ok, what do you make of this???? HG Failure....

[Ben]

(Audible meaning, standing literally right next to the vehicle in a safe location)

 

May I suggest that ideally 'audible' would be using a knock-box and headphones? I know that my tuner could detect the first hints of rattle by my RB25DET way before it became audible to me (and therefore adjust the tune before an observer even knew what was happening).

 

I'm also noticing that a couple of these posted maps seem to have the timing taper off at around 5000rpm. I would think that the point for the least amount of timing would be at peak cylinder pressure - approx. peak tq. My maps (and others in this thread) have reduced timing at around 4500rpm and then we wind it back in as the rpm's increase towards redline.

[mikeatrpi]

I had an issue where I was accidentally running more timing than I knew, when I blew my HG. I received some sound advice from "x64v" which I'll pass along... verify that the timing on the megasquirt screen matches what's actually happening. Set your MS to a fixed angle... 20 degrees, whatever you choose. Check it with a timing light at idle - and across the RPM range.

[ktm]

That is VERY safe/conservative, and in my not so humble opinion, an EXCELLENT beginning timing curve for an initial tune to start tuning a boosted L6 from!

The only thing I would change is to add more timing in the 2500+ RPM columns below the 80KPa rows, maxxing out at approx 45-48 degrees in the 40 KPa row, (will help tremendously in MPG and tip in throttle response, that's about it).

 

Seriously?! That seems like a gawd awful amount of timing. What about temperature issues with that much timing? When I looked at my pistons after I pulled them, they showed signs of running too hot (per a few speed shops I went to and my browsing on the net). The skirt areas were all scraped from contact with the cylinder walls.

 

I was running leaner as well at cruise (15.5+) and around 41 degrees of timing. I've since richened it up to 14.5 and pulled timing to around 38 degrees.

[BRAAP]

Seriously?! That seems like a gawd awful amount of timing. What about temperature issues with that much timing? When I looked at my pistons after I pulled them, they showed signs of running too hot (per a few speed shops I went to and my browsing on the net). The skirt areas were all scraped from contact with the cylinder walls.

 

I was running leaner as well at cruise (15.5+) and around 41 degrees of timing. I've since richened it up to 14.5 and pulled timing to around 38 degrees.

 

Bo,

It's ok, really, just relax. I can appreciate the Turbo L-6 guys skepticism of ignition timing. Where the Turbo guys pop their head gaskets is in the high load high KPa range, above 120-140+. What I am talking about is in the light-to-no load range, in the 40KPa range, (that manifold pressure is below normal cruise conditions), 45-48 degrees is actually still conservative and probably within or less than the OE ign timing range at that manifold pressure range.

 

You guys all caught up in Sequential Distributorless Ignition Sytems, (D.I.S.)! You recall that little vacuum advance canister on the side of the OE Datsun dizzy? Have you ever plotted out the actual ignition timing of mechanical AND vacuum advance when fully activated? Turbo or N/A?

That little device actually ADDs even more timing on top of the mechanical advance during light throttle cruise conditions, (less than WOT conditions) to enchane MPG, overall drivability and even emissions. Trust me on this. at part throttle cruise, say 450-60 MPH on straight level ground, your L-6, Boosted or N/A will run more efficiently between 44-54 degrees total ignition timing, (Mechanical AND vacuum advance, above 3000 RPM)!

 

For those thinking this is new fangled theory, it isn't. This is basic ignition timing 101, has been around since before the Z car was even manufactured, yet still applies to the L-series powerpalnts!

Edited January 8, 2010 by BRAAP

[ktm]

Paul, thanks for the quick response. I don't doubt you, but I was concerned about running hotter at that timing. Ron and I talked a while back and he suggested running around 41ish at cruise, which I was. I also leaned out my map at cruise to run an AFR around 15.5. However, my engine definitely ran hotter with the higher timing and leaner fueling.

[BRAAP]

Paul, thanks for the quick response. I don't doubt you, but I was concerned about running hotter at that timing. Ron and I talked a while back and he suggested running around 41ish at cruise, which I was. I also leaned out my map at cruise to run an AFR around 15.5. However, my engine definitely ran hotter with the higher timing and leaner fueling.

