Timing tuning in boost

[wow]

As the title states

How do i go about this?
I have read that if you detonate once in boost, your engine is done.

I was going to do the typical "back timing off 5* and slowly start adding til it reads knocks then back it off" but now thats kinda scaring me away since the car see's boost.

Turbo LQ4 currently sits at ~4psi making 487whp and 496wtq @13* of timing and 45%IDC

Obviously i want more, but i don't know how far i can push it.
Stock bottom end gen 3
comp cam and valve springs
BTR hardened pushrods

no headstuds, no headgaskets, no rod bolts....... yet. All 3 will be installed before christmas.

Any insight would be great!
Thanks in advance.

Here is a log for reference.4psi.hpl

[5FDP]

You can get knock and still have it live, people do stupid stuff all the time before eventually it kills the engine. How long it takes is a toss up.

Seeing 1-2 degrees of knock is really no big deal if the timing is allowed to be pulled away. If the high octane table has 13 degrees and the low octane has less timing, it can still pull timing away to help.

The rod bolts are not a weak point. The stock I beam rods will break before the rod bolt snaps. You are already close to the limits of the rods if they are indeed I beams. The later H beam rods can handle 800hp no problem but the others will top out around that 500-550ish range.


Your data logs are being skewed as well because you are logging 2 different MAP sensor channels. One channel is reporting 6-7psi and the other is 3-4psi. So you are making more boost that than you think. The 1 bar MAP channel must be removed for accurate data.

If it was me I would keep the timing the same and just bump the boost up 1-2 psi. 13-16 degrees of timing is pretty good on a turbo LS when you want to keep it in the safe zone.

[wow]

You can get knock and still have it live, people do stupid stuff all the time before eventually it kills the engine. How long it takes is a toss up.

Seeing 1-2 degrees of knock is really no big deal if the timing is allowed to be pulled away. If the high octane table has 13 degrees and the low octane has less timing, it can still pull timing away to help.

The rod bolts are not a weak point. The stock I beam rods will break before the rod bolt snaps. You are already close to the limits of the rods if they are indeed I beams. The later H beam rods can handle 800hp no problem but the others will top out around that 500-550ish range.


Your data logs are being skewed as well because you are logging 2 different MAP sensor channels. One channel is reporting 6-7psi and the other is 3-4psi. So you are making more boost that than you think. The 1 bar MAP channel must be removed for accurate data.

If it was me I would keep the timing the same and just bump the boost up 1-2 psi. 13-16 degrees of timing is pretty good on a turbo LS when you want to keep it in the safe zone.

Wow, plethora of information. Thanks
Also, nice catch! I didn?t even notice it. I?ll remove it tomorrow and re-log to see where it?s at.

Thanks again!

[pknowles]

I'm up at 9psi on my stock bottom end 2001 LQ4 with a 78mm turbo and on my way to 12psi. I tune on E85 to be safe and see knock in boost. Still dialing this thing in, but 4-6 psi is not much. If you have e85 in your area, you almost can't hurt the motor at low boost with E85.

[pknowles]

Are you on 93 octane? 13 degrees at 4psi seems very low.

[wow]

you were absolutely 100% correct.
I verified it with my boost gauge in the car [dont know why i didn't do this beforehand]

[kingtal0n]

I have an LM7 (gen3 internals, weak rods) 5.3L
I do not hesitate to push to 550-600rwhp with these "weak" engine rods (~680flywheel HP). The key is to keep timing minimal, IAT low, plenty of fuel (10.8 to 11.2 air fuel on 93 octane usually), and keep the compression ratio low (worn out high mileage engine is great).

Rod strength isn't limited by torque, it is limited by internal stress, just like any beam structure. In combustion engines torque is applied over a range of degrees of rotation, so for example if timing is very advanced there will be a spike in cylinder pressure near TDC which can produce alot of internal rod stress and very little torque, so you can break a rod with very little torque production. Remember that when near TDC it doesn't matter how hard we push down on the piston, it will not produce any usable torque at the crankshaft, because the rod angle is wrong when the piston is up at TDC.

