Timing

[geneass]

well I've tuned with the MAF, I've converted to 2 bar and the ve is 0-4% in the "used" cells. after getting everything working and understanding what to do with the data-this has been fun. I've got a new question(imagine that), what do you guys do to find the best timing? (without a dyno)

[Srblacks13]

Im about to tackle this also. I made a graph for knock retard and then a custom parameter meausing horsepower so I can see if its helping or hurting.

[kingtal0n]

dont ever depend on knock sensors to adjust timing


I guess timing values at first but thats after 20 years of tuning all kinds of engines.
For the LS platform, mostly stock engines at 100KPA prefer 20-25* of timing when using 93 octane after 3k rpm
It depends on fuel quality, temperature, rpm, combustion chamber qualities, technology, and more...

Some example conservative numbers
LM7 5.3L Turbo using 93 octane:
2500rpm and 18psi of boost: -2* to 0* of timing
2800-3200rpm and 18psi of boost: 4* to 7*
3500rpm to 5000rpm and 18psi of boost: roughly 9-10* of timing
After 5k if torque is falling off push an extra 2* by 6500rpm


Notice timing increases with rpm, slightly, but also notice that near very low rpm (below 3200 especially) the timing needs to be very very low for boost engines or it will bend a rod.

If in doubt pull timing out

Watching EGT will give an indication if timing is too far retarded. It works best on a load dyno where you can steady state the engine (hold it at, say, 3000rpm, and adjust timing until EGT drops significantly)
Another way to do similar thing is make pulls on a chassis dyno, add timing, check torque. Torque, EGT, cylinder pressure, and timing, are all interrelated.

So going back to my car, heres how it 'played out'
Because it was my first LS engine, I played it 'safe'.
Low timing is always safe, as long as its low enough. It will create a high EGT, but this is only a danger if you keep your foot in it too long.
You don't want to hammer the engine for a long period of time. Just a couple seconds to see how it 'pulls' SOTP feeling.

there is a timing "plateau" where torque falls wayyy off (noticable without a dyno) and EGT skyrockets, like this:


So, if you are like me, you don't have or want an EGT gauge. I didn't want an extra hole in my exhaust system, In fact I don't even have narrowband O2 sensors for this reason.
SO the only way to tell if timing was doing anything at each interval RPM was to find that timing plateau by SOTP
Basically pull out timing and give it a little pull, you will feel the car massively slow down at some reduced timing number.
Add a couple degrees back in, and walaa you have found your first potential daily driver timing setting.
Add a couple more degrees and make sure the car 'feels the same' and then pull those extra degrees back out.
Yeah they are probably worth something (more timing will almost ALWAYS give you "more" torque) but it might not be safe when things get hotter (longer pulls) so save that for the dyno day.

That is basically how you can set it before you take it to the dyno, you street tune for the minimum timing by SOTP, and if possible verify the EGT somehow (I don't bother, just take it to the dyno)
This method makes a lot more sense when you have boost because each "line" in the VE table and timing table is reflected in a setting on the electronic boost controller. In other words, you tune one line of boost (say 3psi) then turn the knob slightly which raises the boost (now 5psi) and re-tune again. Timing goes down as boost goes up.

however with an Naturally aspirated engine it is far more simple. The engine can only run at 1 distinct pressure at WOT (more or less).
This can actually make things quite complicated when you read online about timing these naturally aspirated engines, because as an NA engine does not have a "boost control dial" You have no way to increase power without adding timing or changing engine parts.
So while with the boost dial you don't need any timing to make power (just turn the dial) with the NA engine it becomes increasingly tempting to add more timing in search of more power.

Don't do it without a dynometer, and significant testing in very hot/harsh conditions, if using 93 octane.
The fuel factor is the biggest issue. 93 octane is severely useless when the temperature is very high inside or around the engine. IAT, cylinder wall, head, coolant, valves, ports, they can all get very hot and this affects the timing. It can get so hot that no matter how much timing you try, the fuel will still explode violently and damage the engine. I mention all of this because it is a factor to be aware of... In some swaps the heat of the engine is not handled properly and 93 gradually becomes more and more violent as the timing window closes up.
So for example if you take a car to the chassis dyno and find that you can run up to 27* of timing without knock, and the plugs look good, etc...
Then you get out on the actual road and heat the car up really good with a highway drive or something and suddenly that 27* is damaging to the engine.
So to say that 'finding best torque/timing' on a chassis dyno is 'important' is not really true. The engine will rarely run best at the track or on the street with the final timing numbers used on a dyno to generate the most torque.
Tuning for torque isn't the same thing as tuning for acceleration, and tuning for ideal steady state torque timing isn't the same as tuning for ideal track acceleration.

Okay, one more thing to watch out for

vehicle weight and gear ratio play a role in the rate of acceleration. when I say rate of change of RPM I am referring to the 2nd derivative of angular position, the first derivative of angular velocity.
In other words, 1st gear runs up the rpm very fast, whereas 5th gear causes the rpm to rise slowly.
In fact if you could keep pulling gears, 7th 8th 9th eventually you will get to a ratio that causes the engine to decelerate, even at WOT.
This is how engine dynometers often work, they hold the engine at each interval RPM (just like a steady state dyno) except they do it quickly so the engine still sounds like its 'accelerating' but its a completely different thing that a chassis dyno which produces a constant load (same weight roller) as opposed to adjusting torque at each interval to control the rate of change of engine RPM (like when changing gears)
Anyways

The key is to realize that vehicle weight and gear ratio play a role in engine timing.
For example if you put a 5000lb truck on the chassis dyno, it will take alot of timing because the roller in the ground is light compared to the truck.
The dyno will report much more torque for additional timing because the engine can accelerate freely.
Imagine for a moment if you stab the engine WOT in neutral- what happens? It zings to redline instantly, right.
So what sort of timing would work for that quick shot to the rev limiter... 10*? probably. 20*? Yeah very likely.
30*, 40* it all works. It all seems to work. The faster you can accelerate the engine, the less load the more timing. Does it make sense?

