oztrack

I am wondering how my best timing values will be effected by cylinder air flow and my AFRS.

I have identified 4 situations i need to tune for

1. When flashing from my stalled up speed of 2000rpm to the stall converters stall speed (3600rpm)

2. When accelerating under high load from the stall speed eg 1st gear doing a 1.6 60 footer.

3. The mid range area from around 4800 to 5600 when g/cylinder is highest - this is meant to be when there is peak torque - is this because g/cylinder is highest??

4. when approaching peak hp ie 5600 and up


My scanned dyncylair values are (at 33deg C) in g/cylinder

4400rpm 0.784378
4800rpm 0.799945
5200rpm 0.809738
5600rpm 0.824718
6000rpm 0.805931
6400rpm 0.766443

My VE table has in the g/cylinder at 33 degrees C

4400rpm 0.821888
4800rpm 0.836880
5200rpm 0.866035
5600rpm 0.881665
6000rpm 0.863483
6400rpm 0.816402

I am led to believe its better to run less timing in situation 3 than in the others and that situation 1 and 4 can run the most timing? Is this correct.

I have a 216 220 114LSA Comp Cam with 1.8 rockers and 10.7:1 ported heads. On the 98 fuel we have in Australia (like 95 in the USA) i have 23 deg around 4800 to 5600 and 26 above that. I am wondering if people can share science to do with this stuff - so i can have some sound principles behind the approach.

oztrack

I am also aiming for AFRs of 12.6 at peak torque and 12.8 at peak hp - measured pre-cats.

jimmyblue

iTrader: (11)

The VE table is a "precentage of ideal", not a g/cyl value.

Your VE table should follow g/cyl but this is somewhat a
chicken-and-egg proposition down low, and depends on
the fidelity of the MAF up top steady state.

High cylinder pressures and low RPM tolerate the least
advance. You want to maximize delivered torque and
intake airflow / cylinder air by the timing you use. You
probably would prefer to work from some acceleration
number (like locked second or third gear pulls, take
acceleration as VSS pulse count deltas or kph deltas,
and look at which settings maximize that, where (you
should find that the ideal spark timing changes w/ RPM).
As well as mixture. This is really a two-variable problem
that probably wants shotgunned, map it out and sift
for the best bits and stitch them together for a final
spark and fuel curve pair (for WOT).

oztrack

EFI live version 7 has g/cylinder , g/sec (both at a given temperature) or % as its choice of units in the VE table.

The car is mafless - its been tuned quite accurately at all cells of MAP and RPM in its VE table using the EFI Live/Flashscan Autotune procedure.

Thanks for the information.

white2001s10

iTrader: (4)

That is a generalization that is not always true.
Bottom line is the burn-speed HAS to match the piston speed, and I don't mean average piston speed, so it is semi-RPM related.
Burn speed can change during operation based on a combination of changing VE, RPM/turbulence, and heat in the chamber. These are things you must keep in mind when estimating when to start the ignition process.

If you assume burn-speed is a constant, then spark advance is determined by a combination of engine speed/RPM, piston speed, and gearing which determines the transition from one engine speed to the next and is more telling of piston speed than simply calculating the average.

You know you can never assume and several things do change the burn-speed.

Here's an example of a car I tuned a while back that was carbureted and using 3 gears of an automatic transmission for a quarter mile & 92 octane fuel.

First gear was 42* advance.
Second gear used a 5* retard for a total of 37*.
After the 2nd/3rd shift around 800 feet into the run I used a 2* retard
for a total of 35* advance through the 1320 ft mark.

In first gear the piston speed is high and the temp in the chamber is still relatively low. 2nd gear is a big change in load and much less piston speed. By 800 feet into the run the load is increasing along with the heat.

HTH

oztrack

Is it helpful to be logging dyncylair_dma and getting values in g/cylinder or other airflow numbers. Then tweak timing to get maximum airflow??? or doesnt this happen - its just a thought.

Slowhawk

iTrader: (12)

As you probly found out.The most timing without KR or maximum AF doesn't mean it will run it's fastest time.Each car is different and for a track car it has to be tested over and over.
I have 1 car that we extensively tested on the dyno/street and track.
Dyno/street tuned it made 450rwhp and ran 1.52 60' ,11.2 at 118mph at 3650lbs.
After track tuning it made 420rwhp and ran 1.54 60' ,11.0 at 120mph at 3645lbs.
Now,same tuneing and deleted KR sensors (no KR present on past runs) it ran 1.51 60' .10.8 at 124mph and stayed consistant.

Track testing takes time to get the best out of the car.