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GT86 Questions

Practical Reflash Tuning

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Discussion and questions related to the course Practical Reflash Tuning

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Hey fellas,

So, I've learned quite a lot in a short amount of time and I am currently building a stock map for my 86 and thanks to the amazing help from the instructional videos, I now have a solid understanding of how to build a quality tune however, there are two maps that I am not so confident about. Those maps are the VVT maps.

As a friendly reminder, my map is being based on a bone stock 86 (fun I know lol). Anyways, I've often heard the term scavenging. I wont go into depth on what that term means but I believe (correct me if I am wrong) scavenging is when air is crammed in during the intake stroke with the exhaust valves "closed" causing the now charged air to be recirculated and then pushed out thus causing for a nice giddy up upon roll-out in first gear. I am wondering how can I refine the stock vvt settings to really benefit from this scavenging effect?

I've experimented and looked at examples for other Subaru's and can see the consensus is to retard the EXH cam 15-20 degrees in this low load/rpm area. Does this apply to a stock 86? How about with a UEL/EL header or with E85? does this change with FI?

Also, in the stock EXH VVT setting, why does Subaru have the exhaust cam set at 40 degrees in the upper rpm/low load range? is it beneficial to retard this area in a stock 86?

Last questions, how can I create a smoother intake and EXH VVT map? Could I send you guys an email of my current base map for you guys to critique and give suggestions as to what areas need improvement?

Thank you all for reading, any feedback is always appreciated!


Edit: If these questions are too specific for the public forum please email me your response to the questions above. I'd love and would greatly appreciate an in depth explanation to help expand my knowledge on the subject.

Edit Edit: I browsed your webinars and found one that literally answered most of my questions! Here's the LINK to anyone who may have the same questions as me.

P.S. I'd still like for you guys to view my map too see if I have it right for a stock 86. Thanks!

Could anyone confirm my logic behind VVT?

Basically, advancing the intake/exhaust cam profile will cause the valves to open and close at a faster rate during the combustion cycle.

So, by retarding the intake/exhaust cams the air will have less time to escape creating the ram effect.

In theory, is this why Subaru decided to retard the intake cam at low rpm and low load? To build up the pressure of air and then advancing the intake cam substantially to push out all the air that was built up.

When and where in the RPM/Load range is overlap beneficial?

Ok quite a few specific questions in here so let me try to do justice to them. I'd start by saying that while there is a lot of theory and science behind the design and development of camshafts, from our perspective it's not essential to delve too deep into the detail. We're dealing with a fixed cam duration and lift and simply advancing or retarding the cams to find where we achieve optimal power and torque. When you're looking at the cam timing maps, you're also only seeing numbers that are a cam angle relative to the cams natural or relaxed position. In order to really know what this means, you'd also need to factor in the camshaft centreline and duration to see what the effect on overlap is. From a tuner's perspective that's honestly not necessary though.

All we need to do is make an adjustment to the cam timing map and see what the effect is on engine torque. If you notice that the torque increases, keep going in that direction. Since you're starting with a factory cam map, you've already got a pretty thorough starting point which makes your life easier. In stock or mildly modified N/A form I personally found limited advantage from adjusting the factory VVT maps in the FA20. That's not to say it's not worth trying, but the results may not be significant. While it's based on a standalone ECU, our webinar on the 86 using a MoTeC M150 might be beneficial to your understanding - https://www.hpacademy.com/previous-webinars/113-dual-vvt-tuning-strategies-motec-m1-2/

Note that adjusting the cam timing has no effect on how quickly the valves open or close. this is defined by the cam profile. The only aspect we are altering is the point in the engine cycle that the valves open and close. The aim is to take advantage of the inertia of the intake air to help produce a ram effect. This is why you'll typically want to advance the cam at lower rpm where there's less air speed/inertia, but retard the cam at higher rpm where we can take advantage of the inertia in the air stack in the intake runners to help force more air into the cylinder as the piston is beginning the compression stroke. OE's aren't always interested in peak power though and particularly in the cruise and light load areas you will find that the cam timing maps may be configured in order to achieve some amount of internal EGR to help reduce NOx levels.

After much experimenting with different VVT maps I've come to a conclusion that using the stock as a base is very effective and makes life easy when cam tuning.

Quick Question Andre, using Ecutek for the 86 and it's D4-S injection system, 1=Port only 2= DI only 3= Mix of Port and DI. I don't think my 86 is switching from 1-2 anymore when it is warmed up. Or at least that is what my data logging is telling me. Any thoughts?

I'd highly doubt that it's running continuously on PI only. This actually damages the DI injectors as they rely on the fuel flow to control injector temp. You can log the relative pulse widths for the DI and PI injectors to confirm exactly what is happening.

Very true thanks Andre.

Alright, so I checked the parameters and here's what is happening, basically at idle, the DI is off and the PI is on. Once I get on the throttle the DI/PI system works as normal.

However, I thought that for the 86 platform the DI system should switch on at idle once oil temps and coolant temps have reached operating temperature. This does not seem to be happening at idle for whatever reason...

The car drives perfectly fine and throttle blips aren't hesitating I just found this to be strange once I no longer heard the "Crickets" at idle anymore I decided to see why. I've reset the battery and have not changed much with the tune besides the basics. Going to try a stock calibration now and see if this will work.

Edit: Went back to a stock calibration, D4-S system switched to DI only at idle. Cleared some DTC's. Went back to my tuned rom, cleared DTC's, D4-S system never switched to DI only at idle.

Will compare roms and see what I changed to effect the D4-S system.

Update: Discovered that changing CL Fueling #1 & CL Fueling #2 tables for some reason does not allow the D4-S to operate normally at idle. I'd really appreciate your thoughts as to why the DI system won't kick on at idle when these tables are altered.

Thanks Andre


That's interesting Mathew. I don't have an answer for you unfortunately which isn't overly helpful. What changes have you made to the CL fuelling tables?

I had the CL fueling tables mimic my OL tables. I figured it'd help with the interpolation between the two. Could you command CL easier with ecutek racerom custom maps?

I wouldn't say you can command CL easier with racerom custom maps, however you can use the custom maps to replicate a closed loop wideband control rather than just commanding stoich under CL conditions. Not something I've tried and this is also of questionable use due to the inaccuracies of the factory wideband as you move richer than stoich, as well as it's rich limit of 12.1:1. You can extend the range and correct the inaccuracies if you want to do this but it's not something I've done myself as yet.

Did you resolve this ? Mat

We usually reply within 12hrs (often sooner)

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