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Join Date: Nov 2001
Location: Stockholm, Sweden
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Quote:
Originally Posted by 911st View Post
I also changed my Bosh compressor surge valve out for an after market unit I reversed and set up so it was open with no load so the turbo would spin faster in reserve. This reduced exhaust back pressure on the freeway and gave me instant boost when the BOV would slam shut with loss of intake manifold vacuum with acceleration.
Yeah, I read about your BOV setup in some other posts but I'm not sure I understand what you did and how it works.

I have a standard Forge unit, did you just change the orientation of the unit, you must have done something more I think?

Somone at another forum recommended this unit:
http://www.forgemotorsport.com/content.asp?inc=product&cat=0006&product=FMDVSPLTR

At first I thought this was for kids who whant their car to go "woosh", but the unit is supposed to be installed reversed and there is a blanking plug so all air is re-circulated. Would the reversed installation indicate that this unit would be able to do what you accomplished?
Old 03-16-2009, 11:53 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #21 (permalink)
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Please. Do not use that valve on a CIS or other car that meters air flow before said valve location unless you just want to get bigger flames on throttle lift. Venting to atmosphere on a CIS motor with enough air can turn you hot turbo into a jet motor.

I used a piston style compressor bypass valve in a reverse orientation. Intake vacuum and boost kept it open at cruse and idle. I adjusted the spring so it had the right tension so the valve would start to close with loss of intake manifold vacuum. Then boost would build on the larger surface area of the upper chamber piston to force it closed against the boost that was trying to push it open. It is important for the upper chamber piston have significantly more surface area than the end of the piston in the lower chamber. I think most of the after market valves do.

The new Synchronic BOV I believe is adopting the same strategy I used with my $125 BOV 6 years ago.
Old 03-16-2009, 12:15 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #22 (permalink)
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Originally Posted by 911st View Post
Might be good to put a volt ohm meter on #12 to verify it is a ground that triggers the enrichment function and not some other type of signal. Studying the factory C2T supplement is not clear. I can find out the conditions required to trigger that function if you need it.

Putting a Dwell meter on the factory lambda valve and triggering the enrichment function could also be an approach.
Found an old email that I saved from a guy owning 964 turbo as well as a Bosch service center (good combination). He mentions a enrichment pin (but says it's #9, could be on the other box) and that you ground it to activate, so that should do it.
Old 03-16-2009, 12:55 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #23 (permalink)
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At the main harness connection in the motor compartment 9&10 are the wires to the frequency valve ("Timing Valve"). You could try to pick up leads there for the test or at the FV its self using a Dwell Meter.

The circuit that you would ground to trigger the 75% duty cycle for more fuel is at the "Control Unit Oxygen Sensor" unit under the drivers seat, pin 12. Or, at the Control Unit Acceleration Enrichment" pin 14. See picture from the 92 Turbo service manual.

I do make mistakes but I got this off the 911 Turbo Model 92 Sheet 5 Engin Fuel, Ignition System wiring digram.

Very interesting!



Quote:
Originally Posted by 911st View Post
Easiest way to get more fuel is to set the idle CO fat.

On a C2T I always wanted to try grounding thermal 12 at the Lambda control unit under the drivers seat to enable the acceleration fuel circuit which triggers the factory frequency valve to 75%. Could be a good place to use one of those MSD rpm switches. This could be the cheapest fueler yet.

Old 03-16-2009, 02:53 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #24 (permalink)
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Here is where the Accel Unit is located"
Old 03-16-2009, 02:59 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #25 (permalink)
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Here is the info on when it is normally triggered. Again, it was a cold start and running feature to add acceleration fuel. We should be able to triger this using a RPM switch somwhere past 5500rpm where we start needing more fuel on a tuned car.

I read an article once that the C2/S2Turbo race car that ran IMSA may have had some electrical trick up its sleave. I suspect this might be part of what they did.

Old 03-16-2009, 03:07 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #26 (permalink)
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Found something else. There seems to be a "Diagnostics Plug Socket", probably in the motor compartment. Pin 19 is the" Impulse Ratio Oxygen Regulator". This is probably where you can test the frequency valve "duty cycle" using a dwell meter. Pin 7 looks to be the ground.

