BTW thanks for the compliments earlier, but always take what I say and use it as one point of view and do some independent research. Then you'll see all sides and be able to make the best-informed opinion for yourself.
Quote: Originally Posted by Lagzilla
so if there is say 7 deg of knock retard that doesnt mean its dangerous, it just means you could do things to gain your timing back
for lets say us big turbo guys the less timing and more boost will yeild more power compaired to stock turbo.
so if we are running 20 psi on pump and pulling 6 deg of knock retard
that is still safe correct? because there is no knock.
even more so if there is 9 deg of knock retard, that is still "safe" because its doing its job in order to eliminate knock, and still making more hp then if oen were to pull boost down to say 17 psi and run more timing.
the ideal way to run would have much higher octain to allow the computer to give you the extra timing + the amount of boost you want.
again, deg of timing retard is not dangerous but is not ideal?
I don't like to give exact numbers when talking about a car and setup over the Internet that I've never seen or worked on. And even if you listed every part there's too many variables such as piggyback settings, fuel pressure, boost, fuel octane, charge temps, and so on that can affect what's safe and what isn't. I can go over some broad guidelines in a minute, but better yet can explain what's going on and give you some ideas on how
you can determine what's safe for
your setup and what you should and shouldn't do.
So keeping that in mind realize that the knock sensor cannot magical protect and keep the engine alive in all cases. When you're near stock it can catch some pretty heavy knock, reduce (pull) timing, and hopefully bring it under control. But on a car with a much larger aftermarket turbo it could be pumping a lot more air into the engine. This creates higher cylinder pressures when the piston compresses the intake charge (air and fuel) and if you get detonation it can be much more damaging. Bust a balloon with a needle and not much might happen. Poke a hole in a SCUBA tank or a fire extinguisher and it's much more violent (e.g. because of the much higher pressure). One big knock event on the large turbo car could be enough to break a piston or beat up the bearings while the same amount of knock on a stock turbo car might be survivable. And your knock sensor and PCM don't know what turbo you're running and can't tell the difference.
Ideally if it helps you grasp the concept, there is
no safe knock and you want to do everything you can to prevent it. And the knock retard on your gauge is an indication the PCM has determined knock is present. The more it tries to pull back timing advance, the more knock there is.
Reducing knock and therefore preventing the timing from being reduced is safer for your engine durability and better for power and EGT's (higher timing advance produces less exhaust heat). In the real world a little knock retard may be unavoidable because of an overactive knock sensor, low octane pump premium, high charge temps and so forth causing a little mild knock. The optimal point for power creation is right on the threshold of knock, so if the PCM doesn't see heavy knock already occurring it will try to advance timing right up to that point, see a tiny bit start to develop, and then back it off again. You may be able to get it to zero under normal operation if you really lowered the boost or ran race gas, but it might not be necessary since the PCM is trying to keep it right around that knock threshold point anyways.
There are also different levels of knock that might be less damaging over the long or short-term. The way you monitor that is by watching the knock retard on your gauge since the PCM will try to correct for it if it can. So what's safe and what can you do? That's a big question and it's hard to give an exact answer in numbers as I already mentioned. But it is something you can monitor for yourself and find out.
Assuming you're using some type of fueling kit and a piggyback like a majority of the SRT-4 owners use, one thing important to remember is that the timing curve programmed into the stock and "Stage" PCM's is optimal for a stock car, but when you add the piggyback or "trick" the sensor and inputs going to the PCM it's going to alter the PCM's response and output (i.e. timing and fuel). Now combine that with a big turbo that has a characteristically different power curve and other factors like much higher pressures in the cylinder/combustion chamber and that timing may be off quite a bit from optimal and safe. That's why a stand-alone or being able to re-program the stock PCM's would offer such a big advantage. You can tailor the timing and fuel exactly to your setup and have direct control over it. With the fuel upgrade and piggyback type of setup you really have no direct control over what timing is doing. Sure you can clamp or alter the map signal or trick the IAT (charge temp) sensor and other things but you can't tell the factory PCM exactly what to do. So the best bet is to monitor it and see what it's doing.
At this point if you still have any doubt on what timing actually is and what it means I hope you already checked out the following thread (paying attention to post #38 for timing explanation):
http://www.srtforums.com/forums/show....php?p=3077281
So unless you have a stand-alone we can't control exactly what the timing does. The first step is to get an idea of what the stock or "Stage" PCM you're using does under normal operating conditions to know what you've got to work with. The best way to do that is to monitor on your gauge before turbo and other upgrades are installed to see what it's doing. That's another reason why it's important to invest in gauges and data logging equipment before the actual performance parts. If it's too late to do that you can read up in some of the threads in the tuning section, search for the data logged timing curve OBD-II charts a couple people have posted, or use a gauge on a few other people's cars in your area to get a feel for what's normal (and the best way to do that is first watch a good running, completely stock car). If you decide for the last one I'd suggest taking your gauge to a dyno day and see if people will let you monitor their car and note their modifications. Like I said I'll also try to get some videos up to show examples of different scenarios.
