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Think it depends on your setup, Iím using a 3 port valve and it works great controlling boost levels at the high end. Running a .7 bar spring and without any duty cycle at the ebc I get a max of .7 bar. Adding duty cycle increases my boost to my target no problems. Also making 300 ft/lbs torque at 3300 rpms with a T4 1.06 hot housing. Funny thing is I had the opposite problem with my old header, overboost when tested with the wastegate removed.

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75 930, 76 930, 83 SC EFI turbo
Old 07-21-2019, 07:23 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #21 (permalink)
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Originally Posted by lite75 View Post
Think it depends on your setup, Iím using a 3 port valve and it works great controlling boost levels at the high end. Running a .7 bar spring and without any duty cycle at the ebc I get a max of .7 bar. Adding duty cycle increases my boost to my target no problems. Also making 300 ft/lbs torque at 3300 rpms with a T4 1.06 hot housing. Funny thing is I had the opposite problem with my old header, overboost when tested with the wastegate removed.
As I remember you are running a Borg Warner EFR turbo in true twin scroll mode right? they use big turbine exducers compared to other brands, and you are running also T4 1.06 housing, so very effecient setup with very LOW backpressure. What boost are you running? and what size WG's?
Old 07-21-2019, 07:29 AM
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Originally Posted by flightlead404 View Post
I current have this 3 port valve. Do you think its inadequate for a 3.3L standard P's and C's with SC cams and a K27/29 with Brian's headers? Tial F46
It depends. But from what Jakob is saying about early WG opening (especially against an overly soft spring), I believe that a 4 port (which would hold pressure to the top port until target reached) would likely work better for me. My 4 port will be turning up Monday and I'll be fitting it almost immediately.

46mm is certainly in the "larger" range of WGs.
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'77 S with '78 930 power and a few other things.
Old 07-21-2019, 07:34 AM
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Originally Posted by JakobM View Post
You have a 0.5 bar spring. That is a SOFT spring right there in a 46mm wg. Try to put pressure under the WG membrane and see when it start open - my guess is as early as 0.2 or 0.3 bar and fully open at 0.5 bar with your 3 port solenoid valve. Meaning easily pressed open by back pressure when start building low boost in your engine. AND you have a large 46mm WG so alot of surface area to push back that tiny 0.5 bar spring.
Last night I ordered a large green (.8) and small yellow (.2) to go with the existing .5 (whatever color that is), so should have some flexibility to play around. And the ability to just fit stronger springs in the WG and get boost, regardless of what ends up being the result with boost control.

Darnit. Seems almost every time I touch the car I end up waiting on parts or tools to proceed...

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Originally Posted by JakobM View Post
I am not sure I understand what you are aiming for with the 0.3 bar (130kpa absolute) in your programming. What is the thought behind?
Yeh, I probably explained it poorly.

At .2 bar manifold (120 kPa) and below, solenoid runs minimum duty cycle- anything that happens is down to the spring.

At .3 bar manifold (130 kPa), solenoid activates, immediately goes maximum duty cycle, diverting air to the top port.

That's the usual MoTeC advice/configuration (which, in almost all respects I've found to be pretty awesome[*]); set activation pressure 20-30 kPa below spring rate.

I believe idea is to have the solenoid involved in the process early as boost is building. I can't see, from you've explained, that boost to the top port would hurt in any way - in fact, as I understand it, seems to be exactly what is needed.

Target boost is 1 bar manifold - or 200 kPa. It just never gets there.

Never noticed this before because I've been tweaking part-throttle/cruise/idle, warm-up compensation, adding sensors and other diversions. And getting a few miles on the motor.

Now that I've actually tested "floor and hold" scenarios, can clearly see that boost doesn't build beyond spring pressure. Car is not exactly slow ya understand - just much of the boost shove you'd expect towards the end of a gear isn't there. Just a corner of the performance envelope I hadn't been focusing on while working on everything else...

[*] standard MoTeC warmup compensations very clearly not what the 930 wants. Not at all..
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Old 07-21-2019, 08:13 AM
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Originally Posted by spuggy View Post
Last night I ordered a large green (.8) and small yellow (.2) to go with the existing .5 (whatever color that is), so should have some flexibility to play around. And the ability to just fit stronger springs in the WG and get boost, regardless of what ends up being the result with boost control.
Exactly, perfect!

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Originally Posted by spuggy View Post
...
At .2 bar manifold (120 kPa) and below, solenoid runs minimum duty cycle- anything that happens is down to the spring.

