I've tuned around 1,000 turbo cars. I always do the same thing no matter what type of engine for max longevity. I've tuned 4 6 8 cylinders this way, sbc, ls, sr, rb, 1zz, 2j, vr6, etc... all engines do the same thing. There are cars with 250,000 miles still running as daily drivers from 2004+ on my tuning including several 700rwhp 3.0L Stock Engines using gasoline for example. I always tune stock engines because this is how you get that 200k 400k miles easily and my tuning method is for safety primarily, not squeezing every last ounce of power.

Remove as much timing as possible to reduce cylinder pressure as much as possible. This is the safest pressure for the combustion event.

You do this while being aware of EGT. If the EGT is out of control you must intervene; there are some good ways to control EGT from water injection to better fuel like alcohols.

Once you find the EGT 'ramp' the point at which torque drops out within 4-8% of peak torque and EGT 'ramps up' you are at the minimum best timing setting for an engine at any particular load/fuel/throughout of power. In other words power throughput (power at some rate with respect to time) will create an EGT rate of rise or steady state. If the engine does not steady state like in a boat application then it may be a drag engine with no steady state EGT conditional in which case the EGT must either be kept below some maximum for a given time span of racing or the EGT must be controlled directly by cooling. The point is this- your cylinder pressure minimum timing setting is the safest place for any engine control and if power is needed then airflow throughput is increased, NOT the timing.

 

thanks for your posts i learned quite a bit from your experience. cheers

 

I made a picture when I was a young kid to illustrate my understanding of this concept.

 

^wtf

Timing also depends on whether you are running good rods/pistons or are SBE. Good tuners will limit timing even more with an SBE combo.

My current combo is similar and my WOT timing advance is a lot like yours. Tuners will suggest you pull plugs to see what timing is safe.

 

Stock block and stock crank with stock main bolts. The rods and pistons are the most budget oriented I could find - Summit Pro LS - 2618 piston that raised the compression minorly and the rods are 'supposedly' an upgrade to a Gen 4 rod - compression 10.4-10.5:1. BTR 7 layer HG, ARP 2000 head stud kit. Trailblazer intake, truck manifold with 2.25" pipes. Plenty of fuel pump, injector and lines so far.

AFR at 29 psi is 11.1 give or take .2.

 

The pistons/rods have nothing to do with timing. The reason people think that is because forged pistons withstand abuse of too much timing- but abuse is still abuse. Why would you abuse the engine in the first place? High cylinder pressure spikes will show as a power peak increase on the dynometer so it looks like more but that is abuse and a jagged torque curve oscillation, a fools errand.

For example, I'm at 15 degrees at 29psi (plugs look good) and 20 degrees at 19 psi. Does that ratio of 1 degree for every 2 psi carry on at 39 psi and 44 psi?

My combo is not atypical - aluminum 5.3, 243 heads, BTR stage 2 turbo cam, 85/102 T6 journal bearing turbo on Ethanol- budget build obviously.

This is too much timing for engine longevity. You may have much too small of a gap and not enough spark energy to use sufficiently low timing numbers.
High timing is a sign of inefficiency. It will eat rod bearings and ruin the bottom end. It also depends on the IAT which was not mentioned.

If 5.3L IAT is roughly 100*F then for 15psi of boost roughly 15 to 18* btdc is typical alcohol E50-E80 setting for that engine at 9:1 compression.

For gasoline it is roughly 11 to 12* btdc only.

For 30psi I would start around 5 to 7* btdc on the dynojet and move up a bit and down a bit, even try negative numbers if necessary, watching EGT and torque curve. You need a smooth curve with smoothing=0 set on the dynojet to see oscillations. The best timing is the least amount of timing which can safely run the engine with sufficiently low EGT to finish the race without melting. Dynojet rollers typically estimate roughly 3000lbs of vehicle weight so the actual track timing is less if the vehicle weight more and visca versa.

Always remember. Too little timing cannot damage anything for a short burst. There is no reason not to pull timing out more and more to see the minimum. You don't need to overheat the engine by holding the throttle open, Just a quick start of the pull to see what torque (cylinder pressure) is doing for some timing setting won't hurt anything. Once you determine the heat output of the engine at some reduced timing setting you can easily tell where the timing can be increased or reduced further.

