Black LS1 T/A

About how many degrees of timing do you think would equate to the number of points of A/F Ratio decrease (resulting in the same amount of power loss)?

IOW, if I start at, say 19 degrees of timing, and get 2.5 degrees of KR, then I can

1. get zero KR by dropping to about 16 or 17 degrees of timing.

OR,

2. I may be able to keep the 19 degrees of timing and lower AFR from, say 11.7 to, say 11.0.

Which scenario of zeroing KR is likely to result in the best power gain (or worst power loss)?
Which is likely better? Reduce timing or add fuel.

This is disregarding other methods of handling the KR, like high octane, Alky, small shot of nitrous, water injection, etc.; just running 93 pump gas.

Thanks!

cablebandit

iTrader: (37)

I say drop timing. You never know when you are gonna get **** gas. I don't see much power gain/loss with a few degrees of timing myself. Hopefully others will chime in.

Black LS1 T/A

Thanks, CB... I'd love to hear other perspectives. I noticed Harlan running 10.5 AFR.

Pro Stock John

iTrader: (34)

I was told by one noted tuner that timing was more important than AF.

Most of my dyno pulls were at 11:1 AF.

98Zam

Do you mean important as in pulling the timing is a better solution compared to adding fuel?

Slowhawk

iTrader: (12)

Agreed You also want no KR at all.1 degree of KR hurts more hp than the 1 degree it indicates.I bet your car would be better with 15 degree's than the 19degree's with 2 degree's of KR.

smokinHawk

iTrader: (48)

i think if your running over 1000 ***** you need more of a safty factor hense the 10.5:1 AF he had.
think most guys making that much power have it set around there

Black LS1 T/A

Between the two:

Leaner = More power
More Timing = More Power

I take PSJ's statement to mean it is better to get as much safe timing as possible... at the cost of being rich, rather than to run as safely lean as possible... at the cost of losing timing, to pick up the most horsepower.

jimmyblue

iTrader: (11)

When you get close to proper power mixture, then
spark makes more incremental difference than fuel;
the power/AFR curve has a "flat top" (+/- a couple
of points makes little difference).

Your spark also has a "flat top" but here you are
"clipped" on one side, nearby by the detonation
limit. So right about the time you are losing power
to excess advance, you are also picking up knock.
Supposedly best spark is about 2 degrees before
detonation for peak torque at any point.

Now, you have to distinguish between the KR you
get on transient throttle, and any sustained ping
you would get if you were maintaining a 100% TPS
and a good solid load. Like what you see in 3rd, 4th
gear wide open should determine your timing limit
for steady state, and use other means to squash
any transitional ping. But in the 1/4 you have a lot
of gear changes and transitional stuff going on that
can put KR all over you, even though the spark is
pretty right in a steady-state sense.

The more you go into power adders and stuff-that-
eventually-might-go-wrong, the more you want to
"err" on the rich side. Error, that is, until stuff does
go minor wrong, and the "error" saves your ***.

When I dialed my WOT mix in from 11.6ish to 12.8:1,
I did not find any need to bring down timing. But my
advance was set up based more on transitional KR
than steady-state. I see 30, just barely, at the big
end.

S_J_H

I think stock K.S. are a waste of time. They will never save your motor from detonation. You will not find any of the aftermarket efi systems using a K.S. on a powerful motor because they simply don't work. So using them to guide your tuning to the detonation threshold is not a good idea. I deactivate mine to take them out of the loop and rely on a proper tune up.

here are some general forced induction tuning effects from Kenne Bell racing as determined from extensive dyno testing-
1.5 octane supports 1 lb of boost.
1 AF Ratio= 2 octane
20 degrees charge temp= 1 octane
1' spark advance= 1/2 to 3/4 octane.

