Problem with boost on the dyno

[PNR Welding]

Well we got to making some pulls today and turning the boost up. The problem is we turn the AEM true boost controller from 65% duty cycle to 70% duty cycle and the car made full boost around 4k or even lower but then the boost just falls off and by the end of the run around 6300 it is seeing 6psi. Before someone says I have a boost leak its been checked and at that boost level if there was a leak it would just blow it off. Its not the boost controller cause there is a 9psi spring in there and when we made a pull with the boost controller off today it went to 8psi then by the end of the pull it was back around 6psi again. We are going to continue this on tuesday cause I have to put new 02 sensor in the passanger side. We are thinking that the only thing that it could be is the blow off valve is opening so the boost isnt reaching the intake. We are going to try to tighten down on the spring on it. Has anyone had a problem like this before? I have datalogs if anyone would like to see.

 

[Bobby]

is it vented to atmosphere or vented back into the exhaust. you need to vent it to atmosphere. i bet this will cure your problem.

 

[Bobby]

also dont take the vacuum from the turbo take it from the intake mani. that is your true boost going to the motor.

 

[chad05gt]

also dont take the vacuum from the turbo take it from the intake mani. that is your true boost going to the motor.

good info...

 

[GI Joe]

hahaha check this shit out I just posted

 

[GI Joe]

also dont take the vacuum from the turbo take it from the intake mani. that is your true boost going to the motor.

you mean wastegate or for blow off???

 

[one eyed willy]

Well we got to making some pulls today and turning the boost up. The problem is we turn the AEM true boost controller from 65% duty cycle to 70% duty cycle and the car made full boost around 4k or even lower but then the boost just falls off and by the end of the run around 6300 it is seeing 6psi. Before someone says I have a boost leak its been checked and at that boost level if there was a leak it would just blow it off. Its not the boost controller cause there is a 9psi spring in there and when we made a pull with the boost controller off today it went to 8psi then by the end of the pull it was back around 6psi again. We are going to continue this on tuesday cause I have to put new 02 sensor in the passanger side. We are thinking that the only thing that it could be is the blow off valve is opening so the boost isnt reaching the intake. We are going to try to tighten down on the spring on it. Has anyone had a problem like this before? I have datalogs if anyone would like to see.

what wastegate?exhaust pressure could be pushing open the wastgate.i used to have this exact issue.i tried everything,re-routing vac lines,closed off the whole cold side and pressurized it to find any leaks.i had to go to a 44mm wastegate, 11psi spring,vent the wastegate to the atmosphere (with a little glasspac),3" exhaust and i changed from the AEM boost controller to a Eboost.i now hold boost no problem at all.

have you checked your back pressure yet?idea pressure is 2:1 ratio,2 pounds of exhaust pressure to every pound you see in the intake.

 

[LuckyH]

Stupid question. What kind of dyno? Is it a load or inertia dyno?

edit:Just to elaborate, an interia dyno could dramatically reduce the load place on your car at higher speeds (especially a boosted car) and could result in lower boost pressures at higher rpms. With an inertia dyno, the most load you have in during the initial rotating of drum to get it moving. With a load based, there is a more constant load througout the entire pull.

 

[GI Joe]

what wastegate?exhaust pressure could be pushing open the wastgate.i used to have this exact issue.i tried everything,re-routing vac lines,closed off the whole cold side and pressurized it to find any leaks.i had to go to a 44mm wastegate, 11psi spring,vent the wastegate to the atmosphere (with a little glasspac),3" exhaust and i changed from the AEM boost controller to a Eboost.i now hold boost no problem at all.

have you checked your back pressure yet?idea pressure is 2:1 ratio,2 pounds of exhaust pressure to every pound you see in the intake.

How do you check the exhaust backpressure. Does going to the bigger W/
G lower the exhaust back pressure or just handle it better.

 

[PNR Welding]

what wastegate?exhaust pressure could be pushing open the wastgate.i used to have this exact issue.i tried everything,re-routing vac lines,closed off the whole cold side and pressurized it to find any leaks.i had to go to a 44mm wastegate, 11psi spring,vent the wastegate to the atmosphere (with a little glasspac),3" exhaust and i changed from the AEM boost controller to a Eboost.i now hold boost no problem at all.

have you checked your back pressure yet?idea pressure is 2:1 ratio,2 pounds of exhaust pressure to every pound you see in the intake.

