Doward

I've got a copy of the bin in spreadsheet format from www.gnttype.org, and am wondering - the decimal values I'm seeing for these timing tables seem quite high. Does the GN actually run 44+ degrees of timing? I'm thinking it must be the total timing, after the base timing is added in.

Is this correct?

*EDIT* Just to clarify... The XLS file of the prom data is showing say.... 2200rpm, LV8 = 44 means there will be 44º of timing there. Now, that seems high - does TunerCat display the value, minus the base timing (aka, 44 in the XLS would equal 32 in TC, assuming 12º base timing)

I see a spark reference angle of 70, but not sure how to factor that in??

RBob

iTrader: (1)

The base timing is subtracted in the ECM but added back in by the physical placement of the crank sensor. On the turbo Buick it is fixed at 70° BTDC. Which gives 10° BTDC SA during crank (it's a DIS system).

What you see in the XLS file is correct. The column labeled DATA is the actual timing at the crank. The reason SA is so high is that the LV8 is so low. Very little load on the engine requires some timing to get the burn to complete is a reasonable amount of time.

Note how much lower the timing is at an LV8 of 255.

RBob.

Grumpy

Just to add to what Bob said:
That's in part why they run an oil cooler, get away without a smog pump, and eat rod bearings (in a relatively speaking manner). Oh, and run a fair amount of EGR.

You can get pretty good mileage going up to as high as 48d, but the AFR gets critical, and the oil temps., go high.

Or, IMO, back it down, and have a longer lasting happier motor.

Ronny

iTrader: (1)

please elaborate/clarify the tunercat Q he posed.

i believe the main spark tables(TC) are real timing the engine sees cept when PE in involved there is an add on of spark in TC assuming it is not zeroed out and added back in main table.

Doward

Eh... I'll just subtract 10º across the board, and see how it runs

Grumpy

Ah, if you're talking about other then the main spark, then there are some tables, that have bias *adders* to them. So you have to subtract the bias back out. As I recall, they use 45 often, which in fact is a ~15d bias.

Doward

I do a see a value of 15 for 'Bias for base coolant adv. corr. table (table F2B)'

Now, the table shows say... 6º under the 'Base coolant advance correction vs. load (CF-KCTBIAS)' @ 32º C. With the bias of 15, am I correct in the following -

6(value @ 32ºC) minus 15(bias) = -9

Assuming 3200rpm @ LV8 = 64 (value of 41.8 in the table) then you would have a total of 32.8º timing sent to the distributor? (this is assuming no other changes, like spark vs mat)

The math is not hard, it's the order of operations that I'm unsure of....

Grumpy

Sounds like ya got it.

Ya, once you have the answers, everthing seems easy..
Thou, at times just figuring out the questions can be a test of one's sanity.

Doward

So for any table with a BIAS constant, the BIAS is subtracted from EACH value in said table - ALL tables are then ADDED together for the FINAL spark advance. The initial advance, is subtracted from this FINAL spark advance (since the distributor already has that mechanically set)

Sound good?

Grumpy

Reread RBob's post,
there is no distributor, the TRs are DIS.

Doward

I apologize, I should have stated that what I was referring to, was a distributor-equipped car. Am I correct on the order of operations, though?

JPrevost

Order of operations? Guys, it's just addition and subtraction. You could do it in any order.
Some programs like TunerCat already have the bias included in the spark table displayed values. To verify this, input a small negative value, save/close, reopen and see if it's still negative. TunerPro ecu files don't support this but the newer version 4 with the xdf file DOES. The 8746 xdf I did has all of the bias values included in the displayed main tables so you never have to worry about it. Just open up the main tables that have the spark bias (MAIN SA, CTS, and TCC) and add them up. The CTS should have some negatives in the high temps, again an indicator that there is a bias already being used in the background.
Back in the day (a couple years ago) you would have to look at everything and do the adding and subtracting. Now it's easier just like TunerCat . Again, the ecu files don't support that feature so it won't have the biases taken into account so you'll have to look at them and subtract them from the main tables to come up with the commanded final.