Let's say you're running a Stage 1 PCM. As a baseline on a car with only S1 and running optimally it might start at around 20° advance near 3.5k rpm's doing a WOT pull in third gear. With no knock it will gradually start increasing advance to maybe 22-24° and as red line is approaching and boost starts to fall off might top out at 30-31° right near red line. Use a piggyback on said stock car and/or try to turn up the boost much and the numbers may drop due to detonation. So by the time you add a big turbo and all the other modifications to support it, the PCM may be acting quite a bit differently. That's why a good baseline is in order. If you knew S1 normally tops out at around 31° advance on a stock car and were seeing 32 or 35° advance at some point during a WOT pull with the big turbo you'd know there's more timing than stock, and can look into things like how much fuel you're trying to pull with the piggyback at those points.
If the stock/Stage PCM's run too much advance for a big turbo trying to run a ton of boost what can you do then? Well you might be able to play around with some other sensors to get it to run less advance but that might be hit or miss. You can also buy aftermarket ignition boxes such as some from MSD that get installed between the PCM and coil pack and can pull/reduce timing advance under boost. That's one of the better things you can do with a piggyback, but by the time you buy the ignition box, piggyback and tach driver, boost controller, and everything else you're getting close to a full stand-alone territory.
With a bigger turbo that doesn't develop boost until up higher combined with running lower boost (and power) levels out on the street you might be ok with stock level timing. You do want to minimize any increases over the stock/Stage levels so that means properly sizing your injectors to your power output and using things like fuel pressure to tune the A/F ratio's first so you can minimize taking excess fuel out with the piggyback. Also make sure you have an efficient intercooler and do things like properly sizing the exhaust to increase efficiency, lowering EGT's, and overall getting decreased chances for detonation. For very mild detonation where you're seeing a few degrees of timing being retarded/pulled you could either lower boost a little more, run higher octane fuel if available, or maybe use water/alky injection (as long as it's only to help with small knock issues and you're not relying on it to keep you engine alive in case it fails).
Now the fun part when you start cranking up the boost. First off is everything just said becomes even more important, but those little events at lower boost pressure become catastrophic at higher pressure, so the stakes are raised. If you really want to push it invest in an ignition setup that can take out timing. If you want to get an idea of how much the timing advance needs reduced you can compare what you're running to the timing curves some of the stand-alone's use with a similarly sized turbo for a
very rough idea. (I can say that on a 400+ whp car I wouldn't be comfortable with 30+ degrees especially if it's a smaller sized turbo and making that power in the mid-range under heavier loads where there's an increased chance of detonation).
For the most part you're going to have to live with that extra timing advance. In order to do that you should consider higher-octane fuel a necessity when you start to turn up the boost. It's nice to brag about how much power you can make on pump gas, but if the PCM is seeing a ton of knock and has to pull a lot of timing to keep your engine alive it's not worth it. The PCM can only do its job so well and if you fight it you can be damaging the engine over time. Watch what the car is doing at lower boost and then compare to what it runs when you turn it up. Then compare both of those to what it should be doing stock. Isolate any causes for timing increase (such as what might happen if you switched between two different maps in an S-AFC or DTEC) and get the timing advance back down to the lower boost levels or better if it's showing knock retard. That might mean you need to adjust fuel pressure or alter the piggyback settings a little.
Maybe its not what you wanted to hear, but beyond investing in a stand-alone that's about it. Combine that with everything else already stated in this thread and you should have an idea what your car is doing. Remember to always try to keep that knock retard number down using some of the suggestions mentioned. Also compare what the overall timing advance is doing compared to a stock car. If you see a stock car running 25° advance and the PCM is pulling 3° timing retard, the total commanded timing should be an optimal 28°. But if you have a big turbo running under similar conditions with the same 25° but the PCM is also pulling 8° at the same time then the PCM thinks 33° is optimal. Look for things like that and try to figure out what's causing them (i.e. because in that example the big turbo car might have to pull a lot of fuel with a piggyback, timing went up because the PCM saw less boost pressure from the MAP sensor, that timing increased the chance it would knock, it did knock, and then got pulled back down; all the while the engine was seeing some nasty knock in those few milliseconds).
On a couple other final thoughts, first being about the PCM's and how something I stated earlier might confuse you. Just because the PCM is always trying to advance timing for best power doesn't make it safe. It's expecting a stock car but you've already changed many variables that affect how it runs. So if you get too much detonation/knock it will make overall corrections to its calculations to start running less maximum advance and the only way to spot that is to be monitoring what overall advance is doing in addition to watching knock retard. (And keep that in mind if you tune the car and do a battery reset and immediately jump on it hard after starting it again). The last thing that's a little expensive is you can start upgrading other components to handle some of those mild detonation hiccups better if you do run into an unavoidable small tuning issue. First thing would be the pistons since the stock ring land design is good for emissions but bad for strength and they're prone to crack/break. But while a set of forged pistons may hold up better to minor tuning issues it doesn't solve the root of the problem and things like the bearings and those expensive pistons are still take a beating.
Also keep in mind the scope of this post and thread is talking primarily about knock retard. If we
could easily and inexpensively control timing advance that would be a whole different discussion on what's safe to run (and again would come down to the individual setup and car in most cases).
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