motoxxxman

Lets start a topic about the squish zone aka the quench area. What shapes are better or worse, and for what purpose (IE: low comp, boost, high comp, etc), and why?

PyroProblem

The little I've read about it is .035" quench clearance is supposed to be the magic number. Too much clearance and you lose quench/squish which actually promotes localized hotspots and then pre ignition/detonation or something like that.. I think the idea is with having good tight squish, your forcing most of the a/f mixture towards the center of the cylinder closer to the ignition source, resulting in a better burn and more power..
And then if you have Aluminum rods, you would want to add a little more clearance for growth @ 9k rpms.

In for some more info.

TomCat39

This is what I've read too. .030-.040" is the perfect range.

I will say, under .030" causes detonation as I have found out with using the .025" D16Y8 head gasket on a D1B7. Piston is flat top (with valve reliefs) and goes to .002" from the deck. That is reducing my squish/quench down to .0252" and I had to reduce ignition timing by 1-2° to reduce high rpm detonation.

I've read the quench area creates a cooling area that is what reduces detonation (pre-ignition). Most of what I read that got me researching quench was from The Old One (ENDYN) archive:

http://www.theoldone.com/archive/quench-area.htm

Based off of that and additional research on quench, I was planning on using the 4 layer MLS gasket with a D16Y8 head on a D15B7 block. The flat pistons going to .002" from the deck top, coupled with the massive flats of the D16Y8 head and the .037" MLS gasket will create a very large quench area on both the intake and the exhaust side of the combustion chamber.

I basically wanted to shoot as close to that .035" margin as I could.

motoxxxman

the above seems to be what I've been reading before too. my engine is a bit different and I've been modifying it to alter the squish.

factory setup of my b20a5/b21a1 engine (same for both) is:
piston to deck ~0.005
HG thickness 0.045
deck to intake squish 0.095
deck to exhaust squish 0.080
total intake squish 0.145
total exhaust squish 0.130

the above is with an unshaved head. my head was shaved about 0.015, (I'M BOOSTED) and about 6 months into DD'ing it I did a few pulls and burned a hole through the piston on the exhaust side and the head pitted all in the quench area, zero audible ping, just some power loss and then a thump from the combustion pressure entering the crankcase.

my next engine I went with a 0.030 thick HG and shaved 0.045 more off the head, and reshaped the combustion chambers a little while polishing and cc matching them and making cyl 3 0.4cc larger than the rest.
total intake squish 0.070
total exhaust squish 0.060

well I went over a year with zero issues. then about a month ago I noticed a mild lack of power in a single pull, pulled the plugs to check, and sure enough the ground strap was melted right off the plug in cyl 3, which coincidentally was the same cyl I burned a piston in my previous motor. threw new plugs in, went out again and did a few pulls and everything was flawless, checked the plugs, flawless. for the past month I've been checking the plugs a couple times a week, and everything has appeared totally normal.

well I currently have my head off, and whatever happened a month ago caused a bunch of pitting in the head and piston on the Intake side squish area (previous motor was exhaust side). I already did a bunch of smoothing to the chamber and got rid of most of the pitting. Tomorrow I'll be dropping the head off to get another 0.015 shaved off, then cc matching them all again. That with my newly worked chambers will put my squish at about:
intake 0.060
exhaust 0.050

I dont know if it's coincidence that the same cyl had the same issue with two totally different motors. the injectors are good, chambers were all cc matched, plugs always read identical between all 4 cyls. the only thing out of whack was valve lash on the exhaust side was at about 0.002-0.003 both times and only in that cyl, spec is 0.006-0.008. So I'm hoping as long as valve lash stays in spec all will remain golden.
What I dont understand is if the quench zone is supposed to run colder, why did I burn a hole in a piston in the exhaust quench zone, and now in a different motor have pitting in the intake quench zone.

PyroProblem

Even with having excellent quench which would help resist pre-ignition/detonation, could you just be pushing too much boost for your octane?

I have "heard/read" that cylinder 3 runs a little hotter due to how the air enters the plenum and somehow #3 gets a little more air than the others. IDK if the same holds true in a forced induction setup.
No signs of running lean (assuming you have a wideband) during the pull?