So now imagine the piston is leaving TDC and moving down the bore, we can push really hard (alot of pressure) suddenly (like a "knock" event) Or we can push gradually, over a longer period. Either way you may still wind up with the same amount of torque, but when the pressure is applied suddenly it generates alot of internal rod stress and can also damage the rod bearings. So our goal is to push gradually, with less total pressure, over a wider range of crankshaft rotation. We do this by using high quality fuel (as possible), minimal timing (will explain more in a sec), low compression, cool IAT (cold mixtures), etc...

Minimal timing means you remove timing until torque falls off significantly and EGT begins to ramp up rapidly. This should be done with a DYNO or EGT gauge. Always use ZERO SMOOTHING and a DYNOJET for best diagnostics.
Always use the least amount of timing to produce within 5-8% of max torque and maintain a safe EGT.
here is an example using random engine with boost:

15psi of boost on 93 octane:
18* 530ft*lbs torque, graph appears spiky, peaks are generated by the spikes which makes more torque on the graph, 1200*F EGT (location is irrelevant)
15* 528ft*lbs torque, slightly less spiky but still getting peaks generated by spikes 1200*F EGT
13* 520ft*lbs torque, smooth graph 1220*F EGT
11* 512ft*lbs torque, graph is smooth but torque dropping and EGT rising 1250*F
09* 485ft*lbs torque, smooth graph, low torque, EGT is ramping up rapidly to 1320*F
07* Engine coughs, misfires, won't run properly

So here is where experience plays a large role,
First, notice the spikes in the graph for higher timing values are causing a higher peak torque. This confuses alot of novices because they keep adding timing and they keep seeing more torque, so they think the timing is OK when it really isn't. Those high timing values are causing pressure spikes which are creating high rod internal stress and spikes to appear on the dyno graph. The engine will fail either from rod bearing or rod failure.
Next notice the EGT tends to level off at some point. My preferred method is to reduce timing until it begins to rise rapidly then add back just enough timing to keep it down on the street pulls. This is where experience has the most profound effect on tuning...
Because we can see in the dyno pulls that 13* gives a fairly smooth graph and a reasonable EGT, but so does 11*, so why wouldn't you just use 13*?
Again, use the least timing possible and I'll explain why. In this example, the ideal timing is probably close to 11* btdc. The reason is because the dynojet roller is usually easier to accelerate that the actual vehicle when on the street. In other words, most performance cars in the 3000lbs to 4000lbs range will accelerate more slowly on the actual road than they do on the dyno, and that means the rate of change of engine RPM is going to be LOWER when the vehicle hits the actual street.
IF we reduce the rate of change of engine RPM then we also need to reduce the timing, because now the engine will spend more time under load "more load". Its just like when you shift from 3rd to 4th, the gear becomes longer, the engine has more time to load, more time to get hot, it will want less timing.
Since the 11* spot is fine for the dyno (good egt, clean smooth graph) and the vehicle is a bit heavy (lets assume its a 3500lb car in this example) then I can predict easily that the 11* value on the dyno is going to act like a 12 or 13* value once the vehicle hits the street.

[wow]

Holy crap; this will take a couple of reads to really buckle down and give it a shot.

I don?t know if this will pertain to it, but here is my Dyno graph.
Thoughts?

[kingtal0n]

what is the smoothing? Always use smoothing=0 for diagnostics. Smoothing=1,2,3,4,5 is just to show off the graph after you are done with diagnostics and can't solve the spiking/wavy appearance.

diagnostically
It is a typical VE curve of healthy engine
something 'happens' at 125mph see the numbers drop and engine flow rate loses momentum.
Most likely a boost control issue. Otherwise valvetrain is next likely, OEM lifter perhaps. Finally the timing or a/f ratio could be another cause.

Some general rule is never trust 1 wideband. Always compare in-car with dynometer unit. The dyno should be more accurate and should read slightly leaner than typical in car downpipe widebands. So we always shoot for at 16+psi of boost range (over 1 atmosphere) say 10.7 to 10.9 air fuel ratio and expect to see maybe 11.2 to 11.3 on the dyno, which leaves us some dyno headroom to add fuel if necessary and bring that back down while watching torque climb possibly. More fuel usually means more torque up until a point, it is rare to see LS engines richer than 10.5, although they seem to still run fine there when setup properly. The timing should be added and removed to generate a series of curves, keep track of which curve is which. Fit the timing profile to the curve and use the minimum timing which generates satisfactory torque with a smooth line