Thread: Timing Maps for Tuning

New here, I'm surprised I have never been on this forum before. Just came across this thread when it popped up in another search topic and thought it was interesting and helpfull. I'm surprised to see more and more SR guys using stand alones. This is the wifes car and have been running this map for about 9 years with no issues. You can see the timing is extremely advanced in the idle section which is the only way I could get enough vacume to be able to run a/c, headlights, ext. Only have run 19 lbs through it because I was already running the 52lb injectors at 90% so I didn't want to chance anymore. I just installed some 1000cc's so we can finally push this turbo a little. Also should be installing solid lifters within the next couple of months because I'm tired of shucking rockers and she is itching to hit the road course.

Here is the setup.
S13 SR20DET
CP 8.5:1 pistons
Eagle rods
Precision SC34
HKS 264/272 step 2's
ported head

OOooo Ignition timing discussion!!!


So, I have some clues. Some variables for you fellows to digest.

1. Ignition timing that is the perfect number... lets say you are at dynojet. Wide open throttle and you keep adding timing until engine stops gaining power.

What have you done? You have tweaked the ignition timing such that it is now "perfect" for that exact situation. That temperature, that load, that gear, those variables.

And what loads the engine on a chassis dynojet?

.... THE ROLLER DOES. hint hint hint.

If your vehicle now loads up on the street, the engine will be at the mercy of a completely different load, the weight of itself, including the scale due to air resistance of your vehicle at high speeds.
In each gear there is a different rate of acceleration of the engine internals as well. Ever notice how you hit boost later in 1st gear than 5th? The speed that the engine accelerates, due to the load (resistance) in each scenario calls for completely different ignition timing.


So what do we do! On the sr20det, I like to do the following:
A. I find the lowest numbers. Remove timing on a dyno with 0psi until power fails miserably. The lowest of the low that you would actually still drive the car. To hit 0psi on a turbo engine pull the wastegate arm off the turbo.

Now, add timing incrementally until power peaks. You add 2* at a time. First step, gain 20ftlbs. next step, gain 8ftlbs. next step, gain 5ftlbs. Notice the diminishing returns.
If you keep adding timing, you will keep gaining, unless another variable starts to pull out the insignificant gains, maybe you gained 2ftlbs by adding timing and lost 2ftlbs because of temperature increase from previous runs. The point is, realize that adding 2* of timing for 5ftlbs of torque is not worth it.

Pull it back some. Find your best spot, and dial it down some. 2-5* should do it! not that hard to understand right?

B. You are not finished. Now add boost, connect the wastegate. On 93 octane, I can usually say this: you will make the same power with 9* as you will with 15*. Ive seen it at least ten real times. The sr20det engines do not like timing. maximum timing on any sr20 producing more than 200 horsepower with 93 was around 10* or less. Forever. All you folks pooling 15-22* BTDC at maximum VE.. have you ever TRIED pulling it back to 8*? Detonation is not the problem; Oh NO the sr20det is very resilient and having too much timing rarely demonstrates detonation when the A/F is in check. No, instead, you will gain a jagged torque line that "peaks" abnormally high, and you will lose horsepower up top, and the major end result is additional wear/tear "abuse" on your pistons and bearings. A built engine would withstand this abuse for years, but most stock sr20 engines lose a ring or spin a rod bearing because of this situation. Furthermore, FWIW, 2JZ engines are AlOT like sr20det engines, but they do enjoy slightly more timing (13* btdc on stock cams is typical at 18psi) in my experience.


"THE RIGHT WAY"
I described the feeler method above, by which a dyno is your feeler. The right way to do this is via exhaust gas temperature. Lower your timing like before, use the same method except this time, watch your EGT drop as you add back in the timing. The idea here is to MINIMIZE the egt AND the ignition timing. Dont keep adding timing for the sake of power- let the turbocharger do the work and make the power. If you want more power turn up the boost or upgrade your turbo. Add timing until EGT stops getting obviously lower- that is a sign that you are extracting as much heat from the combustion process as possible with that ignition setting. To get it lower you can try other things: (upgrade your plugs, upgrade your ignition, try a different fuel, try a higher fuel pressure, adjust engine volumetric efficiency via camshaft gears, etc.. ) there are many ways to extract more power from a given combustion event and lower the EGT.