We originally thought that it could be the wastegate, but with the boost controller off, the wastegate will hold to 8.9 psi and then drop to 6psi at the end. If there was a problem with the wastegate then it would get its ass kicked and stay shut and get boost spikes not lost of boost.

My car is almost vented to the atmosphere. It dumps right out by the front passenger tire. Barely any exhaust.

 

[LuckyH]

We originally thought that it could be the wastegate, but with the boost controller off, the wastegate will hold to 8.9 psi and then drop to 6psi at the end. If there was a problem with the wastegate then it would get its ass kicked and stay shut and get boost spikes not lost of boost.

My car is almost vented to the atmosphere. It dumps right out by the front passenger tire. Barely any exhaust.

Can you drive it down the road? If it doesn't drop boost there it's the dyno not loading your car. Get rid of that variable first, it's the easiest to check in my opinion.

 

[PNR Welding]

Can you drive it down the road? If it doesn't drop boost there it's the dyno not loading your car. Get rid of that variable first, it's the easiest to check in my opinion.

We will try that after we tighten down the BOV. The owner has a Lightning with a 88mm turbo on it that he dynoed and didnt have a problem with that truck with the load. But we will check.

 

[LuckyH]

We will try that after we tighten down the BOV. The owner has a Lightning with a 88mm turbo on it that he dynoed and didnt have a problem with that truck with the load. But we will check.

Does the lightning have a tighter converter? Even on an unloaded dyno a tight converter can create load.

 

[GI Joe]

I have a tighter converter and mine is doing it too...but not nearly as bad..drops 19 to 16 psi about a 3000 stall

 

[PNR Welding]

Does the lightning have a tighter converter? Even on an unloaded dyno a tight converter can create load.

My converter is stalled to about 2900 on the TB also. That was with a tune that had a rich A/F and timing in the single digits at WOT on the Transbrake. The Lightnings converter is also tight like mine.

 

[LuckyH]

I have a tighter converter and mine is doing it too...but not nearly as bad..drops 19 to 16 psi about a 3000 stall

A tighter converter won't get rid of it completly, however all other things the same it could create load for a longer period of time. So you might see the same pressure drop, only it will happen later/higher rpm.

 

[one eyed willy]

We originally thought that it could be the wastegate, but with the boost controller off, the wastegate will hold to 8.9 psi and then drop to 6psi at the end. If there was a problem with the wastegate then it would get its ass kicked and stay shut and get boost spikes not lost of boost.

My car is almost vented to the atmosphere. It dumps right out by the front passenger tire. Barely any exhaust.

i had the same wastegate,i replaced it with a 44mm. the turbonetics 38mm is not a very reliable peice,ive seen a few on turboforums.com that were replaced with other units and fixed the issues. im saying that the your exhaust pressure could be forcing the wastegate open,so it would do exactly what you are saying. when the exhaust pressure increases it pushes againt the valve,forcing it open past the spring.

i started out with almost the same set up as you.
aem boost controller
38mm turbonetics wastage

i replaced the 38 with a 44
replaced the aem with a eboost
vented the wastegate
changed out my 2.5" exhaust to 3" magnaflow

now i hold steady boost.

have you thought about checking the back pressure? put you a bung right before the turbo,then plumb some copper tubing to the bung,coil up a few feet and rout it to a boost gauge.then compare the exhaust pressure to the intake manifold pressure.

 

[Nickoli]

what kind of bov are you using? also do you have stiffer springs in the heads? I dought it would push them open at that boost level but you never know...

 

[Brain_Mach1]

A buddy could was losing boost with RPM on his twin turbo Cobra and it turned out the air filters were too restrictive. It appeared as a flat HP curve.

His kit was the basis for the HPP twin turbo kit once HPP fixed issues from the original kit builder.

 

[PNR Welding]

what kind of bov are you using? also do you have stiffer springs in the heads? I dought it would push them open at that boost level but you never know...

Im using a vortech mondo BOV. I DO have stiffer springs in the heads. Are you talking about floating the valves?
What is it that you thought would push open at that boost level? Are you talking about the BOV