timing vs AFR

[pneumo]

I was down to 12-14* @ 7k 10.5:1 no knock, and 2 pulls later piston slap like a mofo. Got pictures if you wanna see it.

Too much timing retard if you ask me, everything else but EGT's were great.

Cause and effect? Or is it coincidence?
I'd like to hear some theory about how retarded timing can cause engine damage. I suppose it could be possible, it just seems a little far fetched.

 

[dsm-onster]

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Same exact bend as mine, thats Pauls rods (99gst_racer). I'm skeptical to say the least, in regards to it being power. 91 octane just doesn't make that much.
My only thoughts are, that because there is less total area inside the cylinder at a later ignition, it causes more heat. That heat has to go somewhere, and my guesses is that the pistons and rods make better heat sponges, because there isn't anything but oil at the bearings to cool them.

Imagine an explosion in a box, make the box smaller, the explosion is smaller, but probably hotter per square unit.

Excellent pictures!

They still don't prove timing retard can bend rods . High octane gas releases no more energy than 87 octane. 'All it does is contol the combustion so that more of the power can be extracted when it's being used in a high compression engine'.

In a nutshell: High compression causes the fuel to burn faster, resulting in the pistons being hit hard, like a hammer, when the fuel ignites. High octane allows the fuel to burn more evenly, allowing a high compression engine to develop more power. Igniting the fuel earlier on the compression stroke increases compression 'seen' by the ignited gases. Gas at an ignited state wants to expand to a certain volume and that volume increases through time after ignition (this is called an explosion ). The explosion moves (flame front) from the spark plug and fans out to the other non-ignited gas particles. This causes these particles to ignite. And the total gas in the chamber wants to see even MORE volume. So if you start the ignition process earlier, the flame front has a chance to reach more gases to ignite; exponentially increasing the volume the gases 'want to see'. Yet, your piston will still compress the volume to a certain number by TDC.

Low octane fuel does this expanding in a more "spirited" manner. And can more easily begin igniting gases farther away from the flame front (detonation).

Igniting the gases later in the compression stroke only slows this process. It took alot of energy to bend those rods in that manner. No energy can be released at gas engine compression levels w/out an igniting force. If it does occur, it is called pre-ignition and can occur so rapidly that the knock sensor did not detect it. Pre-ignition, a well as detonation, can certainly cause the rods to bend like that. Even at hp levels w/in the limit of what an engine can handle.

If no pre-ignition occurs and the igniting force acts later (less timing advance/more timing retard), then less expanding gases are compressed. And more currently inactive gasses are compressed.

Not only pre-ignition, but running suddenly rich can bend rods like that. The currently unignited gases have nowhere to go and can not compress to the volume of the combustion chamber (tdc) the crank then bends the rods as the piston top, remainder of the cylinder, and head at that point is as small as the inactive gasses can allow. Too much water injection can cause this to happen, as well.

I had a similar tune. When running no water injection, I ran my 60-1 to 25 psi peeked at 13 degrees timing running 11:1 a/f ratio. No bent rods for thousands of miles of abusive driving.

 

[JayRolla]

I had a similar tune. When running no water injection, I ran my 60-1 to 25 psi peeked at 13 degrees timing running 11:1 a/f ratio. No bent rods for thousands of miles of abusive driving.

Where you also running stock rods and pistons? I know that the forged internals can handle the lower timing without any problems. I was talking to a guy about tuning on another thread a long time ago and it was a wiseman that explained I was giving bad info, I think it was andymoraitis. I was telling the guy to run a little lower timing to get more boost and he was around 14*.

He said thats a real bad no no on stock cast pistons, because going below 14* can cause high EGT's and melt pistons or rods. Maybe I should PM him to give his advice.

 

[turboglenn]

Where you also running stock rods and pistons? I know that the forged internals can handle the lower timing without any problems. I was talking to a guy about tuning on another thread a long time ago and it was a wiseman that explained I was giving bad info, I think it was andymoraitis. I was telling the guy to run a little lower timing to get more boost and he was around 14*.