The pitting sounds like detonation. Does it look like someone hit it with a screwdriver and hammer?

The burnt piston is most likely the piston getting too hot and the combustion pressure finds the weakest point (overheating piston reaching the melting point), then all that combustion pressure blows through and you get that melted piston.

Perhaps it was tuned a little too aggressive?

motoxxxman

I've been aware of cyl 3 typically running hotter, which is why when I cc match the chambers I always make cyl 3 0.3-0.5cc larger, and when I had my injectors cleaned and flow tested I put the highest flowing injector on cyl 3. My previous engine was 9psi, current engine is 11psi, it's never been leaner than 11.7 above 5psi, and I only use 93 octane from Mobil. The tune used to be fairly aggressive, with zero issues besides plugs showing a little hot but no signs of det, but I dialed it back 1.5 degrees a few months ago. After the plug melted and new plugs were installed, any time I checked the plugs it showed perfect heat and no det, and af has stayed around 11.6.

I did have a loose connection on the coil + wire going to my msd box, but it's never caused an issue besides occasional no start. Maybe that had something to do with it? I cut off the terminals and soldered it a week ago.

motoxxxman

The head pitting. I'll get a pic of the piston later

PyroProblem

Im not a tuner, but I think that cylinder is running too hot for some reason and causing the pre-ignition/detonation that is melting pistons and doing that to your head.
I wonder if having an EGT gauge would yield any insight.

IDK how the MSD could affect just one cylinder. Like you said, I would think it would either work and run the car, or not work period.

Doesn't melted plugs usually indicate the combustion temps are too high or the plug is too high of a heat range?

Doesn't the EGT usually go up when you retard ignition timing?
Have you ever tuned wot on a dyno or just street pulls?

Just throwing some ideas out there so hopefully it doesn't happen again. From what little I do know in regards to tuning, it seems like you have all the signs of too much heat and/or not enough octane requirement.

Stopsign32v

iTrader: (1)

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motoxxxman

I've thought about this before, but to do it right I'd want to have 4 EGT guages, one for each cylinder.

my thoughts as well. if anything, if it were to break connection at all I'd assume it would just cause delayed timing, aka retarded, not advanced to cause detonation

yes very much so. I just cant figure out what caused the super hotness in that 1 cyl in 2 different motors. plugs looked fine before each issue, and new plugs after this recent issue still showed perfectly fine. I'm starting to wonder if I have a finnicky injector. resistance shows good, and flow testing shows all 4 within 1% of each other still. *shrug*

yes.
yes, dyno and street tuning. and I touch up the tune on the street anytime I see af change even the slightest bit, and I check plugs fairly often and alter timing on occasion according to that as well. after dyno tuning it I retarded it 2 degrees, and never go above that number. I've actually pulled a bit more out since then for lower humidity, and what I'm guessing is slightly higher compression from carbon buildup (very minor, but still there)

I appreciate any and all input from anyone.
I'm fairly certain I'm not maxing out my octane ability, and I'm not seeing any signs of detonation at any time except that once. I'm currently at 11psi, and have run 15psi before with the same setup and fueling with no issues, but I did it a hacked way that I wont mention lol, I'll just say I was still using the stock map sensor at the time, which maxes out at 10psi in my car lol.
besides, If there was detonation from something, I'd assume I'd see it elsewhere in the motor. too much timing usually blows any crud off the pistons and head too, and my pistons and head chambers all have a thin film of carbon on them pretty consistently.

actually, that just gave me an idea. if carbon peels off, it becomes a hotspot, a glowing ember. there was some carbon flaking off a few of my intake valve heads. I wonder if that was the culprit?

PyroProblem

Well in that case, Id start to lean towards a intermittently failing injector, no pun intended.

Each time it happened after a pretty decent pull, right? And all the other cylinders show no signs of overheating? piston skirts ok?

How old and what kind of injectors are you running?

I would have to assume that if ran lean enough to melt a piston, the wideband would pick it up as it became a lean misfire (detecting more oxygen from the misfire).

