Timing
05-31-2016, 06:47 PM
#1
TECH Apprentice
Thread Starter
Timing Read about 100 plus threads and articles about nitrous tuning. Got myself all worked up about timing. So my question is what exactly is the timing number to start with. Is a stock ls motor 25,28,30,32??
So I get pulling 2 degrees per 50HP after 150 but what is the common spot at 150 and below. I have mine set to 32 n/a but I never had a stock tune to start with. Its Holley HP on bone stock lm7. Do you just turn the timing up n/a till you see a knock in the logs?
So I get pulling 2 degrees per 50HP after 150 but what is the common spot at 150 and below. I have mine set to 32 n/a but I never had a stock tune to start with. Its Holley HP on bone stock lm7. Do you just turn the timing up n/a till you see a knock in the logs?
05-31-2016, 09:19 PM
#2
depends what kind of car: race car/competition(max performance) or street/daily driver (safety first)
Assuming daily/street:
Since the car needs to be safe, we would ideally remove the timing until we find the torque is dropping significantly by using a dynometer, there is some number where diminishing returns will appeal. Back this up with an EGT reading that shows increasing EGT at the same time for verification that we are passing energy into the exhaust system instead of burning it. The only danger here with reduced timing is high EGT, so no need to run the engine long or hard, just find out when it starts ramping up. Then, you would add back a slight amount of timing to bring the EGT back down and bring the torque back.
The engines rate of change of acceleration also affects timing. Imagine you put the engine in 5th, and are going up a steep hill at 3500rpm so the car can not accelerate at WOT. Some engine dynometer can simulate this condition. It is important to realize that timing values which would work or be safe for an accelerating engine might not be safe for one that is under more load, and accelerating more slowly, so you have to take these situations into consideration if the ECU is incapable of recognizing the difference between them. A knock sensor might have something to say in this situation, but the key to a good tune is never having the knock sensor "go off". You NEVER want to rely on the knock system to pull timing, they are additional tools but in no way shape or form should be used "regularly" in a daily driving car, it is a safety feature for an extreme condition, or a bad tank of fuel, so that sheep can keep driving without ruining the engine.
Timing is also related to temperature of combustion, a colder combustion (due to methanol injection, E85, water, or even colder plugs to some extent) generally allows for more timing "safely" used, however depending on the engine there might not be a whole lot to gain from adding a bunch of timing, and the odds are against you in a daily driver A/C hot sunny day application that sitting in traffic and suddenly romping on the engine isn't going to tweak something. You can't simulate these terrible conditions on a chassis dynometer, and you can't simulate the load of the vehicle very well either, since terrain conditions change and stuff gets loaded up into the car, like luggage or passengers (we did say its a daily point of view). All these heavy objects SLOW the rate of change of acceleration, so if you tuned the engine on a lightweight dynometer roller and found that 32* of timing was optimal for torque, then take the car on the real road with the full weight of the vehicle and suddenly there is way too much timing and it pings and pops a gasket. That is an extreme example but it is part of learning to tune timing, understanding how vehicle weight is COMPLETELY different from dynometer roller simulated "weight", and how heavier vehicles accelerate more slowly like we talked about, this generally calls for much less timing, and as temperature builds up while the engine is waiting (like our steady 3500 uphill example) the temp may cross some threshold if you do not have those toys (methanol/water/E85) and the standard 93 pump fuel may no longer be suitable, at any timing value, because when temp reaches some critical threshold VS the compression ratio, it could start to explode suddenly, regardless of what timing value you use, this is a well knock behavior of gasoline and many find out when the IAT crosses that threshold.
I could go on all day about timing. I also wanted to say that the timing usually increases as engine RPM increases. It is no uncommon to see 9* or 10* of timing around 800rpm, then by 2400-2800rpm to see "full timing" is standard/typical (like an old-school weighted distributor) and for a modern engine this is often 25-28* of timing range. Many will use more but if you are looking at the dynometer graph you will see the diminishing returns we talked about, and that range of timing is often "not safe" for reasons we talked about (varying terrain/luggage etc). Then from some higher point, say just after peak torque, and torque is falling, it is common to see a bit more timing come in. Always remember that your "soft spot" will be the peak torque area, you want the LEAST timing there out of all the 2500+rpm numbers. SO here is an example for an engine that makes peak torque through 4500-5500rpm:
1000rpm: 18*
2000rpm: 22*
2500rpm: 25*
3000rpm: 28*
4000rpm: 27*
5000rpm: 25*
5500rpm: 25*
6000rpm: 27* (Torque is falling off)
7000rpm: 29*
Notice we ramp it in "fully" by 2500~ then pull it back some for peak torque, then back in again. Some heavily modified engines will not drop peak torque, and so timing will remain relatively flat to redline. You can argue some things like rod/stroke, this and that about timing but the difference is usually negligible, and we always opt for reduced number(daily driver), the lowest number that will get the job done(safe EGT). Usually this will leave 4-8% on the table, so for the dyno run it is perfectly fine to use additional timing just to show off your car's numbers. Just remember to reduce it once you hit the real road.
