OK, so this morning I fired her up, runs fine until hot. At first startup, no noticeable misfire or rough running, warmed it up for 5 minutes in the garage, checked the timing, TDC, no change there. Idling smoothly, revs up, no stumble or anything, instant throttle response. Took it on the highway, just a few minutes on the highway going 65 mph, runs smooth, then the rough running, shuddering vibration begins. I ran it over to the leftmost lane near a barrier wall, punched it down, I could hear some ticking/pinging again. There was none when I first changed the head/gasket.

This all seems consistent with my earlier findings, this thing is running too hot and/or preigniting and burning up head gaskets. NOTE: the first head gasket, when the engine was first built, was an oversized bore gasket, perhaps it simply took longer to burn through that one (maybe it has a better ring structure). The last two were felpro and burned through pretty quickly, like less than 200 miles and this happens: http://s785.photobucket.com/user/67dart ... sort=3&o=1

Anyway, AFR, timing and other metrics all the same, and with hotter plugs, I ran the first head gasket for about 5000 miles before this problem crept up chronically. Fast forward to the recent saga, testing, colder plugs, and still I burn through two felpro gaskets in almost identical timeframe. I'll confirm this, I'll have to pull the head again, but I'd bet $20 there is head gasket damage and at one of the cylinders with the 180 psi compression. I appear to be just on the very edge of AFR, compression and timing where I get this happening. I can richen the mixture to see if that solves the issue.

OK, a couple of questions. First, head gaskets. Will a copper gasket hold up better than these steel ringed gaskets? I don't want to avoid the real issue, but if I'm just on the edge, and copper doesn't burn like these thin stamped steel rings, then why not try a copper one?

Second, and this may be a stupid question bear with me, instead of fooling with my jetting, can't I adjust my choke so that I have a richer air to fuel mixture (provided it gets sufficient air to breath/flow)? I only ask this question because once I forgot to reconnect my electric choke wires and I drove it on the highway and it ran fine; I didn't even realize the choke wires were off until I got it home and opened the hood...

brian

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...also the run on/dieseling being suddenly back is another symptom that points to the head gasket ring having done this again.

http://s785.photobucket.com/user/67dart ... sort=3&o=1

But, again, I'll confirm it. And start researching bigger main jets....

brian

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I would say no. The chokes function is to be on and within minutes completely open. It is not to adjust mixture with once the engine is warm. I don't see it as being a very consistent way of adjusting mixture. One man's 2 cents!

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

What kind of carb's are those?

Rick and Jase,

My carbs are Webers; I've taken the time to research them over the past day. They are easy to tune, it's just trial and error with jetting; I was just hoping that I wouldn't have to, since it was running great for the first 5000 miles.

Anyway, the tuning part comes down to this (big picture):

- idle jets need to be of certain size so as to provide sufficient AFR at idle AND this circuit feeds the system up to 1500-2500 rpm. The key here, and many Weber gurus agree, if you have to turn your idle screws out more than 2-3 turns then your idle jets are too small. My idle AFR is 12.5 (OK against preignition issues), but I have my screws turned out almost all the way. OK for idle, but this is also playing a part in my leaner AFR at higher rpms (on the highway at 70 mph I'm only running 2000 rpms with those 2.76 gears). So, first I need to increase my idle jet sizes (jets are cheap, like $4 each) and reset the idle screws to where I'm only turning them 2-3 turns from closed position. I'll do that and measure AFR at idle and on the road. That may be enough.

- Tuning webers is done iteratively, only change one thing at a time. If the idle jets increase doesn't give me sufficient AFR across the range, then onto the main jets. These are simple devices and have infinite variability. They are a brass tube, the emulsion tube, which has holes, like a flute. On the top is an air corrector jet, and on the bottom of the tube is the main jet. Since I have two barrel carbs, there are two of these setups, a primary and a secondary. Air is drawn down into the emulsion tube through the air corrector jet, and gas is supplied from below into the tube via the main jet, the air and fuel mix, are emulsified in the tube and exits via the holes in the tube. So, in my case, since I'm running lean, I would increase the main jets and leave the air correctors as is, or make them smaller (that answers my question about choking to get lower AFR, that is achieved via the air corrector jets). One can also play with the emulsion tubes, there are many diameters and hole patterns, but that is second order Weber tuning, I may not need to go that far.

