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Questions on tuning VVT Intake (relaive timing) table for knock & boost control
Anyone want to share theories on tuning the VVT intake table for boost, optimizing cylinder pressures and keeping knock in check.
Found several from 18PSI, Vlad, Revereant, Braineack, Savinton, DIY, y8s ext., but most are several years old and not finalized.
Running into an issue with knock from 3300 to 4300 RPM at 10PSI w 14 to 15 degrees timing, smooth's out over that with even more timing and leaner.
My setup is NB2 stock 10.5 compression lower, TS EFR 6258, 4-port EBC, 650 injectors, dual port waste gate, full 3" exhaust, Euro square top manifold. 93 octane Florida E10 gas.
Car is for street use, hot weather advanced roadcourse HPDE and Time Trial.
Was able to use an inertia dyno to get tables close to my 220ft/lb goals but this sneaky knock is rearing up 2k to 1k before torque peak? Sitting at 223TQ and 244HP.
Can pull a bunch of timing and make it smooth out or can ad a ton of fuel and it smooth's out, but spool takes off and my bet is EGT is going up also.
My dyno guy added some duty cycle to the standard MS3 basic table and it seems to make it worse? Only have an inertia based dyno available, want to use load bearing but cant find one local.
My bet is the SuperMiata S1 guys are doing some optimizing tricks to optimize under the curve performance. I'm not restricted by anything but my rods and compression.
From my limited understanding, its better to increase torque using turbo duty cycle (boost) than it is by increasing cylinder pressures using VVT? Makes sense that tables for boost would be very different than NA but searching doesn't support that?
Wanted a few opinions before I start tweaking tables.
Lots of different theories from some really knowledgeable guys.
Granted some maps are very old and not for FI applications.
My basic cam knowledge says advance for low end torque and retard at high end? So some of these maps go against theory?
Is there any benefit of changing to 10-200+ as I thought the RPM aspect was the highest importance?
Y8s map seems to make the most sense to me?
VE? No. The higher the VE, the more efficiently you move air. It also means that in an FI application you need a lower PR to get the same number of O2 molecules. This means you get to add more fuel with less work and at a higher detonation threshold due to charge temperature. More fuel equals more heat, which in turn means more power.
You will be able to run a lower manifold pressure with a higher VE to get equivalent hp.
If you had a magic engine with a VE of 200% you would be able to get more hp than an FI car with the same displacement and VE = 100% at PR = 2 (1 bar boost at sea level) with even perfect adiabatic compression due simply to the fact that it takes power to compress air.
Wondering if at lets say 10 psi from 2500 rpm up changes in the VVT angle and discrepancies due to response time or oil temperature difference make the increased VE a problem to tune.
It seems hard to match boost response time & VVT response time with any kind of consistency. Much less trying to match fuel and spark to put down increased VE without putting a giant dip in both tables?
One of the things I have noticed on pulls is the first pull I will get knock in that range the second and third I wont then it will reappear. None of these times it is audible by my used up ears.
Just seems many maps are very abrupt and would be hard for cam to keep up?
I am glad you decided to post this today. I just started playing with the VVT table on my tune as of today. I have been running the DIYautotune base settings and map for the VVT tables and getting weird knock (or what I think is knock) and had the idea maybe it was VVT related. BTW, how did you get such great resolution in your knock log like that? My signals are spikey and look like crap, hard to tell if I'm seeing actual knock.
For reference this is the base VVT map from DIY
And this is what I came up with just now for testing and logging tomorrow.
I too have determined that the miata motor is knock prone at low RPMs. I need to pull timing in places most people never see on the map, so that is why it doesn't get discussed.
Honestly, VVT is a tough tune. I recommend you log oil pressure to determine where your actuator can reliably be controlled. If you have regions of uncertainty in the cam position vs commanded angle, then you need to keep the commanded angle at the base angle (~5 deg BTDC absolute) until you reliably hit that oil pressure. You may see a strong dependence on oil temp, so limiting the VVT function to just below CLT operating temp can stabilize performance. The min DC parameter is CRITICAL! The integrator term can drive the process variable down below the true minimum usable DC and then the PID needs to slew through the dead zone before the actuator responds again. This will show as a delay or deadspot in the actuator response. Running a little rich in these areas should slow the flame front speed down enough to relax sensitivity to timing.
I have a BE 2 shim with T6. I run ST heavy doubles. My actuator needs ~30psi to be reliable, which I see at ~2000 rpm on a warmed engine.
2000-4500 rpm is a very knock prone area, the engine doesn't spin as much as the air that you push into it.
I have very similar numbers in my nb2, though I have tuned vvt engines where I can push more timing, so yours like mine might be a bit more tired than others.
IOW your numbers seems normal to me.
VVT is not the problem. 10.5 compression + boost is your problem.
The solution to reducing knock is mitigating the conditions that lead to it. You can do this most easily by reducing temperature or pressure.
The simplest way to do both is to drop boost some.
Other ways to do it are:
increase fuel so the conversion from liquid to vapor sucks up some heat.
retard timing so the fireball happens later and some of it gets sucked out your exhaust valve
inject water (again, vaporization sucks up heat
lower compression (ok maybe not this paycheck or the next...)
The real issue the VVT motor runs into with knock is that in order to have good throttle response, you want an ideal "power" air/fuel ratio and a pretty aggressive spark map right below that torque hump in the naturally aspirated dyno curve. In the unboosted 10.5:1 motor, it's very close to the limit already. Run some badgas and you'll probably still hear the occasional tink tink when you lean into the throttle at 3k.
My suggestion (having not looked at how to tune a miata in 7 years) is to run 11.5:1 AFR and retard timing (a reasonable amount) until your EGTs are at least 1400F or even 1500F if only in that problem area.
Dropped some timing and increased fuel a bit in knock area and smoothed out knock nicely.
Done with a bunch of other projects and time to start playing with tune again. Sebring in 4 weeks.
My dyno guy bumped 6 & 7000rpm cells to 15 degrees with no adjustments and seems to lost some rev happiness.
Thinking of smoothing them down to around base tune, but would appreciate if anyone has worked out better tables than those I stole from 18PSI, Vlad, Revereant, Braineack, Savinton, DIY, y8s very old posts.
SA58"s 2nd table looks like something that makes sense instead of the one I currently have. Ramping up and then very low at high rpm.
Any advantage of changing graph to take into account boost sections?
Posted screen shots would be great.
Here is my current table. Pulling some advance really helped smoothness and made motor more rev happy.
One thing I noticed on logs is commanded vs actual follows very closely but only goes down to about degrees even when commanded to 4.
A bit late to the party. Too much timing for 10.5 compression at that low of an RPM, reduce the timing. I wouldn't expect to see any gains from adding more fuel when you are already in the 11.5-11.8 area.
A bit late to the party. Too much timing for 10.5 compression at that low of an RPM, reduce the timing. I wouldn't expect to see any gains from adding more fuel when you are already in the 11.5-11.8 area.
Ironic as its based on your NB2 table
Did drop 2 degrees and it helped. Thinking some of my indicated knock is vibration?
How much can I drop timing on 100% 93 octane to pump E90 gas before getting into EGT problems, as I don't have an EGT setup?
02-13-2019, 05:36 PM
Questions on tuning VVT Intake (relaive timing) table for knock & boost control
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