Thats what this "tuning" is ALL about- keeping the EGT as LOW as possible, that is a CLEAR SIGN that your engine is being efficient.
A truly perfect car would run on the heat in the air molecules- leaving a trail of colder air molecules behind it. But thats impossible for us.

/end part 1

Part 2:
#2 Engine load. Lets play with vehicle weight for a minute. Lets say you are on that chassis dynojet again. you add timing like before and torque stops going up around 15* BTDC and your EGT is nice and low around 1250*F. Nice. Now, pretend we double the weight of that chassis dyno roller. Or triple it.

What do you think will happen? Well, for starters, it will accelerate more slowly. The engine will be under more load even though the air pressure in the engine is the same as before. If there was any boost, it builds faster now because the engine is accelerating more slowly and that gives you more time to build boost.

What about the ignition timing?! As vehicle weight increases (or roller weight) we all realize that ignition timing needs to decrease. That same "perfect" tune from before is now far too advanced, because...

A piston coming up the cylinder, compressing air, gets an ignition signal that starts combustion. But combustion is not a SUDDEN thing. It takes it's time, it starts off slow, and gradually builds pressure up to a PEAK. That peak cylinder pressure is what blows out head gaskets. Push the timing too soon, and you get a peak SPIKE capable of ruining that head gasket (because your compression stroke and combustion event are occurring simultaneously). You want a nice peak pressure, but not a nasty SPIKE. Keep in mind the rotation of the engine, and the fact that we desire a peak cylinder pressure when the connecting rod is in a position capable of applying force to the crankshaft appropriately. When the connecting rod is out of sync, the result will be lost power. Adjusting your ignition timing by using a dynometer to watch engine torque increase is generally moving your peak combustion pressure closer and closer to the best acceptance point of the connecting rod to absorb the energy, if not too soon (on the EDGE or VERGE of being too soon). The rest of the combustion- the rest of the power stroke, will keep it moving down the cylinder as long as possible.

part 3: detonation

I have seen sr20det detonation. The kind that pits up the engine deck, and head, to the point of being trash. It happens when somebody takes a fresh S15 engine and turn the stock engine past 15psi for extended periods of harsh driving. That will eat the engine up in no time, and I used to think it is due to a poor air fuel ratio (14's and 15's).

I know now differently. I have now seen an engine run at 15:1 around 380 horsepower (20psi - sr20det) and NOT detonate after back to back abuse (five runs, no knock, no visible indication of detonation on any internals after a tear down). What fails first on an engine with just a lean air fuel ratio (and proper timing) is the piston/rings (five runs of 15:1 and the rings gave out on CP pistons)
I can only stand to reason that it takes more than just a lean air fuel ratio to cause an sr20det engine to detonate on 93. The factory s15 engine undoubtedly pools more than 9* near the upper RPM range for 18+psi because of the anemic camshafts. Most engines with restrictive camshafts demonstrate quite a bit of a timing advance once the factory camshafts are out of capability. You might see it go from 9* as high as 17*. Somebody with one of those maps can verify.

This is due to a dropping volumetric efficiency. Extra timing is safe when the VE (torque) is falling off. On an engine with a perfectly flat torque curve (and thus nearly perfect VE) you would expect +/- 2* of the same exact identical timing across the board. If you start off around 9* you end up around 11*. Assuming a 4000-8000rpm range. maximum rpm has the final say.

Part 4:
Best Mean Torque

You will see this if you search around other car tuning forums. Evolution engines (4g63) and the tuner "crowd" often refer to BMT as a preferred tuning method when using E85 especially. Its exactly what I already pointed out- remove timing and add it back in incrementally until torque stops going up obviously, then back it down a few (2-5*). The reason I point out the 4g63 is because specifically, you see the most incredible abuse with their OEM turbochargers, and by that I mean, 25-31PSI on 93 octane pump gas, somewhere around 450All Wheel Horsepower. They absolutely max the compressor on those factory turbochargers, on a regular basis. And where is their peak torque timing usually wind up?

