timing vs AFR

[turboglenn]

Originally Posted by hakcenter

So am I lying now about no preignition ? I have the piston sitting right next to me, its my paper weight around here. There are zero signs of preignition, even my tunes, were rock on. I don't think it was hydrolock, I would of expected it to throw the rod or feel some type of power loss during the run.

I'm getting pretty sick of the accusations here, the motor never once gave a single sign which is exactly why I'm looking over at the timing retard. At the end of the second run, it had some piston slap, and it was time to turn it off and call it a night. It must of happened right at the end of the run, there were no signs of lack of performance, etc. I think smart people run bent rods in their motors till they fly out the block right? thats why I reused my block for a stroker build?

My only mishap is that the EGT was on the #1 runner, so I don't know exactly what was going on inside the #4 when it decided to turn my rod into a banana, I'm just glad it never seized and threw the rod.

First off, I'm NOT calling you a lier! I was just trying to point out that retarded timing would not cause the rod to bend like that. Other people besides me have agreedon this in this thread. Somthing like that would come from way too much timing, or if it the wastespark was so extremely retarded that it fired the # 4 while it was barely starting to rise and had some fuel in there to boot.

I cannot say exactly what caused it, but i can say that 12* of timing did NOT do that. I've seen stock DSM's (even mine when i first got it) pulling only 9* at the peak torque areas of the RPM band and never had any adverse effects except high EGT's, and this was through teh stock ecu, it pulls timing to prevent damage, if pulling timing caused damage i seriously doubt they'd make the ECU do it.

There's a really good book on engine tuning theory that deals with everything from timing, cam timing, rod ratio, VE, fuel management and more that is a great read that might help you discover your problem. I'll have to see if i can find the box it's in to give you the name of it. A little reading NEVER hurt anyone.

And don't get so defensive, people here are trying to help, not call you names or make fun of you. Just because most of us are disagreeing with what you think caused the rod to bend does not mean that we're against you in any way.

[dsm-onster]

Originally Posted by hakcenter

At the time I believe it was a 2.0 bottom end rebuild, 1g pistons on 1g rods + arp hardware. stage 3 head 1mm os valves / fp2's, blah blah de blah blah, it was overkill.

60-1 on 950s +dsmap speed density. I forgot what the curve was. All on piss 91 octane w/ 10% alch from the pump. No injection, no extras all turbo.

When I tore it down, I checked all the plugs, no signs of detonation, no signs even on the piston. Only #4 went out. No AFR hiccups, solid 10.5:1 from 4k to 7k.

Same top end, bottom end on forged stroker, had no probs reaching 25psi on 100octane and i think 18*, knock on wood. So I don't get it what happened to that #4 rod, maybe its an anomaly, but I would of expected more than 1 rod to go.

That 60-1 compresser is an oldy-but-goody, isn't it? What airflow did you record?

Straight from me to you, I'm not saying its your lack of skills. You obviously saw no onset of knock detection by the knock sensor. You inspected the engine afterwards to find out what went wrong. And you're using your capable reasoning faculties to draw a plausable conclusion.

[hakcenter]

Originally Posted by dsm-onster

That 60-1 compresser is an oldy-but-goody, isn't it? What airflow did you record?

Straight from me to you, I'm not saying its your lack of skills. You obviously saw no onset of knock detection by the knock sensor. You inspected the engine afterwards to find out what went wrong. And you're using your capable reasoning faculties to draw a plausable conclusion.

60-1 is a greaty, can't give you air flow numbers, too long ago, no maf, ghetto math is not my thing. If i was going to guess, I would of guessed 35-45lbs/min 45 being, lol yah right.

Maybe it was a problem on the waste spark, who knows. I can tell you what it wasn't but I think we've already established that. Either way, I'm too liberal, I won't tune cast lower than 15-16* @7k without 100+ or forged. But with E85 E100 coming around the corner, looks to be a great time to own a turbo car.

If anyone wants my paper weight, you have to beat me in a game of your choosing, but not the iwin game.

[dsm-onster]

I believe it was a rapid preignition event, or an anomaly; just as much as you believe it's timing retard . But only because I've tuned nothing BUT cast on pump gas and run several setups at lower timing to over 40 lbs/min. If I hadn't I'd certainly take your word for it. You've put out certainly plausible evidence.

Preignition *can* leave no traces. It *can* lead to detonation. It also *can* cause fuel to ignite early enough on the compression stroke to bind and bend a rod. Again, IF it occurs early enough, no melted components would result as the explosion is not a RAPID explosion (detonation) but just WAY too early.

The mix of pump fuel and 10% alcy: was this ethenol?

Back to the topic and on the other end of the scale. Tuning in a high timing advance yields more power than leaning out the setup, especially if you're running 11:1 or so a/f ratio. But, don't think a boosted setup will have any advantages by running the stock fuel map and a lot of timing advance. Many guys see no more results at 28* timing than 24* timing, if you can even achieve that tune.

Tune for around 10.5:1 A/F ratio, add as much timing as you can, then go back and lean out where you can. This way you assure the most reasonable timing advance and have a chance at achieving the best a/f ratio for your fuel.

[pneumo]

So you blew the #4 cylinder too? So did I. Coincidence? Cylinder #2 or #1 may burn the leanest and hottest, but #4 has the worst coolant flow and gets the hottest coolant. Coolant flow starts at the block next to cylinder #1 where it's the coolest then goes to cyl #4 where it exits the head right next to the combustion chamber for cyl #4 where it's the hottest.

To make things worse, the EGR passage goes through the head from the exhaust side of cyl #4 to the intake side. EGR isn't used at WOT, but the passage is there, and it's cast into the head adjacent to cyl #4's exhaust port, valve guide, and combustion chamber. These parts see a lot of heat. Instead of having coolant flowing over them, you get a tube of insulating metal cast into the coolant passage and filled with hot exhaust gasses. If you get a chance to remove the thermostat housing, look inside the head. The EGR passage can be seen just inside the opening on the bottom.

The EGR passage meets the exhaust port at a sharp angle. It looks like the factory simply drilled the egr opening with no attempt to radius the junction. There's plenty of surface area to absorb heat, but as I mentioned above, there isn't a good way to remove heat from this area. When I port heads I like to carve a big, smooth radius where the EGR passage meets the exhaust port. This cuts down on the ammount of surface area available to pick up heat.
HTH

[dsm-onster]

I am wondering about the exhaust valve heat. Perhaps we're all right. . .

272 duration cams allow the valve to be lifted off of the head for a lengthy amount of time. SS (Hak mentioned 1mm oversized-- all are SS to my knowledge) absorbes heat very quickly, but more importantly, a bit less evenly vs. cast iron. During peak airflows where there's enough oxygen to really heat things up, his SS exhaust valves in that cylinder could see abnormal amounts of heat because:

1. poor cooling of the head at the #4 cylinder
2. the slightly hotter burn of the 10% alcy mix
3. the significant open time of valve
4. uneven heat absorbtion of SS
4. the added timing retard which always heats the exhaust track up significantly

Considering these would it be possible that there was a hot spot on the exhaust valve that resulted in preignition? Heat from timing retard alone wouldn't cause that rod to bend. But it certain can be on a list of contributers to preignition. Though, so many run 272s w/ SS valves and lazy timing at peak VE (the most oxygen in the combustion chamber), and see no ill effects.