Kind of a general question, I know many factors are involved. I was looking though some TBI tuning notes I've acquired and came across
"What ever you do, don't think you need more SA to make more power. The better the engine, the less SA it needs "

I ask because I'm starting to get a few knocks in areas that previously didn't with more timing. I'm been tuning like a crack addict for months and wondering if I'm starting to get it right or not. Mechanically, things are pretty good. No stuck lifters, etc.

Thanks guys

 

Usually a leaner tune will detonate sooner than a rich tune. It's VERY common for guys to throw timing and fuel at an engine and have it "feel" good. In reality the extra fuel is covering up the detonation and you are really not making any more power. Grumpy tought me that!

 

The other thing is you can also get too much timing advance and it will actually start working against you and you may not be getting any knock counts. Thats where I'm at now. I am running 30 degrees advanced at 65 mph and a MAP of 60 to 65 KPA and it should be around 50-60 KPA. I've dropped timing down to 26 degrees at 65 mph but haven't tested it yet. Fast305 or might be Fast355 on here told me when tuning your timing curve set your advance to what will give you the highest amount of vacuum with the least amount of timing. Any more timing and the combustion process will start to occur before it should and will start pushing the piston back down before its even finished the compression stroke.

 

TRUE TRUE TRUE
It's been said before, you want the MINIMUM advance consistant with best performance.
In other words, an extra degree for good measure is a REAL bad idea.
A degree LESS for good measure, is better.
Ideally, you want zero pressure building in the chamber before TDC, and as much as you can get before the piston outruns the burn rate after.
In nearly ALL engines, this means peak pressure between 10 and 20 degrees after top, depending on rod/crank throw ratio. The vast majority, 13-17.
If it's knocking, back it off ! Most say about 2 degrees, I say 4 or 5 in that cell. My own research shows the ideal window about 5 degrees wide for something like 0.02% difference. ( that's 0.02% NOT 2% )

 

yeah, I've reduced most areas by 2-3 deg. no knocks, little smoother. I agree with the least amount as possible...want the push on the piston as it goes down!!

 

Excellent Post Mr 91chev71.
This is good timing for me (pun intended)

So if I (we) were to run the vehicle at 1600 40kpa and 35.51 deg (80kph) could I lower the timing to 30 deg and expect that my VE would get richer and my kpa might move to 30kpa?
My tps should decrease as well - right?
Assuming 80kph

 

Not necessarily !
You could be going late enough that the piston outruns the flame, and you get poorer performance.
Depends on where "in the window" you are now.
If you have a 5 gas, you should see the HC go down, but lacking that lots of false indications could occur.
Truth is, 5 degrees isn't enough to greatly lose much, unless you are near the edge of the window. Then performance could drop rather noticably.
Remember, you want combustion pressure to build as soon as possible after top center, but NOT before.

 

2 degrees less timing cost me 5 HP at 5400 rpm. That's at WOT, though. My PE SA was 3.11, reduced to 1.25, lost 5 HP. raised it to 2.25 deg and picked the HP back up. Less timing, same HP. pretty cool

 

more efficient heads require less advance, not much of a stretch to say that your most efficient(powerfull) burn would require less timing. if you're truly becoming more efficient, you should have the least spark advance required by the head.

 

without regard to WOT timing for max HP could one establish a more optimal timing at cruise speed? say 50 mph-60mph-70 mph. that is datalog what your change in timing (plus-minus 2 deg) may have affected your speed. IOW if you are at say 30 deg at 60 mph (AT 10% TPS) and you deviate by 2 deg either way and see speed increase to 62 (AT SAME TPS) and not pick up KC would that not be a good thing?

could not the same be said on trap speed in 1/4 mile or whatever distance you chose to log. If max MPH in the 1/4 is 100 and you change timing by 2 deg either way and see improvement W/O KC again a good thing?

Beyond my spoke of knowledge but I thought I read temp of oil can also be logged ?????

 

Last night I loaded up 5 bins into my prominator (thanks Bill/Ken) each with different timing (same VE)
I used a flat road and logged a 1600rpm run in each direction. I used a power pole as the start/ stop for each run. I filled the 1600 row with 29,31,33,35,37 deg of timing in each of the bins.
The results are noted below

#1 - 28.12deg 5.5tps 33.2map
#2 - 30.94deg 6.0tps 34.7map
#3 - 33.05deg 5.0tps 30.3map
#4 - 35.16deg 4.6tps 31.0map
#5 – 36.91deg 5.5tps 32.9map

If you graph the results in excel it shows that I should be using ~33.4deg at 1600 – 30map.