This could also be a way to set ones CO if one wanted. When warm the duty cycle should be 50% for CO to be at spec. Set is at less than 50% and there will be more fuel on WOT and even more when triggering the 75% acceleration function.

For an RPM signal, it looks to come from the Control Unit 69 in the motor compartment as a black/vilot. Is pin #1 at the motor harness. Then is pin 4 under the seat at the Control Unit Turbocharger.

Hope this is not to much and is what you need. I am confident this is a missing opportunity for more fuel on C2 turbos.
Old 03-16-2009, 03:34 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #27 (permalink)
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Quote:
Originally Posted by 911st View Post
Found something else. There seems to be a "Diagnostics Plug Socket", probably in the motor compartment. Pin 19 is the" Impulse Ratio Oxygen Regulator". This is probably where you can test the frequency valve "duty cycle" using a dwell meter. Pin 7 looks to be the ground.

This could also be a way to set ones CO if one wanted. When warm the duty cycle should be 50% for CO to be at spec. Set is at less than 50% and there will be more fuel on WOT and even more when triggering the 75% acceleration function.

For an RPM signal, it looks to come from the Control Unit 69 in the motor compartment as a black/vilot. Is pin #1 at the motor harness. Then is pin 4 under the seat at the Control Unit Turbocharger.

Hope this is not to much and is what you need. I am confident this is a missing opportunity for more fuel on C2 turbos.
Thanks so much for the information!

I haved tried using the pin #19 in the diagnostic plug (it's inside the car on the passenger side) but couldn't get a signal on my dwell meter, but with the other information I will find it one way or the other.

How would I be able to set my CO electronically (if that's what you mean)?

I have taken the RPM signal from another box under the seat (for the Zeitronix unit and shift light), so if grounding the enrichment pin gives me good AFR, the rest is fairly easy to setup I think.

I have some work to do first though, going to send my gearbox to the shop tomorrow.

Thanks again!
Old 03-17-2009, 06:40 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #28 (permalink)
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Quote:
Originally Posted by 911st View Post
Please. Do not use that valve on a CIS or other car that meters air flow before said valve location unless you just want to get bigger flames on throttle lift. Venting to atmosphere on a CIS motor with enough air can turn you hot turbo into a jet motor.

I used a piston style compressor bypass valve in a reverse orientation. Intake vacuum and boost kept it open at cruse and idle. I adjusted the spring so it had the right tension so the valve would start to close with loss of intake manifold vacuum. Then boost would build on the larger surface area of the upper chamber piston to force it closed against the boost that was trying to push it open. It is important for the upper chamber piston have significantly more surface area than the end of the piston in the lower chamber. I think most of the after market valves do.

The new Synchronic BOV I believe is adopting the same strategy I used with my $125 BOV 6 years ago.
So the pressure inside the intercooler is pushing the piston open during cruise since the BOV is installed reversed, is that what you are saying?

If so, don't I have the same pressure pushing the piston from both ends as long as the throttle isn't closed?
Old 03-17-2009, 07:14 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #29 (permalink)
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Yes, the aftermarket BOV style I used has about a .75" in diameter piston that you point toward the IC / presser section. The top chamber has a piston surface area that is about 3 times that. Thus, lets say you have 10 lbs of pressure pushing on the bottom position it has .75 lbs of force pushing up. The upper chamber would then have three times this, 22.5 lbs, plus the spring tension.

I believe you can set the BOV spring tension to start by putting something on it to listen. Blip the throttle from idle and you should be able to hear the piston close with acceleration.

---

Using the diagnostics plug to measure the duty cycle to set idle mix is based on the point that the Lambda will change the duty cycle to achieve its goal AFR. If you can measure it and know what a 50% duty cycle is, you can adjust the head until you get that 50% reading (hot operating temp).

I would set the duty cycle a little fat. Doing this, then the lambda will pull back the AFR at idle and cruse. Then when the throttle angle increases with WOT the lambda will kick off and deliver more fuel when the Lamda triggers the 50% duty cycle.

