SD, $8D, stock cam, stock intake, 355 TPI vette, slightly higher compression, stock aluminium cyl heads. (basically stock ANHT bin –VE and spark untouched).
I made 3 datalog with datamaster. All with similar weather conditions (65 to 75 °F)
All these datalog seems to say I’m a bit rich (BLM about 124 average. Some 128 and some 120..)
Another distinctive and common thing is the knock retard. I think is a REAL knock because it occurs at WOT and in part throttle situations. At WOT I had up to 12 deg of retard expecially in higher speed situation (near 100 Mph) and an average 4 or 6 deg on the WOT runs.
At part throttle I have knock retard when I try to accelerate from lower rpm (1400- 1900) with more than 20- 30% TPS with 60 –90 Kpa Map values. I have a smaller (numerically speaking) rear end: 2.73 and new slightly taller tires so this is a typical Hi load lunge situation that often causes knock.
Someone told me that maybe I have an OVERadvanced timing at the distributor. (I haven’t a timing gun, soon I will check the real timing at the dist.)
I decided to try to retard the base timing just to see if removing a noticeable amount of timing will produce a noticeable difference on knock retard values. ( I had to choice between 2 ways: 1 changing the constant “spark advance Initial –distributor setting-“ to an higher value like from 5.98 to 12 or 15 deg OR manually turn the distributor clockwise . )
I turned the distributor. I don’t know how many deg I pulled out, but looking at the distributor you can see a real difference position from the initial position to the new position. (now the coil is parallel to the windshield, before it was a bit diagonal)
With the same bin I turned On datamaster.
The car idles good (as before) and at the end of my 15 /20 min of datalogging I had these strange results.
Part throttle seems worst than before (!) or similar to before. (light medium throttle and I have from 2 to 8 deg retard).
WOT condition is now without Knock retard. 0 retard (maybe only some fraction of deg just when the TPS comes from 30 to 60 to 90 TPS% before to approach to 100% TPS.)
I made 3 or 4 short WOT attempt and I haven’t knock retard.
My BLM went from an average of 122 124 to 131 133 values (I continue to have richer tasks..in the 125 123 level..).
I pulled timing .. I was expect to see lower BLMs!! (I'm right?).
BLMs always pair (120 122 124 128), now are odd.. 127 129 131 133)…(?!?)
The car seems (SOP) better with less advance even at part throttle even if I continue to have knock retard.
The only difference between the old datalogs, is that the air temp yesterday was a bit cooler (about 55).
I know I have to set the timing once and for all, but if someone can try to explain me these strange result I will thank a lot.
Thanks
-Beppe-

 

If your going to try and tune, then do it right. If your not sure of the timing, correct that before doing anything else. Tuning by *this'll do*, just causes more variables, and can be very misleading.

A timing light is one of the most basic of tuning items, and some of the parts stores have them for very reasonable prices. All you need it a light, forget the dial back timing, and eye candy stuff, just something that flickers when the engine is running is all you need for an EFI car.

If you really want to do it correctly, set the timing, add some GM injector cleaner, make sure the cap/rotor are *like* new, install a new set of plugs, and then do a datalog to see where you are with a good baseline, tunewise. Massively retarding the timing like you've done, can have generated carbon deposits and they'll lead to hot spots and detonation as you start your tuning.

One of the hardest lessions to learn is not shooting yourself in the foot, when trying to do something.

 

You are absolutely right... I'm doing the wrong approch..
...But about "more variables", the only thing I changed is the timing, only one variable just to see what happens, taking in account the only change I made. in any case I'm with you .. this is not the right approch.

I will save money for this.
Here in Italy asked me over 200 Eur ($250!!)

cap and rotor are 6 months old, wires and plugs are 1 month old.

This can explaine what I'm seeing only now?
I explaine. I see that at beginning of the datalog I have spark retard at part throttle (massive spark retard every time I touch the gas pedal more than 20%). As the datalog goes on and after some WOT up to 5,000 RPM, the part throttle spark retard seems minimize up to go to a max retard of only 1 or 2 degrees on the same high load condition with lower RPM that at the beginning of the datalog were very "degrees consumer".
Maybe I generated some "hot spot" (causing detonation at the beginning of the scan) and then after some WOT passes I "cleaned" a bit the "carbon deposit"?

Lesson learned.
Thanks
-Beppe-

 

An inductive pickup timing light shouldn't cost more than $25-$30 US.. And he is right, you HAVE to get the baseline right before you start tweaking, it will make your life easier..

 

I checked timing with an inductive timing light.
(I bougt it from jegs' for $39.99)
The base timing was 0 deg.
This means that when I manually retarded the timing turning the distributor I ended with a base timing of 0 deg.
Since when I made this operation (retarded the timing turning distributor) i recorded the previous position of the distributor, I was courious to see how much base advance was before the retarding action.
So I advanced again the distributor (turning it counterclockwise) up to the registered position.
It was 12-14 deg BTDC!
I set now to 6 deg just as the constant “spark advance Initial –distributor setting-“ .
Now I only have to hope that the ring at the balancer is not slipped and that the #1 piston is at the real TDC when the timing mark is a t ZERO position.
How to check (if it's possible) if the piston is at TDC when the timing mark is at 0 with common tools?
-Beppe-

 

In the Jeg's catalog they sell a TDC finder. It's a series of threaded bars that you screw into the spark plug hole, and then gently spin the motor over until #1 piston hits the finder, then repeat from the other direction, and when you split the difference wala, TDC. HOWEVER, using this means using some finese. ie pulling all the plugs out, and going slowly step by step.

If you're lacking in engine building skills, or have any guestion about your level of *finese*, then just use a pencil, for the finder, and along with a friend you can find TDC by just getting close, and then recording where the pencil stops being pushed out of the cylinder.

There are the short versions, and if you think about it, they should reveal themselves to make sense.

Then with you remarked pulley, set the timing, correct the code if needed, and start over on the spark tables.

Anything, *not right* will bite you later on.