He said thats a real bad no no on stock cast pistons, because going below 14* can cause high EGT's and melt pistons or rods. Maybe I should PM him to give his advice.

Retarding the timing moves the heat from the combustion chamber to the exhaust ports and manifold as the gasses are still burning to an extent when teh exhaust valve opens if timing is too retarded. The heat does not go to the pistons and rodswith less timing, it's more timing that does that by keeping the entire burn cycle in the cylinder before the ex valve opens. The high EGT's are reading in teh manifold, not the cylinder.

Also, anyone who's ever logged a stock ECU should know that the timing gets pulled back to anywhere from 9 - 14* in the beggining of WOT pulls around 4k RPM or so. I don't think Mitsubishi would engineer it that way if it was harmfull to stock internals...

Now, don't take it wrong, i'm not trying to point a finger saying you're wrong, i just want to relay the proper information concerning what gets hot because of certain timing settings.

 

[dsm-onster]

On what fuel ?

I've never run anything but pump gas w/ the 60-1

 

[dsm-onster]

Retarding the timing moves the heat from the combustion chamber to the exhaust ports and manifold as the gasses are still burning to an extent when teh exhaust valve opens if timing is too retarded. The heat does not go to the pistons and rodswith less timing, it's more timing that does that by keeping the entire burn cycle in the cylinder before the ex valve opens. The high EGT's are reading in teh manifold, not the cylinder.

Also, anyone who's ever logged a stock ECU should know that the timing gets pulled back to anywhere from 9 - 14* in the beggining of WOT pulls around 4k RPM or so. I don't think Mitsubishi would engineer it that way if it was harmfull to stock internals...

Now, don't take it wrong, i'm not trying to point a finger saying you're wrong, i just want to relay the proper information concerning what gets hot because of certain timing settings.

Excellent points! You said it better than I could.

 

[dsm-onster]

Where you also running stock rods and pistons? I know that the forged internals can handle the lower timing without any problems. I was talking to a guy about tuning on another thread a long time ago and it was a wiseman that explained I was giving bad info, I think it was andymoraitis. I was telling the guy to run a little lower timing to get more boost and he was around 14*.

He said thats a real bad no no on stock cast pistons, because going below 14* can cause high EGT's and melt pistons or rods. Maybe I should PM him to give his advice.

Stock rods and pistons.

 

[turboglenn]

hack.. I'm not saying it's any cooler the burn will be teh same temp either way, but it's the time at which you start teh burn that will determine where most of the heat is transferred to. Lighting it earlier to get peak cylinder pressure where you want it in correlation to crank angle to make the most use of the burn for power is why we increase timing and generate more heat inside the cylinder instead of in the ex mani.

Just look at anti-lag.. it sparks the plug ATDC causing most of the explosion's pressure to be generated when the Exh valve is open, thus the majority of the energy created from the "burn" is utilized in the manifold, thus spooling the turbo instead of making power...

also, look at EGT's when you're cruising with 35* or so of timing the EGT's are fairly calm 12-1300F and that's burning at almost the hottest mixture available (14.7:1). But when you go wide open and are only dealing with 18-20* advance and a cooler/richer A/F mix, the EGT's shoot up into the 1500F+ range, because more of the burn is happening later in the engine cycle. Im' not being a smart ass, just sharing info that i've learned over the years. Im also not trying to be "mr know it all" just trying to help others become better informed

14* at redline will yield higher EGT's than 20* at the same load/rpm point since less of the burn is completed before teh exhaust valve begins to open. Meaning the manifold and tubro will be hotter, but internal temps won't change much

 

[wishihadatalon]

Retarding the timing moves the heat from the combustion chamber to the exhaust ports and manifold as the gasses are still burning to an extent when teh exhaust valve opens if timing is too retarded. The heat does not go to the pistons and rodswith less timing, it's more timing that does that by keeping the entire burn cycle in the cylinder before the ex valve opens. The high EGT's are reading in teh manifold, not the cylinder.

