Boost Falling off at High RPM & Dyno Graph looks Weird?!
11-19-2012, 09:43 PM
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Boost Falling off at High RPM & Dyno Graph looks Weird?! Hey guys I'm having a problem on the dyno yesterday with Boost falling off at high rpm...
The car is a Rear-mount Comp. Oil-less 76mm Turbo, T4, 0.96 A/R, Billet wheel and its being controlled by a Precision 46mm wastegate that dump's to atmosphere.
The wastegate has a green (9psi) AND a red 6psi spring in it (Both!)
There is NO Boost controller, the wastegate vacuum hose runs directly from the compressor housing to the bottom port of the wastegate, and the top port is vented to atmosphere, the hose is 1 foot long.
I have boost leak tested the entire Cold-Side piping with 20psi of air pressure. It holds pressure for a long time and has NO leaks whatsoever.
The motor has Texas Speed CNC ported Stage 2.5 "5.3" heads.
They run the PRC .650 lift valve springs.
These here:
http://texas-speed.com/p-1172-prc-st...ted-heads.aspx
The car is on 93 octane and 17 degrees of timing under full boost.
11.7-12.0:1 A/F under boost.
HPTuners shows Zero knock. (Brand new GM knock sensors and subharness)
Cam is: 231/239 .617/.624 on a 113LSA Comp cam
Motor is a 346ci Forged LS1. Fresh Motor. 200 miles on it.
Why is my dyno looking like this? Is it because my boost is up and down so much and causing power fluctuation or is something else wrong?
I'm lost!
By the way the car is losing a TON of fuel pressure. Base pressure is 60 and at 5000 rpm it goes down to 25psi!
Its an Aeromotive Stealth in-tank pump, -6AN Hose from the tank to the Aeromotive 1:1 Rising rate regulator, Stock LS1 F-body fuel rail fed to Siemens Injectors, and the -6AN return is on the regulator under the hood.
The A/F is ALWAYS high 11's to 1 though under boost and I am buying another fuel pump ASAP!
Whats wrong with my car!
Video of boost gauge on a Dyno Pull (Middle gauge is boost)
http://www.youtube.com/watch?v=ULUFh...ature=youtu.be
The car is a Rear-mount Comp. Oil-less 76mm Turbo, T4, 0.96 A/R, Billet wheel and its being controlled by a Precision 46mm wastegate that dump's to atmosphere.
The wastegate has a green (9psi) AND a red 6psi spring in it (Both!)
There is NO Boost controller, the wastegate vacuum hose runs directly from the compressor housing to the bottom port of the wastegate, and the top port is vented to atmosphere, the hose is 1 foot long.
I have boost leak tested the entire Cold-Side piping with 20psi of air pressure. It holds pressure for a long time and has NO leaks whatsoever.
The motor has Texas Speed CNC ported Stage 2.5 "5.3" heads.
They run the PRC .650 lift valve springs.
These here:
http://texas-speed.com/p-1172-prc-st...ted-heads.aspx
The car is on 93 octane and 17 degrees of timing under full boost.
11.7-12.0:1 A/F under boost.
HPTuners shows Zero knock. (Brand new GM knock sensors and subharness)
Cam is: 231/239 .617/.624 on a 113LSA Comp cam
Motor is a 346ci Forged LS1. Fresh Motor. 200 miles on it.
Why is my dyno looking like this? Is it because my boost is up and down so much and causing power fluctuation or is something else wrong?
I'm lost!
By the way the car is losing a TON of fuel pressure. Base pressure is 60 and at 5000 rpm it goes down to 25psi!
Its an Aeromotive Stealth in-tank pump, -6AN Hose from the tank to the Aeromotive 1:1 Rising rate regulator, Stock LS1 F-body fuel rail fed to Siemens Injectors, and the -6AN return is on the regulator under the hood.
The A/F is ALWAYS high 11's to 1 though under boost and I am buying another fuel pump ASAP!
Whats wrong with my car!
Video of boost gauge on a Dyno Pull (Middle gauge is boost)
http://www.youtube.com/watch?v=ULUFh...ature=youtu.be
11-19-2012, 10:19 PM
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Its the fuel pump that's not flowing enough volume.
But this is a non-issue as far as the boost and the dyno graph go as the A/F under boost is high 11's under boost anyway...
It is DEFINITELY on my list of things to do ASAP but it can't be causing my problem as again my A/F is spot on.
11-19-2012, 10:24 PM
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So many questions- but your graph is set to smoothing 3, most people "like" to look at them with 5 smoothing. I like to tune with 0 smoothing. That could simply be all it take to fix what you dont like about how it looks. However, it could be anything from plug gap to this fuel issue you discribe. If you are only making 9-12 psi then you shouldn't be at 25 psi @ the rail. I'd check the hoses in the tank for any sort of leaks- if I could go a week without hearing about fueling issues where non submersible fuel lines were used in tank I might die. Just cause the car isn't knocking doesn't mean its not pulling timing. Wouldn't know without seein the tuning.
