Boost Dropping Problem?
Boost Dropping Problem? I have a QMP T76 kit. Car is a 99 6spd Trans Am. Forged motor with TEA heads and 8.75:1 compression. I am using a Turbosmart e-boost controller and have a 10lb spring in the wastegate(referencing the boost for the controller and wastegate from the back of the intake manifold) also using a HKS standard BOV which recirculates the Blow-Off back to pre-turbo. Problem is the boost climbs to my set point in 2nd,3rd&4th gears by around 4900rpm and then falls off about 2.5psi and holds steady at that level until I shift gears. This happens no matter where I set the boost(ex:15psi falls to 12.5, 13psi falls to 10.5). It even happens when I take the boost controller out the equation and run the wastegate just on the spring(10.5psi falls to 8.0psi). I have attached an Text File of a run I did yesterday up about 115mph. I was also having this same problem last year when I had the std T63 turbo and I thought the larger T76 would take care of it.
Any help would be greatly appreciated.
Eric
Any help would be greatly appreciated.
Eric
measure your exhaust pressure, particularly on the crossover.
anything over twice the intake pressure is BAD.
too much exhaust pressure will stall the compressor wheel and your boost will drop
anything over twice the intake pressure is BAD.
too much exhaust pressure will stall the compressor wheel and your boost will drop
could you be getting a boost spike from your watsegate?
i have this problem with my TTi T76 kit and i atributed it to the small wastegate.
:edit: re-reding i dont have this problem as my boost spikes then creeps down to the set level
i have this problem with my TTi T76 kit and i atributed it to the small wastegate.
:edit: re-reding i dont have this problem as my boost spikes then creeps down to the set level
Last edited by smokinHawk; Apr 27, 2004 at 02:51 PM.
Sounds like the wastegate is not bleeding enough boost fast enough. Also could be to much backpressure. Typically those are your main 2 problems with controlling boost if no boost controller is attached.
Jose
Jose
I guess I'll see if I can contact Rob since he claims he is using the std wastegate and crossover that comes with the kit and he is making almost 800 rwhp. I always thought the standard HKS 40mm wastegate that comes with the kit seemed kinda small(HKS rates it to 500hp on the website).
Whats the best way to measure back pressure? I assume I will have to drill a hole in the crossover and weld a bung for a pressure gauge?
I am using a 2.5bar Motorola mini MAP sensor(its about the size of a quarter) and my Innovative Wide band to log my AF,RPM and Boost. I use EFI Live to log everything else, I also log AF with EFI Live using the AC pressure wiring and the Analog out on the Innovative WB.
Whats the best way to measure back pressure? I assume I will have to drill a hole in the crossover and weld a bung for a pressure gauge?
I am using a 2.5bar Motorola mini MAP sensor(its about the size of a quarter) and my Innovative Wide band to log my AF,RPM and Boost. I use EFI Live to log everything else, I also log AF with EFI Live using the AC pressure wiring and the Analog out on the Innovative WB.
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thats cool to measure the boost like that.
yea you can basically just hook a boost gauge up to it
i'm going to take a guess that your backpressure is over 30psi. will be interested to see.
jz97, his problem is not the spike, its the boost falling below spring pressure.
yea you can basically just hook a boost gauge up to it
i'm going to take a guess that your backpressure is over 30psi. will be interested to see.
jz97, his problem is not the spike, its the boost falling below spring pressure.
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Originally Posted by MIGHTYMOUSE
measure your exhaust pressure, particularly on the crossover.
anything over twice the intake pressure is BAD.
too much exhaust pressure will stall the compressor wheel and your boost will drop
anything over twice the intake pressure is BAD.
too much exhaust pressure will stall the compressor wheel and your boost will drop
On The Tree
Joined: Nov 2001
Posts: 1,100
Likes: 0
From: Charlestown, Indiana
Backpressure isn't the problem. It won't cause the problem he described. My car has no problem holding steady boost at wherever I set it.
1. Are you sure you have a 10lb spring and not a 9lb? (I thought we sent you a 9lb'er) The E-Boost will cause a spike and the boost should settle down lower than the initial boost reading. That's normal.
2. First guess, I believe you have the Gate Pressure setting incorrect on the E-Boost. Try playing with it until you get the spike out of it. (though a small spike isn't a bad thing, IMHO). A wrong GP setting will cause the EXACT problem you describe.
3. Next, check to make sure you have the Overboost setting set correctly on the E-Boost (at least 2lbs higher than you have the boost set at)
4. Lastly, it could also be the sensitivity on the E-Boost set incorrectly.
Let us all know what you find...
1. Are you sure you have a 10lb spring and not a 9lb? (I thought we sent you a 9lb'er) The E-Boost will cause a spike and the boost should settle down lower than the initial boost reading. That's normal.
2. First guess, I believe you have the Gate Pressure setting incorrect on the E-Boost. Try playing with it until you get the spike out of it. (though a small spike isn't a bad thing, IMHO). A wrong GP setting will cause the EXACT problem you describe.
3. Next, check to make sure you have the Overboost setting set correctly on the E-Boost (at least 2lbs higher than you have the boost set at)
4. Lastly, it could also be the sensitivity on the E-Boost set incorrectly.
Let us all know what you find...