At peak torque, its around 3* btdc. As you run off the right, 8,000rpm, because of a massive drop in engine VE (and torque) the timing will often be as high as 10*. Boost falls from 32psi to about 25psi at that point on the OEM turbochargers.


Take a long careful look at those numbers. 3* of timing at peak VE (torque), guys, 30psi on 93 octane. Just because the number is below 10 does not make it wrong.

I made a quick little excel file, that explains a beginner method for timing an engine

just. now. cause bored


This is alot of fun. lets get a healthy discussion from people with dyno experience up in here!!

Thanks for the information, very good read and on par with a lot of the DIY tuning magazines I have read!

Excellent post kingtal0n! Now what kind of turbos are you dealing with? Fairly efficient T3+ or fairly inefficient stock sized T2's? My 9.5:1 SR20RR runs a GT28r, at 10-11 psi I'm running 17-18* peak (7,000 rpm). John Kerr and I were making more and more power up until that point basically. I didn't try as low as 10*, but definitely picked up a good amount of hp from original timing 14-15* at peak.

Thanks Vadim, I appreciate your enthusiasm for the subject.



All turbochargers can act different under circumstances. Even two similar T-25s can provide vastly different results given the combination of the engine components and air path and more. Each individual car is an individual and the smaller the turbocharger gets, the more personal it gets. The faster you get a response from the combination, the more personal the wide open throttle tune becomes.



If boost is always available, even at 2000rpm, the timing map can hit any spot between 0psi and full boost anytime the engine is between 2000 and 3000, because its 2000+ there is no upper limit. It is different tuning the Idle-3000rpm range, and drive train weight plays more of a role in timing advance.

Examining your particular engine, which I assume also has a typical front mount intercooler, it is 2.0L with a water cooled GT28r garret ball bearing turbocharger on a bottom mount T-25 manifold?
It must have a full boost potential around 3600rpm.

and you forgot to mention how much torque, and where. probably when discussing the wide open throttle performance, a dyno chart should be provided for examination.
If Torque is falling because the turbine is too small and engine volumetric efficiency is suffering because of an exhaust gas pressure ratio it may be beneficial to increase the timing for more torque- because it will promote more complete combustion of the exhaust gas constituents in the cylinder reducing the heat production of the turbocharger. If you are already timed at best torque, obviously you will not add more timing. The only fix for that situation is a larger turbine, or a improved wastegate. Sometimes more boost works, if the compressor can handle it. The exhaust pressure would go up, but so would the intake manifold pressure. If you get more mass on the intake side into the cylinder and burned then of course the engine will make more torque if the fuel quality allows for the blatant increase in compression ratio.

Anything you can do to reduce the temperature of the turbocharger while demanding performance from the turbocharger will cause the exhaust gasses to take up less space. Which is exactly what a turbocharger needs when the temperature is so high that the pressure is rising in the exhaust manifold to a significant height. Heat is beneficial when trying to get the turbocharger to spin, for the same reason in reverse. The largest mass of hottest as possible air in the combustion chamber makes the most torque- if fuel quality allows. n-heptane is 0 octane, do you think that would work? The reason we usually try to cool the incoming air is because low temperatures lower the sensitivity to fuel quality, AND colder air contains more mass per unit area. Spraying water or methanol into the engine is an extreme example of intercoolering. The idea is to increase the mass of air caught between the valves and start the reaction at the right instant to get the best possible use of the expanding gasses. Increasing the compression ratio at any time (especially by altering the head or piston) will always give you more torque, until fuel quality limits.