Assuming daily/street:
Since the car needs to be safe, we would ideally remove the timing until we find the torque is dropping significantly by using a dynometer, there is some number where diminishing returns will appeal. Back this up with an EGT reading that shows increasing EGT at the same time for verification that we are passing energy into the exhaust system instead of burning it. The only danger here with reduced timing is high EGT, so no need to run the engine long or hard, just find out when it starts ramping up. Then, you would add back a slight amount of timing to bring the EGT back down and bring the torque back.
The engines rate of change of acceleration also affects timing. Imagine you put the engine in 5th, and are going up a steep hill at 3500rpm so the car can not accelerate at WOT. Some engine dynometer can simulate this condition. It is important to realize that timing values which would work or be safe for an accelerating engine might not be safe for one that is under more load, and accelerating more slowly, so you have to take these situations into consideration if the ECU is incapable of recognizing the difference between them. A knock sensor might have something to say in this situation, but the key to a good tune is never having the knock sensor "go off". You NEVER want to rely on the knock system to pull timing, they are additional tools but in no way shape or form should be used "regularly" in a daily driving car, it is a safety feature for an extreme condition, or a bad tank of fuel, so that sheep can keep driving without ruining the engine.
Timing is also related to temperature of combustion, a colder combustion (due to methanol injection, E85, water, or even colder plugs to some extent) generally allows for more timing "safely" used, however depending on the engine there might not be a whole lot to gain from adding a bunch of timing, and the odds are against you in a daily driver A/C hot sunny day application that sitting in traffic and suddenly romping on the engine isn't going to tweak something. You can't simulate these terrible conditions on a chassis dynometer, and you can't simulate the load of the vehicle very well either, since terrain conditions change and stuff gets loaded up into the car, like luggage or passengers (we did say its a daily point of view). All these heavy objects SLOW the rate of change of acceleration, so if you tuned the engine on a lightweight dynometer roller and found that 32* of timing was optimal for torque, then take the car on the real road with the full weight of the vehicle and suddenly there is way too much timing and it pings and pops a gasket. That is an extreme example but it is part of learning to tune timing, understanding how vehicle weight is COMPLETELY different from dynometer roller simulated "weight", and how heavier vehicles accelerate more slowly like we talked about, this generally calls for much less timing, and as temperature builds up while the engine is waiting (like our steady 3500 uphill example) the temp may cross some threshold if you do not have those toys (methanol/water/E85) and the standard 93 pump fuel may no longer be suitable, at any timing value, because when temp reaches some critical threshold VS the compression ratio, it could start to explode suddenly, regardless of what timing value you use, this is a well knock behavior of gasoline and many find out when the IAT crosses that threshold.
I could go on all day about timing. I also wanted to say that the timing usually increases as engine RPM increases. It is no uncommon to see 9* or 10* of timing around 800rpm, then by 2400-2800rpm to see "full timing" is standard/typical (like an old-school weighted distributor) and for a modern engine this is often 25-28* of timing range. Many will use more but if you are looking at the dynometer graph you will see the diminishing returns we talked about, and that range of timing is often "not safe" for reasons we talked about (varying terrain/luggage etc). Then from some higher point, say just after peak torque, and torque is falling, it is common to see a bit more timing come in. Always remember that your "soft spot" will be the peak torque area, you want the LEAST timing there out of all the 2500+rpm numbers. SO here is an example for an engine that makes peak torque through 4500-5500rpm:
1000rpm: 18*
2000rpm: 22*
2500rpm: 25*
3000rpm: 28*
4000rpm: 27*
5000rpm: 25*
5500rpm: 25*
6000rpm: 27* (Torque is falling off)
7000rpm: 29*
Notice we ramp it in "fully" by 2500~ then pull it back some for peak torque, then back in again. Some heavily modified engines will not drop peak torque, and so timing will remain relatively flat to redline. You can argue some things like rod/stroke, this and that about timing but the difference is usually negligible, and we always opt for reduced number(daily driver), the lowest number that will get the job done(safe EGT). Usually this will leave 4-8% on the table, so for the dyno run it is perfectly fine to use additional timing just to show off your car's numbers. Just remember to reduce it once you hit the real road.
Last edited by kingtal0n; 05-31-2016 at 09:25 PM.
05-31-2016, 09:32 PM
#3
TECH Apprentice
Thread Starter
Thats some good info. I pretty much understand. This is a 1/4 mile only car. I am still confused were to start. Is it best to hit the dyno to get a decent base line? Car runs from 3700 to 6k under load. Tc is 3800 and launch at 3700 with nitrous on at 4k to 5800.
