With a cam over advanced it will not break up at high rpm, it will just lay over.

Is this an N/A motor?

As far as running rough after it gets hot, have you tried a different coil?

Orange boxes normally work OK or quit, usually at the most inconvenient time and place.

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OK, good to know, I have no knowledge of what happens when a cam is a tooth off other than what I read or what others tell me.

If you mean naturally aspirated, then yes.

I have not tried another coil, I'm running a Pertronix Flamethrower with a built in resistor, so no ballast resistor. Seems like a coil either throws spark or it doesn't, the timing/control of the spark is from the ECU and distributor. If it got hot and didn't throw spark, I suppose it would act like it does.

I have another coil, I can swap that out and also reground my ECU, make sure that's good.

b

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I have seen Petronix units go bad and do what you have going on too. Brand new, less than 50 street miles.

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You've given me a hint of hope in a desperate situation....I'll try my other coil for sure...

b

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I don't want a cigar...firstly I don't smoke and they stink bad plus my girlfriend will likely kick me out of our house
What I would like is to see your engine sorted,that's all. This metal thing has me worried,the more you run the thing the more something is getting worn and spreading metal into the bearings piston skirts etc etc. I'm not disrespecting anyone but there's a recent thread about cam timing where guys need to actually jump a tooth on the gear just to be in the ball park when degreeing the cam! I'm sure the engine was built well and with care and getting it a tooth out is something people may think is unlikely ,but hey it's making metal too..Stuff happens.

DD built your motor as a street engine? That would indicate that the compression is NOT too high. It may be high, but street-able.

I would guess you have a tuning issue. Nothing wrong with the long block except showing indications of detonation.

The following is my opinion: that you are making real progress in fattening up the mixture. There has been a lot of side work to get to that point, but the plugs showed you were lean... sort out your ignition and take it for a drive and then check the plugs. NO you can not really tell if you are fat or lean with plugs, but it is more information that can be useful...

I've never tuned twin carbs. One is plenty for me to try and juggle... if it gets to the point where you are truly out of ideas, then find some type of vehicle dyno where the operator has some real depth. Spend the 200 or what ever the fee is and be amazed with the amount of real time info you walk away with. While driving, you just can not process the same amount of information.. Then you can get back to Enjoying the car you have created. Professional's use them for the information that they provide, and I am not in any way talking about bragging rights. This is about getting your engine and your car sorted out. We can make guesses all day long, but we seem to only be helping you chase your tail in circles. Furthermore what you learn will be of huge benefit to the next one who comes along with a stubborn issue.

I've got the carbs balanced and the AFR is plenty rich enough across the rpm range (I have wide band sensors in the down pipes and did several road tests, jetting experiements). It's now down to an ignition issue or a valve timing issue. The answer is there, just haven't found it yet...

I've heard of coils overheating and shorting out, causing misfires, I suppose that could be a possibility, but it seems like that would be more about a dead cylinder, not a super hot one that burns through head gaskets....that seems more like a timing issue, i.e. sparking too soon. The coil can't deliver a spark unless the distributor tells it to. I suppose the coil could be sending way more spark that it's supposed to...but one would think the dizzy cap would be carbon arced or something (perhaps not), it's clean as a whistle.

Brian

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The cam is not off a tooth, verified by builder, it dialed in at 3 degrees advance.

Swapped out coil, checked ground on ECU; took for a road test, same thing, after it warms up it starts to shudder, misfire. Diesels on shut down. Check timing, it's still at TDC, distributor looks good, reluctor gap is correct.

Checked plugs, they look like new (they only have 20 miles on them) - AFR is in the 12.5-13.5 range across rpms, under load or not.

Next thing is playing with intake valve lash....

b

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verified? Did he come around and physically check the timing in the car? If so what is the dcr?
If he checked the cam timing for you today, and you must have the head cc and comp ratio from the build sheets,you should be able to calculate that. It's not giving such high compression while cranking for no good reason. Even if you found the problem I'd still put money on gaskets blowing for all the reasons previously mentioned.

The DCR was calculated to be 8:1.

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So the cam timing has been physically rechecked and confirmed to be ok?

Nope, not yet.

b

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I made the intake lash tighter by a few thousands, took it for a test drive, it made the issue worse. So, I loosened the intake valve lash by 0.003, it was a bit better on the next test drive, loosened another 0.002, better yet on test drive....hmmm....seems drivable, but pretty chattery that loose...

b

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...so, given that backing off on the lash improves the situation, would seem to indicate cam timing, at least to me. Spec. lash settings were too snug, which suggests the cam is in the wrong place at the wrong time, hence the metal. Steve, I think your intuition is good. At least now I've got some feedback from the system. This really had me scratching my head. Thank you for your valuable input.

b

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Let's not forget the detonation issue though. I'm not sure if that was purely a lean mix thing or also related to cam timing. Certainly since I've enriched the mixture, I'm not getting that loud sound any longer, so that must have helped. Also, detonation would cause metal due to the conflicting forces at work. I suppose advanced cam timing could also promote detonation. One variable at a time...seems like I'm honing in on the issue.

I'll see if I can run it with the lash loose, if I'm still getting metal or driveability issues. If so, I'll have to pull the engine and adjust the cam timing.

b

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