Rob,
I have a green spring(10.2 psi). I dont know if you looked at the text file log I posted but it was WITHOUT the e-boost controller even hooked up(boost reference hose going directly to the waste-gate). In 2nd gear I maxxed 10.6psi@4900rpm and then fell to 8.5psi by 5200rpm and hovered between 7.5psi & 9.0psi until I shifted into 3rd. In 3rd a max boost of 10.1@5030rpm and fell to 8.0 by 5550rpm and hovered between 7.5psi & 8.75psi until until i shifted into 4th @ 6360rpm. In 4th a max boost of 10.1 @ 5170rpm and it dropped to 8.5psi by 5220 rpm and hovered between 8.0 psi and 9.0 psi until I shut it down at 5500rpm. Is this normal for running just the spring?
Thanks for the quick reply!!!
I have a green spring(10.2 psi). I dont know if you looked at the text file log I posted but it was WITHOUT the e-boost controller even hooked up(boost reference hose going directly to the waste-gate). In 2nd gear I maxxed 10.6psi@4900rpm and then fell to 8.5psi by 5200rpm and hovered between 7.5psi & 9.0psi until I shifted into 3rd. In 3rd a max boost of 10.1@5030rpm and fell to 8.0 by 5550rpm and hovered between 7.5psi & 8.75psi until until i shifted into 4th @ 6360rpm. In 4th a max boost of 10.1 @ 5170rpm and it dropped to 8.5psi by 5220 rpm and hovered between 8.0 psi and 9.0 psi until I shut it down at 5500rpm. Is this normal for running just the spring?
Thanks for the quick reply!!!
i have a 10# spring in my current set up and it spikes to 10.3 and settles to 9.9. i figure thats an appropriate half pound window
when the e boost is hooked up my gate pressures are 3.9 and overboost is 18 , sensitivity is 20 i think.. anyone else care to contribute their e boost settings?
when the e boost is hooked up my gate pressures are 3.9 and overboost is 18 , sensitivity is 20 i think.. anyone else care to contribute their e boost settings?
TECH Resident
Joined: Aug 2003
Posts: 948
Likes: 0
From: orlando, florida
Originally Posted by Rob Raymer
Backpressure isn't the problem. It won't cause the problem he described. My car has no problem holding steady boost at wherever I set it.
1. Are you sure you have a 10lb spring and not a 9lb? (I thought we sent you a 9lb'er) The E-Boost will cause a spike and the boost should settle down lower than the initial boost reading. That's normal.
Let us all know what you find...
1. Are you sure you have a 10lb spring and not a 9lb? (I thought we sent you a 9lb'er) The E-Boost will cause a spike and the boost should settle down lower than the initial boost reading. That's normal.
Let us all know what you find...
O.K i've never questioned your knowledge in Turbos, you know your crap but. To much back pressure WILL cause boost loss because the exhaust can not flow fast enough to spin the turbine at the required speed to reach the set boost level. In other words the turbine stalls out. Most likely the reson your not having any problems is because your running a Q-trim turbine.
The E-boost if set up correctly and if the rest of the system is functioning correctly should NOT cause a spike.
ws6rufs: My guess would be that somthings either not right with the controler or the way the vacume lines are connected. I'm kinda skeptical on thinking it's a backpressure issue cause I'm having a backpressure issue with my kit and my symptoms are similar except that my boost drops to a specific level. I/E If i set my controler to 13psi my boost drops to 9psi, if i set the controler to 10psi it drops to 9psi. no matter what level i set the controler to above 9psi it always drops to 9psi by 6000rpm. If you think about it why would the point which the turbine stalls change exactly 2.5psi with each change in boost. Don't hurt me too bad this is just my .02
On The Tree
Joined: Nov 2001
Posts: 1,100
Likes: 0
From: Charlestown, Indiana
Originally Posted by MYTURBOT/A
Most likely the reson your not having any problems is because your running a Q-trim turbine.
I'm pretty sure it's just an E-Boost setting problem. A boost spike is normal.
Originally Posted by Rob Raymer
He DOES have a Q-Trim. He has the exact same turbo I have, same wastegate, same piping, IC, engine ci, etc. That's why I said backpressure wasn't his problem.
I'm pretty sure it's just an E-Boost setting problem. A boost spike is normal.
I'm pretty sure it's just an E-Boost setting problem. A boost spike is normal.
Where are you getting the boost reference for the e-boost controller and for the controller selonoid/waste-gate? Im using the back of the manifold for everything including the BOV. Should I be using the tap on the compressor for some of these?
Eric
On The Tree
Joined: Nov 2001
Posts: 1,100
Likes: 0
From: Charlestown, Indiana
The reference comes from the intake. But the E-Boost MUST hook into the compressor side also. I'm not sure exactly how mine is hooked up (been too long), I'd have to look at it, but I'm not at the shop. You could call the guys at Turbosmart and they can tell you over the phone exactly how it should be connected, 443-557-0086.
It even happens when I take the boost controller out the equation and run the wastegate just on the spring(10.5psi falls to 8.0psi).
I dont know if you looked at the text file log I posted but it was WITHOUT the e-boost controller even hooked up(boost reference hose going directly to the waste-gate).
TECH Resident
Joined: Aug 2003
Posts: 948
Likes: 0
From: orlando, florida
Originally Posted by Rob Raymer
He DOES have a Q-Trim. He has the exact same turbo I have, same wastegate, same piping, IC, engine ci, etc. That's why I said backpressure wasn't his problem.
Is it posible that maybe he has to many things pulling off the same vacume port in the back of the manifold? I think it would be better to find a seperate source for the wastgate/boost controler.