downpipe
decat
3" Veilside exhaust
ported stock manifolds
divided twin turbo pipe
Apexi power intake
Greddy intercooler
HKS/Greddy I/C hardpiping
HKS SSQV BOVs
HKS 264deg 9.5mm cams
Custom adj cam gears
HKS EVC-S electronic boost controller


i've had this problem for years now

2011;


2010;



i know this problem is not from the fuel nor the ignition system
its not from the catback, since i changed it last year and gained 30whp but with the same boost curve

could it be the BOVs leaking? in my opinion the way the SSQV work its kind of impossible to leak
don't think its the dumpipes, since the ones i got are not the big like the Tomei, but still much bigger than OE, the downpipe though might not be big enough
so i checked my turbos in 2011, to find R34 GTR N1 in perfect condition
i though it was du to the wastegate actuators, so at that moment i swapped them for brand new Garret units, and adjusted them the same length as OE



now i really think thats where the issue is, i bet the WG actuator springs aren't stiff enough

basically, when you get into boost, trigger the controller, the selenoid sends the pressure to the actuators, lets say 17psi, the actuator spring is rated at 12psi, so of course the actuator opens, but wayy too much, so too much exhaust by-passes the turbine and boost drops, but the actuator is not stiff enough to close the WG a little to keep the boost stable, so it just slowly decreases towards the value on the actuator spring

so now i've started working on the car again, to get it in shape for the 2013 season,
i'm thinking of removing all of the piping over the turbos to access the actuators without taking the turbos out -again-
i'm thinking if i shorten the actuator rod by 2 turns, so about 1/8", it will add preload to the spring at its neutral "closed" position, so instead of 12psi required to open it, it might be 15-16psi, basically meaning the spring will have a big more force to close the WG when/if the boost drops because its too open

basically, what i would want is to set my boost controller at 17,5psi, get my boost to flatline there
i'd loose a bit of torque in the mid range, but would gain soooo much more in the high end
then to balance things out, i'd play with cam timing to get a bit more overlap for quicker spool and better mid range torque, and loose a bit of top end
basically i'd add ~30-40whp from 4500rpm till redline..

as anyone attempted to adjust the actuators on the spot?
can the rod simply rotate inside the actuator or i need to unclip the rod's end to spin it 2 turns? because i would hate to do that in that cramped space..


toughts? ideas? comments? tell me why i'm gay and stupid?

[nick-nismo]

my boost curve tapers off as well, much like yours (23 spike then 21 or 20 at red line) even my low boost tune does it, i just figured it was the turbo running out of steam up top or could be boost controller related? what are you using ? i have the greddy prof b spec II

[Dragon Humper]

Shorten up the rod, you won't loose any mid range, if anything you gain midrange because the wastegate will be more tightly closed as you build boost steepening the ramp on your boost curve. Try removing the BOVs as well if that doesn't work to see if they are leaking a bit. If both of those don't work then its your controler because your exhaust should be big enough to handle the power you are shooting for (you could always go bigger).



Jon.

[Skym]

Going by what I see on dyno graph, lean ECU tune. Why I say that, as it reaches peak boost it starts to drop off and is running 12.0:1.

On my car, just running engine roughly 0.2:1 richer than 12.0:1 it gained 2psi on boost plot. That's with running the same ignition timing.

Also boost controller is another, as HKS or Blitz boost control solenoids prevent this happening at anything higher than 1bar.

From what I understand, if adjust the actuators too tight it can wear out the springs earlier. Look at stock actuator rod length.

[bobbo]

Looks like you and I have a very similar set up this year Frank. I don't mean to hijack but what is your actuator length? I'll need to set mine before installing.