So if you get this big heavy truck on the roller and make peak power passes, then put it back on the real road where it accelerates "the real roller" (the drivetrain) in gear more slowly, especially in high gears (overdrive), the same number that worked for peak power on the dyno is now a deadly dangerous over-timing.

So this is where experience helps alot. If you know the roller weight, and the vehicle is within the same range (typical 3000lb cars are very close to the 'smaller' dynojet rollers I think) Then the timing will be similar. Furthermore you should take into account vehicle application load range, for example if the vehicle will be used at WOT in OVERDRIVE then it will use less timing than the dyno pull in 1:1 gear which is typical for sure.
Just as a general rule, never use the same max timing that gave a peak number on any dyno, on the real road. Always pull it back a couple degrees. It should still be so far from the plateau at that point it won't barely budge the EGT.

Sorry this is so long and kind of meanders but I just felt like sharing a bunch of info

[Srblacks13]

Thanks.

[ttz06vette]

Meth changes everything for ability to add timing with boost

[kingtal0n]

While its true that methanol significant raises fuel octane

And that more meth = better

shit why not just spray 100% meth forget gasoline all together...

That is the attitude of many meth addicts... and while it is perfectly true that methanol is an incredible fuel...

The down side for street applications is that eventually the system will stop working. Methanol pumps have a life expectancy and eventually fail.
They are a 'disposable' part, almost, and replacement is necessary after significant use.
Furthermore there can be complications with running low (typically how disaster occurs), clogs, faulty fittings (ive seen the meth nozzle literally fall out of a pipe before for some reason, wasn't my car) and other small issues..

My point being that. Although methanol is incredible, if it ever stops working for any reason, the engine could be trashed instantly.
For this reason I do not lean on methanol, and I do not recommend tuning for additional timing when using methanol.

You CAN tune for additional boost pressure, however, because there is a big difference between over-timed when the meth shuts off, and over-boosting when the meth shuts off.

When the meth quits unexpectedly and there is any additional timing "meth timing" the engine will immediately be forced to use LOW octane fuel (93) instead of the 100+ octane meth system fuel, pressure spikes instantly in every cylinder and the engine could explode violently or rip a hole in something.

When the meth system quits unexpectedly and there is any additional boost pressure "meth boost" the engine will immediately be forced to use the LOW octane fuel (93) etc
however because the methanol system has JUST shut down, there is some residual cooling in the cylinders and intake air pathways which will temporarily raise the detonation resistance of the engine. If there was enough methanol spraying and only a little bit of additional boost pressure the engine should be safe to run for a short length of time- long enough to realize the meth system had shut off and save the engine (some kind of indicator light would be nice)

In short, I use meth systems as boost pressure "safety" feature, to squeeze a couple extra PSI (say from 15 to 20psi on 93 octane) but keep the timing pulled back for pump fuels so the engine will still be somewhat safe even around 20psi of boost without the meth, long enough to save it.
I also tend to keep the A/F influence as low as possible, in other words when the meth system kicks on I don't want to see a big fat a/f ratio drop.
It means you are spraying way too much methanol for the street IMO
Many will argue as above that "more is better" and like I said that is true, however when you spray so much meth it becomes very blurry as to what is safe tuning wise for 93 vs methanol, the fine line becomes blurry and a slight change to the aux meth system can cost the engine.
I typically use 50/50 or 30/70 (mostly water) because water cools EGT and combustion MUCH superior to methanol, residual cooling is more guaranteed, and also it allows you to inject much less (water goes ALOT farther than methanol when we are talking about heat capacity/cooling)
It also helps with the a/f ratio drop (not as much of a drop when using mostly water)

[ttz06vette]

I use 60/40(meth weighted) for reasons you mention and pump life. I get about 5 years out of the pump on a mix. I am limited to 16psi due to my setup and am able to get about 15/16 degrees total timing at peak torque without Kr at about 11.0 AFR with meth. So far it has held up for 12 years. I finally got around to checking my inline meth filter last year and it was as clean as the day it was installed. I did have a problem where my nozzle ripped through my silicone connector, but my trims immediately reflected a problem when it happened.

[geneass]

wow you guys are way ahead of me maybe in the future i'll be able to use the info but for now i'm just trying to get the most out of this cam I just installed.

[jsllc]

Nice to see the detail to back the logic. I always use dyno -5 on timing for cars after they make the glory run. Never had one have an issue.

[JonathanLeskewich]

Thanks, this is the best timing thread I have read! I have an 8.1 twin turbo set up and I thought I was too retarded on the timing running 5-7 degrees at 2500 rpm at 4 psi of boost. Now I know a bit of what is going on because the motor is in a 14,000 lb motorhome so it can't rev quick therefore my timing has to be lower. Still what doesn't make sense though is I seem to be able to run more timing (11 degrees) at below 2000 rpm... but I guess somehow the motor maybe doesn't get as hot...