And then I always hear these stories about how buggy Crome is and that the timing tables wonder around and whatnot. Is there any chance something in the software is bugging out? Ive never used Crome as the horror stories always scared me. Sounds like you have a pretty good handle on it though.

Only other thing I can think of would be an injector driver, but I think once they crap out, they're out for good, unlike how coils in an injector might fail.

motoxxxman

Wideband showed very little change. It twitched for an instant though it was only a couple tenths and I think it actually showed richer iirc.
Injectors are dsm 450's, and I get them tested, cleaned, New pintles and filters, and balanced every year. Just did a resistance test on them just now and they all read exactly 2.5 ohms. Tested my oem Honda resistor box too, and exactly 11 ohms on all 4. For the injector drivers in the ecu, in my experience they either work or they don't.

Skirts all looked great in my last motor, and though I haven't pulled the pistons in this motor the cyl walls all look darn near brand new leading me to assume skirts are good currently.

Crome has been good to me in my car. I'm aware of all the issues with Crome and have been fully able to work around them, especially with my engine being non-vtec.

I really am wondering if I simply had a carbon flake become a hotspot, both times, and that it's just coincidence that it happened in the same cyl. Especially considering the previous time it happened on the exhaust side and this time was on the intake side.

TomCat39

You said your best squish/quench is .060-.070" yet everything I've read is ideal is .040" max on down to .030" minimum.

What's been stated is you don't get the same cooling effect aka "quench" outside of that ideal range.

I'm trying to understand how you think all is well and not going to run hot when you are outside that range?

Add just a bit of carbon build up and you went from the very edge to over the edge methinks as it's running at the top end of the heat scale from the lack of actual real quench.

Basically what comes to my mind is you've tuned it to the very edge of the no real quench status of your builds and after awhile the motor naturally pushes over that edge. Where if you had a real quench zone you'd likely have a much larger buffer zone for changes. But I suppose the end result would be you would push that setup to the very limit and back off only a touch, giving you only a 1% buffer if that. The slightest change will push you over the edge even then.

You are running it like it's a race car on the track getting every last little ounce out of it but not rebuilding it every 100 hours of use and expecting it to stay the same.

PyroProblem

Being the cause of the cylinder over heating seems intermittent, I have to point the finger at the injector.

Even though tested fine at the time of testing, consider how long and how much youve boosted and it was fine.

That coil inside the injector I believe can fail just like an ignition coil and a relay. Intermittently. Are the injectors old?

PyroProblem

The thing is about the tune being questionable, I'm sure he's done plenty of street tuning and dyno tuning to find where his ignition curve needs to be and then he removed more timing out of it as another safety buffer. None of the other cylinders appear to have any signs of detonation knock or pre ignition and the car has been running great except for the couple instances where number 3 melted down. Does Chrome have individual cylinder fuel trims? It might be time to invest in one egt probe and four bungs for your manifold do your tuning and then fine tune the cylinders per EGT. But honestly at only 12 lbs it may not even be a factor yet.

motoxxxman

Not my best, just the lowest I've set it to yet via massive head shaving.
I'm thinking about taking my spare head and welding the quench area to fill it in then shaping and shaving so I can get a good quench without having to shave the head so much.

And timing is currently 3.5 degrees retarded from what the dyno showed as ideal, which is actually a fairly decent amount. Enough that it lost about 3%-4% torque through the whole peak boost range. And I did it universally through the whole map, not just peak boost. So part throttle is also a bit retarded. Everywhere except below 1200 rpm so timing can still be set properly.

TomCat39

I wasn't saying the tune was questionable. What I'm saying is the tune takes it up to max just before exploding, then back off just a little bit.

Works fine for awhile but isn't a big enough buffer for an engine that isn't decarbonized every 6 months or better.

A stock Honda engine I suspect has a much larger buffer just for the changes that take place due to carbon build up.

A race car on the other hand gets rebuilt sometimes after every race depending on the venue. So you can run everything right to the very edge with no buffer.

I was suggesting the buffer setup in the tune/timing was enough for awhile but probably not enough for a year plus. Especially if the car ever goes a touch rich momentarily. It will add up over time. Increasing CR a little, creating micro hot spots etc etc.