 

@64nailhead do you have someone tuning your car? Using a Holley system?

 

No one tunes it other than myself, and yes, I'm using Holley.

 

Random guess time

Maybe you are using 581 or 514A on copper plugs @ .014" gap ?



I recommend switch to D585 or Holley coils with proper dwell

On an iridum plug gapped to 0.019" to 0.022" as much gap as you can get, 0.025" Is ideal but I don't see that happening easily past 25psi of boost without a voltage step up

You want a larger gap for more spark area and efficiency, more fuel will burn when its supposed to, EGT will reduce
The D585 and Holley have more spark energy and tolerate higher dwell periods
These will let you pull back the timing, reduce peak cylinder pressure, engine will last longer.
It will burn less fuel and reduce the EGT

Main weak point of factory piston is temperature, high temperature differential causes internal stress crystal lattice fracture, they begin to crumble to dust from the inside
The fix to make these engines last 200,000 miles with 1000hp on stock pistons is to regulate piston temperature. Since there is no oil squirts we can only do this using high quality alcohol fuel and Water Injection while maintaining a low EGT and cylinder head temperature with minimum timing. Cylinder pressure is heating and pressure is stress which causes brittle fracture failure so we maintain the low cylinder pressure and temperature to preserve the pistons.

 

Discussion
Analytical Study of Fatigue Failure of Aluminium Alloy Piston in IC Engines

Analytical Study of Fatigue Failure of Aluminium Alloy Piston in IC Engines

https://irjet.net/archives/V3/i4/IRJET-V3I4330.pdf

www.academia.edu

 

I talk to a buddy of mine with a build similar to ours about twice a week. We share the same tuner, and the consistent message is to pull plugs when increasing boost. That combo is 3300, forged 370 iron block, 83mm, gone from 9.20 to 8.50. Been watching the timing mark. Around 20-22 degrees on C16.

For some combos that aren't very efficient, let's say a $100 a/a intercooler, SBE, there would be a point where the person is pulling all the timing out of it to keep it from coming apart. You could end up with a budget'y combo that is running 10 degrees of timing and 30 lbs of boost and it's not picking a lot of power... Essentially finding the limit of the combo.

But for example with this other car he upgraded from a Mishimotor a/a to a Shearer and saw a really good drop in IATs. Had he kept the $300 intercooler he'd be pulling more timing. IATS dropped like 50F and gave him more room.

 

You could end up with a budget'y combo that is running 10 degrees of timing and 30 lbs of boost and it's not picking a lot of power... Essentially finding the limit of the combo.

That is not really how timing works

Low timing is generally desirable in modern engines. High timing is undesirable. Compare SBC vs LS timing maps, LS is far superior and much lower btdc timing because of chamber design. Thanks to computers, combustion has been computer modeled improving the combustion reaction rate with respect to molecular velocity component vector, the improved (statistical) normal distribution for incidence of collisions during a given range of crank and rod positions, is a general way to refer to the changes made.


This issue with low timing can be onerous to discuss with respect to 'racing' and 'performance' in particular with over-valve injection because adjusting start and end of spray for injection period will influence soot formation, flame propagation, reaction efficiency (total reacted mass), BSFC, all of which may be vastly different in a clean burning economy vehicle with a turbocharger vs a full out race car with no emission or fuel consumption concerns, or a vehicle with carbon cycle concerns, please observe research

Effect of Injection Phasing on Valves and Chamber Fuel Deposition Burning in a PFI Boosted Spark-Ignition Engine

A satisfactory answer to the future severe normative on emissions and to the market request for spark ignition engines seems to be the use of downsized engines for passenger cars. Downsizing permits the increase in engines power and torque without the increase in cylinder capacity. The downsizing be

www.sae.org

2008-01-0428: Effect of Injection Phasing on Valves and Chamber Fuel Deposition Burning in a PFI Boosted Spark-Ignition Engine - Journal Article

<div class="htmlview paragraph">A satisfactory answer to the future severe normative on emissions and to the market request for spark ignition engines seems to be the use of downsized engines for passenger cars. Downsizing permits the increase in engines power and torque without the increase in...

saemobilus.sae.org

In general at WOT I prefer injecting to an open intake valve as the WOT condition promotes the mixing and vaporization energy while the intake stroke provides kinetic energy to piggy back the injection energy, allowing a greater cylinder fill than would take place on a closed valve injection like the OEM uses.