If the torque is failing due to anemia, that is, poor valvetrain performance, the turbo will not be getting hotter if it is large enough. Your particular engine would be held back significantly around 7,000rpm if it has a stock valvetrain and head. The oem sr20det cams always have a trouble with making good VE(volumetric efficiency) after 5500rpm. When VE is lower, it is ok to add timing, just like when you cruise, and maybe not for the same reason. When you cruise, VE is very very low, maybe 25% or less, and air fuel ratio is lean. When you are at WOT, and VE is low, the air fuel ratio is rich, AND VE is still above 100% on a turbo application. At 10psi on that engine you would expect about 170% VE around 5500rpm. Maybe more if it's a redtop with the oem long runner intake. A 12:1 Rich condition cools things off in the engine, egt usually drops, and ultimately results with less horsepower. From a chemistry point of view, the reason that you add timing when VE is dropping is comparing only these: compression, [temperature + fuel quality].
1. Dynamic compression is lower when VE drops.
2. temperature is controlled and lowered by a 12:1 rich condition, and fuel quality has the final say.

A fuel like ethanol has properties that make it a better choice for high performance turbocharged applications, and having issues with heat is much less likely. So using a fairly small turbocharger on a small displacement 2.0L engine with fuel properties that include excellent control of temperature results with better performance.

Now consider our 93 octane pump gas in the above situation. If your best torque number starts dropping because of this exact situation, (VE drops and 12:1) You can do one of two things. You can either bring the air fuel ratio up, (and thus the temperature), and the engine will make more torque. Also, you can increase ignition timing, and that will ALMOST ALWAYS give you more torque- with the one demand that the pressure in the combustion chamber occurs when the connecting rod is in a position to accept the force. And that happens AROUND Top Dead Center, but for each individual engine, because of varying rod and stroke combinations, and weight and even metallic properties, (and more) is different.

The reason this involves fuel type is because when advancing the ignition timing you are moving the starting point of the combustion process sooner, and different fuel qualitys have different reaction rates. there is a rate limiting step somewhere in the process, otherwise it would always happen instantaneously. Both cooling it off to (12:1) and decreasing the compression ratio both have the effect of lowering the reaction rate, which could be compensated by with an earlier ignition point.

In your particular situation, if you had FOUND best torque already previously around 5500rpm, whatever maximum timing displayed there at that point might also be slower than necessary for best torque when compression starts to fall. On the other hand...

There are other reasons to consider adding timing is when the engine needs it strictly due to rpm increase. This could be because of actual timing at the crankshaft beginning to waver from displayed values on a computer- (have you actually verified the engine timing at 7,000rpm? That sounds dangerous and difficult even on a dyno) Or because of one of many other reasons, as I will quote

http://www.eng-tips.com/viewthread.cfm?qid=193560


Always good to have results to analyze to figure things out. If you want I will post some of mine.

Also
http://www.contactmagazine.com/Issue54/EngineBasics.html

I just want to add that I literally googled those two websites at the original time of this posting. The information is out there, some of it is accurate, but what really is truly for every single engine in turn? I just felt those two websites were helpful from the frame of mind of the original question, as to be helpful when discussing ignition timing and detonation.
The overall syntrast, comparison, meaning of this post is a more general look at combustion engines as individual exceptions to each rule in turn. You modify something- you break a different rule.

The combustion of gasoline involves intermediates. To be honest, I am not a gasoline inspector, but I could imagine that different fuels (93 octane) from different sources will sometimes give different results. But they all say 93, and they are all mostly just light 8 carbon chains. Sometimes (usually?) there are additives.

stock 1995 auto G20 ecu

stock 1994 B13 Auto sr20de

@kingtal0n thanks for another great post. What I was referring to is, our FWD SR20's are not efficient enough (RWD is probably the same) with stock parts to run max of 10* at say 10psi. Now if your run a free flowing enough of an exhaust mani, plus a giant turbo like say 6262, then 10psi is going to yield you enough power that 10* would be more then enough.

It is all about efficiency of your setup though. When I had an SR20VE, switching to VET cams (smaller low lobes then VE cams), I had to increase timing majorly to gain back the low end torque and MPG. What I'm referring to is, the more efficient your setup (Intake, cams, exhaust), the less timing you need to get MBT.

You are saying timing follows VE, which is generally true. You should be aware that there are exceptions, such as when the intake charge is being trashed or contaminated by the valvetrain profile, or EGR or exhaust gas scavenging effects.