Great update and pics. Systematically eliminating weak spots piece by piece towards an extremely reliable (hopefully) build.

I'll have to do a little practice with heel-and-toe shifting on my own car - I think I have stock pedals.

A bit of a stupid question, but does this project car eliminate enough stock parts to almost make an entire new FD? Is there a second FD shell being built from the parts?

Also, have the goals and details of the build diverged in the 5 years since its inception?

 

I am curious to see how the car drives on a DBW. I know there are lots of discussions about the tip in and low speed drivability on some DBW tunes. Now, is this a fault of the DBW itself or the tuner? I know that I've tuned a number of JZ engines that are DBW without any issue, but the FD has a very unique throttle setup to allow for varying the inrush of air into the engine.

 

I too am curious about this, especially since mazda specifically divided the primary and secondary ports with throttle blades at a specific throttle position. The decreased velocity of air through 4 ports vs. 2 at low throttle inputs, as well as proper fuel atomization from the 2 vs. 4 air paths probably has some impact on low load conditions. I've been hesitant to ditch the stock throttle body for these reasons, and while DBW does offer a lot more simplicity with idle control, traction control and other neat features, I wonder if this has been well sorted or just "good enough" for the limitations on the mazda intake design.

 

I'm running a GM 90mm DBW throttle on my FD, with the 13B-RE Cosmo UIM/LIM, and I'm happy to say I have zero driveability or throttle tip-in issues with it. Tuned it myself, key is getting the accel pedal position vs. throttle position relationship right. What you don't want is a straight linear 1:1 relationship between the two, especially at small throttle openings.

Here's a screen grab of my current throttle map, running a Link G5 Neo4 ECU. On the Y axis, you have accelerator pedal position (APS, %) and on the X axis is Engine Speed (RPM). You'll notice that at low APS positions, below 60%, the corresponding commanded throttle opening (E-Throttle 1 Target, %) in the 3D map is always less than the APS %. You'll also notice at the 8500 RPM column that the throttle targets are roughly divided by 4; this functions as a soft rev limiter because the ECU interpolates between cells as the revs climb between 8000 - 8500 RPMs.

 

Was this done on street tuning or dyno? That usually is a very good way to modulate the throttle and not make the pedal so linear.

 

Street tuning, lots of trial & error!

One thing to add - the ECU used has a lot to do with how much resolution you really need when you build these kinds of tables. My Link G5 Neo4 does a great job of interpolating the target values between adjacent cells, so I'm able to setup my rows (APS %) in 10% steps with no ill effects. If you find on the road that the tip-in response is a bit herky-jerky at low throttle openings, you may need to add more rows for resolution, say row break points every 5% for throttle openings < 30% or so.

 

Its all in the DBW tuning.
Been running my Haltech R3 with RX8 TB, DBW setup for almost 2yrs now and the car is snappy just like the stock throttle body.
Mine is street tuned.... it works great.. im glad i made the DBW jump.

Steve

 

@Billj747 any chance that the Camaro pedal cover might be available? Even as an STL file?
I have a very similar throttle setup, and while I like the Camaro pedal better than the FD pedal, I think that cover might make it even better.

 

Raceonly and Outsider Garage make complete DBW kits as well. I sell both.

 

Haha, that's the goal! To improve the platform with modern technology. I probably could have built another FD with all of the parts I removed, sold, gave away, or threw away. The goals have not changed in the past 5 years. To build a car that can be driven on the street that is comfortable with A/C, a compliant ride, and does not drone or beat you up like a racecar, yet is highly capable and competent on track.

Spoiler: The car drives GREAT with the DBW - on both an Emtron KV8 and Haltech R3. As you pointed out, there are a lot of conversations online that talk bout drivability issues with DBW vs the stock 3-butteryfly throttle body. After tuning and driving the car on two different ECUs, I think the majority of the negative feedback on DBW tip in and throttle response is probably due to improper tuning of the pedal and transient fueling.

I worked as a development driver for Ford and heavily influenced the throttle tuning on the Ford GT and most S550 Mustangs (2015-2023) including the GT350 & GT500. I also worked on the throttle calibrations of Guntherwerk's Turbo. Needless to say, I really enjoy the significant flexibility of DBW pedal tuning and how you can change the entire car's response and feel based on the pedal map (which I use a 3D map with RPM & Pedal Position). The transient fueling tuning is very important to get the crisp response of engine based on the throttle body size. I'm using an 82mm Bosch TB but for anything under 600hp, the 74mm might be a better bet. I'd like to back to back and try both in the future.
I was a bit hesitant too based off what I read online and not knowing how a single TB would affect the air velocities going into the primary and secondaries, but after experiencing it myself, with 2 different ECUs, I wouldn't ever go back to a cable. I will add a disclaimer that I have a Semi-P and full bridgeport and my car idles at 1,500rpm with a lot of overlap. Its possible the stock throttle body is far more crucial keeping up the air velocities between 800-1,500rpm, but i'm not sure how relevant that is since you don't really lug a rotary off the line below 1,500rpm.
You don't really want a linear throttle pedal. Even the stock throttle body does not have a linear throttle blade opening. Playing around with different conditions of when the throttle body opens and how much based off the input is a lot of fun to make the car act in completely different ways and be more responsive at lower rpm.

​​​​​​​I've sold a few pedals. It makes a huge difference.

​​​​​​​

 

Oh I agree the pedal shouldn't be linear. Generally speaking while on a dyno you can tune the pedal to your desired "feel" and really dial in transient response before getting onto the road to fine tune it.

What is nice with a DBW pedal setup is also the ability to create different maps. It is much like the modern Subaru STI that switch between sport and sport + and most modern cars... it just is changing the pedal feel to make the car feel faster than it is.

I do plan to build a wiring harness for my RX-7 to incorporate DBW in the future. I will be using a Haltech R3 to manage the car. However, I don't think I'm ready to bite the bullet yet on DBW for the rotary. It works great on my Supra, but this is, at least for me, something that can wait. Plus the use of all autosport connectors makes the task of building out a DBW setup very simple.