This is an 82vet, 350ci, no cats, egr disabled, th350tran, 7747. Engine is almost stock. Premium fuel - 2100’ – 25deg C

 

You can use the TPS position or injector duty cycle/pulse width for a given MAP/RPM combination, or speed on the same stretch of highway as I understand it. RPM and MPH are directly linked, so timing changes will not show a difference. Regardless of whether you are running 20* or 40*, if it is at 2200RPM at 60 MPH it will always be at 2200RPM at 60MPH provided you are in the same gear and/or converter condition (locked up or not).

The Vette BINs have the oil temp capability, the F-body binarys do not. No oil temp sensor on the F-body cars, either (though one could be added if you can find the right ECM pin for the output and change the binary to read it...)

 

I edited my post to add a TPS constant. Does that seem accurate?

 

Ron,

My post above proves exactly that. You want the timing that yields the least amount of tps and map for a given rpm.

In my logs for the tests above the blm changed with the timing (no surprise) the best blm was best between test 3&4 which both had 128:

Blm were 127,129,128,128,132

Hope this helps

 

Ron - Sean is right. But I think you're still thinking about the RPM and MPH changing - those two are locked together. If one changes the other one does too.

As Sean put it:
You want the timing that yields the least amount of tps (or injector duty cycle/pulse width) and map for a given rpm.

 

Sean's got it right !!
You must first define performance.
Then, wash out variables. ( TPS is much to much of a variable except on a long-term average )
Personally, since cruise is not a race condition, I'd be looking at fuel economy as the benchmark, though the MAP required to hold speed, assuming no change in wind, should be equally as valid, but maybe not.
Leaner will usually require more TPS, and more MAP, but still produce better economy if the timing is adjusted to produce the max output from the leaner mix.
Depends how you define "better."

 

I'm gonna do some test runs like Sean82 and see what happens. Nice to have 8 slots in the flash EBL, beats burning chips!!!

 

I did some tests last night at 2000rpm
timing was best at ~34deg

I went back and lowered my entire main spark table to suit
Could someone please give me some guidence on the spark at say 3600 30kpa? should I have more spark than 34deg?

The stock timing table seem to have way to much timing, why do they have so much?

everything I read on this forum tells me that I am on the right track, but it seems very different from stock

 

Then, at 2000 RPM and whatever MAP you had, 34 is what the engine wants.
Possibly.
My mill likes lots of advance at high vacuum low map. More than most would think, but the motor likes it. As much as 42 at 20 map, BUT as low as 11 at 90 map. ( 3000 RPM or so )
AND, it's NOT linear.

At high map low load conditions, you'll generally see more. How much depends on your engine, and what it wants. That's why we had vacuum advance in the old days.
Remember, stock is a compromise for McTiming. All things to all people, and is NOT optimsed for you, or for anyone in particular.
I consider it a place to start, and don't expect a whole lot of deviation on a stock vehicle, but I consider it to be nothing more.

 

here's my latest timing stuff. It seems a little low, but it doesn't knock and runs pretty well. I idle at 20.39 deg with the EBL's IdlSA option code, FWIW

I'm gonna try Fast's timing stuff and see if I get any knocks anywhere. It's a little more steep in the lower MAP areas, but it shouldn't be too big of a deal

CUrrent SA
NOV3.JPG


Fast's stuff w/ a tiny bit of smoothing
modifiedFAST305.JPG

 

wow this thread needs to be stickied.
i just am at the point where i have a descent baseline for VE and SA, and had nooo idea you could end up covering up detonation with fuel and not even know it.

figured get the ve table close.... then bring SA up until you get retard back it off a degree or two then add just a little more fuel to compensate for the extra timing and you should be pretty close

this is definitly a more scientific way of doing it tho lol
im gonna read this all again when its not 3am

 

If you think so, then you need to post it in the link below, which is a "sticky" to identify it as a "useful post". But we don't make any individual post a sticky anymore as we eventually end up with the entire front page being just stickies - like we had before...

So we just add them to that sticky link I posted below to identify it as a useful post and to possible included it in any future re-writes of the tuning guide.




https://www.thirdgen.org/forums/diy-...ns-needed.html

 

Well, Fast's table works better. I changed it a little, but this spark table works great for my truck.
Here's what I'm using


latestspark.jpg