Glen McCartney

John, Dave, great work. The enhancements and upgrades for the 928 are coming fast and furious thanks to the work of Dave, John, Mark, Marc and others. Great to see this. Dave, put me on the list when the '85 is ready, I'll come down to casa Roberts and we can have some fun tuning my car and drinking a few tequilas later.

Glen

Louie928

Maybe, but... Spark timing should be the minimum advance where the power doesn't increase with more advance. Detonation happens with several degrees more advance. As you advance spark timing, the power will increase quite dramatically with only a degree or two additional advance. As you approach optimum, a degree more advance won't get you more power. Back the timing off to the previous value, or even slightly more for "safety". Running advance between the minimum max power advance and the detonation level advance value means you will be into the danger zone all the time. How much advance difference between the threshold of maximum power and detonation isn't a fixed value. At low loads it can be, say 10 degrees, at higher loads only a few degrees. You don't want to be bumping the knock sensor retard in normal operation. The knock sensor will retard spark several degrees which will cost significant power and the EZ-K will rather slowly advance it back again while checking for knock. All the while you are suffering power loss. The knock sensor is a safety against bad fuel. Setting timing should only be done on a dyno. It can take quite a while to get right.

ErnestSw

Hi Louie,
Thanks for the lesson. Am I correct in thinking that AFM becomes a variable when spark timing? What about dyno alternatives such a 60-100mph times or something like a Gtech pro?

John Speake

Thanks Louie,
I did say "could" :-) And I don't have the dyno experience you have. Sounds as though the dyno will be an essential tool for remapping the EZK.

We will provide the means to do it.....but it is going to take several months. (So don't hold your breath, Ernest...)

Regards

ErnestSw

Better hurry up, the competition is breathing down your neck!!

John Speake

So who's that then ?

ErnestSw

I refer to the millions of electronic specialists all over the world currently taking time out from their defense contracts to work on the Porsche 928 EZK in order to tap into the mega billions of dollars available in the 928 marketplace.

DR

>I refer to the millions of electronic specialists all over the world currently taking time out from
>their defense contracts to work on the Porsche 928 EZK in order to tap into
> the mega billions of dollars available in the 928 marketplace.

John Speake

........OK, my humour radar deserted me :-)

Only the Goverment could afford such a money pit !!

Louie928

Hi Ernest,
I'd better watch what I say now, or I'm going to really step into it. The air fuel mixture and spark timing are separatly tuned engine parameters. Now it's true that if you have incorrect timing with too much spark advance, and/or too much compression for the fuel octane, or combustion chamber temp too high, or too much boost for the compression ratio, you can dump in so much fuel that you'll inhibit the burn and slow the flame to the point that you might prevent detonation, or at least delay it's onset. Sounds like a cure-all doesn't it and I see a lot of people thinking that's the way to go. Just throw excess fuel at it until the fire almost goes out then everything is fine. I witnessed this sort of thinking at a supercharger install party this spring. When one of the higher boost cars got on the dyno. First they worked through several partial throttle runs to check things out and make adjustments to the RRFPR. This FPR had another feature which had a bleed orfice to permit fuel pressure change with boost, but apparently also with time on boost. It seemed to put in a lot of pressure on initial throttle, but the pressure reduced the longer the boost was on through an air bleed screw. I was initially puzzled by this action because it seemed backwards to how I thought it should be. On the first near full throttle run I just about broke and ran for cover. The engine detonated so bad when the throttle was opened, I thought it would jump out of the mounts. I didn't even know the engine could move that much. Of course the operator immediately shut it down. What was the fix? Dump in even more fuel initially (pressure spike) then let the pressure fall to a more normal level. It did help, but didn't cure it. The A/F ratio was I remember was around 9:1 initially, then rose to about 13, or higher, near the end of the run. I might not be 100% correct on those numbers, but not far off either. Completely backwards to how it should be, but the tuning was pronounced done. It was about 2:30 am so "done" had a different meaning than if it had been 2:30 pm. I was appalled that this was considered "normal". It wasn't my party so I couldn't, and didn't, say anything about it. The detonation problem wasn't a lack of fuel, it was too much spark advance for the boost (high load) at that RPM which was maybe around 3000.

Now that I have a significant number of folks upset at me, here is what I understand about air/fuel mixture values. When you tune an engine you set up the A/F mixture first. This assumes you have some form of baseline timing set that may be around 0 to 10 degrees at idle and up to 20 -22 degrees at 3500 rpm and above. This will insure that the engine at least runs. Ignition timing will not affect the A/F ratio. The IC engine is a heat machine. It burns air and fuel, produces heat, and makes power. How much heat the engine can tolerate pretty much determines it's power producing potential. The use of an engine in a car requires that it have a wide range of operating characteristics. Minimally, we need idle, low load cruise, mid range power such as climbing a hill, and lastly, full on wide open high rpm max power. The optimum air fuel ratio will probably be different in each of those operational areas. We know that it takes about 14.7 as much air (by weight) as gasoline (by weight) for both all the fuel and all the air to burn. This also gives low emissions so that's the A/F ratio we'd like to see for idle and some low load mixture. We've also found that using slightly more fuel can produce more power because the excess fuel will cool the intake charge a little allowing a more dense charge, and it will cool the combustion chamber too. This air fuel ratio may be around 13 or 13.5:1. It will be different for different engines. That's the A/F ratio you might see at mid to high loads. Now for wide open high rpm where a lot of fuel per unit of time is being burned, the A/F ratio is more determined by just how much heat the engine can withstand at that power level. If the engine is not highly stressed, or the engine may not be subject to the high power level for a long time (drag strip run), you may be able to keep the ~13.5:1 A/F ratio. However, for a highly stressed engine, one under boost, or one where you need high power for a significant period of time (aircraft engine, open road race, Bonneville record run) you are going to need to use even more fuel just to keep the engine internals from overheating. The fuel isn't used to make more power, but only to keep the engine alive at that power level for that period of time. That's where you'll see 12.5:1, or for high boost engines even 10:1 may be necessary. Point is that you don't need a 10:1 A/F ratio if you are only going to use full power for a few seconds at a time in a high power blast to the next traffic light, or even down the 1/4 mile. 13:1, or 13.5:1 would probably be ok for you in that usage. One last situation is in light load, low rpm, freeway cruising. The engine is not burning much fuel per unit of time. The cylinder pressures and temperatures are not high. It's perfectly ok to have an A/F ratio of 15.5:1 or even leaner as long as the engine runs smooth and doesn't miss. This will help fuel economy, but will wreak havok with emissions, mostly NOX. That's where exhaust gas recirculation comes in and I'll just skip that whole scene. The A/F can be set on the road if you have a safe place to do the tests, and there is no better test conditions than to use the vehicle itself at the velocity it will encounter. Using a dyno is normally quicker and safer to get the A/F very close.