[frankiman]

my boost curve tapers off as well, much like yours (23 spike then 21 or 20 at red line) even my low boost tune does it, i just figured it was the turbo running out of steam up top or could be boost controller related? what are you using ? i have the greddy prof b spec II

i know its not the turbos running out of breath in my case since they are rated for 600hp @ ~20psi
the boost controller is an HKS EVC-S 2010 edition, single selenoid, i've tried every possible setting on it, i was able stablize the curve a bit but still have the same decline

Shorten up the rod, you won't loose any mid range, if anything you gain midrange because the wastegate will be more tightly closed as you build boost steepening the ramp on your boost curve. Try removing the BOVs as well if that doesn't work to see if they are leaking a bit. If both of those don't work then its your controler because your exhaust should be big enough to handle the power you are shooting for (you could always go bigger).

Jon.

do you think 2 turns is enough?
what i meant by "loosing midrange" is that if i can flatten te curve, i won't need to set my peak at 18psi, only ~17,5 meaning ill have 0.5psi less of boost at 4500rpm, thus loosing a bit midrange

Going by what I see on dyno graph, lean ECU tune. Why I say that, as it reaches peak boost it starts to drop off and is running 12.0:1.

On my car, just running engine roughly 0.2:1 richer than 12.0:1 it gained 2psi on boost plot. That's with running the same ignition timing.

Also boost controller is another, as HKS or Blitz boost control solenoids prevent this happening at anything higher than 1bar.

From what I understand, if adjust the actuators too tight it can wear out the springs earlier. Look at stock actuator rod length.

that doesn't make any sens, 12;1 is rich enough, not lean at all
increasing .2 alone could not give 2psi of boost more, it doesn't make any sens, something else was also done
i do have an HKS boost controller, fiddled with it and didn't cure the problem
and maybe putting a bit of preload on the spring will make it wear out faster, it will "only" last 5-6 years instead of 8...

Looks like you and I have a very similar set up this year Frank. I don't mean to hijack but what is your actuator length? I'll need to set mine before installing.

i haven't measured it, its the OE length..

[bobbo]

i haven't measured it, its the OE length..

I don't have my oe rods to measure.

[Skym]

that doesn't make any sens, 12;1 is rich enough, not lean at all

That's lean for a turbocharged engine, rich is more like 11.4:1 (what most tuners use). From what I understand, why you run it that rich is voltage drops to fuelpump with light's, aircon, etc on and causes engine to run leaner hence the extra fuel. Also widebands can be out by up to 0.6:1, so tuners put that safety margin in with customers cars. Ideally high 10's is best to make 100% sure it doesn't happen (100% reliability) hence one of the reasons why factory run it that rich.

increasing .2 alone could not give 2psi of boost more, it doesn't make any sens, something else was also done

Also wastegate was adjusted tighter, but stayed 2psi lower until ran 0.2:1 richer and gained 2psi. Dynochart shows this. It was just something I noticed on dyno chart and other dynochart's where they claim to produce more hp with a lower boost level. A tuner probably could explain better than I could, but I would think it has to do with less exhaust gas driving turbine. Adjusting internal wastegate actuator arm might produce a similar result (more exhaust gas driving exhaust wheel instead of getting bleed off through wastegate hole on exhaust housing).

i do have an HKS boost controller, fiddled with it and didn't cure the problem

The EVC-S solenoid might be a problem. One of the tuners mentioned the single solenoid types are usually good to 1bar, after that it's best to go to top of the line HKS boost controller (better solenoid) or Blitz runs a similar boost controller solenoid. I learnt it has something to do with taking out the stock restrictor that caused problems with single solenoids controlling boost. One person I know put a good quality adjustable valve from US? just before boost control solenoid that helped to control boost better above 1bar.

and maybe putting a bit of preload on the spring will make it wear out faster, it will "only" last 5-6 years instead of 8...

It's just what they said, and mentioned that was when really tight, so I guess there's a limit to how tight you can make it vs longevity of spring.

[Black BNR32]

This is normal IMO. crank up the preload and try some different boost reference locations for the EBC. plenum, intercooler, compressor, etc.

and try some larger hoses for your reference lines. say, 1/4" ID.