 

Bo,

I totally sympathize with your concerns regarding the posting of ignition timing figures, especially being a Turbo L-6 operator. At the higher load bands where damage is more severe and happens much quicker, i.e. under WOT, concern is definitely warranted. At light loads such as cruise, ignition timing requirements for N/A and Boosted will be similar and neither will be more damaging than the other under those same light-load conditions, generally speaking. At cruise, depending on the amount of load, 41 degrees is even considered conservative. It is common to see as much as 55 degrees at light load moderate RPM, in OE or high performance tune. Moderate to hot engines, boosted or N/A under the same load conditions can still run that much timing advance, in that light-load band.

[zdizeeze]

quite an education Thanks you guys Reuel

[Noddle]

You recall that little vacuum advance canister on the side of the OE Datsun dizzy? Have you ever plotted out the actual ignition timing of mechanical AND vacuum advance when fully activated? Turbo or N/A?

That little device actually ADDs even more timing on top of the mechanical advance during light throttle cruise conditions, (less than WOT conditions) to enchane MPG, overall drivability and even emissions. Trust me on this. at part throttle cruise, say 450-60 MPH on straight level ground, your L-6, Boosted or N/A will run more efficiently between 44-54 degrees total ignition timing, (Mechanical AND vacuum advance, above 3000 RPM)!

 

Paul, do you have a plot of this (kpa vs RPM) that you are willing to share, I would like to compare it to my low kpa settings on my tune.

 

Nigel

[Daeron]

wow, what a thread!! Bookmarked!

[Ben]

You guys with Direct-fire systems could pretty much run whatever timing you like (physically speaking). Bus those of us running a locked distributor can only adjust our maps until we run out of wipe on the rotor button. This is still plenty, but it could be a stretch trying to get 45+ deg total advance with this kind of setup. It also depends on how much you can actually dial into your EMS, but you can always adjust the trigger angle to get a little more

[mikeatrpi]

Now that's an interesting point. When one sets their trigger angle in MS, you wonder where in the "wipe" is referencing as '0'. Because, Ben - the maximum could be different for different configurations. If one needed more advance, they would have to rotate the distributor clocking and correspondingly adjust the trigger angle.

Edited January 14, 2010 by mikeatrpi
not step on toes

[jc052685]

Rotor wipe has nothing to do with this topic.....

 

 

Thanks.

 

 

.

[Ben]

Apologies for the digression.

[Noddle]

Paul, do you have a plot of this (kpa vs RPM) that you are willing to share, I would like to compare it to my low kpa settings on my tune.

Nigel

 

I was reading another post

 

http://forums.hybridz.org/showpost.php?p=1113697&postcount=19

 

and it had a link to this,

 

http://www.corvette-restoration.com/resources/technical_papers/Timing101.pdf

 

it's a nice read.

 

Nigel

[rejracer]

http://www.corvette-restoration.com/.../Timing101.pdf

 

There is a couple of errors in the above article, but there is also some good information in it as well. I'll point out what I know to be either partially correct or wrong as well as try to explain how it ties back to detonation, and how to avoid it.

 

First:

"Fuel/Air Mixture and “Burn Rate”: At idle and steady cruising speed, the load on the engine is low, and the air-fuel mixture is “lean” (more air/less fuel); when accelerating, the load on the engine is higher, and it’s fed a “rich” air-fuel mixture (more fuel/less air). These are two very different conditions, as a lean mixture burns relatively slowly, and a rich mixture burns faster. Remember this distinction – it’s a key factor in ignition timing."

 

There is an ideal mixture which provides the fastest burn rate, I've read that is at 11:1, but the fuel is going to dictate that. Above and below that point the flame front travels slower. So the statement is partially true. In other words if your engine is running on the pingy side, just lean it out, and slow down the burn? He is right it's a key factor, but the partial information is a disservice when we are talking about blowing headgaskets and managing KPA / RPM.

 

the reason I am beating on this is:

Anyway. Got the car all back together the other day. Finally drove it today and POP. Fresh Nissan HG dead. Got maybe 3 miles out of this one. So pretty much gonna burn this car to the ground!

 

Not really. Gonna double check the timming again since the oil pump gasket is leaking. I added some fuel @ peak tq but did not pull any timming to I will have it apart and back together before Sunday si I will report back.

 

Adding fuel to a slightly lean mixture with too much timing can increase the burn rate. Increasing the burn rate will cause peak cylinder pressure to arrive sooner, increasing the chance of detonation. To have adding fuel effective in combating detonation, you would need to move the AFR to a place that has a burn rate slower than where you are now, which means you need to know your AFR at the point of failure. Otherwise playing with fuel and timing is just guessing. This of course is ignoring that richer mixtures will be more detonation resistant. Regardless in your tuning experience, I would surmise that you learned that the increased detonation resistance of the added fuel did not outweigh the increased burn rate, and timing settings.

