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Good day, I have watched both webinar's relating to this subject. Wondering if I am at the level of power to balance the fueling by cylinder. I build and tune (Cobb Accesstuner) on my 2005 STi. Running a PTE 6466 with the ETS rotated kit. I street drive the car with occasional trips to the drag strip. I am holding off on increasing boost until I determine if balancing is necessary to avoid engine go boom. I am using E85 fuel, LM1 wide band corrected for the 0.03 rich reading.. targeting 11.2 AFR. If I go with balancing I consider using the LM1 cylinder by cylinder (no backpressure comp) to understand the out of balance then adjust using the per cylinder fuel injector trim. Target wheel HP is 750
I may stand to be corrected on this but I believe there are three main reasons for individual cylinder trimming.
a/ to correct variations in the injectors. While the intent is to have exactly the same fuel delivery for all, it's common for manufacturing toerances to have slight variations. While the best approach is to test a number of them and match them is sets, this is not always practical. So it may be an option to add/subtract open times to get the same net fuelling.
b/ to correct for differing amounts of oxidant (fresh air) in the cylinders. This is usually a problem where there is a poor intake and/or exhaust design(s) that compromise cylinder VE and hence filling/scavenging. High VE will usually require more fuel.
c/ I suspect pressure variations in the fuel lines, line pressure and/or pressure spikes, may require some tailoring in some instances. I surmise the 'dead head', or non-return, fuel rails may be more susceptible to this?
With your engine, there may be issues with the exhaust side - are you running equal length exhaust manifolds, as unequal lengths 'may' be a potential issue?
I would advise caution using any calculated values (except maybe a/ above) as theory and practice can sometimes be out of step and there's potential for making things worse. Best option would be individual cylinder lambda, but expensive and fiddly.
It's a tough one to put a line in the sand and say 'at this power level you MUST compensate for cylinder to cylinder variation'. That's simply not black and white. With our 4 cylinder drag engines I'd usually use individual cylinder EGT on any engines running methanol (since it's not very forgiving when you get close to the lean limit, or at power levels north of about 200 hp per litre (which you're pretty close to). To be clear though, NONE of our high powered drag engines used individual cylinder lambda though since back then the options were very limited and expensive.
I would say that your AFR target is probably pretty conservative for E85 though which will protect you against a lean cylinder but possibly at the expense of a little power, so it really depends what you're trying to achieve. Personally if I'm pushing an engine very hard and don't have EGT or cylinder lambda I'd simply target a little richer and be conservative (which essentially you're doing). Alternatively if you can go to the trouble of fitting 4 weld bosses to your manifold then swapping the LM1 between the various runners for 1-2 ramp runs is a great way to get a solid idea of what variation exists.
Thank you both for the feedback, I appreciate it!
BTW, I am running equal length headers. My thought is to perhaps run the summer as is with a little HP on the table in rich running, then remove header (which I believe will involve removal of turbo etc) and go at welding bungs in.
Shoot, just thought of another question... first is background: I do not use dyno for tuning, my ramp runs are on the road under somewhat controlled conditions. Is my thinking correct that I can perform a 3rd gear road ramp run instead of using 4th gear (2005 Subaru STi). I can ramp 3rd without exceeding the limit of speed ;-)
Well, I decided to go for it.. had bungs welded in my ETS header, collected data and balanced. Was well worth the effort!!! Summary of before and after is attached.