Also, anyone who's ever logged a stock ECU should know that the timing gets pulled back to anywhere from 9 - 14* in the beggining of WOT pulls around 4k RPM or so. I don't think Mitsubishi would engineer it that way if it was harmfull to stock internals...

Now, don't take it wrong, i'm not trying to point a finger saying you're wrong, i just want to relay the proper information concerning what gets hot because of certain timing settings.

Only one thing that bugs me about this and that is the timing being pulled back on a stock ecu. I can only speculate but to use that as part of the argument is just wrong. Timing is pulled back because peak tq should be right at the onset of boost, so keeping timing low there will help stay away from knock, and also the higher heat generated with the lower timing "should" help spool the turbo.

 

[wishihadatalon]

hack.. I'm not saying it's any cooler the burn will be teh same temp either way, but it's the time at which you start teh burn that will determine where most of the heat is transferred to. Lighting it earlier to get peak cylinder pressure where you want it in correlation to crank angle to make the most use of the burn for power is why we increase timing and generate more heat inside the cylinder instead of in the ex mani.

Just look at anti-lag.. it sparks the plug ATDC causing most of the explosion's pressure to be generated when the Exh valve is open, thus the majority of the energy created from the "burn" is utilized in the manifold, thus spooling the turbo instead of making power...

also, look at EGT's when you're cruising with 35* or so of timing the EGT's are fairly calm 12-1300F and that's burning at almost the hottest mixture available (14.7:1). But when you go wide open and are only dealing with 18-20* advance and a cooler/richer A/F mix, the EGT's shoot up into the 1500F+ range, because more of the burn is happening later in the engine cycle. Im' not being a smart ass, just sharing info that i've learned over the years. Im also not trying to be "mr know it all" just trying to help others become better informed

14* at redline will yield higher EGT's than 20* at the same load/rpm point since less of the burn is completed before teh exhaust valve begins to open. Meaning the manifold and tubro will be hotter, but internal temps won't change much

You are completely right. I don't understand how this is such a hard concept to grasp.

Hey Hakcenter If you would like to find some good tuning talk, check out EFI University - Electronic Fuel Injection Tuning, Training and Certification

 

[wishihadatalon]

14* @ 7k rpm, that is where we are all talking about.

What your trying to say is that the gases are 100F - 300F degree's cooler because the explosion happens 8 degree's sooner ? That's a lot of temp for a small amount of duration.

Timing advance increases cylinder pressure, mostly from an entire burn, but somehow the burn being 8 degree's later, is hotter 4 inches away down in the header pipe because its burning up in the pipe as it passes ?

I'm not sold at all, I think something with the fuel atomization during high rpm is the culprit, and the end result being monitor'd istoo far away to register an accurate description of the AFR that really happened. If the AFR is the same, and timing is changed, I think retarded timing would have a more complete atomization, increasing overall heat instead of advanced timing, especially in the short duration that it happens in, in comparison between 8 degree's retarded.

Monster, what pump gas, 91 or 93 ? what % of corny goodness ?

I guess to be sold on this you should experiment with an egt gauge. Run low timing on a wot pull and monitor your egt's. Then start to add some advance, maybe all the way up to 18-20ish degrees on pump gas, and see what the egt gauge does.

One more thing to support this is the fact that other fuels burn slower and require more timing advance to properly burn and begin to extract more power out of your motor.

 

[turboglenn]

I guess to be sold on this you should experiment with an egt gauge. Run low timing on a wot pull and monitor your egt's. Then start to add some advance, maybe all the way up to 18-20ish degrees on pump gas, and see what the egt gauge does.

One more thing to support this is the fact that other fuels burn slower and require more timing advance to properly burn and begin to extract more power out of your motor.

