Battling backpressure at RPM with AMS-1000

[karolko]

I am posting here because most of us are running larger turbos and AMS-1000's.

I have a Precision turbo on my Stage motor and looking at the datalog from last weekend i was watching the boost pressure decrease in my higher rpm, when the AMS-1000 is programmed to hold a straight line of boost by that point.

I called AMS and told them what's happening and they quickly determined it was due to backpressure. The also said the only way to fix this is to step up to their AMS-2000. ( Lots of cash, by the way).

I know i'm not the only one running a 76 on a stage motor, so i'm wondering what you guys are doing to offset this issue.

I'm also wondering if i might have too small of a wastegate? Would that help at all? I am currently running a Tial 44.

Thanks for the help.

Adrian

 

[Eticket]

Two questions: are you running co2? When is the last time you checked or changed valve springs?

 

[Chuck Leeper]

B4 taking their conclusion as gospel, and throwing $ at it, I would log back psi, and see what it really is.

 

[Eticket]

I agree, seems like buying another boost controller is plain silly....

 

[tbone87]

I was told the 2000 can bleed off back pressure. Also would that not fall back to the exhaust housing. What exhaust housing do u have?

 

[karolko]

Two questions: are you running co2? When is the last time you checked or changed valve springs?

Running co2 with 110psi on the regulator and only pushing 25psi to the gate

Also the valve springs are brand new so I know they are not the issue.

What should back pressure be at 25psu?

 

[karolko]

I was told the 2000 can bleed off back pressure. Also would that not fall back to the exhaust housing. What exhaust housing do u have?

It is a precision 7675 with the largest housing (1.25 or 1.27 a/r) so the housing should not be a factor.

I have the waste hate plumbed in the most ideal way so it gets a straight shot of exhaust on the valve as well. Maybe it's too good.

 

[karolko]

Are any of you guys also experiencing this issue?

 

[ijames]

I also think you need to log your back pressure. If the boost is dropping off below the wastegate/controller setpoint then the wastegate should be completely closed and therefore its size isn't an issue, right? Wastegate size is typically only a problem when too small causes boost creep up, not down. On a very efficient system the back pressure can be a bit below the boost pressure, and when the turbine/housing is a real cork the backpressure will get over twice the boost. Don't think I've ever heard of someone logging three times the boost, so that would be "very bad" . Is this a new behavior for a combination you have lots of runs on, or a new combo you are beginning to sort out? How much does the MAT climb during the pass, and is the MAT climbing while the boost is dropping? That's a good telltale for leaks, either exhaust or on the intake side, if you suddenly see more MAT gain than normal.

 

[karolko]

I also think you need to log your back pressure. If the boost is dropping off below the wastegate/controller setpoint then the wastegate should be completely closed and therefore its size isn't an issue, right? Wastegate size is typically only a problem when too small causes boost creep up, not down. On a very efficient system the back pressure can be a bit below the boost pressure, and when the turbine/housing is a real cork the backpressure will get over twice the boost. Don't think I've ever heard of someone logging three times the boost, so that would be "very bad" . Is this a new behavior for a combination you have lots of runs on, or a new combo you are beginning to sort out? How much does the MAT climb during the pass, and is the MAT climbing while the boost is dropping? That's a good telltale for leaks, either exhaust or on the intake side, if you suddenly see more MAT gain than normal.

This is a new combo. Had it dynoed with Cal, but I did not notice that during the time (probably because I was stressed about everything going on)

Went to the track last week and noticed it was doing this in the Data log. I need to look at the lower boost logs to see if it was also doing that around 10-12psi and only 6000 rpm.

I guess a back pressure gauge is on the way.

I just didn't think I would have that you ch back pressure to effect boos at lower levels.

I have a 5"down pipe and TA 4 bolt headers.

 

[karolko]

Okay after reviewing my logs it appears I have ever a different issue.

I am seeing the same problem with boost decreasinsug at even 12 psi and 6500 rpm which leads me to believe that this is not a back pressure issue.

Take a look at this photo
White is air temp
Orange is boost
Grey is gate pressure
Green is rpm.
Remember this is only at 12psi boost

 

[karolko]

Second photo is at 23 psi

 

[gnxtc2]

You need to log backpressure before you do anything. Check the wastegate, the exhaust could possibly pushing open the valve or you have a leak in the diaphram.

I believe there is a 1.44 exhaust housing for the 76.

There are a lot of variables that affect back pressure, ie: cam, heads, headers, wastegate, exhaust wheel design, bla, bla

Billy T.
gnxtc2@aol.com

 

[karolko]

Hanks for the reply billy.
I will install a sensor for the back pressure, but I have no idea how to interpret the results.

Can you point me in the right direction?

Also, do you have a spare ssi sensor I could buy from you? Will a 100 psi work or should I get a 200psi?

 

[gnxtc2]

Hanks for the reply billy.
I will install a sensor for the back pressure, but I have no idea how to interpret the results.

Can you point me in the right direction?

Also, do you have a spare ssi sensor I could buy from you? Will a 100 psi work or should I get a 200psi?

You need a 100 psi one. Either a 12v or 5v one. Then you need to wire in the return into the XFI. I get my sensors from AEM which can be purchased through Summit.

Once your backpressure gets to 2:1, you're done.

I have no spare sensors.

You need to weld a bung by the turbo flange to attach a steel tube. I ran a piece 18" tube from the bung. The sensor is not made to take high heat hence the reason for the tube.

PM me your number and I'll send you a pic.

Billy T.
gnxtc2@aol.com

 

[lazaris]

Hanks for the reply billy.
I will install a sensor for the back pressure, but I have no idea how to interpret the results.

Can you point me in the right direction?

Also, do you have a spare ssi sensor I could buy from you? Will a 100 psi work or should I get a 200psi?

Adrian there is a way to fix this. Its easier to explain over the phone. Dont believe your done at 2:1 either if thats what the sensor would show. I have a BP sensor as well. Give me a call if you like. 516 805-4634

 

[karolko]

Hi Laz,

I will call you friday sometime, but it will be froma number in Europe so don't get freaked out.

Also, would too tight of valve lash cause this? maybe the valves are opening too early?

 

[Eticket]

After you figure out your issue, if you want to move up to a larger A/R housing, I have a 1.44 for you.. if you have a GT42 style turbo which sounds like it if your current a/r is 1.28

 

[karolko]

i do have the GT42 style turbo, but i never knew that Precision had a 1.44 A/R. There website does not list it.

I don't know how much that will effect low end spool. Obviously it will be longer, but how much worse?

Adrian

 

[ttypewhite]

I think your wastegate spring seems to be suspect. Get the highest possible spring and re test it. I found that when I was going thru the growing pains of this very same thing, that the lower the spring pressure, the harder it becomes to control the boost. I got a 16psi spring and it was a lot more stable.