06-01-2016, 11:37 AM
#5
Tune it clean as with any engine that you expect to last, drive it around and clean it up so that it consistently remains in the 14.5;15:1 range while driving. the plugs come out looking clean and the engine oil is clean, then you can move on to the power stuff. We are not talking about fuel here? Just Timing? The timing in a street car is setup for economy, so that when the engine touches higher vacuum areas there is alot of additional timing for fuel economy reasons. (they call this vacuum advance in a traditional distributor). You will not need this if the car is never driven on the highway or public roads. If you had a manual trans you would also want to keep the high vacuum areas in the 25-30* range but that wont matter for the auto since the engine doesnt see vacuum between shifts. The timing under WOT we discussed already, those values I gave would work for a mostly stock, modern V8 engine, they are fairly conservative for those Natural aspirated applications. There is no need to adjust the timing values while street tuning unless the knock sensor or your ears/touch detects something amiss. You won't be able to feel the extra 2 or 4 horsepower for example, from adding 2* of timing at some point, so just make sure nothing complains audibly or visually and leave the timing increments for the dyno.
So then the dyno time comes, the car is already running clean from the street N/A so you can strap it down and make an N/A pass. You can throw 2* at it (+ and -)looking for that diminishing returns we talked about, clean the fuel up a little if necessary (whatever your target A/F which depends on many factors we arn't discussing here), if you are on a cast piston you still want to use the "daily driver" routine since a single hiccup will shatter that fragile casting, so we still use the minimum number possible, i.e. remove timing until power suddenly drops rapidly/obviously then add back a little timing and verify the EGT is good if possible.
Then you can play with the nitrous. Use the smallest shot possible at first, use the recommended timing increment removal, and check the plugs. With nitrous it seems like I am always looking at the plugs, usually the engine is too loud to get anything diagnostically useful from listening to it or watching it, your only real way to "check how its doing" is to pull the plugs. They say do not use anti seize with nitrous also, fwiw, but I would still use a tiny dab near the O-ring/washer just to facilitate easy removal for the dyno tuning. Make sure you talk to whoever is providing you with the nitrous kit for more details, I only know that I want to see clean plugs coming out and smooth power transition (use smoothing:0) for the dyno run, preferably from a progressive shot. You will want a colder plug for the nitrous also, "too cold" is probably fine since you have no intention of getting fuel economy from it. the gap should be very small 0.023 or 0.026~ I would guess (depends on ignition), because a misfire/backfire during nitrous is dangerous. And since you already tuned the engine to minimum timing, the recommended retard should be more than adequate. What COULD be a problem is if you tuned it to the "bleeding edge" (lets say you picked up 10rwhp going from 25* to 30* when running the engine at WOT N/A on the dyno, and left it there) well if you are pulling the recommended increment you might realize at this point that your "final retarded nitrous number" is actually the safe N/A number you originally found, making it a dangerous compromise on the juice.
Last edited by kingtal0n; 06-01-2016 at 11:46 AM.
06-01-2016, 08:42 PM
#6
TECH Apprentice
Thread Starter
Man. Good job thanks. Read that several times. So I get no more performance above 30 n/a so I am gonna assume this to be max. I will pull 2 from that up to a 150 and run 110 fuel.
You mentioned progressive shot. I have that ability but am trying to learn the best way to approach the ramp. I want to launch at max nitrous and ramp down at peak torque based on rpm but not sure if thats wise.
Also with the Holley self tune I just set the Afr and its been spot on every run. So thankfully thats not a problem.
You mentioned progressive shot. I have that ability but am trying to learn the best way to approach the ramp. I want to launch at max nitrous and ramp down at peak torque based on rpm but not sure if thats wise.
Also with the Holley self tune I just set the Afr and its been spot on every run. So thankfully thats not a problem.
06-02-2016, 11:36 AM
#7
You mentioned progressive shot. I have that ability but am trying to learn the best way to approach the ramp. I want to launch at max nitrous and ramp down at peak torque based on rpm but not sure if thats wise.
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06-05-2016, 01:02 PM
#8
TECH Apprentice
Thread Starter
Just in case anyone cares. Tried 26,28,30,32. Best it ran was at 30 on 125 shot.1.53 60'.
Nothing noticed on the plugs at all timing ranges. Next up br7ef plugs and 175 shot at 25.
Nothing noticed on the plugs at all timing ranges. Next up br7ef plugs and 175 shot at 25.
06-08-2016, 05:13 PM
#9
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my motor on the dyno was happy at 26 to 28 range NA. We never pulled timing till we passed 175 mark. What's funny after that mark we started to pull heavy timing, up to 10 degrees on a 250 shot and went from 7's to BR8's and x116 in the standalone. Seemed like 200 and above we had to make he most changes to optimize the 200 shot. We have run 300 for some sub 6 sec runs.
06-12-2016, 09:36 PM
#12
TECH Apprentice
Thread Starter
Ran a few passes today on 64n 38f jets had bad lean spikes then as it corrected it would run all the way down to the 8s on the afr. Best times were at 24degrees and 12.5. Times to setup the progressive and try and stop the lean spikes. Goes to 29 afr as soon as the nitrous comes on for .09 seconds then goes the other way to 8 afr and doesn't rebound back to 12.5 for approx 4 seconds.