I have seen teh differences in EGT's due to timing changes. I have an EGT right on teh pillar, and with a full stand alone, my timing is where i program it to be..no fluctuations unless i program them in and the only one i have is to retard timing at super high temps ( or incase of a boost spike on my curretn street map ) I had higer EGT's when emulating a stock timing curve, they are quite a bit lower on my own timing map that i run now, i never get near 1600*F like some people say to tune to, and my AFR's are great

And you are correct, higher octane burns slower and has a higher flash point

 

[wishihadatalon]

I have seen teh differences in EGT's due to timing changes. I have an EGT right on teh pillar, and with a full stand alone, my timing is where i program it to be..no fluctuations unless i program them in and the only one i have is to retard timing at super high temps ( or incase of a boost spike on my curretn street map ) I had higer EGT's when emulating a stock timing curve, they are quite a bit lower on my own timing map that i run now, i never get near 1600*F like some people say to tune to, and my AFR's are great

And you are correct, higher octane burns slower and has a higher flash point

I didn't quote you just so you know I agree with everything you are saying except for the way you tried to use the lower timing at lower rpms argument.

What standalone if you don't mind me asking?

 

[turboglenn]

I didn't quote you just so you know I agree with everything you are saying except for the way you tried to use the lower timing at lower rpms argument.

What standalone if you don't mind me asking?

No worries, i wasn't taking it as any type of arguement. I was stating the timing drop at the beggining of a pull on the stock ECU just as a reference to show that retarded timing isn't going to melt stock internals.

AS for teh ECU, I use a Haltech E6k, very flexible, and will run anything from 1 to 16 cylinders. I use to be a dealer and north US tech support, but i gave that up several years back because I got out of the main import scene around here. Mainly because everyone talks sh!t and people/rich kids would come in asking "what should i do?? I want to make X amountn of power" and then after taking up hours of my time and me explaining what's good and what's not. They go off and buy teh shit on the "net.

So i work soley by reference of current clientel or if i know you i will do work for you, but no "walk ins" strangers etc... too much a pain in teh ass. I have 2 other businesses to run and that takes up enough of my time I mainly just subcontract my tuning abilities to some local shops and people that i know and help with their cars

 

[wishihadatalon]

No worries, i wasn't taking it as any type of arguement. I was stating the timing drop at the beggining of a pull on the stock ECU just as a reference to show that retarded timing isn't going to melt stock internals.

AS for teh ECU, I use a Haltech E6k, very flexible, and will run anything from 1 to 16 cylinders. I use to be a dealer and north US tech support, but i gave that up several years back because I got out of the main import scene around here. Mainly because everyone talks sh!t and people/rich kids would come in asking "what should i do?? I want to make X amountn of power" and then after taking up hours of my time and me explaining what's good and what's not. They go off and buy teh shit on the "net.

So i work soley by reference of current clientel or if i know you i will do work for you, but no "walk ins" strangers etc... too much a pain in teh ass. I have 2 other businesses to run and that takes up enough of my time I mainly just subcontract my tuning abilities to some local shops and people that i know and help with their cars

Good stuff. I use Mega Squirt, not nearly as advanced, but still very potent and does everything that I could want it to do.

 

[dsm-onster]

I didn't quote you just so you know I agree with everything you are saying except for the way you tried to use the lower timing at lower rpms argument.

What standalone if you don't mind me asking?

What's wrong w/ the arguement that retarded timing yields quicker spool because of increased heat in the exhaust track? Not pecking a fight. I'm curious about your thoughts on this.

Hakcenter, I run 93 octane. No corny goodness . Considering the speed of the flame front and how quickly peak cylinder pressure is achieved, around 15* ATDC at MBT; it seams that small increments can have a great affect.

