Boost Lee

iTrader: (3)

I just got my first FD back in December. I've been an FC owner for over 10 years and while I recognize the ECU's are similar, I also see that there is a major change in air metering, ie. Flow vs. Pressure.

As I put the car together, I managed to come across some pretty cool parts that I'm sure assisted with power increases by reducing air flow restrictions... HKS Ti Exhaust, Apex Cone Filters, 3 in pre-catless downpipe and when I had the engine rebuilt early this summer, the ports were smoothed out (not extended at all).

Looking at all of these upgrades as I put the car back together, my only thought / fear was the boost increase this would cause with the stock system... sensors / actuators in place. I wanted the car to perform as close to stock as possible. So ported the heck out of the primary turbo wastegate and made sure the door opened as far as possible.

I seem to be pretty lucky, because those 2 little turbos still make my gauge read 11-9-11 when I'm driving hard in cold air, and even better my AFRs are perfect: 14-15 at cruise, 12 to high 13 at light throttle, 10.5-11 at WOT. I'm sure keeping the stock main cat in place has helped. The question I have is this...

With the reduction in air flow restriction from the aforementioned upgrades, are my boost levels (11-9-11) maintaining the same or airflow as stock? Should I need to worry about that if my AFRs are in check? If airflow HAS increased, is timing a concern at this point?

Thanks

dguy

iTrader: (8)

I'm of the mind that the first thing that should be pitched on an FD, or really any turbocharged and speed density metered car for that matter, is the ECU unless its programmable/hackable.

For what its worth the first thing I did ot my FD and most of my FCs after I bought them was slap an SM4 on them.

Sgtblue

iTrader: (16)

Your probably just be within the margin of error of your boost gauge...and you're still (essentially) at stock boost. And if your at stock boost, your fine on the stock ECU with those mods.

j9fd3s

iTrader: (3)

we used to call the midpipe the apex seal removal tool..

year and years ago, a guy named Wade did some testing with the stock ECU, and he found that up to around 10-11psi the stock ECU was able to supply enough fuel, over that and it seems the ECU can't compensate

the next step in japan would be colder spark plugs, and or a power FC

adam c

iTrader: (2)

All is well. Your stock ecu will be fine. Just dont let that boost get any higher.

jacobcartmill

iTrader: (6)

the stock ECU is pre-mapped (like hard-coded fuel map) to deliver X amount of fuel. you can't change this fuel map. the stock ECU also runs in the low 10s AFRs at full throttle / full boost.

the mods you installed just leaned it out enough to make it make good power and still be safe. this is the same reason you can basically sneeze on and FD and gain 20whp. you're not only freeing up airflow, you're leaning out that pre-set fuel mixture that you can't otherwise change. you just can't lean it out too much

as j9fd3s said above (man, he and i have been on this forum for a long time now) don't mod it any further on the stock ECU and you'll be golden.

Boost Lee

iTrader: (3)

For me the next question for all of you would be... what is the issue the stock ECU presents? The AFR's seem to be perfect for 11psi. What is it that goes wrong when an individual pushes past this? I'm pretty familiar with tuning (Roms on stock ECU's and even standalones) Does the stock ecu lack proper fuel map values above a 11-12 psi? Are the timing values no good? Do you have any more detail to Wade's discovery?

Here's my thinking, please correct me where I'm wrong. This is all theoretical, I'm speaking for discussion purposes only.

Let's say I go to 14psi
If the AFR's stay in the 10.5 - 11 range, I believe that would be a healthy range... and there should be no complaints UNLESS the timing values in the stock ECU for that pressure are too aggressive. I wouldn't expect the OEM programming around knock to do much more than dump fuel in an effort to "Make the noises go away, daddy!"

The only other thought I have that could answer where there would be an issue is if the stock injectors were being pushed past 90% duty at 14psi which seems unlikely when you look at the kind of power being made with stock injectors.

I value your feedback as I wrap my brain around this new but dangerous world.

Sgtblue

iTrader: (16)

https://www.rx7club.com/3rd-generati...d-rule-767399/
https://www.rx7club.com/3rd-gen-arch...i-myth-308996/

j9fd3s

iTrader: (3)

like Jacob says the ECU map is hard coded in, and on a STOCK car is actually totally fine up to fuel cut*. so the ECU does have proper fuel maps, but its proper fuel maps for a stock engine.

when you add a bunch of airflow, the stock ecu map is no longer rich enough over 10-11psi. the timing is also pretty aggressive.

so this guy Wade used to have a webpage, and an FD, but basically there is no more detail, under 10-11psi, the FD runs in the 11's, which is fine. over that its leaner…

*fuel cut is PSI vs RPM, so some rpm's let you have more boost than others.