Battling backpressure at RPM with AMS-1000

[karolko]

T type,

I can try that, but in theory there should be no difference if there was 20 psi on the gate with 2psi from the spring and 18psi from co2, or 16 psi from the spring or 4 psi from co2

Also I would like to keep a lighter spring in the gate so I actually have control for the launch.

I can try this how're because I have higher poundage springs.


I'm beginning to suspect that my calve lash is set a little too tight. I noticed at low boost I was loosing around 2psi at higher rpm and at higher boost I'm loosing the same 2 psi.

All these ideas and I'm on the ther side of the world right now so I can't test anything.

 

[Reggie West]

Test off of the spring first so you know what it is doing. And I would put the highest pressure spring you have as well.

That spring should never open any sooner than whatever psi it is rated for.

 

[gnxtc2]

You want the lightest spring in the wastegate. AMS even recommends the lightest spring. Let the AMS control the gate.

Yes, you should make a run down the track with no CO2 so you know what pressure spring you have.

Billy T.
gnxtc2@aol.com

 

[Dusty Bradford]

#1 log backpressure. It's a must for any turbo car to understand what's going on.

#2 you just don't have enough gate pressure to keep the boost from dropping. If your only commanding 25psi on the AMS and the motor is making 23psi, backpressure isn't to high yet and you just need to ramp more gate pressure to maintain the boost. As rpm climbs your engine is consuming more than your turbo can supply at that pressure ratio. Increasing gate pressure will increase boost but it will also increase back pressure. By logging backpressure you will get an idea of what's going on.

I have to put 55-60psi on my gate to make 32psi boost.

#3 you don't need the AMS2000 yet but it can control backpressure, boost pressure, turbo rpm or several other items while it also controls gate pressure. It's a very sweet controller that I've just started using. You would have to have the pro version to program in a Co2 ramp that takes info from the backpressure sensor and adjusts itself down track to maintain the pressure where you want it.


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[norbs]

I agree with Dusty you need to target your co2 psi 2 x your boost psi on the top of the gate. You could experiment with the 1.44 it would definitely slow the spool time, but on my car it had very little effect on lag as it was laggy before and it still is now

 

[forcefed3.8's]

I am running an ams1000 with a 7675 gt42 style 1.28ar turbo on a 274" stage 2. I have a tial 44 with a 4lbs spring. With no co2 on the gate, it will make 4 to 6psi. Right now it has 36lbs to make 32psi.

 

[karolko]

forcefed, you said that it take you 36psi at the gate ( technically 40psi if you include the spring) to make 32 psi of boost.

Now with your AMS-1000 do you just hold 36psi straight across or are you ramping it upward as RPM increases?

As most guys said, i need a backpressure gauge and it is on the list for the winter...

I am attaching a screenshot of RPM, AMS-1000 gate pressure and Boost pressure. What i am finding interesting is between the 2-3 shift. I am not increasing any gate pressure but my bost pressure goes up drastically. What gives? maybe someone smarter than me will chime in and spread there wealth of knowledge.

I did notice that my ramping of boost during 3rd gear is close to keeping the boost pressure level ( i only lost 1.4 psi overall, but that is still power)

 

[forcefed3.8's]

No ramping in boost.

 

[karolko]

hmmm. i am stumped.

 

[turbobitt]

I would say your turbo speed is up on the top of 2nd gear and when the RPM's drop there is a surplus of compressor flow. If your RPM's where to increase to the same level in 3rd gear I'm sure the boost would drop down to the same level as the top of 2nd and 1st. Can't really tell but I'm guessing you are over 7K and the 1-2 and 2-3 shift ? That would explain a lot since you are probably approaching the mass flow limit of the turbine.
AG.

 

[karolko]

I am shifting at 7500 rpm when on race fuel, but on the dyno the motor was still making power a little past that point and i am sure it will make more power up to around 35 psi and at a slightly higher RPM.

From what i understand, if i am approaching the mass limit of the turbo, then my motor is consuming more than the turbo can give it. I guess my simple assumption would be to counter that "over consumption" is by pushing more boost at it.

That sort of makes sense, having an excess of compressor flow after the 2-3 shift: in second gear the motor is rotating so much faster and therefore consuming air that much faster, after the shift, the turbo is still spinning the same speed, but the engine RPM ( air consumption) is less and therefore motor air gets crammed in). Am i on the right track?

I guess the next thing would be to make a AMS-1000 target graph to help keep everything level.

 

[turbobitt]

Another possibility is that at the high RPM you are running the compressor way out of its efficiency or just plain out of compress

I am shifting at 7500 rpm when on race fuel, but on the dyno the motor was still making power a little past that point and i am sure it will make more power up to around 35 psi and at a slightly higher RPM.

From what i understand, if i am approaching the mass limit of the turbo, then my motor is consuming more than the turbo can give it. I guess my simple assumption would be to counter that "over consumption" is by pushing more boost at it.

That sort of makes sense, having an excess of compressor flow after the 2-3 shift: in second gear the motor is rotating so much faster and therefore consuming air that much faster, after the shift, the turbo is still spinning the same speed, but the engine RPM ( air consumption) is less and therefore motor air gets crammed in). Am i on the right track?