But, primarily considering that a perfoance cam like an fp2, w/ an exhaust duration of 212*, is open for 106 degrees of crank rotation and is at .05" lift 35* before bottom dead center, one can see how 8* of timing advance can have a significant influence. 16* BTDC (ignition timing) plus 145* until the exhaust valve reaches 0.05" lift equals 161* of burn time used to push the piston. It is easier to burn higher-burn-rate pump gas octane fuel w/in such a time frame than higher octane fuel. MBT is the timing number that causes all of the fuel to be burned before the exhaust valve opens at a certain rpm. This is the reason why we see a timing curve. If you tune for less than MBT, then some exhaust gases are still burning as the exhaust valve opens and sends exhaust gas heat soaring.

 

[turboglenn]

Anyways, when most of the flame ends up out in the manifold burning up, how does that help with emissions, or does a loaded respond differently with retard than no load at all ?

Not sure what you're asking there, about load and emmisions ( i really don't mess with emmisions although i have access to an emmisions testing station ) But most emmisions important things are, correct plug, good cat, coolant temp of 190 or above, a functioning EGR and damn near perfect AFRs (depending on if it's the idle or 2500RPM test for unburned hydrocarbons)

But, I don't see any way that retarding the timing could have bent that rod. Seems more like a hydrolock or some serious pre-ignition to me. I've seen pre-ignition bust 2 pistons right at the wrist pin , same motor twice becasue of a bad tune that was too lean and too much timing ( now i tuned that car since the last guy broke 2 motors in 2 months) They were even forged pistons. But I've never seen detonation bend a rod, the only way that would happen is if the plug fired before the piston was about 1/4 of the way up on it's compression stroke. (which if that was your pic i saw of teh 2 bent rods WOW..that's something to think on )

Were you running any "extra agents" such as alky or meth wehn the rod bent? I'd like to get to the bottom of that one. Also what # cylinder rod was it and what were teh operating parameters ( i.e. boost, timing, AFR and a basic outlineof your setup) PM me if it's too far off topic in your opinion

 

[turboglenn]

What's wrong w/ the arguement that retarded timing yields quicker spool because of increased heat in the exhaust track? Not pecking a fight. I'm curious about your thoughts on this.

That's not even an arguement, pure fact; more fuel and retarded timing spools turbos faster

 

[wishihadatalon]

What's wrong w/ the arguement that retarded timing yields quicker spool because of increased heat in the exhaust track? Not pecking a fight. I'm curious about your thoughts on this.

Hakcenter, I run 93 octane. No corny goodness . Considering the speed of the flame front and how quickly peak cylinder pressure is achieved, around 15* ATDC at MBT; it seams that small increments can have a great affect.

But, primarily considering that a perfoance cam like an fp2, w/ an exhaust duration of 212*, is open for 106 degrees of crank rotation and is at .05" lift 35* before bottom dead center, one can see how 8* of timing advance can have a significant influence. 16* BTDC (ignition timing) plus 145* until the exhaust valve reaches 0.05" lift equals 161* of burn time used to push the piston. It is easier to burn higher-burn-rate pump gas octane fuel w/in such a time frame than higher octane fuel. MBT is the timing number that causes all of the fuel to be burned before the exhaust valve opens at a certain rpm. This is the reason why we see a timing curve. If you tune for less than MBT, then some exhaust gases are still burning as the exhaust valve opens and sends exhaust gas heat soaring.

It was more him comparing low timing at low rpm situations to low timing at high rpm situations. I completely agree that low timing will give quicker spool, but you will lose some off boost tq if you pull the timing down too soon.

 

[dsm-onster]

Don't insult me with a EFI learning website, not cool at all.

My motor had been recently rebuilt, all in spec, and a rock solid tune from 10psi to 15psi @ 10.5:1 17* advance @ 7k.

I wanted a bit more brang it up to 18psi and chopped 4* off and 2 pulls later bent #4 rod. During the entire life of that motor, there was never signs of pre-ignition, not even on the plugs, and I seriously seriously doubt, that I was ever making that much power, I would of expected more than 1 piston to go if that was the problem.