[NismoS-tune]

Dual port wastegates work wonders. You can make 20 psi on 7psi spring rates without issues! They do make some for IWG turbos but you need to find a match.

Also, I think those turbos are rated at 600crank HP and you're at 580crank at 450whp if that car is in perfect condition. Have you thought about running bigger turbos for more power? Fast response comes with less top end unless you get stiffer canisters?

[Dragon Humper]

You can make 25 psi on a 7 psi spring if you have no boost reference at all on the can....lol. Found that out on my Omni when the vacuum hose split and fell off the nipple on the can. A well set up controller should completely cure this.




Jon.

[frankiman]

This is normal IMO. crank up the preload and try some different boost reference locations for the EBC. plenum, intercooler, compressor, etc.

and try some larger hoses for your reference lines. say, 1/4" ID.

is closer to the turbo better?
i know BorgWarner has some internaly wastegated turbos that have the reference directly from the compressor housing
right now, my vaccum signal comes from the very back of the intake manifold, close to the brake master
and i already have 1/4 hoses

Dual port wastegates work wonders. You can make 20 psi on 7psi spring rates without issues! They do make some for IWG turbos but you need to find a match.

Also, I think those turbos are rated at 600crank HP and you're at 580crank at 450whp if that car is in perfect condition. Have you thought about running bigger turbos for more power? Fast response comes with less top end unless you get stiffer canisters?

its my understanding that 450whp is 530bhp, so i'm still 70bhp shy of the turbo's max
i don't want bigger turbos, i want to maximise potential of the setup
if i can eleminate that boost drop, i'll effectively make 50 more hp with exactly the same setup

This is normal IMO. crank up the preload and try some different boost reference locations for the EBC. plenum, intercooler, compressor, etc.

and try some larger hoses for your reference lines. say, 1/4" ID.

You can make 25 psi on a 7 psi spring if you have no boost reference at all on the can....lol. Found that out on my Omni when the vacuum hose split and fell off the nipple on the can. A well set up controller should completely cure this.
Jon.

i had already fiddled with the settings last year while on the dyno, guess i'll try again with another approach

[Black BNR32]

I believe the intake plenum is best, but tapping another hole or 2 at other locations might be worth a try

[NismoS-tune]

Odd, for some reason I thought these cars were around 23% drivetrain loss which isn't bad consider a much better engineered car (for its time) like a gt500 loses 10-18% or something.

Anyway, what's your spring rate on the wastegates? 1.3bar? Could be as simple as a weak spring allowing the wastegate to pull open.

I know I had no boost controller on my -5 turbos and the wastegates would open up around 16 psi on their own and tapper/flutter down. The springs were 1bar. If adding 2mm preload doesnt work, Could always run no wastegate vacuum (plugged hose) or wire the wastegates shut. That's what Morrison did if I recall. Max boost all the time. Or get dual port wastegates and 4 port controller if it is a wastegate getting sucked open.

[frankiman]

Odd, for some reason I thought these cars were around 23% drivetrain loss which isn't bad consider a much better engineered car (for its time) like a gt500 loses 10-18% or something.

Anyway, what's your spring rate on the wastegates? 1.3bar? Could be as simple as a weak spring allowing the wastegate to pull open.

I know I had no boost controller on my -5 turbos and the wastegates would open up around 16 psi on their own and tapper/flutter down. The springs were 1bar. If adding 2mm preload doesnt work, Could always run no wastegate vacuum (plugged hose) or wire the wastegates shut. That's what Morrison did if I recall. Max boost all the time. Or get dual port wastegates and 4 port controller if it is a wastegate getting sucked open.

my bad, i used a 15% loss ratio in my case, since i dynoed it on a 2wd dynapack which bolts directly to the axles

i believe the Garret actuators i got are 12psi (.83bar)

and the thing is i know these turbos will go well over 22psi if the wastegates stay closed - we had a little mishap when setting the EBC for the first time
so running max boost would be dangerous