Two questions here, guys.

First is simple. For an 85 LB9, the stock BASE timing is 6* advanced BTDC, right?

The second is going to draw in all different sorts of opinions, but is it best to leave it at the stock setting of 6* or can you get an all around power increase by going to say 8*? I know the theorized consequences, and I know how playing with the base timing vs tuning through the ECM works.

The ECM adjusts timing using the stock setting as a base to work off of. By advancing the base timing, the ECM still thinks it is at the stock setting since it has no way to check and adjusts timing accordingly. Therefore, you are actually running the timing more advanced than what the ECM calls for. However, I am also aware of the consequences being the ECM adds too much timing and causes the engine to knock, which is heard by the knock sensor and causes the ECM to retard the timing to stop it thus hurting performance rather than helping it. That's why I'm asking will this measly 2* advancement on the base timing net me a gain all around by fooling the ECM into further advancing the timing or will it most likely play out with the knock sensor role? I'm looking for opinions of people who have been there done that or have sufficient data to back it up not just speculation.

I know this doesn't make much difference if any, but thought it would be worth mentioning that I run a 180 thermostat so my engine does run a little cooler than stock.

 

what you are saying is not computing with me "the stock BASE timing is 6* advanced"

that is contradicting itself Before would be retarded After is Advanced. stock timing for a LB9 is 6* BTDC so it would be -6* not +6*

 

Yeah sorry you're right I got confused for a second. So putting the timing to 4 rather than 8 would actually be advancing the base timing?

 

Correct. I've ran 0* and +6 before when I was chasing some ESC issues just to see what would happen and in my experience (that was hampered by funky ESC) it just created more pinging and rather poor performance. I have not tried advancing it since I got the car running right though.

 

6 vs 8 (or any other number) would depend on the motor and other factors. Try it and see if it runs faster for you.

We generally consider advancing the timing to mean that the spark comes earlier in the cycle. A spark that occurs before top dead center would happen sooner than a spark that comes after top dead center. Retarded timing = late.

 

If that is the case then I'm sorry, what you say makes sense.

 

So BTDC = advanced and ATDC = retarded? Sorry I've never dabbled with timing before. This is gonna be a first for me.

 

This is whats confusing you.

As the engine rotates faster, you need to initiate the spark sooner to properly ignite the mixture. BTDC is advanced, because its before Top Dead Center or 0*. ATDC is after the piston has reached the top and is on its way down on the exhaust stroke.

I used to try slightly advanced static timing that gives it a little performance boost but the better way, as you know, is to do it in the chip. I used to run up to 13* degrees at the track, and it did improve my time slip slightly. This was on a stock 86 LB9 but with the 85 LB9 camshaft.

Have you considered repinning to a later style 165 ECM and jumping into the tuning obsession?

http://www.cis.udel.edu/~davis/z28/ecm_swap/

 

Bumping this thread because I have another question.

At what RPM should base timing be read/set?

I pulled the base timing with the engine idling at about 600RPM with the timing bypass connector unplugged and it read +4. So if that's correct the mechanic who installed the engine was just a hair off.

 

600 rpm is fine.

 

anybody got a pic of the timing tab to make this clearer ?

 

One of the parameters that is set in the prom is the base timing. It comes from the factory set at 6 degrees BTDC. The ECM then uses a table to decide how much timing to add based upon other parameters ( speed, rpm, tps, etc). I think you'll find it runs best when your actual timing matches the PROM, If you want a more advanced spark action, then modifying the tables is pretty easy using Tunerpro, but be aware that it doesn't take much to get into some serious pinging. JMHO

 

Here we go with another bump.

I reset my base timing to 6* which really helped the motor run much smoother. Before it would hesitate badly with a light touch of the throttle until warm and now it runs exactly as it should regardless of temperature.

HOWEVER, I was thinking of running 10* and seeing if I get any knock. The motor in my car is a 9:1 compression motor with 14cc dished pistons and 53cc 601 heads. I did some researching and found out that dished pistons with small combustion chambers is a very good combination when it comes to avoiding knock and was hoping that a 10* base would be do-able on premium gas. What do you all think of this?

 

Shouldn't be a problem. Many people get away with more than that.
It all depends on conditions, - temperature of the engine and how much you're loading the engine.
For instance running the temp up to 220*F and lugging the engine in high gear will cause knock, even with premium.

 

Advance it a few degrees, does it run better? If yes, advance it a bit more, does it run better? Repeat until it runs worse then go back to the previous setting.

 

I am new to TPI but not to small block Chevys, and am wondering what about total timing. You guys are all taking about base timing, if you are adjusting the base timing that will affect total timing. You could be gaining torque lower in the powerband and losing HP / causing detonation at full advance in the upper RPM range tuning it this way.

For instance, my 350HO crate engine ran 12.6's at 108 with 38* total advance, retarding the timing back to 36* picked up 2 MPH and 3 tenths.

Also, nobody has mentioned yet that without a start retard, advancing the base timing is harder on the starter.

Just some food for thought.

 

Also, nobody has mentioned yet that without a start retard, advancing the base timing {to far} is harder on the starter

fixed for ya.

Yes, there is a point of diminishing return on timing advancement and every motor will be different in what they want to run good.

 

I have mine on 3deg- in your tune you need to program the base timing, the ecu defaults to this with cranking and maybe limp home- your timing maps take over for regular driving. RBob is the guy to talk to.
You need to set this up right, I wasn't aware of this when I changed my truck from TBI (0) to TPI (6) so was running 6deg retarded all the time until I found that scalar.

 

Every motor is different. That's why adjusting it in small increments until it runs best is the optimal way to set base timing without reprogramming. You'll find that your base will be somewhere between 0 and 8, not enough to affect start up timing (which the ECM pulls it back anyway). There's no way someone's going to find an optimal base setting much more advanced than 6 degrees, that would add too much timing on the top end.

The other consideration this method discounts is the possibility of a slipped, or mismatched timing mark.

 

The ECM initial timing is set for 6 degrees btdc in stock form. This is with the timing wire disconnected. If you change that setting manually it changes it across the entire spark table. In other words, if you set it at 10 degrees that will add 4 degrees at every mapped RPM setting in the spark tables. Also with the wire disconnected, and at 6 degrees, the engine may not necessarily run best but when you hook up the wire and the ECM takes over, it should be optimal.

 

Can you guys explain to me what point on the tab means what degree? or possible show me a picture? im doing timing again this weekend and would like to know where the the timing mark needs to be at what point

 

Here you go. This one is pointing at 8 degrees but you get the point. 6 degrees is the mark between 4 and 8.

 

Something else worth mentioning is make sure you are looking at the timing tab straight down relative to the angle it is fixed to the block.

The amount of space between the balanced and tab is enough to make it appear +/- 2 degrees depending on the angle you are looking at it by.

 

you can run 8*-10* BTDC and see a gain. but your emissions will suffer, so just be aware that you will probobly have to back it off a little bit before you go through inspection if you live in a state that requires it

 

Just be aware that if you do that, it will not match the initial timing setting in the programming and you will be taking those extra degree off across the entire spark table. In my opinion is it is best to leave initial timing alone and tweak the tables at whatever rpms you feel it is needed if at all.

 

i am running my stock 305 TPI at 10 deg BTDC.i have a 30 over motor with cast flat tops and 416 heads.initally i set base timing at 4 deg BTDC .it hesitated, bogged ,and had generally sucky mpg.setting the time forward helped with all that and i notice no problems