Perfect timing

[maudyZ28]

Hi all,

a while back I discussed with weatherman shawn about afr and timing, but this was before I had the wideband.

Now I run OPSL with VE dialed in pretty good when driving and fuel at WOT ramps from 13.2-12.9 from 3000-6000 rpm. So just about right for fastest burn speed.

However I'm still running my 99 timing table, which is VERY aggressive, running 28 at peak with only a dip to around 24 deg at peak torque around 4400 rpm. I dont NOT get knock though.

after reading this again that weatherman shawn kindly directed me to earlier
http://www.innovatemotorsports.com/resources/myths.php

Im wondering if im actually running too much timing. Such that I am sparking too early and peak pressure is built before TDC rather than after it, ie sparking far too early. For those of you out there running ~ same AFR at WOT, what timing do you run. If according to the innovate link that perfect timing is based on engine geometry then there should be a best timing for a given fueling? For standard LS1 block and heads

The only research I could find was at high load but low RPM where best mean torque timing is about 32 deg, obviously not applicable to high rpm where there is much more mixture in the cylinders to burn faster.

[WeathermanShawn]

Long time Maudy..See ya finally got that wideband..:grin:.

I run a little richer than you at WOT..~12.6. I run 22-25 degrees Timing at WOT, but with higher CR heads.

A dyno will really tell you. But if you really are not getting any KR, I might just stick with the Timing you have...

[maudyZ28]

yeah long time, hows it going?

Finally got one and have chance to get back into tuning, no reports for a year or so :D

I asssumed a dyno day might be only way to run multiple pulls and see which is best, it's too hard to test on the track due to wind conditions, and getting a good laugh on street tires.

Are the LS1 standard knock sensors good enough to detect knock, i've never seem the infamous saw tooth in any logs so assume all is ok. Your timing is pretty sinilar then accounting for higher CR heads.
I might have a fiddle with dropping fueling to 12.6-12.8 ish, don't think it will make much noticeable 'seat of the pants' difference. Although with the fueling right now and VE dialed in it does seem faster and is much more responsive using the open loop table rather than waiting till PE parameter is met in usual closed loop

[WeathermanShawn]

The Knock Sensors on my LS1 are right on. Some may even think too sensitive, but as soon as my ear hears pinging it shows KR.

You might try some tests on your sensors to make sure. Maybe your gas is just better there? I might try your test on a Dyno.

Do you ever hear pinging? The sound is pretty unforgettable if you ever hear it.

Otherwise, consider yourself lucky. Most of us always have to fight KR..:).

[maudyZ28]

nope not heard anything, my grandad is a mechanic and says i'd hear it, if it's there? Dunno, I have LT headers, de cat, true duals (3") and its loud when at WOT?

only time i've seen know retard is one spike etc but no saw tooths, which i presume would make a constant pinging noice? Hopefully all is good, might up timing a bit? and keep and eye out for any knock that way. I'll see what the others put regarding timing.

The strange thing is my pal has had a tune, by a 'pro' apparently, but i'm sure it's a fugde tune. either way his car commands 13.0 AFR and only 19 deg of timing as it knocked at 22?? very strange. I told him to get a WB and let me log it :D

[eficalibrator]

By the time you can actually hear the knock over the exhaust, tires, wind, induction, or whatever chances are that you're already into it pretty good.

The only way to be sure if you've hit the best timing point is with a dyno or in-cylinder pressure transducers. The dyno runs are usually much cheaper in this arena.

[joecar]

My understanding is that even if there is no audible knock, the combustion chamber temperatures are elevated (i.e. just because it can't be heard doesn't mean there's other potential damage occurring).

A dyno really is necessary to explore ignition timing... if there's no knock then the minimum advance producing best torque can be found.

[Sid447]

Are the LS1 standard knock sensors good enough to detect knock, i've never seem the infamous saw tooth in any logs so assume all is ok.

....... rather than waiting till PE parameter is met in usual closed loop

Hello maudy,

IIRC GM changed the KS part number around MY 2000-or 2001, you might want to double-check that as apparently the later ones were "better."

It's possible to get rid of virtually all of the PE delay, CL logs I have show between .170 and .205 sec with an average of .188 for PE to activate once the rpm/tps parameters are met.

[SSpdDmon]

I'd say - timing alterations/improvements need to be measured on a dyno. The next best thing is a race track where you can measure changes over a sampling of trap speeds/ET's. Ideally, you want the best results with the least amount of timing. Personally, I'd dial the AFR into something good, but safe (like 12.7~12.8:1). Then, make changes to the WOT timing a little bit at a time (1 maybe 2 degree changes). In other words, make a change, make 2 or 3 pulls/passes, and review results. As you make changes, you're not limited to all or nothing. You might be able to see gains with 3* up top, 2* at peak torque, and 3* in the mid range. That's why a dyno is prefered. You can really see the effects at all RPMs.

[maudyZ28]

thanks all, well at present is the car safe if i'm not hearing or detecting knock on the sensors? I've read something somewhere saying most cars turn them off at 4000rpm + as they cannot detect knock over other engine noises? is there any truth in this?

Currently my fueling is dialed in just like the autoVE shows, is the general consensus that from about 4000-6000 at high loads it should be more in the 12.6-12.8 area?

I'll look into dynoing the car, last time I asked one guy he said it was £400 for half a day, I know its necessary to see the whole power and torque curve but I spend more time at the track which I pay to run in the bracket series. To be honsest i'm not looking to squeeze the last 1 or 2 hp out of the car with exact timing on the limit, just want to do the best I can safely but better than stock! :D

[SSpdDmon]

I'm pretty sure I've seen KR over 4K rpms before. So, I don't think they deactivate. Their sensitivity levels change though. IMO - if you're looking for an improvement, but want to stay safe....stay within 2* above stock timing and keep an eye on the knock sensors the first couple of times to the track. If it seems to run better times without knocking, I'd leave it at that and call it good.

As for AFR, I would say yes - 12.5~12.6 is a good target for peak torque and 12.7~12.9 is good for peak HP. That gives you a little buffer just in case.

[joecar]

Yes, I have seen KR above 4K rpm.

[maudyZ28]

i dont plan on going past stock as it is 28 deg already. I was wondering as I mentioned to Shawn, my pal had a tune by a 'pro' and he can only run 19 deg of timing from 3500+ otherwise it knock loads? his commanded fuel is about 13 deg but i'm not sure if it is a fudge or not. I was probably more concerend that I was too far the other was with too much advance causing me a power loss, but thinking about it that would prob require 40+ deg of timing for peak pressure to occur much before TDC. I'll have to wait till the track, rool on 2 weeks :D

thanks again guys

[SSpdDmon]

Model year matters too. The newer cars with the 241 heads and the newer intake design don't take as much timing as the pre-2001 cars. So, don't necessarily put too much concern into your buddy's car only taking 19*. As for going above 28*, it's not some magical number. The LT1 cars ran 34*~36* of timing IIRC. So, try like I said - add a little. If it works out for the better and you're not seeing any problems, keep it and enjoy. :)

[maudyZ28]

oh yeah, i didn't think of that, i've got the poo 99 853 heads :(

i was just interested what everyone else runs for a given fueling, as per the original file I link at the start of the thread, timing is based on engine geometry so for a given fueling there is an 'optimum'. However as you say, i dont know how much difference 2-3 deg makes, 5-10 hp but danger of knock. I'll see how I get on, need someone to watch for knock like a hawk if I tune it in, hard when your by yourself on the strip :D