Just checked Goggle and found this very good explanation: http://www.allpar.com/fix/fixcarb.html

Also, it looks like you need 12v and pin 19 at the diagnostics port.
Old 03-17-2009, 07:49 AM
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Sorry, only use the info in the link for how a dwell meter can read duty cycle. That is a frequency valve on a GM carb motor, not CIS.

Found a better referance here on Pelican how it is done on an SC, we just need to get the right wires for the C2T: See part way down here: http://www.pelicanparts.com/911/911qa/911Q_misc2.htm

This is the meat of what it says:

" How do I set the mixture properly on my 911 CIS motor?
The procedure is to use a high-impedance (digital) dwell meter to measure the duty cycle of the CIS frequency valve. You can do this from the test connection inside the electrical panel at the left rear driverís side of the engine compartment. Itís the little black plug with a cap, near the CD box. Inside are three connector pins. Connect the positive lead of the dwell meter to the green/white wire pin, and the ground to the brown wire pin. When the engine is at normal operating temperature, the reading on the dwell meter should dither around 45 degrees (using the 4-cylinder scale), typically ranging from 40 to 50 degrees. This translates to 50 percent duty cycle, meaning that the frequency valve is on half the time, and that your basic mixture setting is good. (If you are lucky enough to have a meter that measure duty cycle, obviously you are looking for about 50 percent.)

If you see a higher dwell reading, say 70 percent, it means that the system is trying to control a basic mixture setting that is too lean. Conversely, if you see a low reading, say 30 percent, it means that the basic setting is too rich.

The mixture is adjusted using a special 3mm Allen wrench, through the hole between the fuel distributor and the rubber air duct. Turning this screw to the right makes the mixture richer, left makes it leaner. Never blip the throttle while the wrench is in the hole, or you may bend the air sensor plate. Also, you want to finish the adjustment by turning to the right.

All of the above assumes that you are working on a 80-83SC, with the Lambda oxygen sensor. Correct basic mixture setting helps smooth transition from cold start to warm running, and overall efficient operation."
Old 03-17-2009, 02:11 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #31 (permalink)
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Ok, got you about the idle co, thanks.

Sorry for asking so many questions, but this really sorts out many thoughts and ideas I had for years.

What puzzels me about your BOV configuration is how the BOV piston could be open during cruise since the throttle is partly open and there is (in my mind) the same pressure acting on the BOV piston from below and above. In my mind that would lead to that the piston would stay closed due to the larger area above the piston + the spring tension.
Old 03-19-2009, 12:20 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #32 (permalink)
 
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Originally Posted by staffanbe View Post
Ok, got you about the idle co, thanks.

Sorry for asking so many questions, but this really sorts out many thoughts and ideas I had for years.

What puzzels me about your BOV configuration is how the BOV piston could be open during cruise since the throttle is partly open and there is (in my mind) the same pressure acting on the BOV piston from below and above. In my mind that would lead to that the piston would stay closed due to the larger area above the piston + the spring tension.

At cruse there is actually vacuum in the intake manifold between the throttle plate and the intake valve. This is the section the small hose that connects to the top of the BOV is hooked to. Thus, at curse you have a vacuum trying to pull the larger surface area piston up (valve open) , and you have positive air pressure made in the pressurized / intercooler section pushing up on the end of the small position.

When the throttle plate is opened, air from the intercooler section rushes into the manifold area past the throttle plate and the vacuum starts to go away instantly and depending on the throttle angel, may become equalized to the same level of pressure.

---

Look at it this way. At cruse, there as about 6 lbs of vacunm force pulling up on the internal BOV piston and say 7lbs of force (.5 bar) pushing up on the piston. The is also a small spring trying to pushing the piston closed.

Under 1 bar boost there will be about 45 lbs of pressure pushing down on the piston (3 times larger surfice area), plus some added pressure from the internal BOV spring, and about 10 lbs of boost pressure pushing up on it (less than 1 sq inch of surface area) .

What else is good about doing it this way is the internal BOV piston is not longer side loaded and no longer has much potental to bind and alow the turbo shaft to snap when the TP snaps closed at 6800rpm between shifts.

Hope this helps some.

Old 03-19-2009, 12:31 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #33 (permalink)
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