Im struggling to understand the third spark plug theory, actually Im very confused about the whole ignition sequence now.
I need to read some more about this

 

This is a good place to start.
http://foxed.ca/rx7manual/manuals/RE...amoto-1981.pdf

Look at pg 43 (48 of the PDF) as well as the timings that cause knock on pg 45(50)

Flame speed is very slow in the direction of the rotor trailing edge because of squish flow and quench. This is also (for that reason) the area where knock occurs. I call it the fuel/air heel.

At low rpm this isn't a problem because at 1000rpm there is 60ms available for a complete rotation. At 10krpm there is only 6ms available for a complete rotation in each case only a fraction of that time is available for each combustion. Since flame speed is related to temperature and pressure, it doesn't get any quicker as rpm goes up, which is why timing normally has to be advanced as RPM goes up. Unfortunately even with timing advance it gets harder and harder to burn the heel.

If pressure gets high enough (high load and advanced timing) and the heel hasn't ignited yet (high rpm) it causes knock. Add a third plug and you can eliminate some knock at high rpm and reclaim some power too. Alternatively you can advance the trailing timing, if you do then the trailing is exposed to combustion temperatures longer and will eventually get hot enough to cause preignition.


The problem is the linear size of the combustion chamber. You can have big combustion chambers, you can have high rpm engines, but you can't easily have high rpm engines with big combustion chambers.

Hope that helps you wrap your head around it.

 

Found this one, a lot of good and accurate information here:
Understanding Tuning! - Rx7 Forum and Owners Club

Or if you really feel like going in depth here:
Not2Fast: NACA Paper List

There is a lot you can do NA without blowing up your engine. Turbo is a whole other animal.

 

Good stuff, thanx.
Im gonna spend some quality time with this :P

 

So I flattened my maps to do some constant load logging to try and get some accurate results for MAF scaling. Pretty much a base map with the following changes:
- flat VE table on 1.
- Flat throttle enrichment tables of 14.7 (tip in, so shouldn't apply to constant load/speed)
- flat open loop fuelling tables at 13.02

After warming the engine up I loaded the above map then went for a drive. I went for a 10 minute logging session in 4th gear, 4200rpm. It was a flat road and my speed and load were constant. Strange thing is that the commanded AFR was logged (MazdaEdit) at around 14.81 with a bit of variation. I was expecting the exact figure of 13.02 with no fluctuations. WTF?
I can only assume that there are other tables that significantly contribute to the commanded AFR, even when at constant load/speed.

 

Most of that os probably because you flatenes your ve table.

Did you tune in your maf and injectors before doing this stuff?

 

Based on what was posted you have no business attempting to tune it yourself

 

There is a hidden closed loop that is driven by the rear o2 sensor. When in cruise conditions it puts a trim on commanded AFR to make the rear o2 sensor oscillate around 14.7:1. It's there to protect the cat and only applies below a certain load/rpm and above a certain temperature. I don't recall the numbers offhand. This even happens in regular open loop!

If you want to scale your maf you need have everything setup stock and then check commanded AFR vs actual AFR. Then just adjust the maf. The engine VE does change with RPM, the injectors become less effective with higher deamand and higher pressures (lower vac) and all these things can mask what you are trying to find if you null the tables. Above all realize that placing 12.5 (or any other value) AFR on a table is the equivilent of asking Santa, the numbers do not directly correspond to the AFR the car is going to give you, but the closer you get all the other values (MAF, VE, Injector scaling, etc) the more acurate they will be. The goal should be to have the AFR you want indicated out the tailpipe and not on a table.

 

I think it may be a lot simpler than this. I'm now thinking the commanded AFR as seen and logged in MazdaEdit is the AFR after trim corrections have been applied. Big difference when the scaling is out by a bit.

I get the deal with arbitrary AFRs in the fuelling tables. While I'm learning, I'm going to shoot for the "Fazda" method using scaling and VE to get the table values as close to real world as possible. When I run out of patience, I'll do the quick and dirty fuel table adjustments

 

https://www.rx8club.com/group-buy-ce...eattle-251516/ - Webinar


May save you a lot of headaches.

 

I don't like headaches. They stop me getting laid.

 

 

Thanks for your concern. Most folks just don't appreciate your caring side.
BTW my Q was specifically about commanded not measured AFRs.

 

Bumping an old thread but I'm wondering which method is correct to edit idle rpm/speed, the upper edits only one cell, and the lower says to change every table correspondingly. Contradicting info here..

 

1) You should change each of the tables equally

That one.

 

Appreciate it Kane!

 

 

I would suggest that you change them equivallenty. The difference is that there are some variations in idle maps A-E and IMO those variations should be maintained rather than making them all identical.

Also don't agree with changing all the speeds across each map line. You only care about the end value when the engine warms up. So why would you want to change the idle speeds when the engine is going through it's warm-up cycle? That was the MM method and after thinking it through it I concluded it was 't how I wanted to do it. The values you change ultimately depend on what the new idle speed is. In the case above changing the end value is fine for me. If the end value is higher than the cell before it then obviously that one needs to change too.



.

 

Got it. So either or is fine I'm guessing.

 

You're engine won't blow up if that's what you mean.

However, what I'm presenting to you is a philosophy of not just blindly following what someone else tells you. It's best to get your mind wrapped around what the software strategy is and what makes the sense to achieve your goal.

The factory PCM has a lot of complication and we only have access to a small part of it. We can't know all the dependency entanglements of how one setting may affect something else. I'm personally not a fan of making any more changes than are necessary to achieve 'close enough'

 

Get a ECU and Laptop

 

¿what? Its alot more complicated than that.

 

everything is easy in Nooblandia

seriously though, I suspect RX8cha is not a native English speaker, so the response might be lost in translation

... or not

 

Since he lives in PNW...I imagine it's simpler than that

 

look how I put "A-E" I was just too lazy to paste all the idle tables.