LFX Fuel Injector Dwell Time

[KillboyPowerhead]

I still haven't been to the dyno... One day. Got a little hesitation at the lower RPMs that I've been meaning to figure out; haven't done any tuning/logging in months, but plan to get back to it shortly. Once I'm satisfied I'll get 'er to a dyno - hoping to see at least 330 HP at the heels, based on what I've heard from others with similar mods and the Mace cams, which would also put this 3.6 at around 400 at the crank, or ~110 HP/liter - not too shabby! And this is only spinning to ~7,300 RPM, so it still has more in 'er.

[Scott02]

I still haven't been to the dyno... One day. Got a little hesitation at the lower RPMs that I've been meaning to figure out; haven't done any tuning/logging in months, but plan to get back to it shortly. Once I'm satisfied I'll get 'er to a dyno - hoping to see at least 330 HP at the heels, based on what I've heard from others with similar mods and the Mace cams, which would also put this 3.6 at around 400 at the crank, or ~110 HP/liter - not too shabby! And this is only spinning to ~7,300 RPM, so it still has more in 'er.

If you can send me a log with rpm, mph, throttle pedal %, the various ambient weather condition / temp type items (baro pressure, IAT, ECT, etc.), then the rear end ratio, and the trans gear ratio you did the pull in, and weight of your car, I can make a virtual dyno plot and compare it to my LFX-RX8 data, which has a hot-air-intake, and reasonably good exhaust up to the stock RX8 muffler (restrictive but quiet) and a tune. I'm definitely interested in seeing the overall HP/TQ curve shape change (or possibly lack thereof?) of the mace cams vs. the stock cams. Oh, it would be best if you can get a long pull from 1500 to redline in a single gear on a flat road. Which ever tallest gear you feel comfortable speed-wise with and will not end up in jail. And I usually average 2-3 runs together going the same direction with the same cool down period, and I always throw out the data from the first pull, as it technically didn't use the same cool down period as the rest of the pulls. So yeah, it's kind of a pain, so if you're not into it, I understand. Just let me know if you're willing or not. I usually find a large country block to go all the way around for 'cool down'. Then do the subsequent pull when I get back to the same place in the same direction on the same flat road spot. Personally I've found, that if IAT or ECT or Oil temps (which typically are not logged) vary much more than 1-2 degC then the data can be pretty not repeatable/skewed. Virtual dyno can be a great tool for comparing tuning tweak changes as well... you just have to be on your A-game when trying to compare runs after a tune tweak, as stated above, a few degrees can change a lot (especially with all the various temp compensations in tuning these days).

[KillboyPowerhead]

I can possibly send you a log sometime in the next few weeks if you're interested. Once I've dealt with the minor hesitation and done a few more full throttle pulls (would like to compare to when I originally tuned as well as try out what zenon222 suggested) then I'll schedule a dyno run.

I remember hitting near 120% volumetric efficiency according to the scanner, and using some power/torque calculators (who knows how accurate they are, but tried ones taking into account lots of different variables) some say well over 400 HP. A full intake, exhaust, tune gets the LFX to ~290 - 300 WHP, so ~360 - 375 at the crank, and the cams are advertised as adding 40 HP but that's at 6,800 RPM (where the stock cams max out), and the Mace cams can keep making power past that (to ~7,500 or so, I've heard), so assuming my tune is decent I'd expect to see at least 330 at the wheels/400 crank, but hopefully more as I'm going to ~7,300 RPM.

Second gear maxes out at ~125 km/hr so that's doable on an empty highway, but third gear is 50 above the impound limit, so probably jail time ^.^

[KillboyPowerhead]

Starting to get back into this...

Just made up a quick cam chart (attached) based on the cam card provided by Mace (again, they would only provide the exhaust card, so I had to infer the intake specs knowing that the intake and exhaust cams have the same profile, and assuming the centerlines are the same as the LY7/LLT, according to the specs I found; see post #22. I also realized I made a mistake for IVC, see edit in post #22).

Mace cams.JPG

This whole time I've been using a wideband sensor, but going to use the factory sensors and LTFT and STFT and go back over the VVE and MAF, and then do some more WOT pulls with some different cam specs again, just to see if I notice anything different than before.

[[email protected]]

I've been playing around with cam phasing lately. I found at low RPM the motor did not like much overlap at all, I think it's because of the MAF.
The previous phasing had a severe "chugging" or "surging" at 1200 RPM at low load, this was seen when driving along in a parking lot at very low speed, if on the road at speed there was not a chugging, but there was a "soft" spot at 1200 RPM.

The attached 2024-08-14 tune changed the ramp rate to keep the LSA a little wider at 1200 RPM and this completely eliminated the issue at 1200 RPM.

For my most recent try I've widened the LSA even a little more at 1200 RPM.

