3 replies to this topic

[luvin_the_rings]

Hey All, 

 

Struggling to figure out the engine management on the 1.6.  

 

We have been running without the exhaust O2 sensor plugged in for a year now with decent power results.  We have been using the stock header bung to locate our after market O2 sensor for the AFR Gauge.  We have not been running the OEM narrowband O2 sensor at all because I was under the impression that it does not needed, since the engine uses the AFM and a speed / density table programmed into the ECU to make the mixture right.  

 

Is this true? Or should I hook up a new OEM narrowband sensor to the ECU, and weld a new bung for the aftermarket gauge further down past the muffler?  Am I missing something? Sanity check needed.  

 

Also, I have included a first and last run dyno graphs.  We are seeing a strange curve on the Power.  It goes dead flat at around 5500, I noticed this might be because of overheating on the dyno, we have since replaced the radiator with a high effeciency unit and expect to not run into this again next session. 

Any comments or help appreciated. Dyno was done on a Dynapack Hydraulic Hub dyno about 80 deg F with a 3.9:1 diff.  (we have since also installed a 4.3:1)

 

Help, 

 

Thx, 

 

-Z

Attached Files

•  SM83_AFR_Aug16.JPG   152.22KB   0 downloads
•  SM83_Pwr_Aug16.JPG   138.31KB   1 downloads
•  SM83_Vac_Aug16.JPG   152.05KB   1 downloads

[Steve Scheifler]

Short answer for now:
Per SM rules, both SCCA and NASA afaik, you must run the stock sensor, so add a bung in the down-pipe for your wideband. Many wideband units include a secondary output to simulate the stock one and can be used as the input to the ECU, but technically not allowed because it changes an ECU signal or source. Arguably OK as an equivalent aftermarket part providing identical function, but I never argued it expecting to lose because "no" is always easiest when not required to explain the rationale. In any case, it has no effect under racing conditions but if functioning correctly can help maintain a cleaner idle so you don't stall or foul plugs.

On the dyno, very important to keep coolant temps in a narrow range but also critical to keep intake air temps in a narrow range. Even if you place the dyna pack temp sensor at the intake (and switch the setup off the default "ambient" setting), actual temps inside the intake climb much higher.

You will likely see power increase each pull during warmup as the dyno gets up to temp and particularly as your Eng/trans/diff temps come up. Then power may level off a bit and start to fall as intake temps climb. Run with hood up, use a small squirrel cage high velocity floor drying fan to blow ambient air down though the engine compartment, past the intake and exhaust to under the car. That will help keep intake temps down but they will still build from the rest of the intake manifold and plumbing heating up, particularly where the front fan blows through the radiator right onto the plastic. Have you wrapped that yet per the rules?

The more you control those variables the better you can tune. Example: everything warmed up and power is stable so you make some changes you've been wanting to try and wow, instant power! What really happened is that you were slow enough that the intake cooled. A few more pulls and you are back where you started.

If you use the Packs a lot and want the long answer send me a PM and I'll give you my phone number.

[SaulSpeedwell]

Rules aside, I can promise you your 1.6 isn't using the 02 sensor for anything under race conditions.  There are a billion posts (half a billion of them may be in the "old" SpecMiata.Com threads) on how the 1.6 EFI works, but the FSM tells you 90% of it.  The unrestricted 1.6 is all about flow (head and header/DP), intake air temp (colder), AFR to a lesser degree, and timing (or "swapping ECUs") are tied for the most overrated power adders. 

[luvin_the_rings]

Steve thanks for reaching out. 

 

Looks like we'll be busting out the welder for a new bung.  Good to know that we're not grossly de-tuning the engine by not running an O2 sensor.  But our idol could use some work after the AFM adjustment.  

 

Did anybody look at the dyno graphs? I mean whats up with that AFM spread? Its worse than all the other dyno graphs I've seen.  14.4-12.2? seriously?

I mean it goes from 13.4 to 14.4 in the span of 800 RPM. Seems abnormal, but maybe I'm over thinking it.  As they say "perfect AFR doesn't mean anything really."

Check out the AFM curves on this Sunbelt 1.6.  They don't move nearly as much: http://mazdaracers.c...sults-w-graphs/

 

We'll have to wrap the intake for the next session, maybe make a little cardboard deflector to keep the hot air off it and keep a closer eye on coolant temps.

 

We have a Drago built head with all the core correction and we've ground the header welds.  Compression is even across the board at 189-193 on a 50k mile bottom end, measured with a Longacre gauge. I'm hesitant to blame it on flow.  Maybe our compression could go up a little bit?

 

Just want it to get it good enough to run with the mid-pack in regionals.  I just need it to be enough to hang with the other SM drivers so when we do driver training, we can generally forget using the car as an excuse as why were getting lapped.  

 

-Z