At .3 bar manifold (130 kPa), solenoid activates, immediately goes maximum duty cycle, diverting air to the top port.

That's the usual MoTeC advice/configuration (which, in almost all respects I've found to be pretty awesome[*]); set activation pressure 20-30 kPa below spring rate.

I believe idea is to have the solenoid involved in the process early as boost is building. I can't see, from you've explained, that boost to the top port would hurt in any way - in fact, as I understand it, seems to be exactly what is needed.

Target boost is 1 bar manifold - or 200 kPa. It just never gets there.
Ok now understood - Perfect! Yes the all boost should go the top of the WG port as early as poosible. Good!

You will have the issue fixed with the new springs and 4 port valve, interesting will be whether if the spool-up will do better also
Old 07-21-2019, 08:20 AM
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JakobM

Yes, twin scroll GT35 with 2 38mm wastegates ran up to 1.1 bar.
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Last edited by lite75; 07-21-2019 at 10:44 AM..
Old 07-21-2019, 10:38 AM
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Ok, great package! GT35 is a smaller turbo around 62mm exducer. I mixed you up with a BW 366 turbo.
Twin scroll is KING and will hold a lower overall average back-pressure, but it also builds higher peak pressure in system per puls (hence quicker spool-up), so also higher peak back pressure. So you are properly running around a steady 1:1 in ratio of boost vs. back pressure up to the 1.1 bar target boost level with the 62mm turbine wheel exducer and appr. 16-17cm2 in turbine area (the T4 A/R 1.06). Maybe you even have a slightly lower back pressure than boost due to the Twin scroll setup and still "only" 1.1 bar of target boost, but I believe not much.

Reaching target boost is one thing, and as mentioned MANY people are running happy with the 3 port valve setup. However, my experience - and I beleive it is simple psysics - the WG(s) cannot hold the WG valve closed between the DELTA of spring load and boost pressure with a 3 port boost solenoid setup (asuming 1:1 boost vs. back pressure).

You have a delta of appr. ~0.4 bar gab/time area between 0.7 bar and the 1.1 bar if running a 1:1 boost vs. back-pressure ratio. My estimation is you do not have as low as 0.7 bar back pressure all to the end of your boost target. I guess your back pressure climes past 0.7 bar before you reach 0.8-1 bar of boost. You do not hear it, it does not impact on target boost level in your case, you still have awesome results overall, however gains on spool-up in the Delta area are still there to be achieved. The gains can be irrelevant or quit major. Just my experience

You have a very efficient setup with twin scroll and two WG's building boost fine, but I bet you, if you where to test a cover plate on those two WG's, you would find a difference on spool-up time in that particular area between 0.7 - 1.1 bar boost build-up If you where to aim for higher boost, the difference would be even greater.

With a 3 port valve, any back pressure above spring level WILL have to open WG valve regardless how it is set up in EFI management. There is simply no "amo" left mechanically to hold it back when the back pressure force exceed the spring load.

The greater the DELTA becomes between WG spring load and boost level, the greater the need for a 4 port valve
Old 07-21-2019, 12:41 PM
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Question for Jakob,

How does all this apply to a EBC? I assume itís the same as your 3 port comments? When I installed mine boost response got MUCH better and I was able to dial in more. I was encouraged to install a smaller wastegate spring since the magic EBC box can control 2x base rate spring. I opted for a 7psi base spring for 10-11psi target. It just made more sense to me.

Itís a older Greddy Profec A. It matches the simple ness of the car.

I noticed I canít seem to get boost much higher than the 11psi. Was thinking my IC is at its limits for flow. Now I wonder if I just need more WG spring. Thoughts?

Last edited by K24madness; 07-22-2019 at 07:22 AM..
Old 07-22-2019, 07:20 AM
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JakobM

Ok I see what your saying, so the more boost you add over spring pressure the more chance you have of the valve cracking open before you want it too.
bet I'm almost out of spring pressure.
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Old 07-22-2019, 12:13 PM
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[QUOTE=JakobM;10530260]My advise - go with a 4 port MAC valve and you get a better solution - you get to add your boost pressure as your "amo" to fight against your back-pressure. A 3 port valve can not do this. A 4 port valve will provide you a 2:1 force ratio (double force compared to a 3 port valve) to fight back-pressure.

Excellent post thank you very much. This is exactly what I needed to know and it seems I've wasted my money buying a 3 port. Never mind it's a small amount of $$ and I'm glad I'll now have the functionality of the 4 port EBC.

Old 07-23-2019, 12:42 AM
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