What I found with the 2024-08-14 tune was that it ran hard to 4000 RPM and then went flat, or tailed off. It's hard to tell which so I'm trying something a little different to see what happens.
Flat torque curve motors are funny to drive...

The attached should help you calculate what your motor likes with those cams, I would expect you need wider LSA's in the low RPM range than the OEM cams.
I have so far made the cam phasing only dependent on RPM, but with the extra duration of the MACE cams maybe you want to change the phasing based on intake pressure.....

Posting the file isn't working so I'll try posting it in a new message

[flatpick13]

Posting the table for zenon.

[KillboyPowerhead]

Haven't played with the cams much in awhile but will get back to that shortly, just been retuning the MAF and VVE with the factory sensors; used a wideband previously, seeing a few % difference but I guess that's expected since I have only one WB, and one bank is likely more rich/lean than the other.

Makes sense to me to want more intake advance at lower RPMs since at the home position the piston is nearly half way up by the time the intake valve closes (with Mace cams) - this would, however, increase overlap, so I guess keeping the exhaust cam in the home position at lower RPMs would help.

Did a few WOT pulls just for the heck of it and noticed my cylinder airmass (which I understand replicates the torque curve) peaks around ~5000 - 5200 RPM, dips a bit and bottoms out around 5600, then heads back up and tops out again around ~6400 to ~7300; once the MAF/VVE are dialed in I'll start playing with the cams (and eventually spark, SOI) from 5200 - 6400 to see if I can flatten out the curve, and so on.

Will work on the cruising areas/fuel economy too with respect to VVT; thinking I'll just test them like a did with WOT pulls, so start with the intake at 0 and try various exhaust cam positions, 0, 5, 10, etc., bump the intake to 5, etc., and monitor fuel usage, see what combo uses the least amount.

[KillboyPowerhead]

While (re)adjusting the VVE I played around with some numbers and think I finally figured out where the VVE numbers come from (not sure if this is common knowledge but couldn't find any direct/obvious explanation); looks like those numbers are:

"VE Cylinder airmass" (mg) * Intake air temp (K) / Intake manifold pressure (kPa)

Where "VE cylinder airmass" (as I'll call it) is calculated based on "VE Airflow" ([2311]), so VE Airflow (g/s) divided by RPS (RPM/60) divided by 3 (or half # of cylinders), and then multiplied by 1000 to get mg.

Think I mentioned this earlier in the thread, or in another thread, but based on what Tunercharged said (https://forum.hptuners.com/showthrea...for-gen4/page9, post #169) I started tuning my VVE by simply comparing the MAF airflow (with MAF accurate to ~2%) and simply calculating the error between MAF airflow and VE airflow and adjusting VE airflow by the difference (using data at steady state conditions).

After playing around with the numbers and formulas I see that this make sense. Believe cylinder airmass is calculated based on dynamic airflow (the airflow that the ECU is currently using), and at steady state dynamic airflow = MAF airflow, and if the MAF is accurate, by making VE airflow = MAF airflow you're making Cylinder Airmass used in the VVE accurate, and so "VE cylinder airmass" (a term I made up, but is the cylinder airmass calculated from VE airflow, rather than dynamic airflow, and shown in the VVE table) is equal to the actual Cylinder Airmass parameter used by the ECU. With the MAF accurate and VE airflow = MAF airflow, use the first equation above and you should get a number pretty close to what's on the VVE table (remember to consider cam angles).

Might be well known, but now it makes more sense to me

FYI still playing with the MAF/VVE and intake cam timing; getting everything dialed in pretty close and will start playing with the exhaust cam. From what I understand, IVC (intake valve close) is the most important event to get right for an NA engine as it most determines how much air gets into the engine, and the objective of adjusting the exhaust cam is more or less to control overlap.

Think I got the intake cam set pretty much where it needs to be to give me max airflow, just a few more tests to confirm then I'll play with the exhaust timing. In an earlier post I mentioned that the factory exhaust cam timing profile seems odd in that it advances toward redline instead of retarding like one might expect, but now it makes more sense (with the Mace cams, at least). At 7200 RPM, to finish injection by 180 BTDC, with EVC at 334 BTDC and a pulse width of ~3.6 ms, you're finishing nearly at 180 BTDC with no extra retard (cam at 0) so you can't move them much near redline unless you make EOI past 180 BTDC (remember that the cam tables are in cam degrees, so every 1 degree = 2 crank degrees). But before 7200 you can add about 4 degrees to each column, so 6800 = 4, 6400 = 8, 6000 = 12, and if you're starting injection at EVC then you'll end just before 180 BTDC with a 3.6 ms pulse width (before 6000 there's much more freedom, but the general trend starting at 5600, 6000 is you need to advance toward redline just to finish injection in time). So that's where I'm going to start I think.