So I'm kinda new to engine tuning and have been reading this forum religiously for the past couple months trying to get my new motor to run decently. Tons of good info here and I would not have gotten to the point I am at now without it.

Anyway, I think the motor runs well (at least in my newb estimation of what I think it should run like). I've got the VE tables setup pretty good and BLMs are anywhere from like 125 to like 131. I also have a wideband O2 sensor hooked up so I know my AFRs are where I want them.

I've been working on tweaking the main spark advance table for quite a while now and from what I gather, there isn't really any way to tell if it is "correct" short of putting the car on a dyno or going to the track. So, I'm really interested to see what other people are running for their spark advance tables or if anyone can tell me if what I have is even remotely optimal. At the very least hopefully someone else with a similar combo can use my table as a starting point.

Here is my current setup:

350 roller block
Summit 152123 heads
ZZ4 cam (208/221 .474/.510)
Compression about 9.1
Stock TBI setup with 350 injectors
8746 ECM

And here is my SA table:

 

are you seeing any knock counts anywhere?

a couple of good threads on spark timing,
https://www.thirdgen.org/forums/diy-...xplained.html?

https://www.thirdgen.org/forums/diy-...g-timing.html?

https://www.thirdgen.org/forums/diy-...l-answer.html?

if you havn't read it yet, this is a good general TBI tuning thread,

https://www.thirdgen.org/forums/tbi/...free-tune.html

 

Thanks for those links. I've read most of them before but some were new to me. I do get a few knocks at 100MAP and like 2400-ish so I'll probably back off about 2 degrees in those cells and see how it goes.

I guess I'm just kind of wondering what determines the shape and placement of the RPM and MAP curves on the graph and how people are arriving on the values they are using. I guess one could drive the car at a fixed MAP and RPM and get a good spark advance value based on TPS, but thats just one cell. How many cells does it usually take to get a decent table and what cells are best to use this method on to guesstimate the others?

 

most of my tuning has been for fuel mileage, highest MAP and lowest TPS, so im pretty aggressive in my cruise area.

with my car, other than a certain area, i shoot for 0 knock counts. but i don't worry too much if i get a few counts during a data log.
also look for the ECM pulling timing out. if the ECM is pulling timing, i pull 2 degrees more than the ECM pulled in those cells.
say if i see counts at 1600 rpm and 70 map and the ECM pulled 3 degrees, i back the timing down 5 degrees in that cell and also the 1500 rpm 70 map cell. if i still see counts, i'll back it down in the 1600 & 1500 rpm 60 map cells and do another log.
you also have to watch your fuel too, if its lean in those cells it can cause knock.
if my fuel looks good, and im still getting counts and i think it shouldn't be, i'll pull some from the 1400 rpm 60 & 70 map cells.
don't forget about the cells above where your seeing knock, you may need to pull some there too.
when you get the spark map working good, you'll be back to the fuel map.

on my car i get a ton of knock at part throttle when my trans goes into lockup in fourth gear.
if you look my spark and fuel tables, you can see im adding a lot of fuel in the 800~1500 rpm 80~100 map range and pulling a lot of timing in the 1000~1600 rpm 90~100 map range.
even with as much added fuel and pulled timing, still i get some knock in that area even with 93 gas. i don't have any knock in any other areas with 87 gas.
i've pulled enough timing that my car has a very noticeable flat spot when its in those cells.
i attribute the spark knock in that area to my less than desirable gearing.

 

I can see that this is definitely gonna take some time. I guess I'll just try and focus on my cruise cells first. Thanks for the info.

 

read this carefully
https://www.thirdgen.org/forums/diy-...s-require.html

 

There are a few basic tips that can get you pointed in the right direction.

The main objective of timing is to ignite the fuel early enough so that the fuel has finished burning and the cylinder pressure reaches its maximum after the piston has gone a few degrees past TDC. This will extract the most power from the fuel. Too early and the piston will be forced to compress the already burned and hot mixture, which can lead to overheating and detonation. The engine can also shudder if the timing is too early due to the rapidly rising cylinder pressure. Too late, and the fuel is still burning after the piston passes TDC. This will cause the exhaust to pop, the engine to run poorly, use lots of gas, cause the exhaust to glow, etc.

With timing at low loads, it helps to keep the timing uniform for the most part when the engine load drops below around 50-60 kPa. This means that from about 20-50 kPa, the engine will see constant SA at each RPM range. This helps to keep the motor smooth. Sudden transients in SA will cause the engines power output to fluctuate, which leads to engine surging or bucking. It also makes it harder for the ECM to control the idle as the engine will hunt as the SA changes.

The part throttle timing is usually a mix of things. Your shooting for engine smoothness, good throttle response, and fuel economy. But, you also have to keep the timing within reason. Ive found that sometimes the timing that produces the best fuel economy and throttle response causes the EGTs to be too high (glowing headers). Too much timing can also cause the engine to overheat as your dumping a lot of heat into the pistons. Usually you'll know when your getting close. The engine will start to run smoothly, have good response and a good exhaust note. Usually you have to play around with the P/T timing a good deal until you find the curve that works best.

With WOT timing, your shooting for peak performance while staying out of detonation. If you have good heads and reasonable compression, a lot of times you can get the peak timing while still having a good margin between the operating range and the range of advance values that result in detonation. Usually the WOT timing starts at around 4-16 degrees at low RPMs and comes to a peak of around 28-36 degrees at around 3000-3600 RPM. It usually doesnt help much to change the timing after 3600 RPM. The cylinder pressure can also effect how much timing is needed. Sometimes around peak VE, you will need to pull a few degrees due to the increased burn speed and tendancy to knock. The best measure for how your timing stacks up is your 0-60 time and a good datalog. Shoot for best performance while still staying out of detonation. If you hit detonation first, then youll want to pull a few degrees around those areas to maintain some safety factor.

Each setup is unique, and there wont be a specific curve that will 'do it', but as a good starting point, you can use similar values to what would be used with a vacuum advance dist. Setting the timing curve up to emulate what would be had with an older non-CC HEI is usually a good starting point with a standard V8.

Below is the timing table I used with my vortec 350. It took a good deal of time to iron it out, but this is ultimatly what my engine wanted.