Injector timing spreadsheet-anyone familiar?

120063 i used this excel spreadsheet to adjust injector timing, then i dialed in my Injector tip temps.. My question is, how accurate is the spreadsheet? the car definitely feels better and im hoping that ive not adjusted things too much. i have attached my current tune in hopes that someone...

forum.hptuners.com

I would argue that with my dying breath Boosted applications especially it is a VERY keen player - I have gained up to 120hp with injection timing alone on twin turbo setups below 3000 rpms Not to mention if when done correctly and at a linear retard rate with rpms IT WILL increase torque enough to rip the tires loose whereas it may not have before... Just takes some playing and getting right for the particular application.

Injection timing is a major player in the performance venue which will influence combustion outcome and cannot be ignored when discussing ignition timing.

Now, real world results
Here is an 2.0L engine, the famous '4g63' using 93 octane gasoline

taking -1* of timing at ~35psi of boost on 93 octane fuel for 600rwhp

Timing map, notice negative numbers where needed

Actual dynojet

Conclusion
The timing number does not matter. The timing is only necessary to start the combustion reaction at appropriate time, it can be a negative number depending on the temperature, fuel, compression rate, &c

We can easily tell whether the combustion reaction is efficient by the EGT and BSFC, in other words the mass of fuel per unit time going into the engine vs the heat being produced and power being produced as a product of that fuel mass flow rate. No matter what the timing number is, if the engine is using the fuel to make power at a safe pressure and low EGT then the timing number itself is unimportant.

The reaction propagation takes some time to get started depending on the chamber design, rate of compression, fuel conditions, energy supply, temperature, fuel quality, variables. Once the reaction can provide significant pressure to the piston area (stress) it only needs the piston to be in appropriate positioning with respect to rod and stroke angles with an acceptable reaction rate. A later ignition and later combustion may help contribute to more ideal angles as the connecting rod and crankshaft form superior cross product vector, which is why it is possible in forced induction engines making two or four times the power of natural aspirated engines with extremely reduced timing numbers can produce even less cylinder pressure than a naturally aspirated application despite 4x the output.

 

@64nailhead if you're having to dump the timing to stay safe, wouldn't that mean you reached the limits of the fuel being used?
Would it make sense to change to a higher-grade fuel of the same type for track days?

 

You’re Rephrasing my question (I think).
When should I expect to see no benefit from retarding timing based on boost?

 

Yes. There is absolutely a point of diminishing returns timing wise. And you are probably already there. But that’s not a bad thing IMO. Its not the fuel that’s done, it’s the strength of the combo that requires the baby timing around PK TQ to keep PK cyl pressure down in the areas the rotating assy can’t handle it and the heads can't seal it.

From what I’ve seen/read. When dealing with big power SBE LS combos. It’s a balancing act with cylinder pressure/RPM. Especially when running a factory head. They will deform eventually no matter what you do. But to keep the block and bottom end alive while maintaining the most AVG power across a useable RPM range you will likely need 8* or so near PK TQ… To counter act that you stall and rev the thing to the moon to get a large useable power band back.

Also kinda feel you are tuning backwards. Instead of deciding how much timing to take away (once you are past PK TQ). Decide how much timing to add. I start at a known low… dial in the boost and AFR with something stupid like 9* in the tune. Then add a degree at a time from say 5800-7800 and watch MPH/plugs. When it stops making at least 1 mph per degree. (or making good gains on the dyno) You are done!