Once you have the A/F set where you want for all the different driving conditions you'll encounter, then you set ignition timing. Timing is set for the minumum advance to get you just to maximum power for that load and RPM and no more. If you needed to make a large change in timing, you can go back and touch up the A/F ratio, but it won't change much, if any. The only effective way I know to do this is on a dyno. If you use a loading type dyno, you hold RPM constant and set timing at each different load value in the tuning map. On an inertia dyno, you hold throttle position constant and run through the RPM range to get a torque reading for each load value. Make a change and do it again to see the effect. Holding throttle position constant with your foot exactly enough to make runs repeatable is hard. Some sort of mechanical throttle position limit is helpful. Something like vise grips on the throttle cable. The problem with trying to set the timing on the road is that it's impossible to hold rpm and change the load while simultaneously measuring the torque and changing the timing. Timing a 60 to 100 mph run would get an average measure of performance, and that's fine for a quick check, but the RPM changes by a factor of 1.67 across those speeds. If you see a gain, or a loss, which RPM do you adjust, and would you advance, or retard the timing? Some RPMs might be good, some too far advanced, and some have too much retard.

I've tried all the "performance monitors" I can find and can't find one that is consistent enough and also gives a torque vs rpm readout. I have a GTech Pro which is pretty useless, a unit from England that uses an accelerometer to produce nice torque & hp charts printed out in pretty colors. The problem is that I can't make two runs that are within 15 hp of each other. I have another unit from Australia that measures the time difference between ignition pulses to calculate torque, but again it isn't consistent. The only thing I've found that is consistent and accurate is a dyno.

ErnestSw

Thanks for the lesson Louie, it helps to understand the variables involved in the process.
Several questions:
Using established AFM parameters under varying loads gives a baseline for timing adjustment. When advancing timing to maximum HP will knock be avoided by using this method or will knock prevent maximization of HP under some conditions?
I'm afraid you've lost me here. It SOUNDS like you're holding the throttle in one position AND running through the RPM range. Can you help me understand the process better?

Louie928

Ernest,
Knock will be avoided. There is some knock "cushion" between the minimum advance for max power and the advance where knock will happen. Actually it's a good idea to leave a little on the table and not advance all the way to max power. With a knock sensor to retard spark if you get bad fuel, you can safely go closer to max power than if you had no knock sensor. You don't want to run so much advance that you will be running into the knock sensor although some cars are set up to do that. You'll just lose power.

You have it exactly regarding holding the throttle position and running through the RPMs on an inertia dyno. It's the same as doing a full throttle run, but you do it at less than full throttle. That's how you work up to full throttle. Start with something like 10% (estimate) throttle and do a run. The load (MAF voltage) will change through the run, but analysis of the sharktuner and dyno logged data will show power at each RMP/Load point. Change timing a degree or two and do it again at the same throttle position. Analyze the data to see if you gained or not at each RMP & load cell point. If no gain, then put the timing back where it was. If a gain at a certain load/RPM point, advance spark a degree at that point and do it again. Keep at it until no more power can be had and you have minimum advance to make that power. Change throttle stop to a greater opening and make runs at that setting until you have that throttle opening optimized. Keep going until you get to full throttle. If you miss some load points exactly as if one throttle position was below a load value and the next throttle position was above it, interpolate the timing value from the lower, and the upper points, for that missed point. At the lower throttle openings, timing seems to be fairly non critical. I mean that you can change timing several degrees without seeing much power change.

If setting timing on a boosted engine, I'd back the timing down (retard) maybe 5 or 8 degrees in the boost region and start from there since you don't want to be testing if the timing is already too far advanced.

Does that help?

Rick Carter

Louie,
Take a look at this link: http://www.mrdyno.com/
After I had the heads P&P and put om Tom C's exhaust I had the car tuned on load bearing dyno exactly the way you describe using the SMT-6 from you and ended up with 276 rwhp on the Land & Sea load bearing dyno and 291 rwhp on the dynojet.
I bought Mr.Dyno for tweaking under real driving conditions but have never used it. Since I'm adding a SC I dug it out again. After the SC install the car wil be tuned on a Mustang dyno using the same procedure you describe. Later I'll find a dynojet to post the numbers people like to see.
Rick
85 32v modified

Louie928

Hi Rick,
Long time no talk. I'd be interested in your impression after you have used it. Make two or three runs from 2000 to redline, probably 3rd gear, and see how repeatable they are. The price is sure right if it works.

Rick Carter

Louie,
If you would like I can send it to you for your evaluation.
Rick