MicroSquirt.com read only forum (Jan.15,2018)

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QldRobbo wrote:
I must be missing something....

I'm assuming that 20kpa at 800rpm would be able idle, using the formulas above I get 31 degrees of advance at idle.... shouldn't this be more like 10 degrees?
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Try more like 60-80kpa at idle.
The formulas are intended as a good starting point and will never be perfect.
Use whatever advance works on your engine, like you say 10-15 deg is more reasonable for idle.

James
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Does there exist a spark table estimator that works better (10-15 deg at idle w/ ~20kpa @ ~800rpm). I don't think that most people have 60-80 kpa at idle. I also don't think that 30+ degrees is close for advance at idle. Am I missing something?

SSDD wrote:Hi all can someone tell me what the equivalent of your US:
is in Europe, we have here:

Unleaded 98
Unleaded 95
super

It goes by octane rating from lowest to highest. In the US, regular is generally 87 octane, mid-grade is 89, and premium is 91. So yours is probably in order of 95, 98, super. That is assuming those numbers represent octane rating. Octane is the measurement of resistance to knock.

Octane is actually a carbon chain, 8 units long. Gasoline is made up of these carbon chains, but most of what's in gasoline is more along the lines of pentane (5 carbon units long). Octane is a very stable carbon chain and is more resistant to detonation. So having a higher octane concentration in gasoline makes it less likely to pre-ignite.

There are two octane rating methods the "motor" method (producing the "motor octane number" or MON) and the "research" method ("research octane number" == RON). The MON is a more realistic number for performance application, as it is a harsher test and gives lower numbers. In the US our octane numbers are (MON+RON)/2, in the rest of the world, they are typically RON. Your 98 is nearly our 93, but maybe not, as the RON testing method doesn't really focus on the thing that is important to hot rodders.

Google "ron mon octane" and you will find about 75000 hits, all of which give better information that I do.

Eric

What I don't understand from the original post is if I am running an estimated timing max of 37 (chevy 355 w/ vortec heads, no boost), shouldn't I enter that at 20kpa/6000rpm, and subtract down to the 100kpa line?

Even stranger is this stock LT1 ignition table I planned on using. It's not linear at all:

Have a look at this ignition map. It comes from the Jeff Hartman book, Fuel Injection installation, performance tuning, modifications. I modeled this map for my car.

Note the valley at 800rpm for some level of idle adjustment. As the idle drops, the ignition advances and will increase the idle. The advance at idle is very low, but as the rpm increases (ie when first touching the throttle) the idle is advanced for a quick boost in power.

Thanks woh. That graph makes me feel better. Mine looks very similar when you consider my torque peak is higher (around 4100), and I haven't added extra advance at the idle end. Maybe I should add some.

Please read through my numbers and give me some advice:

Engine: Volkswagen Golf II 1600 cc. Carburator Pierberg 2E2 (engine code RF).
Now it's turbocharged (up to 150 kPa). Garret T25 with intercooler. Carburator changed to Weber 34DMTR.
1) at 1000 rpm (idle speed) i've got 40 kPa and 18° timing
2) at 1000 rpm and 100 kPa must be 6° (as by manual)
(these 2 points taken from volkswagen manual).

With 0.3° per 1 kPa at stated in your manual I can't get these points, that's why I try 0.2° per 1 kPa.
After trying these calculations I get 4° at 1000 rpm and more then 100 kPa which is not good for the engine ang manually changed it to 6°.

Why is maximum advance for further timing calculations (for boosted or NA engines) is assumed to be reached at 3000 rpm and not at higher rpm?

What do you think about my calculations (shown in xls file)?

QldRobbo wrote:I must be missing something....

I'm assuming that 20kpa at 800rpm would be able idle, using the formulas above I get 31 degrees of advance at idle.... shouldn't this be more like 10 degrees?

I was always told that the correct spark timing @ idle is the value that produces the lowest MAP.

When I megasquirted my Rover V8, the best idle was achieved @ about 35 deg BTDC on 98 RON fuel. I also got the idle MAP down to 30 kPa. The timing was taken care of the old fashioned way with a distributor and so with that timing, although I didn't get any detonation, the power was noticably lower and dropped 15-20 RWKW on the dyno. So I had to settle for less advance, a rougher idle but more power and better economy.

Of course, keeping in mind that that engine had an 8.13:1 CR.

Is it just me or does the "you can update this with your RPM values" table not work? mark

ahhh because all advance above 3000rpm is the same for the same MAP , gotcha