03-31-2006, 07:47 PM
Join Date: Nov 2005
Location: Down Under
Total Cats: 0
I was reading a topic on another forum and one particular post by an engineer who works for Ford Australia caught my attention. This engineer spends most of his days doing; "My day gig is performing OEM engine power curves, and VCT engine developement, among other things".
One of his points that I found really interesting was; "One other point...pay attention to spark...this is MUCH more important to power than fuel. Everyone tosses off about 12.5 AFR (lambda 0.85), but never does spark loops to find MBT optimum spark!!!!!!
Going 10% rich on fuel might lose 2-3% power at the most, but 2-3 degress of retarded (or over advanced!!!) spark around pk tq or power will cost you 10% or more!!!! You could run a carby, and digital mapped ingnition, and make nearly the same power....this is where most of the gains in engine output have occured...optimising the spark at ALL engine operating points (non knock-sensor engines are generally 4 deg away from optimum already, to allow for variation in engines, drivers, etc)...and it gets worse the higher the CR!!! But show many any tuner who spends much time on spark loops????? Coz customers only want to pay the time for AFR mapping, getting that magic 12.5 AFR!!! Most modern engines i know make more power down in the 10's AFR...manufactureres aren't silly you know!!!! That's why so many cars run down there, but if you don't do the loops to optimise ALL parameters, you'll never know, ya??"
My next step was to have a proper read of "Mazda Miata Performance Handbook" by Norman H. Garrett III. In the chapter on ignition Norm mentions some facts about ignition advance for a 1.6 NA. The first was that 20% more torque can be found at 1000 rpm by advancing the ignition to 18 DBTDC. His second interesting point was that a stock 1.6 NA will go from 90.7 HP to 99.5 HP with an ignition advance to 14 DBTDC. He also had a graph representing a timing map of a stock 1.6 NA at WOT. This graph started out at 0 DBTDC until well over 1000 rpm and ended up at about 27-28 DBTDC at 7000 rpm.
Spark Experiment 1
So with this information in mind I decided to play with the spark settings that I had developed from the FM Link settings. My first step was to increase the settings on the spark table at the low rpm/low MAP area. The table is attached below.
I went for a drive with this table loaded into the MS and I felt a definite improvement in the low down torque. Prior to this change my car was a little hesitant in situations where I was accelerating from low speed such as after the car had gone over a speed hump. With the spark changes the car was much more willing to accelerate at these speeds.
The rest of the spark table was left unchanged.
Spark Experiment 2
I had previously downloaded an excel spreadsheet that gave the fuel and spark tables from the OEM 1.6 NA computer. This table was running at 10 DBTDC so I used this table to develop a hybrid spark table of the OEM 1.6 spark settings at 18 DBTDC for all of the values below 5000 rpm and the settings at 14 DBTDC for everything over 5000 rpm.
The table is attached below and you can certainly see the differences to the FM Link table. I drove for about 30 mins this morning using this table and it felt different to the FM Link table. The car accelerated in a different manner. With the FM table it seemed to be a great rush of speed and the car felt like it was going flat out. Now it seems to be more of a progression of speed, with the car less fussed in it's urgency but the thing is still accelerating really quickly.
Well the further advance at low rpm/low MAp values is a definite improvement to the FM spark table that I was using.
The new hybrid 18/14 DBTDC table based on the 1.6 OEM map didn't give any definite improvements over the first experimental table but I am really interested in getting the car on a dyno and running it with both maps to see if there is a torque/HP difference between them.
And the main point that probably isn't as obvious is that the BP engines seem to be pretty resistant to knock which is good for us to try and optimise the spark tables for our different applications and as my experiments have shown me, the spark table changes certainly can make for a more powerful and more responsive car.
Last edited by Aussie Driver; 04-01-2006 at 05:11 PM.