LSPI tests with Tomm.BRZ

[dholloway543]

I do not know to the full extent of how it worked officially tomm.brz would need to comment but due to the lack of information that we both could find I figured this might help someone.


My car in short is a built stock block with the compression ratio of 12.5:1 with the sbd500x turbo kit installed on it so LSPI(Low Speed Pre-Ignition) is most defiantly an issue on my car.


I was told to put dextos2 oil in my car because it would help resist lspi which it did on 91 octane, and from there it went good with no lspi issues until we started tuning flex fuel.


The sad part is that when we started testing flex it had first blown up my cat's and it was rattling in its cup causing false knock and it had ripped my motor mounts apart so we were pulling our hair out to find knock regions that were simply false knock of metal components touching.



Due to the lack of information on tuning around lspi tomm.brz had set out to try different tricks. From what I remember he had tried different fueling strategies most PI or most DI. I think he tried different DI angles. But like i said in the beginning he would need to post the exacts.


In the end what seems to have worked is lowering timings in the bad zones. Limiting throttle to a percentage of max to prevent massive amounts of air from entering the cylinder. Those 2 had gotten us 80% of the way there but in the end he also leaned out the fueling a little bit. The reasoning behind that is due to dextos2 oil not being designed for alcohol fuels. I found this study performed if you would like to read it, but in summery the high fuel content needed for e85 can cause fuel to sweep more oil off the side of the cylinder causing pre-ignition. The charge cooling properties of ethanol means the fuel will be warmer in the cylinder which is contributed to the fact that it evaporates easier.



https://www.jstor.org/stable/2627389...n_tab_contents




This could be slightly off, tomm.brz knows a more complete story but I thought it be good to share our findings.

[tomm.brz]

Hi,

the complete story would involve also the fact that worn engine mounts, a leaking EBCS and don t know what else, brought the engine or the exhaust to touch the frame somewhere and to have me rising the WG duty more and more every release erratically

we gotrandom corrections even outside the region of 3k rpm (the zone we got the most problems tuning with pure e85) and dropped the advance multiplier so much during a sustained 6th gear in highway that car overheated and burnt the cat

WOT in 6th gear is hard enough when not knocking, with low ignition timings was simply too much

Anyway you fixed the leaks and random corrections stopped everywhere.... BUT around 3200-3600 when WOT with 6h gear mostly and 5th gear (with other gears i never saw corrections)

Actually what worked most was to go to the opposite direction of what you do with non-ethanol fuel.... LEAN afr out under 4000rpm
Lowering timings seems not to correct it at all, it would drop advance multiiplier even with negative ignition timings with E85


The limiting of throttle i set up for you is active only on 5th and 6th gear, to ease a bit when you WOT on such gears at low rpm

the article you linked is good and the pic shows exactly the lspi zone.,. in fact we had acvance multiplier dropping basically on 6th gear under 3200 rpm, that's coehrent
It seems a leaning out with E85 in that zone in the zone of 13 AFR helps the most



where did you find that dexos2 is bad with ethanol? i ve always thought Dexos2 is a specific involved with LSPI bench test

[dholloway543]

I don't think dextos2 is bad with ethanol. More just the fact that it probably doesn't make any difference on ethanol.