My temperature is normal throughout this testing, it's not running hot or anything, even when I'm crawling up the hill with detonation/pinging, the temp gauge only rises slightly, as normal under load.

brian

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I want to hear the noise. At this point with all that you have posted I do not believe in the diagnosis of pinging.

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Joshua

I posted a few videos, but the sound quality doesn't really pick up the sound.

http://s785.photobucket.com/user/67dart ... sort=3&o=9

Here's at the exhaust pipe, at idle, not making the sound during this video, but I hear a faint mechanical sound in there: http://s785.photobucket.com/user/67dart ... sort=3&o=8

It sounds like a rapping or loud exhaust tick, but really loud and I lose power. Think of an exhaust manifold leak, but on steroids, like "tack" "tack" "tack" regular rhythm, I can hear it in the exhaust pipe if I stick my head out the window and listen. This is where I started, I thought it was a bad exhaust leak, but there is no leak. I suspect #4 simply because that is where the head gasket burned through.

b

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I increased my octane, to see if that helped, but alas it did not. The thought there was that my compression was actually too high for pump gas. I considered that (180 psi per cylinder, 8:1 DCR calculated), but that wouldn't explain the issue getting progressively worse over time (unless the gas around my parts is also worsening over time).

I did check the exhaust back pressure under load. The peak back pressure in each down pipe, under full acceleration (uphill or on flats) and warmed up, was 1.75 psi, so I don't think it's a back pressure issue. It was interesting to see the numbers (AFR as well) in the garage vs under load. Recall the back pressure was nil in the garage, at low and high rpms.

I have noted a very brief spike in AFR to 16 when I tramp on the pedal, but it quickly goes to safe range of 14.5 under load (when the noise starts). Cruising at 70 mph the AFR is 14.7, at idle it's 12.5. Anyway, when it's cold, everything works fine, acceleration, no noise, lots of power. After it warms up the detonation or sticky valve or whatever is going on starts up; loss of power, crawls home.

OK, time to pull the head. I have another head prepped. It's been milled and a valve job, but not larger valves or ported like the one I have now. I'll do a compression test once it's installed, I have no idea of the cc's or how much was milled from it. I can check the current head for valve stickiness, but first is whether the engine exhibits the same issue with an entirely different head. I can't think of anything else to check. I've checked exhaust back pressure, intake vacuum, timing (dialed way back, same issue), distributor (installed newly rebuilt unit), ECU, plugs, AFR, intake and exhaust leaks (none), valve lash, lifter surfaces look good...all seem to be operating in normal way or range. I'm left with valves sticking when hot or some such thing. It burned through a head gasket, so it has to do with what's going on in the cylinder.

I suppose I could start playing with emulsion tubes and jets in my Webers, to enrich the AFR under load, but I suspect that's not the issue. My last engine before this build didn't have any issues with these carbs, it ran fantastic until the cam's oil pump drive gear failed.

I'll report back my findings.

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Are you sure your muffler hasn't failed internally?

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Well the peak back pressure under load at the down pipes was 1.75 psi, that doesn't seem like too high a pressure. Cruising at 70 mph it was less than 1 psi.

Hey, anyone have a part number for a cold spark plug I can try? I'm using an NGK ZRF5N, maybe a short tip plug is better?

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I used this as a guide, let me know if it's bs

http://www.aa1car.com/library/exhaust_backpressure.htm

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No, exhaust backpressure isn't bs. I was wondering if you had themuffler fail internally in some way that didn't restrict flow but alowed a baffle to rattle around inside the case. Have you tried whacking the muffler with a rubber mallet to hear if it rattles? I have had mufflers rust out internally and rattle and drive me crazy.

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Reed,

No I didn't mean if back pressure was bs, I meant if the numbers they quote are bs.

They say at idle, BP should be less than say 1.5 and under load less than 3-4psi.

If those numbers are ball game correct, then I don't have a back pressure issue, as mine is 1.75 psi under full acceleration load, and typically is less than 1 psi cruising. At idle my back pressure is zero.

brian

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Here is an article I read on cold vs hot plugs: http://www.hotrod.com/how-to/engine/spark-plugs-tips/

I'm hoping a colder plug will help me out, maybe it's today's fuels and my high compression.

b

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If higher octane fuel didn't do it then colder plugs are unlikely to help.