I guess the next thing would be to make a AMS-1000 target graph to help keep everything level.

Yes I would say your explanation is on the right track. Also Keep in mind that the compressor is really working hard at your high engine RPM of 7500 and is really requiring a lot more exhaust energy to keep up with the compressor mass flow capability. At some point the compressor wheel and compressor cover just can't keep up with the flow and therefore the turbo speed and back pressure will just keep going up just to maintain boost level or even drop off. If you can keep the turbo in its sweet spot with a little less engine RPM it may be capable of more mass flow.
I am by no means an expert but I am also a data junky and always analyzing this stuff on my own combo.
AG.

 

[turbobitt]

Another possibility is intercooler pressure drop. At higher RPM you will have a lot more mass flow and pressure drop. If the intercooler is not flowing or hitting a brick wall it can cause this issue. I log Hot boost and hot boost temp to monitor the pressure drop and on my CAS intercooler at about 30 psi manifold I'm about 36-37 psi on the hot side.

AG.

 

[Dusty Bradford]

Backpressure would tell you what you need to do. From the graph you either need more CO2 pressure as rpm climbs or your running out of comp wheel. A good indication of seeing boost drop as rpm climbs means your compressor limited.


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[forcefed3.8's]

I bet the rpms are causing the problems. I shift at 7000. With the old 3 bolt turbo, which ran about the same, i shifted at 6400, but with this bigger turbo i switched to a 20 blade converter that flashes to 6400, and a 12 bolt rear with a 3.73 gear over the old 10 bolt 3.42.

 

[karolko]

Backpressure would tell you what you need to do. From the graph you either need more CO2 pressure as rpm climbs or your running out of comp wheel. A good indication of seeing boost drop as rpm climbs means your compressor limited.


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Dusty and allan,

Thank you for the replies and insight. It is helping a lot.

I hope to tell I am by out of compressor because I would honestly be disappointed if the car could only run 8.90's. The motor has all the right parts to make go, and Harmon and Willard brown have dipped there cars into the 8.60's at a higher race weight with old school 76mm's in the past. Hell in sure there are many more guys who have run deeper into the 8's with 76mm turbos.

No need to speculate further, I just need to collect more data and come back to the drawing board.

So here is my next question: should install the port for the back pressure sensor just before the turbo and after the waste gate, or could i weld a port onto the cross over to keep things hidden a little more?

My gut tells me just before the turbo as it would give the most accurate reading of back pressure after incorporating the release of pressure from the wastegate. Just looking to confirm.

Thanks again guys. Once I get this put together I will update everyone and ask for some more feedback.

I appreciate all the help and advice. It is nice to learn new stuff in the name of goof faster

 

[turbobitt]

Dusty and allan,

Thank you for the replies and insight. It is helping a lot.

I hope to tell I am by out of compressor because I would honestly be disappointed if the car could only run 8.90's. The motor has all the right parts to make go, and Harmon and Willard brown have dipped there cars into the 8.60's at a higher race weight with old school 76mm's in the past. Hell in sure there are many more guys who have run deeper into the 8's with 76mm turbos.

No need to speculate further, I just need to collect more data and come back to the drawing board.

So here is my next question: should install the port for the back pressure sensor just before the turbo and after the waste gate, or could i weld a port onto the cross over to keep things hidden a little more?

My gut tells me just before the turbo as it would give the most accurate reading of back pressure after incorporating the release of pressure from the wastegate. Just looking to confirm.

Thanks again guys. Once I get this put together I will update everyone and ask for some more feedback.

I appreciate all the help and advice. It is nice to learn new stuff in the name of goof faster

I would go just before the turbo inlet. The crossover pipe may give a false average reading due to the pulse energy not being the same. I run a Stainless Steel hard line up the intake where the pressure sensor is mounted. I used an old piece of fuel rail and bored it out to mount the pressure sensor into and mounted it in the fuel rail.

As for as out of turbo, I'm sure its capable of producing more power but its all about keeping it in its sweet spot. To me it looks like your engine wants to breath at high RPM and its just out of reach on the efficiency range of the current turbo.

 

[forcefed3.8's]

What cam and compression?

 

[norbs]

What rpm is your torque peak?

 

[karolko]

Motor is 9.5:1 compression and the can is a 224/224 with 112lsa. Nothing exotic

As for peak torque, when cal was here doing the tuning we had to abort the last run because my fuel pump couldn't keep up so I do not have a perfect No. But it was still pulling hard and the slope on the dyno sheet was still increasing steeply at 6100 rpm for both hp and torque.when at the track I feel it still pulling at the higher rpm. I know for certain it pulls hard up to 7000, does it pull hard from 7000-7500? That's hard to say, but when looking at the mph and driveshaft speed on the log, they are increasing at the same high rate.

If I am out of compressor I would have to step up to a 88mm or something wouldn't I? Going to a larger 1.44 A/R wouldn't do anything if this is in fact a air consumption issue and not a back pressure issue, correct?