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Discussion Starter #1
I believe this is kind of a "generic" question but I'll give some basic info anyway. 363 SBF, twin T3 turbos, each with 38mm Tial Waste gate. Right now I'm running 5lbs springs and using boost pressure before the intercooler to control the wastegates.

Right around 25-26lbs boost the increase in boost stops following the increase in controller PWM. How do you know if you are running out of turbo capacity or if the wastegates are not being held open by exhaust system backpressure?

I suspect I'm at the end of the turbo capacity(s) but this question has been something I've wondered about.
 

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Discussion Starter #3

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I know the new fancy gates have a gate position sensor on the valve on them. If you could log gate position and check backpressure together I believe you will know if your turbos are done. Or just close the wastegate completely and keep it from opening and see if it makes more power which is the sure way to break something lol
 

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Discussion Starter #6 (Edited)
You haven't even stated how anything is configured, I assume it is a 4 port guessing by what you said??
Wastegates each have a fitting above/below the diaphragm. Boost pressure is supplied to both fittings. Single solenoid controller bleeds off pressure of hose(s) that would hold wastegate(s) "closed".

Put another way, at 100% duty cycle both side of diaphragm are equally pressurized and the 5lb spring is what is holding the wastegate closed against the exhaust flow.
 

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Discussion Starter #7
I know the new fancy gates have a gate position sensor on the valve on them. If you could log gate position and check backpressure together I believe you will know if your turbos are done. Or just close the wastegate completely and keep it from opening and see if it makes more power which is the sure way to break something lol
No position indicator. Not going to try other method. :p
 

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So what I take from that


Lower chamber is full boost reference un altered at all times...

The dome is bled completely at 0% DC.... And full boost reference at 100% DC

Is this correct?


If so im surprised you can even make that much boost with only a 5lb spring behind it configured like that... and there is a lot more in it if that's the case

You are only seeing a max of dome pressure equivalent to boost with a 5lb spring behind it

Going to a 4 port where you would bleed the lower reference and apply the dome as DC increases would get you more range...... if you don't want to do a dual solenoid with fixed source or increase the spring pressure
 

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Discussion Starter #9
So what I take from that


Lower chamber is full boost reference un altered at all times...

The dome is bled completely at 0% DC.... And full boost reference at 100% DC

Is this correct?

If so im surprised you can even make that much boost with only a 5lb spring behind it configured like that... and there is a lot more in it if that's the case

You are only seeing a max of dome pressure equivalent to boost with a 5lb spring behind it

Going to a 4 port where you would bleed the lower reference and apply the dome as DC increases would get you more range...... if you don't want to do a dual solenoid with fixed source or increase the spring pressure
Yep, I believe that's it. I found a diagram showing the operation.

 

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Discussion Starter #10 (Edited)
There is an alternative way to use that solenoid for additional boost that I could possibly try first before changing solenoids. This shows it for a single turbo but I'm sure it would work like the other method with 2 turbos.

 

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Ha yeah buddy. Trust me they aren't done

It actually sounds like it is breathing fairly well to me

Say 25psi of boost... You are making that with 25psi on the dome and a 5lb spring. (Looking at it how the typical dual solenoid fixed source guys look at stuff) which still looks like there is plenty left


You have a couple options.

Replace with a 4 port and a little plumbing change

Leave as is but Install another 3 port in the lower chamber lines with the solenoid wired parallel to the current solenoid, that vents that line as DC increases

Increase spring rate

Or go to a dual solenoid setup with compressed air or CO2


Should be noted as the turbos do start "getting there" dome require to deliver more boost is going to get exponential
 

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There is an alternative way to use that solenoid for additional boost that I could possibly try first before changing solenoids. This shows it for a single turbo but I'm sure it would work like the other method with 2 turbos.


Should be noted that is a 3 port plumbed to mimic a 4 port.... You better have a pin hole drilled in the dome suppy to vent
 

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Discussion Starter #13
Should be noted that is a 3 port plumbed to mimic a 4 port.... You better have a pin hole drilled in the dome suppy to vent
Do you mean the bottom side of the dome?
 

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Should be noted that is a 3 port plumbed to mimic a 4 port.... You better have a pin hole drilled in the dome suppy to vent
Do you mean the bottom side of the dome?
No. The line from the solenoid to the dome needs a pin hole drilled in it to vent the dome pressure once you’re not sending pressure to it. If there’s no hole, it’ll trap the pressure in the dome and boost control will/could be all over the place. We’re talking a hole that’s .030. Even with the small hole it’ll still fill the dome when you need it to. I ran mine like that and while control was good, the control with onboard air is phenomenal.
 

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I ran my car both ways pictured and could not get it to hold boost it would spike say 17lbs and drop to 11-12lbs I finally switched to co2 boost control and what a difference it made I could get the boost in faster and hold it the whole run it’s honestly the best upgrade I’ve made to the car
 

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Hi randy love your car, here's my 2 cents on the whole wastegate deal, i have worked at a dyno shop over here in Australian for some years and used my own car as a test bed , it is a 5.0l ford falcon with twin cheap Chinese t3/t4 56mm turbos and two 50mm gates.

I had 6psi springs in the gate and with the hose to the bottom of the gate it made 6psi, with it plumbed up like yours and with 100% duty cycle to the top of the gate i could only get 16psi, i thought the turbos were done and my best et was about a 10.0 , thinking about this and what was opening the gate if i had 16 on top of the gate and 16 in the bottom it had to be back pressure blowing the gate open to test this out i decided to take both hoses off the gates and see what happens, and geuss what exactly 16 psi.

So what i did then was run no hose to the bottom of the gate and i used an air regulator to regulate boost pressure to the top of the gates and with 10 psi to the top of the gates i got 22 psi and ran a 9.6 at 142 goes to show the turbos were not done and had more left in them, i didn't push it much more then that as this was a stock roller short block.

My next combo with twin GT35r turbos from an aussie xr6 will be using regulated Co2 , its simple and just works

Brett
 

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Discussion Starter #18 (Edited)
Thanks Brett and everyone else.

I suspected that the current wastegate control might be limiting my boost so I will try to reconfigure it. I will probably go to the 4 port solenoid, I suspect it will be easier to setup the control curve. I know CO2 systems are superior in some aspects but I want to avoid adding another "system" to the car. I've not really had any problems controlling boost with the current system other than what appears to be a limitation on maximum boost.

A couple of observations. When I first started this project 11 years ago I did communicate with Tial about maximum boost and the tech suggested the limitation of control would be around 10 psi above the spring pressure. However, the data I got during the runs never showed a limitation until I reached 24-26 lbs boost. Up to that boost level the boost control settings were close to linear and data during the run showed the boost rise following the controller response. Based on this it was difficult to recognize the limitation though it seems logical.
 

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Yes true I think with me having 50mm gates and possibly more back pressure I reached the limit when back pressure was opening the gates before you with your 38mm gates the smaller gates would have less force acting against the valve
 

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Another thought Randy if you don't want to run CO2 is run full boost pressure to the top of the gate and use your solenoid to bleed off pressure to the bottom I don't think it would take much duty cycle to see a boost increase
 
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