Never had good luck with aeromotive pumps.
GL - keep us posted.
Never had good luck with aeromotive pumps.
GL - keep us posted.
11-20-2012, 10:24 PM
#6
Your boys can't figure it out? 
That's a lot of spring. I'd be willing to bet your drive pressure is through the roof, potentially opening the gate? I don't know, but boost usually falls off due to insufficient compressor flow (ie small turbo) or back pressure.
Hook up a boost controller, see what happens. Or try a larger turbine housing.
What are the turbine wheel specs?
That's a lot of spring. I'd be willing to bet your drive pressure is through the roof, potentially opening the gate? I don't know, but boost usually falls off due to insufficient compressor flow (ie small turbo) or back pressure.
Hook up a boost controller, see what happens. Or try a larger turbine housing.
What are the turbine wheel specs?
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11-20-2012, 11:38 PM
#8
FormerVendor
Easy, wastegate needs to be referenced off of the intake manifold to compensate for pressure drop across the cold side. Only way it would keep steady boost when referenced off the compressor cover is if you have zero cold side pressure loss which is highly unlikely on a rear mount setup.
11-21-2012, 01:15 PM
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Easy, wastegate needs to be referenced off of the intake manifold to compensate for pressure drop across the cold side. Only way it would keep steady boost when referenced off the compressor cover is if you have zero cold side pressure loss which is highly unlikely on a rear mount setup.
O.o
...Louis... I thought it spooled much faster and it confused me to but then we over-layed the old dyno to the new dyno graph and the new graph beats the old graph big time... Until 5000rpm for whatever reason the boost drops off and power goes down... On the street though it spools so fast!
3500rpm and its almost full tilt...
Should I romove the 6psi spring and leave the 9psi spring and then use the manual boost controller to help keep the waste gate shut? ..or keep the 9 and 6psi spring in it and then aid the top of the gate?
Turbine Wheel:
713C inconel material
76mm exducer
Here's the link to my exact turbo:
http://www.compturbo.com/products/ct43billet/ct43_7076
Last edited by 1SIKZ31; 11-21-2012 at 01:21 PM.
11-21-2012, 09:10 PM
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Thanks guys!
Oh and just to let you guys know..
All True Street is doing is Tuning and Dyno'ing my car...
I am on a budget so I'm doing the mechanical work myself...
Oh and just to let you guys know..
All True Street is doing is Tuning and Dyno'ing my car...
I am on a budget so I'm doing the mechanical work myself...
11-21-2012, 09:33 PM
#13
FormerVendor
11-22-2012, 01:41 PM
#15
I wouldn't worry about the dyno readings at this point. Probably would be best to remove the wastegate springs completely until you get the fuel pressure issue fixed just to be safe.
You can also turn up your base pressure to 75psi to simulate 15psi boost and see if the regulator holds it there or if the pump is bypassing in the tank. If it holds the pressure fine at idle the regulator is fine and the pump is toast.
As far as spool up, the way you currently have the wastegate vacuum lines will be the slowest spooling possible, opening the gate a little as soon as you build any boost above spring pressure. Like was mentioned, run a vacuum line from your manifold to the top of the gate, or even a manual grainger valve with the small ball/spring .
You can also turn up your base pressure to 75psi to simulate 15psi boost and see if the regulator holds it there or if the pump is bypassing in the tank. If it holds the pressure fine at idle the regulator is fine and the pump is toast.
As far as spool up, the way you currently have the wastegate vacuum lines will be the slowest spooling possible, opening the gate a little as soon as you build any boost above spring pressure. Like was mentioned, run a vacuum line from your manifold to the top of the gate, or even a manual grainger valve with the small ball/spring .
11-22-2012, 01:51 PM
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I wouldn't worry about the dyno readings at this point. Probably would be best to remove the wastegate springs completely until you get the fuel pressure issue fixed just to be safe.
You can also turn up your base pressure to 75psi to simulate 15psi boost and see if the regulator holds it there or if the pump is bypassing in the tank. If it holds the pressure fine at idle the regulator is fine and the pump is toast.
As far as spool up, the way you currently have the wastegate vacuum lines will be the slowest spooling possible, opening the gate a little as soon as you build any boost above spring pressure. Like was mentioned, run a vacuum line from your manifold to the top of the gate, or even a manual grainger valve with the small ball/spring .
You can also turn up your base pressure to 75psi to simulate 15psi boost and see if the regulator holds it there or if the pump is bypassing in the tank. If it holds the pressure fine at idle the regulator is fine and the pump is toast.
As far as spool up, the way you currently have the wastegate vacuum lines will be the slowest spooling possible, opening the gate a little as soon as you build any boost above spring pressure. Like was mentioned, run a vacuum line from your manifold to the top of the gate, or even a manual grainger valve with the small ball/spring .
You said the way I have my vacuum lines it's the slowest spooling possible as when boost pressure hits spring pressure it'll open.. The thing is... It has a HEAVY *** springs in it... 15psi worth of spring in it!!!
I just bought a manual boost controller as well.