So you adjusted two aspects of the tune, and attribute the bent rods to retarding the timing instead of upping the boost. Being that so many have run lazy timing curves w/ no ill effect on the rods, I'd really look at other possible causes. At cain airflows and boost levels, 1 more psi can yield 2-3 times more hp than 1* of advance.

Is it really impossible for pre-ignition/detonation to occur and not be detectable?

Arn't those 6-bolt rods? What was your logged airflow during the pull that bent the rods? Or what was the airflow at 15 psi.

Anyways, when most of the flame ends up out in the manifold burning up, how does that help with emissions, or does a loaded respond differently with retard than no load at all ?

It's not that 'most of the flame ends up out in the manifold'. If that were the case then melting turbines would be common, like serious antilag setups can do.

 

[wishihadatalon]

Not sure what you're asking there, about load and emmisions ( i really don't mess with emmisions although i have access to an emmisions testing station ) But most emmisions important things are, correct plug, good cat, coolant temp of 190 or above, a functioning EGR and damn near perfect AFRs (depending on if it's the idle or 2500RPM test for unburned hydrocarbons)

But, I don't see any way that retarding the timing could have bent that rod. Seems more like a hydrolock or some serious pre-ignition to me. I've seen pre-ignition bust 2 pistons right at the wrist pin , same motor twice becasue of a bad tune that was too lean and too much timing ( now i tuned that car since the last guy broke 2 motors in 2 months) They were even forged pistons. But I've never seen detonation bend a rod, the only way that would happen is if the plug fired before the piston was about 1/4 of the way up on it's compression stroke. (which if that was your pic i saw of teh 2 bent rods WOW..that's something to think on )

Were you running any "extra agents" such as alky or meth wehn the rod bent? I'd like to get to the bottom of that one. Also what # cylinder rod was it and what were teh operating parameters ( i.e. boost, timing, AFR and a basic outlineof your setup) PM me if it's too far off topic in your opinion

The rods above bent because Paul over boosted the hell out of his motor. His boost controller was hooked up wrong and I guess the rest is in the pictures.

 

[dsm-onster]

That's not even an arguement, pure fact; more fuel and retarded timing spools turbos faster

Oh. I misunderstood you.

 

[pneumo]

Lots of good info in here. Thanks all for adding to the knowledge base on this site.

I blew a motor from pre-ignition once. It was nasty! I had forged rods and pistons, so they held up, but the head was built with backcut valves that were also trimmed slightly thinner at the seats, so they caved in. The damage was limited to one cylinder, the other 3 were fine. Closer inspection revealed that the head was cast slightly out of alignment. Pre-ignition was caused by part of the head overhanging the cylinder, creating a hot spot.

Air/fuel mixtures ignite easiest at low density. Higher density A/F mixtures (high boost and/or rich A/F ratios) are harder to ignite. That's why we get misfires at high boost and rich A/F ratios.
Mixture density is lowest at BDC of the compression stroke. Imagine what happens when a hot spot ignites the mixture at BDC of the compression stroke! The fuel burns as the piston is going up, pressure builds but has no where to go.

 

[FonZ454]

I'll stay out of this thread, just want to say, lots of good info in here!

 

[turboglenn]

Hack, normally when one rod goes, it's enough to make a person let out and not damage anything else. Plus the power loss and drag in the motor from one bet rod would hinder performance enough to keep it from damaging anything else. Just like my friend who had a local shop tune his car and 2 times in a row he broke the #1 piston at the wrist pin from detonation. Everything else was okay. The #1 gets the most air from the way the intake is designed and runs the leanest. That's why EGT probes are recomended in the #1 runner since it will be the hottest. So your #4 going out is a bit confusing, but i would still blame it on pre-ignition or some sort of hydro locking. Heat would normally melt a small hole in the piston or burn up a few valves if that was the problem.