After reading lots of posts on timing, I am wondering if it really does anything to these 305 TBI engines. As someone stated in a post somewhere on here, the cars are set at 0* base from the factory for a reason: The swirl port heads. The factory chip and ECM are programmed for this 0* base. How does increasing the base help performance and gas mileage? If it helped gas mileage, why didn't they do it from the factory? This engine was made as a sturdy, emission friendly, good MPG V8. It was designed to run on 87 Octane fuel, not 93.

I have been running my RS at 2* base timing for the last 6 months or so and I do not feel much, if any difference in power. I had it running at 6* when I first changed the timing and it was popping all over the place. I left it set at 2* to see if I really did get any power or mileage increases. Contrary to what is believed here, I don't feel any power increase, and my MPG are actually lower at 24 MPG highway. Before I changed my timing, I had all new sensors put in when I did my intake swap: new plugs, wires, cap, rotor, IAC, TPS, rebuilt the TBI, O2 Sensor, CTS, EVERYTHING. I was getting 26 MPG all day long, but after changing my timing I have gotten no higher than the 24. I run 89 Octane with the 2* advance. I am going to switch back to the 0* in the next couple days and use 87 Octane.

Does anyone have any real proof, numbers, charts, that show increasing the timing does anything good for the L03?

 

This weekend I am going to a Dyno. If I get my way I am going to do 3 runs with 3 different base timigns: 0*, 4*, and 6*.

Right now, I'm at 8*. Maybe I'll start with that and then go to 4* and then zero. I'm guessing you've read this thread. So if I am lucky, I'll have results from 3 different timings to show you aftyer this weekend. Who knows what other factors will confound my experiment?

 

TBI motors with swirl port heads do not need a lot of base timing. That is one of the inherent properties of swirl port heads. Other stock heads need some advance to run the way GM wanted them to (don't have as much swirl so timing is added to aid combustion). The reason why you don't see any advance at all is for safety and emissions reasons. A few degrees more in your timing curve can drastically effect emissions. GM also dialed in a worst case secenero timing value to accomodate for the possibility of bad gas and adverse engine running conditions (super hot etc etc). My car ran best ecomony wise with 4° adavance and no more. I have no track time to quantify the slight boost my butt dyno detected. The only gains I saw were at the pump. Any more than 4° caused excessive audible knock and I didn't feel like paying for 91 octane to use it as a band aid.

 

I picked up 10hp and 8 lb/ft with just a K&N and advanced timing to 8*. . . I don't know exactly which part contributed the most, but that's what I got.

 

FWIW, on the dyno time I have, small timing changes had almost no effect on power output, the big effect was in the AFR. changing timing 2* might make a 2-3 hp diffrence, where as correcting the AFR can get a 10-30hp.

 

Thats interesting Dewey, its the exact opposite to what i saw when dyno tuning mine. I picked up 60rwhp going from 32-36 degs total, but when leaning AFR from ~12.0 to 12.8, I picked up only about 8 hp at the peak... Goes to show they all are different huh!

 

Yeah it does.

Of course, I was going from about 36* - 32*, and taking the AFR from about 11.0 - 12.6

On edit:

The tech.


This graph shows the change in only the AFR, there was no timing change between those two pulls.

With a 4* timing change, on the new AFR there was less than a 5hp change.

EDIT AGAIN:
Maybe this will be the good one. I think this all goes to show that proper tuning in general is needed, Your results showed that your timing curve was way off for you engine, and by fixing that, you found the power there. This motor the timing curve fit, but was being held back by a bad AFR. I am guessing, that fitting the two together is where the big gain is. Not in one or the other.

 

I agree, I think both are definitely equally important and both must be right on the money to get the best results.

I think why so many people advance timing at the distributor and feel a difference is because it tends to smooth out the idle a little. Also, these cars stock are running at most 18-19* of spark advance at WOT with the added Power Enrichment spark. You add 4* to that and you probably would pick up a little extra consider they were soo conservative from the factory.

The problem with advancing at the distributor so much is at cruising areas, the stock cal has about 31* of spark advance. So, the people that are kicking the base timing up to 8* advanced are running 39* of spark advance cruising. This MAY not be bad, and MAY not do any harm but then again it MIGHT knock like crazy or wait until one bad tank of gas to start detonating all over the place.

One thing I've learned is that it is not wise to run your spark advance at the threshold of detonation. That's a poor indicator of how much to run with.

 

To follow up on my original post, I changed my base timing back to 0* and man what a difference. It runs out strong and doesn't hesitat at WOT like it did at 2* advance. I am betting I see better gas mileage too. I'm a believer that these cars were meant for 0* and anything above messes with things too much.