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Joshua

Joshua,

I tried off the shelf octane booster, which likely doesn't bump up octane much. I read independent tests where most of them (with 15 gallons) bump it up less than a point. I used two bottles, but maybe I didn't get it up very much. There are many new sources of octane boost that provide specific ratios to mix for more precise octane result; I just haven't gone there yet. It was easier when I was a kid, our local Shell station had one pump dedicated to 98 octane, all the hot rodders used that station. Of course it was also leaded gas, and it's good we left that behind.

Anyway, to your point, I disagree. I would think that these effects would be additive. Higher octane will curb detonation, but so will a colder plug. As I understand detonation, you have e.g. high compression and/or a hot spot like a hotter plug (acting like a glow plug in a diesel essentially) or a sharp edge or carbon deposit that is heated up. The high compression acts to promote combustion early as well as the hot spot. It seems intuitive to me that higher octane and colder plug would be synergistic in their effects to thwart that condition.

A good example to show how compression promotes heat and combustion, without a spark, is here: https://www.youtube.com/watch?v=4qe1Ueifekg

Note, my compression numbers were 180 in #2 through #6, but #1 was only 150 psi. After a quick road test, you can see (below) that #1's electrode (far right) looks normal, brown, but the remaining plugs are white and speckled, so it seems like there is a clear difference in how they are burning and it correlates completely with the compression numbers. So, I believe my intermittent issue with detonation is indeed related to gas supply, but it's because my compression is so good in #2-#6. If all cylinders were 150 psi, I likely wouldn't be having this issue (i'm not ruling out a sticky valve, but it's looking less likely based on what I'm seeing).

http://s785.photobucket.com/user/67dart ... sort=3&o=6


I'm hoping a colder plug will help out and I won't have to use octane boost. Also, I'm told one might actually tweak the intake valve lash to lower compression a bit. Another knob I could try is getting more fuel in the cylinders under load; as I said above, this would require me to play with jetting, emulsion tubes, etc. in my Webers. I can go there, but I don't want to if I don't have to, as the AFR readings I'm getting are fine and were giving me good gas mileage and power (before this issue came up).

I'm trying to be methodical and scientific about this issue, so far I've eliminated a number of possible causes; I think it's related to the high compression along with newer fuel stocks.

brian

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I realize that plug reading is not an exact science, but If I was trying to chase a detonation issue I would want more color on those plugs. Could a fuel delivery issue be causing one of your carb's make one cylinder to go lean? All of the manufactures tune their engines to run a bit rich at full power because it provides more insurance against destroying engine parts in the event that you have a bad tank of gas or something. I would be pulling the carbs off and looking inside them for a blocked jet, or borrow a carb from someone else and swap one at a time.

Also I have read that advancing the ignition will cause spark plugs to run hot. Why not pull 2-5 degrees of total advance out before swapping plugs. It is cheaper, faster, and if it works then change to a colder plug and dial more advance in..

White speckled plug indicates too lean mix. Tan plug is preferred.

I was able to balance out compression of my engine by fine tuning valve lash and with the help of a compression tester. When I started range was 149 psi to 168psi, now all six are at 163 last time I checked. Lash with my non stock cam runs 0.023" to 0.029" both I & E depending what the compression tester dictated.

You need to step up to larger jets, and play around with lash to lift up that low reading in #1, to richen up the other five.

If you are able to even out pressures so that #1 is 5 psi lower, and that plug looks darker then the other five, try a hotter plug in #1 it may be enough to lighten its color.

Once you get even compression on all six, idle quality will improve and vacuum will increase slightly with a more stable gage needle.

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Yes, I tried dialing back the timing already. Took it back 5 degrees, then 10 to TDC (didn't idle or perform well there). My idle is very smooth.

I agree, #1 is looking way different (better) than the rest, and it aligns with the compression readings, #1 is about 30 psi lower than the rest. I think the lean look to the plugs is that the mix is too lean with that much compression. That is, I believe the cylinders are getting the same level of gas (can't prove that, but AFR numbers are consistent from before the problem), and sufficient amount of gas at 150 psi, but the higher compression cylinders are suffering from detonation because it is not enough fuel for that level of compression (and perhaps my fuel supply has changed over time).

I could increase the fuel to the cylinders, lower the compression with lash adjustment, use a colder plug, raise the octane significantly, perhaps all four or various combinations of these.

I believe we're all speaking the same language, and that I'm getting to the heart of the issue. I just need to see what the best solution is. I'm hoping a colder plug will do the trick, the AFR readings are within normal range; I'd hate to richen it up if I can solve it another way.

Brian

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