I just had my 8 tuned using an universal emu and boomslang harness. It was tuned on a dyna pack dyno. My tuner ran at wot a afr of about 13.8 and ignition advance of about 3 degrees. Manage to get 195.7whp and 232.4NM of torque(flywheel).

My question is is 13.8 too lean a afr to run and is 3 degree of advance too little?

The mods I have are:
1) Blitz Sus Filter
2) KS Extractor
3) RP Cat
4) KS Muffler

Another thing would be because the boomslang harness is not long enough, I have to put my emu unit at the side of my blitz airbox. Would it be affected by heat? Thanks.

 

The heat is not good for the EMU, though it won't complain about it until it just dies.
At least it is cooler on that side of the engine bay.
13.8 is fine for N/A as long as it isn't pinging.
3° of advance is plenty - the OEM PCM already uses a ton of advance.

Did he do any negative split in the vacuum load ranges?

 

Congrats! 195.7 hp is pretty good. I would be interested to see what your cat temp and fuel trims look like.

 

So far no pinging. Erm..he just did ignition timing as a whole. Never play with split timing as both of us are not sure how to go about doing it. Still waiting for your video MM.

 

I would like to find out too. Probably need to borrow a scanguage to monitor for awhile. But so far the car seem fine. No pinging or marbles sound.

 

It's very rare to find anyone who knows anything about negative split. It's always been a sort of black art when it comes to rotary tuning.

 

Care to explain on it rotarygod??? I am interested to know wat it can do.

 

Just curious what was your baseline on the dyno before you tuned it? How much improvement did you see and along what rpm range, peak and average?

 

Ended up with 5deg retarded on mine - definately more power than with any advance .

 

^^ That isn't a surprise.
The OEM tune has ENORMOUS amounts of advance in some places.
This is largely and emissions and fuel economy strategy - the earlier you can light it off, the more of it that will be burned before it leaves the motor.
Of course, there are diminishing returns in that since it is counter-productive to power and can damage the motor.

I'm sure Fred can and will add to this, but the theory goes that since the charge is moving (because the entire combustion area is moving - something that does not occur in a reciprocating motor), it is beneficial to get the "back" of the charge ignited early so that complete combustion occurs at the 15° ATDC rather than just what is possible with the normal firing order.
Usually, you would fire off the leading plug some amount BTDC so that peak pressure happens at 15° at which time you fire the trailing plug as a suppliment.
If you fire the trailing plug first - as much as 20° sooner that the leading - the charge is already igniting as the leading plug fires.
Sounds scary, and it is. You should only do it in the vacuum ranges (mild to low load) and NEVER in boost because it is a strategy that depends on the laziness of combustion.
As the charge density goes up, flame front speed increases and the premature split will cause catastrophic detonation.

 

Eneded up with 25 deg advance from 6500 to redline didn't touch anything below that.
Interestingly doing this made the AFR lean out quite a bit .

 

The retarded timing led to continued combustion in the ports, which consumed marginally more O2.

 

It doesn't have any effect on power though does it?

 

What does? Negative split?
Well, technically, it does in that you produce more combustion pressure in the low load ranges.
But, no - it is not useful in the high torque ranges.

 

Yeah, I was talking about negative split. I knew it wasn't useful up top but I wasn't sure about producing any extra torque down low. Sound like the fuel savings and emissions are the biggest benefits...

 

Is your 8 tced or NA? What is your afr after 6500rpm? Thanks.

 

Sorry I do not know how to post up my dyno in here but in base run I got 180whp. Low rpm ranges there is only a slight gain of about 5 to 10hp. High rpm we manage a gain of bout 15hp. Peak torque is at about 5500-6000rpm. generally torque increase bout 20-30NM(flywheel).

 

This is interesting. Thanks for sharing.

 

well I recently spent some time reviewing some of what is hundreds of hours of extensive NA Renesis dyno testing and discussing them with a very talented individual, theory and reality often don't match up

 

Care to elaborate, or are you just flapping your gums again?

 

I'm only flapping my gums, never mind

 

The rotary engine is very unique when it comes to the way it does compression but we all knew this already. When a piston engine compresses the mixture, it does it in one place. When a rotary does it, it is also moving the air to a different location. This creates some interesting problems and is the main reason why there really isn't any more power to be had from increasing the compression ratio any further. You really need to have a rotor and housing in front of you to fully comprehend what is going on here but I'll try to explain it anyways.

When the rotor is on the compression side getting towards it's smallest point, all of the air in the engine has to pass through the dish in the rotor. The problem is that at this point the air is moving from the leading side of the dish to the trailing side for a moment. This concentrates a richer mixture on the trailing side of the dish right when the leading plug fires. This means that there is a lot of mixture not getting burned on the initial ignition and we are wasting some of this fuel. That means we are running richer than we need to. The trailing plug doesn't really ignite to give us power. It is there to clean up the chamber. There are people that fire them at the same time as the leading but you need to realize how load comes into play in this. You need to be careful that you don't have 2 flame fronts colliding with each other which can lead to detonation. This is why a greater timing split reduces the possibility that detonation will occur. We give the main flamefront enough time to lose it's energy and not interfere with the trailing flame front.

Negative split is used to control the backflow in the engine in the rotor dish during compression. It happens at a location early enough in the cycle to do something very unique. At this point in time most of the mixture is still pretty evenly mixed and not favoring the training side. When you fire the trailing plug at this point it will create a small flamefront that won't really burn the main mixture but it will create enough pressure to hold the primary mixture towards the leading side of the rotor dish which is where we want it to be when the leading plug fires. As a result of a more efficient burn, we can run it leaner and still get good performance.

Now the key to this is that the air and fuel amounts in the engine at these loads and rpms are fairly small. If we were to try this under load or boost or at high rpms, very bad things would happen. The biggest negative splits can be had at the lowest rpms and load levels. Don't try to go too far at idle though. You only need a few degrees of it.

How much you can run is also dependent on your compression ratio. A high compression ratio such as the Renesis may only be able to do about 30 degrees or so of it max. A low compression engine such as an 8.5:1 Turbo II RX-7 might get up to 50 degrees or so of negative split. It really depends but it all goes back to the total amount of pressure in the engine. We all know pressures are greater on a high compression engine than a low compression engine just as they are at loads. You really want to taper off negative split as you get closer to ambient pressures or basically 100 kpa. By this point you should have at least 0 split but I prefer to be at this point a little before this load just because you never know how accurate your ecu is when it comes to firing leading and trailing in relation to each other. As a general rule, negative pressure, negative split. Positive pressure, positive split.

It takes a bit of learning and it's best to start conservatively and work your way up from there. As a guideline keep your leading timing the same as always and adjust the split in relation to it. This is not something that has anything to do with the leading when it comes to making changes. The leading timing does not change from what you would normally do.

 

As it stands now, I do +15° trailing, -5° leading at idle (20° total negative split).
At manifold vacuum of approximately -45 kPa and less (down to the limit of normal running, which is about -65 kPa), I keep the trailing 20° ahead of the leading, putting it at a maximum of 58° BTDC at the lightest loads and vacuum.
Above 6800 RPM, I begine to diminish and negative split until there is none at 8200 RPM.
I taper to positive split (up to 20° around torque peak at all loading points) starting at -15 kPa.

 

Thanks RG. Your simple explanation of this complex event has given me some epiphanic understanding of rotary engine combustion.

You have a certain way with explaining concepts. One day, perhaps you might consider compiling the Great Rotary Engine cookbook !

spin

 

Are you doing this with your EMU or your InteceptorX?