 

there is a good write up by Greg Banish on the "hook test" You slowly advance timing until you see signs of detonation and the engine doesn't make more power. Then back off a couple of degrees. This is tuning at the limit for power and will make the most cyl pressure the engine can take at various rpms. You should pull timing at peak torq where loads are highest and adv timing at the higher rpms. Revving high, the high pressure events are shorter in duration and the engine can handle a bit more timing, but don't get greedy. Better to make power with less timing and more boost as long as you are still in the sweet spot of the turbo maps.

Engine and combustion chamber design make a big difference on the best timing curve (as does boost curve)

For example, the pent roof combustion chamber and dished piston of the LT5 vette engine is very detonation resistant. LPE found the engine made same power at 29 deg at 31 even though no detonation.

 

there is a good write up by Greg Banish on the "hook test" You slowly advance timing until you see signs of detonation and the engine doesn't make more power. Then back off a couple of degrees. This is tuning at the limit for power and will make the most cyl pressure the engine can take at various rpms. You should pull timing at peak torq where loads are highest and adv timing at the higher rpms. Revving high, the high pressure events are shorter in duration and the engine can handle a bit more timing, but don't get greedy. Better to make power with less timing and more boost as long as you are still in the sweet spot of the turbo maps.

Engine and combustion chamber design make a big difference on the best timing curve (as does boost curve)

For example, the pent roof combustion chamber and dished piston of the LT5 vette engine is very detonation resistant. LPE found the engine made same power at 29 deg at 31 even though no detonation.

The danger of that is assuming the rotating assy can handle MBT timing at all points in the RPM band without breaking parts. In the case of factory “SBE” LS engines like the OP runs… you can’t tune that way. Cyl pressure peaks will happen near peak TQ… not pk HP. So you either have to blow well past PK TQ and rev the snot out of it… or reduce the timing to crazy low levels to get the cyl pressures down at Pk TQ.

This is why some guys bend rods and bust the ringlands out of SBE LS motors at 600whp... and some guys make 1400whp without issue. (for awhile anyway!)

 

I have 4 degrees out below 6000 and feed it back in starting between 6100-6200. And spin it between 7700-8000.

 

You really need to rethink your converter if you’re spinning it all the way up there and you’re worried about anything below 6000 rpm. It shouldn’t spend enough time in that range to matter if it’s correct. If you have to pull timing there you are hurting the acceleration and slowing yourself down. Most guys have converters that are wayyyyy to tight for the power they’re making and have a lot of issues that they are trying to band aid with tuning that actually hurts the et. I shift my sbc at 7400 and it drops to 6600 currently at 28psi. It’s never down near peak tq anywhere but first gear for the second as it accelerates through it. No need to pull timing other than traction management and overall boost. To answer one of your first questions though, I pull timing down to 24 degrees at 26 psi and dont pull any more all the way out to 30 psi. That’s all the farther I’ve tested to so I’m not sure what’s past that.

 

If you tune using VE, you can see exactly where peak Tq is, and set your timing strategy up accordingly

 

Assuming you’re indicating that peak torque is where the VE table values are the highest?

 

You shouldn’t need the timing to be near single digits with a decent converter with a tight converter that doesn’t flash high enough I still run 12-14 degrees and on my car I run 16 ish degrees at 28-32 lbs

 

Is that on an SBE a small bore motor with factory heads though?

 

And presently I feel that I'm not at the limit of this turbo- basing this on exh back pressure still at 1.6:1 and IAT increase is linear and under control.

 

I recalled you having the great running 6.2. I was under the impression the larger bore and larger chamber square port heads are a different animal all together. Smaller bores and chambers generally require less IGN lead. Im going by what Capizzi and Roberts have discussed over and over regarding the small bore LS setups. They seem to have it down to pretty easy to follow recipe for the cam only SBE long blocks.

 

I’ve tuned both and there pretty similar and I’ve talked with capizzi a bunch and he definitely likes less timing around peak torque but very close in timing at higher rpm

 

LS stage 4 btr cam. I'm not sure we ever are loaded at peak torque. Do you guys pull timing during the flash when the rpm is climbing quickly? I figure that is low load.

 

With something like this where it flashes past peak torque I wouldn’t pull timing around peak torque