Individual combustion chamber tuning
 

Has anyone tried individual combustion chamber tunning?

It adds in more complexity and a few more I/O, but the benefits as seen on pistons engines seem to be very much worth it.

At boost creep in Colorado, we just had a stock ej257 in a 2014 STI make 278.4 WHP up from 228 WHP. The only thing done was having individual O2 +EGT + MAF sensor for each cylinder and then a few days worth of tunning. I'll be asking the owner how MPG and drive-ability has changed.
I was told that cylinder temperatures dropped dramatically in cylinder 2 and 4, these two cylinders run much hotter than 1 and 3 because of our unequal length headers.


Moe Greene

Moe,

Take a look at David Hayes' 3 Rotor FD build thread, here: https://www.rx7club.com/build-thread...25733/page184/. He had great success with tuning the EGT from each chamber. You can also reach out to him to get more insight that may not be included in the above thread.

Cheers,
George

Almost any good modern ecu allows some independent adjustment for cylinders (rotors in this case). A properly constructed equal length manifold also plays a huge factor in maintaining even egts.

Any concensus on what the best current quick-response EGT probe is for a 1700*F exhaust stream?

http://thesensorconnection.com/egt-p...ss_probe.shtml

150ms response, designed for extreme duty (supposedly)

Not sure if it's possible with a controller like the PFC. Need to step up to Haltech or Adaptronic to get that level of discrete tunability, correct?

I've used those probes and they are more responsive than the fully sheathed probes; however, they didn't last very long. Maybe a year, iirc. (The 150ms response is equivalent to 15 crank revolutions at 6000rpm, fwiw.)

https://cimg9.ibsrv.net/gimg/www.rx7...1c579abf58.png


Definitely worth doing. Because of the entry angle of the throttle and plenum design, rotor 1 had a 15% air-flow bias. Multiple EGT measurement caught this early on. Now all rotors are within 50* of one another by adjusting fuel trims to each rotor individually. TIming is setup to pull on any rotor that trips 1800F. The 15% difference from 1 to 4 is nearly a full AFR point. So if you imagine wideband reading a 12.0, it could really have been a 12.5 on rotor 1, and an 11.5 on rotor 4. Gives a much greater peace of mind once you equalize rotors as now you can trust your AFR

The 3 rotor favors the middle rotor, because of throttle position

.

Checked out his build, I have to say I was pleasantly surprised! Thanks for sharing that with me.

Does the powerFC allow for this?

Did you run 3 map sensors and 3 o2 sensors?

So I finally met up with owner of the STI at a local cars and coffee, he noticed a 3mpg gain! The biggest difference he said with the car was city driving, he noticed he was shifting at lower rpms then he normally would, he suspects that the increase in torque under 3k rpm played a massive role in that. The weird thing that was really surprising was when he told me the car sounded a little bit different than before (exhaust note)

IMHO I don't think you will see as much of a gain on a 2 rotor. 3 rotor is a whole 'nuther deal. Same goes for the guy with the STI, he has 4 cylinders to equalize, if you just have 2 it's not as big of a change.

Dale

I've done it on 8 cylinder cars before using a very expensive setup (individual cylinder EGT and cylinder pressure). Usually there are at least 2 cylinders that burn faster or slower than the others and can really benefit, or they don't breathe as well and need less fuel.

On a 2 rotor the simple way is to go on a dyno, bias one rotor rich or lean in steps (5% richer, 10% richer, 5% leaner, 10% leaner, etc) and see if you pick up any power. The same can be done with spark. You need an ECU can support it.

so the comments mostly mention 2-rotor individual tuning but, what about tuning each rotor face? Anyone evr tried it? There's always variation between faces.

You'd want at least a 60-2 Trigger Wheel and Label Each Rotor by it's Degree Location. Then you have to figure out where on the rotor face is a good point to label that degree location. Tip of Apex Seal? No. Center of Combustion Chamber? Ehh, maybe. The problem is that combustion occurs at different angles as engine speed changes, at least to my understanding.

This is a great thread by the way. I'm doing Exhaust Gas Technologies Analog Kit (because I hate the idea of converting to CAN).

Exhaust Gas Technologies Inc. - Motorsports Catalog

https://cimg7.ibsrv.net/gimg/www.rx7...d69afc8488.png

do not think there is an ecu out there that is capable of doing that. if there was, it would be in the Rx8, stock

So... the combustion event will be at the same "angle" of eccentric shaft rotation for each face. The Eccentric shaft rotates once completely for each rotor face in the epitrochoidal pattern. To track which rotor face is where, would require the ecu to keep track of revolutions. so revolution 1 is face 1, 2 is face 2, 3 is face 3. then it would have to start over. The hardest part of keeping track of this is when the engine is at low speeds (start up and shutdown) where the reluctor may not be getting enough of a signal to reliably count the revolutions all the way to zero motion and back up to idle on the next start up. plus, even a slight amount of interference would knock the running revolution count off, and make the entire process moot (at best). The only way to do this would be to have a method of tracking rotor position within the engine, as the crank position sensor is not a reliable way of doing so.

Maybe I'm thinking ahead or maybe I have no idea what I'm talking about but couldn't there be a solution where a sensor/ecu combination can follow individual O2, pressure and temperature peaks and valleys along with crank angle and use that info to tune locate the combustion faces?

i feel like a stock ecu would assign faces on start up, and it wouldn't be the same one each time.

You'd have to have some sort of trigger wheel driven at a 1:3 ratio relative to the crank in order for the ECU to determine which rotor face was where.

Fortunately, it is not to any benefit. Individual cylinder tuning is a benefit because each cylinder in a piston engine sees different intake tuning, different exhaust tuning, and different cooling system characteristics, for many different reasons beyond the scope of this post. Each rotor face on a given rotor will have the same intake tuning, same exhaust tuning, and same cooling system, so there is no need to go further than individual rotor tuning.