If you figure your motor can run on 87 octane as it's detonation threshold fuel, and you add 8psi boost, you now need to find a way to get the equivalent of 99 octane.
If you can keep charge temp near normal then that puts that parameter out of the equation other wise you'll have to figure that in, you could drop A/F from a N.A. 13-1 to 11.5-1 and pickup 3 points. Retarding timing 8 degrees gives 4 points at least. Use 93 octane and that's another 6 points.
Total=13 points and should work out unless you have a poor intercooler.
Just an example on how to go about a baseline tune up when using a fuel of suffucient octane is out of the question.
Use common sense. You can only push any of those effects so far before they reach a threshold.
Steve

Billf6531

Now there's a useful post.

Black LS1 T/A

Thanks, guys. Lots of good info.

But, I don't know if my basic question is answered. Let me ask another way:

If you were sitting at 19 degrees timing with A/F of, say 11.4:1 and was seeing 2 degrees of KR, what would be your choice to eliminate the 2 degrees of KR yet retain the most power?

a) Decrease timing?

b) Decrease A/F ratio?

Choose: a or b

Grant B

Knock sensors a waste of time? Do you know how much work goes into good knock sensors? I don't know if the LS1's setup is good or not, but there is a lot of hardware involved in processing knock sensor signals, and some is better than others. I agree that on a race motor that sees the same (good) gas all the time it doesn't really matter. But on a street car that sees all kinds of crap they can be very usefull.

I would try both and see which traps better in the 1/4 mile.

My last car, a single turbo Supra, liked a 10.5:1 a/f on pump gas. All the other Supras I knew ran ~11.5:1, and they all said mine was too rich. But it trapped the best at 10.5:1, intake temps were low, and timing was good. I even got the injectors balanced, still no difference. It would rather run at 10.5:1 with higher timing than 11.5:1 with less timing. But, all cars should be a little different with different setups, engine tolerances, etc.

S_J_H

If a forced inducted( or nitrous) motor gets into any kind of real detonation, in order to stop that detonation once it has begun, timing needs to be pulled back massively on the order of 20 degrees retard or more to stop the detonation process in the cylinder. A couple degrees of spark retard once serious detonation as started will NOT do anything to stop it. Detonation is a very evil process once it has started and it takes a lot to stop it. The best and only real counter measure against detonation is stop it before it ever begins. If they were effective then you would not see factory motors with stock pistons shattering left and right.
You can try and program the pcm to remove a lot of timing with knock sensor activity to actually make them effective. However this is EXTREMELY difficult to do without having them pull to much timing whenever they have been triggered.The pcm's knock learn feature makes this even harder.
I have run straight race gas in my motor N.A. and detuned with only 14' advance and still saw sensor activity all over the place with no rhyme or reason. These sensors were designed for factory motors with stock output. They were setup for the occasions when 87 octane or poor fuel might cause some minor spark knock. MINOR spark knock. Not piston shattering, bearing hammering, cyl wall shattering detonation.
I put a lot of time into the ls1 KS over the last 5 years and eventually just took them out of the loop.

I agree though, run a richer A-F mix and more timing for best power. But no richer than 10.5 -1 or power will drop off quite a bit and you may risk washing down the cyls.
Steve

Grant B

I think maybe it depends on the knock sensor setup. As you probably know, knock sensors are just microphones. The ECU does some heavy number-crunching to split the signal up into its component frequencies (FFTs). The specific frequencies the show knock can vary from engine to engine, dependant on bore size, combustion temps, any probably some other stuff I don't know about.

In theory, a good knock sensor setup could detect knock the moment it happens. A bad setup (such as the amplitude types, used by some standalones like the AEM EMS) can't detect it until it gets pretty bad, since it can't distinguish the knock noise from the rest of the noise in the engine.

I never got my Supra's knock sensors to show false knock. In fact, I don't think I've ever heard of a Supra ECU showing false knock. I think its because of their ECU, and how it interprits the noise.

Just IMO.

Black LS1 T/A

With my engine, I don't hear audible knock, yet I get KR from time to time (I've heard knock on my stock engine before). I think an engine cammed up, headers with exhaust sometimes so big it bangs occasionally under load... just the louder setup in general... can't that give you false KR? My builder thinks I should be able to run more timing and has suggested to try to use audible knock as a gauge as well as the PCM safeguards.

This can all be a tricky business.