 

Detonation happens at given pressure/temperature for a specific air fuel mixture (variables=octane and AFR), when this line is crossed too early in the combustion cycle, things break.

 

Secondly:

" as upward piston speed increases with rpm, effectively shortening the time for the compression stroke, the spark has to fire sooner, as the air/fuel mixture still takes the same amount of time to burn as it does at lower rpm. "

 

The issue with this is that the burn rate increases with RPM. The article is dead wrong. The flame front travel speed increases as engine RPM increases at a volumetric efficiency. The rate of change is not 1:1 with engine RPM, but it's not very far behind it. To illustrate, if the combustion process at WOT at 600 rpm burns the entire mixture in 150*(just a random figure) of crank rotation that works out to .041 seconds. At 5000 rpm 1 degree of rotation is .0000333333 seconds. If the fuel burns at the same rate (.041 seconds) regardless of RPM then the combustion process would be complete in 1250 degrees of rotation (once again at 5k rpm). Another way of saying the same thing is that at 150* degrees of rotation only 12% of the intake charge has been consumed at 5k rpm. (actually it's less than this but I wont take the time to explain why). If only 12% of the charge has combusted, then cylinder pressures are not high enough to make the engine run, let alone "support" detonation.

 

Now how do I know this?

1. Mathmatically it's impossible knowing how much power engines produce, and a few calculations based on a constant burn rate.

2. In the 1950's GM engineers wanted to watch the combustion process, as their math did not add up when they were ASSUMING the burn rate was constant. So with their then unlimited budget, they cast lenses into pistons, placed a mirror and window in a modified pan and filmed the process with a high speed camera. They watched the combustion process from the pistons perspective. What did they learn?

1. Burn rate increases with RPM.

2. Burn rate increases with increased quench, turbulence as they called it.

 

We studied these videos (and corresponding documents) in college for MPG competition vehicles. The types of vehicles we were building were in the 3000 - 4500 mpg range. To attain those numbers one must understand the combustion process from beginning to end. Failure to understand and your scratching your head as to why you just lost 1500 mpg.

 

Mechanical advance is not there to ensure maximum power at WOT, it is there to retard the timing at lower RPM's so you don't blow head gaskets or blow holes in pistons below ~3k RPM. Think of timing this way: Based on the engine mechanical design and AFR,

1: At what timing is PEAK power safely obtained?

2: At what timing is peak torque at 600 RPM WOT safely obtained?

 

The difference between the two is the ideal mechanical advance. Please note that I am purposely omitting things like driveability, vaccume advance, chamber design and the like. What I am explaining is the basic principle of mechanical advance, aka Low RPM retard.

 

This relationship of burn rate (fuel mixture) and timing is all about managing chamber pressures and temperatures from the start of the ignition event until all fuel is consumed during the combustion process. The game is how close can we get to the line without crossing it like the original poster did. Not only how close we can get to it at one point, but how closely can we stay to it from just below idle to red line. It's a really fun game, until you cross the line, at which point it becomes more educational, rather than fun.

 

The last point is around the tuning of light load conditions. When managing chamber pressures and temperatures, it's possible to advance ignition timing because at light loads there is not enough pressure in the chambers due to those troublesome throttle plates blocking all the air flow. With this lack of airflow (from the chambers perspective, density) it's impossible for chamber pressures to get very high. To take advantage of this it's possible to increase temperatures (leaning it out) and adding timing without detonation risks. Remember detonation is caused by a combination of temperature and pressure. Since pressure is no longer a player in detonation, increase the timing, and decrease the ratio to get the temps up so the process can build what pressure it can.

 

Just a few links:

http://pcwww.liv.ac.uk/~goodhew/Student%20webs/Turtle%20AMAC/Amac/Flashversion/CombustionProcess.htm

 

http://forums.turbobricks.com/showthread.php?t=170270

[ozconnection]

Nice!

[Zmanco]

Thanks rejracer for the additional insights - I was having a hard time too with his statement that the burn rate was independent of rpm.

 

And thanks for the turbobricks link - there's a discussion of tuning strategies at various boost levels in the #9 post that gave me some ideas to try.

[woldson]

Not only how close we can get to it at one point, but how closely can we stay to it from just below idle to red line. It's a really fun game, until you cross the line, at which point it becomes more educational, rather than fun.

 

 

I soo had to laugh at this, well put, thanks!