TomU

iTrader: (11)

I am running a PFC with stock twins and have been doing some reading (what little is out there) on the subject of controlling boost with a PFC and stock twins. I would like to clear up some things that are not clear (at least to me). My understanding is:

1. A PFC will control boost up to about 12 psi via the stock solenoids, but is less than ideal. However, why it's not ideal is not clear.

2. Electronic Boost Control, to include the PFC kit, may (or may not be) an improvement to the PFC for controlling stock twin boost.

3. A PFC boost control kit is plumbed similar to an Apexi AVC-R where the COM is connected to the stock wastegate and pre-control actuators (boost side) via a 'T' and the NO is connected to the boost via a 'T' (i.e. the single solenoid is connected to both the wastegate and pre-control actuators)

4. The vacuum side of the actuators is capped (the Apexi instruction is not clear on this, but others recommend capping)

5. The Apexi boost control solenoid is wired to (and replaces) the pre-control solenoid

I have also read that one solenoid in a 'T' fashion may not control both the wastegate and pre-control actuators very well. I have also read that the Apexi solenoid should be wired to the wastegate solenoid.

So here are my questions:

1. Is my understanding above correct?
2. Is an EBC better than PFC boost control for stock twins?
3. Should the single solenoid simultaneously control both the wastegate and pre-control?
4. If not, should the solenoid just control the wategate leaving the stock solenoid to control the pre-control (or visa versa, control the pre-control, leaving the wastegate stock)?

Think the answers lie in how the PFC controls boost with the boost control kit installed. Unfortunately, there is not much on how this works to understand how it should be hooked up. Any insights are appreciated.

DaleClark

iTrader: (55)

Good question here.

First off, the factory boost control solenoids were designed around the stock restriction in the car (intake and exhaust). Once that's opened up, they cannot regulate boost properly. You can start messing with pill size, drilling out pills, swapping in carb jets, etc. - IMHO, that's not boost control, that's voodoo.

If you took the pills out completely and tried to use the factory solenoids, you'd get a bunch of nothing - you'd be at 7psi, that's it.

FYI, a pet peeve of mine - the factory boost control vents to the primary turbo duct, which is ATMOSPHERIC PRESSURE, not vacuum. Only place in the engine with vacuum is after the throttle body - you need restriction to create vacuum.

That said, the boost control kit uses a standard 3-way solenoid to control boost. IMHO, adjusting it can be a little bit of work - some with the Commander, some with the Datalogit.

Plumbing it is like any other boost controller - boost output nipple from the primary compressor housing to the input on the solenoid, then from there T'd to the wastegate and precontrol actuators. The output on both actuators (which goes to the factory solenoids then the primary turbo inlet) is capped.

In theory, running wastegate and precontrol together should have some sort of problems or weirdness. In practice, it does just fine.

I've been running an Apexi AVC-R boost controller for YEARS. I have fast response, ZERO spiking, and NO transition spike. My car has a totally smooth and linear power curve to redline, running 12-13 pounds of boost. I can easily switch between 2 settings (high and low) or turn it totally off. I also have my water injection wired into it - if the water runs out, it shuts off the boost controller.

You can do something similar with many of the electronic boost controllers out there - Greddy Profec, Blitz SBC, etc. Used they are pretty reasonable.

Manual boost controllers can do well, but IMHO they're a pain to setup and you can't simply switch them off in bad weather or whatnot. For not much more money you can have a good electronic boost controller.

Dale

Houstonderk

iTrader: (3)

I run the stock wastegate solonoid on mine with single. Control it to 25psi so far.

TomU

iTrader: (11)

Thanks Dale. What I gather from your informative reply is:

1. Stock solenoids suck when intake and exhaust are opened up and even though a PFC may be able to control boost via the stock solenoids, if the car is modified, even that will not be able to control boost very well - due to the limitations of the stock solenoids

2. Don't need to understand why, but a single aftermarket EBC solenoid will be able to control both the wastegate and PC actuators when tee'd together.

Good stuff! Thanks

Houstonderk, you are blowing some serious pressure! Think you need to crank it up to 30 tho

arghx

iTrader: (3)

On stick twins, opinions/experiences vary. It depends on the level of restriction on the intake and exhaust.

You're changing out the solenoids from a 2 port "bleeder" style to a 3 port "interrupt" style. You can google "2 port vs 3 port boost solenoid" and it will explain.

You can just swap out both solenoids with off the shelf MAC valves. It's been done here before, a guy with forum name Sandro did it.

a 3 port solenoid "interrupts" the pressure signal going to the actuator. The other port on the actuator needs to be capped for that to work.

...mostly because, why should Apex'i give you two solenoids when they can sell you 1 for the same price? They could have provided 2, but 1 gets the job done usually, even if it doesn't have the same flexibility of adjusting precontrol and wastegate separately.

Controlling well depends on the metrics. If you are fine tuning your settings with the datalogit and actual duty cycle charts, it's nice to be able to adjust precontrol and wastegate independently. If you aren't into that level complexity, you can run one. The self-tuner types who dig into datalogs benefit from two solenoids, the "I just want to drive my car and not get into those details" won't notice much of a difference usually.

That's probably something I wrote a while back, before Banzai Racing informed me that it can be wired to the precontrol.



See above


An EBC in this context is a solenoid(s), a device to drive the solenoid, some kind of software to control the duty cycle, and the actual settings on the controller. They're all a little different. The PFC is a boost controller. It's got its advantages and its annoying quirks. The same can be said for other EBC's. See my big thread about it.

Sure, it will work. I would argue that running 2 solenoids independently gives an additional freedom of adjustment, but that's only good if you intend to use it.

It's hard to give hard and fast advice as it depends on the modifications to your engine. The MAC solenoids are like $40-$50 each on Ebay or Amazon.

this is the thread you want https://www.rx7club.com/3rd-generati...tegies-874031/

IRPerformance

iTrader: (41)

Run the Apexi solenoid in place of the stock wastegate solenoid. It reacts faster than the stock solenoid, helping control boost in modified cars. I have put together several stock twin and BNR twin turbo cars like this and they perform well. Leave the precontrol stock. Its a good idea to go with Dale's viton check valves.

Wiring the Apexi boost solenoid to the precontrol is for single turbo cars. When you turn off sequential turbo control via the power fc, for whatever reason it will only control the precontrol solenoid.

DaleClark

iTrader: (55)

Ihor, when you use the apexi solenoid instead of the stock solenoid, do you keep the pills in the lines or remove them?

Dale

IRPerformance

iTrader: (41)

Leave the pills as is. You are only using the apexi solenoid in place of the stock solenoid.