Pistonkilla1

No, but you can make it simpler. Many of us have disabled or completely removed it to clean up the intake tract (removed some restriction in the extension manifold). My car drove the same with it disabled as it did with it enabled so I decided to completely remove the butterflies. With the butterflies completely out my high RPM boost creep was higher than ever, so it did seem to increase airflow.

wb123

Should i be closing the hose at the end where i took it off? I have the actuator capped off but the hose is still open the the atmosphere and sux in air, would it be good idea to pinc the hose completely shutting it off from sucking in aiR?

SLOASFK

iTrader: (5)

It's more important that you cap off the solenoid(or the hose that runs from the solenoid) than the actuator. I did this on my friends FD with a zip tie, but you could use a golf tee, too.

wb123

So by doing this it wont "suck" air any more through that black hose?

SLOASFK

iTrader: (5)

right

wb123

What is the black hose connected to? if its sucking air and you block it wont this cause an ill effect on the other end?

Pistonkilla1

You dont really need to cap off the solenoids, just remove the hose. The only things you want to cap is things that will leak like the nipples on the IM.

SLOASFK

iTrader: (5)

Nah, it's a standard ghetto rig, if you have a vac leak, you can plug it with a Tee, since it'll just be sucking anyway.

wb123

Ok right now i just have the hose open to the atmospher i can here it very vaguely when i drive and i dont have any boost issues.
Should i still crimp the hose shut ?

Gadd

The DT does more than limit boost at low coolant temps. Refer to the Service Highlights section F page 48.

I'll data log the solenoid and see if the PFC controls it.

Paul

DigDug

I've read that section of the FSM, and it would appear that the DT valves are used as a sort of acceleration enrichment (via limiting airflow/boost) by the stock ECU. Some people say the car is more responsive after disabling it (i.e. Rob Robinette), but then I've read about someone monitoring the solenoid with a stock ECU and never saw it do anything except stay open below a certain temp (160F or so).

My PFC doesn't do anything with it. The DT is still plumbed on my car, as I observed it working with the stock ECU before installing the PFC a couple years ago. After installing the PFC, the actuator no longer saw vacuum and closed the valves at startup.

Gadd

Got ya. I'm not going to repeat work that's been done then.

Paul

BobfisH

Thats the ECU limiting the boost when the cars cold, not the DT. The turbos wastegate actuator is operated by a boost line from the intake, when it sees 10psi, the wastegate opens - this is how the car regulates boost. The car is only making 7psi because either his intake and exhaust is so restrictive that at the given flow rate of the engine the turbos can only make 7psi with the WG closed, or the ECU opens the wastegate earlier (by pulsing its turbo control solenoid faster to allow more boost to the WG actuator, thus opening it sooner)

My car makes 10psi all day long, hot or cold.

rajeevx7

iTrader: (11)

Where are you talking about measuring from?? Ofcourse the turbos boost more than what you want 'all day long'. But, what everybody else is talking about is what the manifold sees.

Closed butterflies LIMIT boost. No, it doesn't try to mechanically slow the turbos down, but this situation won't let the manifold see your 'all day boost, hot or cold'. Because, what you are saying, is that with your closed butterflies closed you see 10psi 'all day, hot or cold' in your manifold?? WTF??

Kento

If his car is "only making 7psi because either his intake or exhaust is so restrictive that at the given flow rate of the engine the turbos can only make 7psi with the WG closed", then how is it making 11.5 psi with the DT open?

Because a solenoid is a pretty primitive method of actively controlling a valve, and the original FD's 8-bit ECU didn't exactly have a lot of room for a ton of control operations, it was a lot easier for Mazda's engineers to use the DT to limit boost during initial operation by retricting the intake flow. What other reason would there be for the DT to be there in the first place?

scotty305

iTrader: (2)

I know from experience that the 2001 Suzuki GSX-R 600cc sportbike uses secondary throttles (albeit controlled by motors, not primitive on/off solenoids). It's been a while, but I think the service manual claims the secondary-throttle system enhances low-end torque (by decreasing airflow in order to keep velocity sufficiently high). I doubt a sportbike, especially a 600cc repli-racer, would add that much weight (it's about 3 pounds worth of throttles, motors, and control units) if it didn't improve performance in some way.

Kento, you're a motorcycle guy, is this still common on modern sportbikes?


I agree that the 93-95 RX-7's ECU isn't controlling the Double Throttle Valve very well, but if you've got an ECU that will let you control it based on RPM and throttle position, it might be worth exploring.


