LFX Fuel Injector Dwell Time

[KillboyPowerhead]

Did multiple WOT pulls with two different SOI settings, as described above: one early where SOI was set so injection would finish near 180 BTDC from 4000 - 7000 RPM, and one late where SOI was set to EVC (plus 0.3 ms dwell time). With the early SOI I was seeing the RPM go from 4 to 7k in about 1.82, 1.83 seconds and with the late SOI I was seeing 1.71, 1.72 seconds. Seemed somewhat repeatable taking into account air/manifold temps, same road every time. Also found a few papers suggesting earlier SOI is better for torque/power as it results in greater cylinder pressure, although in both cases they only advanced to 300 BTDC and no further.

https://www.frontiersin.org/articles...22.823386/full
https://journals.sagepub.com/doi/10....lar-articles.3

Going to test a few different PE settings and then update again.

[KillboyPowerhead]

FYI did some more looking around for factory cam specs; still can't find anything specific about the LFX but did find specs for the LY7/LLT.

At 0.006" lift:

EVO = 49 BBDC
EVC = 9 ATDC
Centreline = 70 ABDC
Duration = 238 (0.006" lift)

IVO = 14 ATDC (typo in the Cadillac forum)
IVC = 71 ABDC
Centreline = 48 BBDC
Duration = 237 (0.006" lift)

As mentioned I got the cam card for the Mace exhaust cam and it also shows a centreline of about 70 ABDC. Assuming the LFX intake has the same centreline that means for the Mace cams at 0.006" lift IVO = 1 ATDC and IVC = 83 ABDC (about 262 duration at 0.006"; Mace told me that the intake cam has the same profile as the exhaust).

https://forum.hptuners.com/showthrea...LFX-Cam-tuning
https://www.cadillacforums.com/threa....267609/page-2 (post 34)

Edit: adding the Mace cam cards since I hadn't before. As mentioned, the exhaust cam was provided by Mace via email, and the intake should be as this if it has the same centreline as the LY7 and LLT cams - if not, then since the Mace cams share the same profile, I guess whatever the centreline actually is the open/close values would just shift by that difference. Used the above 0.006" lift numbers as a reference so these numbers won't be exact.

Mace cam cards.JPG

[KillboyPowerhead]

Tried a few PE settings (0.885, 0.865, 0.85 lambda, or 13/12.7/12.5 AFR) and didn't notice a big difference between them, although if anything I think 0.85/12.5 performed a bit better, and this is also where my previous tuner (Overkill) set it so I'm going to leave it there. Read that a higher AFR can help reduce knock but didn't notice much difference - sometimes I got a couple degrees knock with 13.0 and sometimes none; other times I'd get about the same knock with 12.5 and sometimes none.

For the SOI, as mentioned it seemed like an earlier SOI (higher number) performed a bit better. All said and done my numbers aren't too far from factory. Using the math below (think I posted this earlier) you can find where SOI needs to be to finish before 180 degrees BTDC. Knowing the Mace exhaust cam closes at ~334 BTDC (minus VVT settings), you can basically keep the factory SOI table except where the numbers are past EVC, in which case set to 334 - [VVT settings], and then if the math says your SOI needs to be even earlier than this you can add the 0.3 ms dwell time (0.36 degrees per 200 RPM). In my case, for 5000 RPM and up I'm only 1 - 5 degrees earlier than stock.

(([50112.254]/(1/([50070.56]/60/1000)))*360)+180

Attaching my cam tables too. Haven't been to a dyno yet so can't say that these tables are ideal and I'm sure they're not perfect, but I seem to be getting the best airflows with these settings. As tunerpro mentioned, the profile of the tables is pretty similar to the stock tables at WOT. These tables are also fairly consistent with the trials I did as described in an earlier post (setting the whole table to 0, then 5, then 10, etc.).

Intake cams current.jpgExhaust cams current.jpg

Going to fill up with 93 now (been on 91 this whole time) and start adjusting spark. Currently using the factory table but going to slowly transition to what Overkill did and see what happens, and then schedule a dyno. Will update again if I see anything with changing spark. I suspect there are gains to be made since the recommended fuel is 87 and thus the factory spark tables will be tuned as such.

Edit: just re-read a thread about how the VVT acts in these engines and immediately realized I hadn't been taking into account the fact that the cams are being adjusted in cam degrees while the SOI table is in crank degrees. So whatever the VVT table says you'll need to double that when adjusting the SOI when trying to inject right at/after EVC. D'oh.