- third area to play with, if needed, is the accelerator pump jet. If you are getting a lean condition when you floor the pedal, I am, just for a second it raises to 16-17, then drops down to 14.7 pretty quickly, then you might increase the pump jet size.

All these components are tiny little deally's and only a few dollars at piercemanifolds.com Also if they don't have the jet size one needs, folks use tiny drill bits to bore out jets, or fill them with lead or solder and drill back out to smaller bore.

Before I pull the head, I'm going to adjust my carbs to get steady AFR across the rpm range, say around 12-13; that should help the preignition issue. Since I drove the last head gasket for a few hundred miles and my misfire got really bad when it heats up, I think I've fried another head gasket. I don't want to install a new one until I've got the AFR in the right range.

brian

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So, consistent with all my tests, the issue seems to be that with this higher compression build, and the gas supply in my area, I'm right on the cusp of having an engine that will run fine on pump gas, or not, depending on the mixture. I should be able to correct this with a richer fuel mixture and dialing the timing back. I could go to octane boost but I want to run on pump gas. I'm hoping that if the richer mix fixes the issue, then I can try going back to ZRF5N's which, as Dan will tell you, provide optimum efficient combustion. In my build they, along with my lean condition and high compression, where too hot.

brian

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None of that will fix your wildly varying comps,or the oil breathing. Have you actually confirmed valve timing is correct ? Check exactly what the distributors are advancing to at rpm? I'd pull the engine now and check for what other damage has been inflicted,at best new rings and resurface the faces for the head gasket. Then build it checking valve timing,comp ratios etc etc....seriously,perhaps get a friend who's experienced to help you with assembly. Then you have a known quantity to work with. ZFR5N plugs on a hi comp engine isn't the best idea,I'm sure you can do it but you need to be careful if it's been milled on the head or decks. On a stocker maybe OK, I found they need less advance probably due to a more centrally located electrode,that's a good thing,but by less advance I mean less at wot,not just grabbing the distributor and turning it back some,you need to adjust the actual curve.

I still don't know why your high compression moved to other cylinders? Were they all in the 180 range when the engine was new? Just thinking out loud.

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

http://www.agcoauto.com/content/news/p2_articleid/200 Leak into valve train area mlght cause more pressure in crank case,or pcv hose colapse.Wild guess

Most definitely could,very good point...but he's still got those big variations in compression... If it's been that hot to burn a gasket/s I'd be really worried about Pistons and rings,plus those gasket faces have copped a pounding, 180 psi is pretty high,that's why I'm thinking valve timing.

I can't explain the variation in compression readings, but these were two different heads. I did find fuzz on my magnetic oil plug, so something's getting a beating. The lifters looked good, not flat or cupped or worn that I could tell.

Now that I know it's not the head, I can go back to the other one, it had more consistent compression numbers, only one cylinder was lower.

I'll get the AFR to 12-13 across the rpm range that should help.

You know, now that I think of it, I did install that cold air intake, that would also raise my AFR, right? Cold air is denser than hot air.

Brian

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This weekend was playing with my Webers to richen up the AFR across the range. Below are the original setup and new configuration. These numbers are for one carb, I just did the same thing for both carbs. They are balanced, same readings for both banks (front and rear down pipes off DD's).

Factory Setup
Weber 32/34 DFT Primary Secondary
air correction jet 1.60 2.20
emulsion tube F-53 F-22
main jet 1.05 0.95
idle jet 0.50 0.60
pump jet 0.40

New Configuration
Weber 32/34 DFT Primary Secondary
air correction jet 1.60 2.20
emulsion tube F-53 F-22
main jet 1.05 0.95
idle jet 0.65 0.70
pump jet 0.70


