When talking with jim mederer at racing beat sunday i learned that the leading and trailing plugs are on 2 COMPLETELY different maps in the stock pcm. the trailings dont fire x amount later than the leading, they just fire whenever their map tells them to do so. the dont fire at all based on when the leads do and vice-versa. there is no consistent split as jim mederer put it "they are up and down and all over".

does the cz advance/retard leading AND trailing igniton? i just read a post by mazda maniac saying he does not. after the talk with jim mederer sunday im not sure its a good thing to do. but without getting at both you arent going to get a consistent split.

 

Now thats interesting, that opens up a whole can of worms when it comes to ECU tuning. Does the emanage/CZ box hanve the ability to handle this?

 

Yeah that was really weird. I like to run a fixed split regardless of load. At least I do as a base map. There usually isn't much change that needs to take place. If you are using an ecu that does not adjust leading and trailing independently, you are not getting the performance that you could be getting.

 

Would supplementing an AEM ignition unit to the CZ help? It states that it can control both leading and trailing independently. It seem that there aren't any piggyback ECU that has the ability to control the leading and trailing ignitions without addition an addition unit like the AEM.

 

The Ric Shaw ecu can control both. You could add the AEM unit to Canzoomers. My concern though is that the more things you piggyback, the more things you have to control and worry about. ti is so much nicer to just have everything in one unit.

 

I've heard about the strange timing split elsewhere. Why do you think Mazda did this? What would happen if there were only a fixed timing split on the RENESIS?

 

I could be wrong, but the older 1.1 CZ looks like it does not control trailing ignition, although it could.. It appears to be wired in but the dip switches are shut off. I could be wrong.

 

shelley's im not sure but it must be related to either fuel eficiency or emissions. it doesnt make sense that they would do it for power as at times when it has less split it would be making les power

 

Was the original design so bad at emissions they had to resort to the current timing split?

I'm with rotarygod on using a fixed timing split as part of a base fuel map. As for how to control it, I'm at a crossroad.

 

thanks for that info jeff good to know. what is the stock split under load?

did i mention that they said there were also 4 different a/f maps? 1 for gears 1-4, one for gears 5 and 6 and 2 for when decelerating- one for when decelerating in gear and the other for when you are just coasting. no wonder the "runs out of the box" piggybacks have trouble working for everyone even if there wasnt a "mafs issue".

 

Ouch. That sounds worse when you think about it. Is that one of the drawbacks of piggyback computers? Switching to a stand-alone is my last resort.

 

Find out if you can. That would be good to know. I like a fixed split of 10 degrees. Any more than that and you will lose power and any less than that and you probably will too. Many of the RX-7 guys are sorely misinformed when it comes to timing split. They insist that the less split you have the more power you have. This isn't always true. When we were at Racing Beat and were listening to Jim Mederer talk, he mentioned the timing split making less power if it was too little. He also mentioned the magic 10 degree split number. zoom44 heard this too. I just looked at him and smiled when Jim said that because it confirms what I have discovered from playing around with rotary timing. If you look at Paul Yaw's website he also mentions that the 13B's run best with a fixed split of 10 degrees with a total of 26 degrees max advance. 8 degree split for the 12A engines.

Jeff, if you only advance the leading plugs, how are you decreasing the timing split? You would be increasing it since the trailing isn't increasing. This would hurt power. The only way you could decrease the split in this scenario is if the trailings were always firing first.

 

I found this timing map for an aftermarket ecu that an RX-7 guy is using. You'll notice that it is almost exactly what I say I like to use. The timing itself is basically the same. His car is a turbo so that will give an idea of why a map sensor is important to tuning a forced induction setup.

Total leading timing per rpm

Idle ~ 00
1000 ~ 10
1500 ~ 15
2000 ~ 20
2500 ~ 25
3000 ~ 25
3500 ~ 25
4000 ~ 25
4500 ~ 25
5000 ~ 25
5500 ~ 25
6000 ~ 25
6500 ~ 25
7000 ~ 25
7500 ~ 25
8000 ~ 25
9000 ~ 25

leading/trailing timing split per rpm

0500 ~ 15
1000 ~ 15
1500 ~ 15
2000 ~ 14
2500 ~ 12
3000 ~ 10
3500 ~ 10
4000 ~ 10
4500 ~ 10
5000 ~ 10
5500 ~ 10
6000 ~ 10
6500 ~ 10
7000 ~ 10
8000 ~ 10

Under boost the map sensor adjusts the total timing advance a little but the split remains the same. If detonation is still encountered there are 2 options. One is to retard the timing further. The other is to increase the timing split.

Idle ~ 00
25 ~ 05
20 ~ 04
15 ~ 03
10 ~ 02
05 ~ 00
00 ~ 00
2psi ~ 00
4psi ~ 00
6psi ~ 00
8psi ~ -02
10psi ~ -03
12psi ~ -04
14psi ~ -04
16psi ~ -05
18 psi ~ -06
20 psi ~ -06


It is a little more complex than this and I am leaving some stuff out but I thought you guys might want to see it to get a frame of reference. Keep it simple.

 

yep i heard jim mederer say that and i didnt miss the smile on your face when he did either. its good to get confirmation from someone of his caliber. when i asked jim why Mazda would do it this way he just kinda shrugged- i dont think he is at the point in his testing to start figuring out the why just yet as he is still tracking all the things that the pcm does. i bet he has an idea but didnt want to just speculate.

 

I'm aware of the fact a MAP sensor is ideal for forced induction, but wouldn't it be difficult to wire one in along with the MAF sensor?

Off-topic: I've been looking at Pro-M's blow-through MAF for the Mustangs. I wonder if something like that may be ideal for forced induction rotarys.

 

Its kind of ironic, but over at the RX7 forum there's an on-again, off-again perpetual thread about how they want to convert the twin-turbo 3rd gens to a MAF system. Everybody wants what they don't have

jds

 

Yeah. Either way, you have to figure out flow rates. :D

 

How does the ECM determine what gear the transmission is in? Is it looking at Engine RPM compared to wheel speed?


Sorry for the necro, but I find this interesting as to how to could affect the manual swap I've been driving.

 

I wouldn’t trust anything on this subject from back in 2004

nice necro bump though.
.

 

Yes and no
There are unknown tables in ECU ( unknown to us aka public) which vary from year to year and market to market.
The question is, does it matter? and answer is not.
over 90% of power is made by L spark plug, T other less than 10% to clean combustion. if you want to nick-picking you should add back the 3rd spark plug for less than 5% improvement.