One clue is no detonation being heard but the chamber is peppered and the splugs melted. And there is a bit of carbon build up seen on the valves, so likely a bit on the piston tops too. A .010" variance can have a drastic difference on that safety margin.

I'm not saying I'm right, just saying that it probably is a fairly significant factor as the motor ran great for quite some time and developed the problem after a fair amount of driving. One thing that is going to change over that time is a pristine clean motor being far from pristine with carbon build up.

So maybe you run the small buffer for 6 months then increase that buffer another 3-4% the next six months.

Not sure what the ideal buffer is for the long haul of 300K but I'm sure it's more than the original 3-4% you had.

PyroProblem

If you do this, PLEASE start a thread with lots of pics. Chamber design and rework is another topic I find intriguing.
Well whatever is the cause, hope you get it figured out. Now that you mention it Tomcat, there does seem to be a lot of carbon flaking off. I wonder if there might be an underlying oil ingestion issue?

motoxxxman

Tomcat, thanks for the input, I will definitely keep that in mind. I have all along for the most part, which is why I frequently check plugs and make changes accordingly. I also do frequent compression and leakdown tests, which helps with this idea. I also rebuild my motors about every 20k, or sooner if anything seems off. This motor has around 15k on it since its original build.

Pyro, my valve seals were leaking a little, but, mainly just in cyl 1. 4 not at all, and 2 and 3 only a tiny amount. And this damage is in cyl 3 as a reminder. The wetness in the chamber pic is actually kerosene from leak testing the intake valves. When I tipped the head some dribbled out of the port and ran around the valve heads lol.

To be fair, this whole teardown actually started because I was replacing the valve seals, and during that process discovered a very small leak in the hg to coolant in cyl 4, and a small exhaust valve leak in cyl 1.

motoxxxman

I'm in the middle of cleaning the piston tops, and #3 has definitely gotten a bit hot across the whole dome. It's not coming clean anywhere near as easily as the rest. They were all polished previously. I plan to keep using it, but if anything seems awry I'll tear it down again and replace it.

Also, I'll be using the same injectors for a few days to see what happens, but I do have a brand new set of 650's I'll be throwing in within a week of it running again.

pogeeboy27

iTrader: (3)

I think you're correct in this assumption. Lancer Evos have the same problem, albeit with cylinder #2. The only way to approach the problem would be to tune the whole engine around cylinder #3 or to adjust fuel in cylinder #3 to compensate for the added air flow.

OP, do you have access to E85 in your area? You would have lower combustion temperatures and your carbon buildup problems would disappear.

In general, you may want to start thinking about upgrading parts that you feel are "good enough" to more reliable parts. The less time you spend worrying about your engine, the more time you have on your hands to focus on the important stuff.

motoxxxman

I currently have cyl 3 set 1% higher fuel flow, I'll probably go to 3% or 4% and see how she does.

I do not have access to e85 unfortunately.

I will be upgrading my injectors in the very near future. I will also be cc'ing the head chambers after I get it back from being shaved and will make cyl 3 around 0.75cc larger than the rest as compared to 0.3-0.4 like before.

TomCat39

This right here I think negates the whole concept of long term carbon buildup.

There is no long term to your motor.

motoxxxman

Yeah no kidding, tell me about it lol. I do still build up carbon awefully quick though as I always seem to go through valve seals like you wouldn't believe. Valve stems are always pristine, guides are new, and I've tried like 5 different brands of seals. This time around I'm using supertech seals for the first time, we'll see how they do.

Another question in my mind is whether oil is seeping past the guides, as I know the machine shop did not use guide sealant when they installed them. When I get the head back I'll be testing for that too by putting some kerosene or maybe rubbing alcohol in the spring seat reliefs around the guides then inspecting the ports for any evidence of seepage. Haven't fully decided yet what to do if they are leaking. My spring seats have a recess, so there's room to put a small bead of something around the guides to seal them up if necessary.
Suggestions? Loctite, jb weld, etc, etc?

PyroProblem

Guides are an interference fit if I'm not mistaken. There's really no way I can see them leaking between the head and guide. What Do you have for venting the crankcase? Perhaps oil is being forced past the rings from excessive crank case pressures?