With original 0.5/0.60 idle jets, there was no idle adjustment window, but good steady idle at 12.5 AFR. Moved up to 0.65/0.70 idle jets, this gave me a wide idle jet adjustment range, could go from 10-14 AFR with steady idle along entire range. Set AFR at 13 with ~ 2 turns of screws out from closed position, this is what Weber gurus say is appropriate (I was at 4-5 turns out). Took test drive, on acceleration AFR jumps to 15-17. Tried 1.20/110 main jets, way too rich, fouled plugs after 5 minutes. Changed plugs, installed 110/105 main jets, still too rich, idle adjustment lost, idle AFR at 10. Moved back to original 1.05/0.95 main jets, idle adjustment window returned, test run reconfirmed AFR raises to 15-17 on acceleration. Moved to larger pump jets, from 0.4 to 0.5. Idle setting stable, on acceleration AFR raises to 14-15 but settles to 14. Moved to larger pump jets, from 0.50 to 0.70. Test run showed idle still at 13 AFR, acceleration 13-14 AFR, highway cruise 13.5 AFR. Looks like I'm in the zone; I don't think I can tweak it much better than that, pretty much 13 or so average across rpm's.

In sum, the idle jet increase was important for idle adjustment range, the main jets were very sensitive to increases, mixture was way too rich even with 0.05 mm increase in primary jet and 0.10 mm increase in secondary jet. Pump jet increase was 0.3 mm to get 13 AFR (thereabouts) across range.

Now to change the head gasket again. Maybe this fixed the issue, certainly can't hurt. NOTE: definite noticeable increase in power at richer mixture across range, this is a strong build. No telling what my gas mileage will be, but at this point I just need my commute car back in action. I will go with the head from the build, it had more consistent compression numbers across the board - might end up with a big improvement in power given what I saw today with this other head.

Brian

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Before I pulled the head (again) I took a few more test runs. There was a little spike above 14 AFR on initial acceleration. I increased the pump jets to 1.10 mm, that took care of it. Now I'm solidly in 12.5-13 AFR along the rpms. I did not check AFR above 4000 rpms, but I never go there anyway with my 2.76's.

Pulled the head, the Felpro head gasket had damage to the fire rings in the cylinders with the 180 psi numbers, the lower compression cylinders' fire rings were smooth. I hope that damage occurred in the first couple hundred miles of driving, before I richened up the mixture.

I installed new head gasket. I used an Endurotech graphite one (3.6" fire rings) with copper spray as indicated. Set valve lash cold. Ran compression test, below are my compression numbers:

#1 - 180
#2 - 180
#3 - 180
#4 - 180
#5 - 180
#6 - 180

This is the head from the build. Not sure why #1 is now consistent, must be me, but anyhow they are all consistent at 180 psi this time.

If this fattened up fuel mixture solves my detonation/pre-ignition issue, I expect this head to give me even more power than that other one (it had a few cylinders at 180 psi, but a few lower as well). Cross your fingers for me, knock on wood, whatever.

Brian

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This makes no sense to me? Why are they all the same now? But I'm glad for you that they are. And I hope all you tweaking fixes your issue.

Rick

PS Maybe your Compression tester was acting up?

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

I have no idea, Rick. I'm setting the lash according to the cam specs, I thought I did exactly the same thing last time, perhaps I messed up. I don't think so, but I can't rule that out. I've done this enough times that I'm comfortable with it. Last time, when I did the compression test on this head, only #1 was lower at 150 psi. I played with lash, a little snugger, then loosened it up past specs, still it was 150. This time I installed the head, set the lash to spec, ran the compression test and they all read the same, 180.

Yeah, when I fattened up the mixture before changing heads back, it had a noticeable increase in power/torque, so it definitely likes more gas. With this head being all high compression cylinders, I should see a marked increase in power. The question is will that solve the detonation issue. I'm hopeful it will. I can tell you that before I fattened up the mixture, it was doing that dieseling thing, undoubtedly from the fire ring damage (acting like glow plugs) and the lean mixture heating it up. After I fattened up the mixture, even with the damaged fire rings, it didn't diesel at all on shut down. So, now with a new gasket and the fat mix, maybe I'll avoid the detonation issue altogether. I will still use a colder plug and keep the timing at TDC.

Brian

b

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