-s-

BobfisH

because the total flow through the engine with the DTC fully open @ 10psi is 3 times the total flow through the engine with the DTC closed @ 10psi.

The DTC does not limit boost. The one and ONLY thing that "controls" boost is the wastegate. It could be possibly for the DTC to limit flow through the engine so much that the turbos simply cannot produce 10psi of boost, but that doesnt really count as the DTC limiting boost per-se.

Lets consider X as a unit of area. You understand that potential airflow through an area of X at a given pressure is going to be LESS than the potential airflow through an area of 3x at the same pressure dont you? The amount of boost your car makes is ENTIRELY and COMPLETELY dependant on restriction. Blow a baloon up through a straw, put in a constant amount of effort and time how long it takes to inflate the baloon. Now get a thinner straw and do the same test.

if youve given constant and consistent levels of effort it will take you longer to blow up the baloon with the thinner straw, even though the pressure stays the same, the potential for flow is reduced. This is exactly the same principle as the DTC.

Since the car adds fuel based on the pressure it see's and not the airflow (our cars are MAP based fuelling not MAF) it doesnt care whether the DTC is open or not, its going to add the same amount of fuel for 10psi whatever the flow.

This is the reason why de-catting your car makes it blow up. Theres more airflow, but the same amount of fuel. Rx7s run rich anyway so sometimes you can get away with it, but whatever you say and however you look at it, removing the stock cat WILL make your car run leaner than it did before. Whether or not that is TOO lean is debatable and entirely depends on the car, the fuels used, atmospheric conditions etc etc. But its going to run leaner. Decat a car that runs at 100m below sea level with ambient air temps of 2 degree's C and run it on 92 octane fuel and itll probably go bang. However, do the same to a car at 200m above sea level with ambient temps of 30c and run 110ron aviation fuel and your going to have no problems at all! (apart from maybe EGTS and big *** flames lol)

sorry ive gone completely off subject havent i? haha.

BobfisH

mind you, all of what i say is dependant on where the takeoff for the wastegate is taken. If its before the DTC, it could be entirely possible that the wastegate is limiting boost because it thinks the car has made full boost, but the DTC is limiting the airflow through it so the manifold doesnt actually see 10psi (i.e engine is using the air quicker than it can be provided to maintain a 10psi boost level)

does anyone out there know more about this than me?

adam c

iTrader: (2)

Bobfish:

You are completely missing the point of where boost is measured. Measuring it before the throttle body doesn't matter. All that matters is what the engine sees, and that is AFTER the DT. As you have pointed out, the DT being closed limits the amount of pressure that can pass. 10 psi at the turbos, with the DT closed probably means only about 2 psi at the engine, and that is what really matters.

MADDSLOW

iTrader: (11)

I removed the DT to eliminate the very slight loss of restriction, but I don't have to worry about "boosting on a cold motor", because as discussed on an earlier thread, I always warm up my vehicle first.

And before anyone tries to come back with some weak comment, I don't punch it after I leave my driveway; I let the transmission warm up as well.

Kento

Well, there is the turbo pre-control that controls boost on the primary turbo below the 4500 rpm transition; the WG door remains closed.
Umm...how does that not "really count as the DTC limiting boost per se"? "Doesn't count"? Why should semantics be involved?
Note that I'm not saying that the DTC is one and only component that limits boost during initial operation. But that is the reason for its inclusion in the intake tract.
Yes, I know about airflow/pressure, but you're not looking at how the DT works. It either is closed or open. In the closed position, it is providing so much restriction in the intake that (using your straw analogy) it would be like trying to blow up a balloon through a syringe. See what I'm getting at here?
The secondary throttle plates in the Suzuki EFI systems don't really enhance low-end torque; they're there to reduce abrupt throttle response resulting from the massive intake airflow fluctuations that occur at very light throttle openings.

Kento

This is basically what I'm saying the DT does. It doesn't "control" boost by itself, but it can help limit boost. That is the reason for the DT plates in the intake tract. Otherwise, there's no reason for them to be there, they'd just be a useless obstruction in the intake tract.

rajeevx7

iTrader: (11)

Bobfish, I like you. You tore two motors apart and put together some nice cars in your own garage. But seriously.......


One mechanical contraption dumps air so the turbos don't spin as fast. The other contraption backs up air so the turbos don't spin as fast. But one 'controls' boost and the other doesn't? WTF??




To the original poster: The butt-dyno is great because it validates every mod we do to our little cars