New Cam Stumble

[Charlesvolare]

Borrowed a coil from work, didn't make too much of a difference. Checked the grounds, everything looks good there. With this coil I just stayed on the throttle to see if it went away, it didn't. So it continues to pop and run rough until I let off. I'm stumped. It was doing great before, would the cam change be enough to need so much more fuel?

 

[Charlesvolare]

Being that it ran smoothly before the change would lead me to believe fuel system too. I would ohm out the plug wires, just because. It’s possible they were getting weak and not showing it until the extra fuel air charge at high rpm. Sometimes a little extra resistance across the plug gap will show weakness, hence new cooler copper plugs being a good idea, too. But that’s going to something of a fuel thirsty beast anyway, it may need a little extra secondary jet and maybe some cam and squirter tuning on the secondary pump, too.

Brand new wires, I'll check them all still just to be sure

 

[RustyRatRod]

What all did you change with the cam?

 

[AJ/FormS]

Borrowed a coil from work, didn't make too much of a difference. Checked the grounds, everything looks good there. With this coil I just stayed on the throttle to see if it went away, it didn't. So it continues to pop and run rough until I let off. I'm stumped. It was doing great before, would the cam change be enough to need so much more fuel?
View attachment 1715344518

That looks like an E-core coil. They work well with MSDs and 550 volts into the primary, but not so much with an 8 volt input. So, if you're running a Multi-strike, those work; but I never had any luck with firing them off a Mopar Ecu. With HEI I can't say but I wouldn't try it in any case.

Running lean overheats wrong-heatrange plugs, which can then cause pre-ignition which just about instantly causes detonation. At mild detonation, it just causes a rattle. As it it gets worse it begins to crackle and pop as the ignition is now controlled by heat of compression in the 180 psi iron-chambers. So the mixture is now lit before the intake valve closes, and the rising piston sends the fire up into the intake ports and manifold.... and there is your crackling and popping.
If the valve timing is also out, IDK know what will happen. At 180 and more psi, there's a good chance the intakes are closing earlier than the timing card calls for.
To make 180psi @300ft elevation,with a 60*Ica (a 268/110 cam), a 360 would need ~10.5Scr, which is a total chamber volume of 77.6cc @4.00 bore. If the cam is in 4* more advanced, to 102*, then the Scr would need to be reduced to 10.2 to not exceed 180psi.
Some guys get 4* advanced,confused with 4* advance already built in to the keyway. That's not right. If you add 4* and truly have 4* in the keyway, and you install it like that, then you will have 8* advanced, properly called; in at 102*. That will mess up your Dcr, and drive your pressure up about 1 to 1.5 psi per degree.
To have a 20 psi difference or more like your results are indicating, something is wrong! It may be the gauge, or it may be your method,IDK, but I'd get a second opinion. And if the results stand, then I would be looking for the why of it. And I'm kindof suspecting some valves are not closing. That kindof points to the 185psi cylinder being correct, and then the others all being leakers..... doesn't it?

Decided to do a compression test this morning (cold, carb off, plugs out), just to go through everything, and these are the results:
1 to 8: 165/175/165/160/170/185/175/160

 

[Charlesvolare]

What all did you change with the cam?

Both cams have the same duration, I'd need to look up the specs and do the math for the rockers, but old cam was about .500/.510 lift and new is .536/.544. Thethe roller cam probably has a bit more aggressive ramp to it. I guess about .030" more lift to it at the valve.

The heads weren't really set up well for the old cam before, now they are. Springs match the cam, .060 from bind.

 

[Charlesvolare]

That looks like an E-core coil. They work well with MSDs and 550 volts into the primary, but not so much with an 8 volt input. So, if you're running a Multi-strike, those work; but I never had any luck with firing them off a Mopar Ecu. With HEI I can't say but I wouldn't try it in any case.

I put it on just to see if maybe my coil was not outputting enough. I bypassed the ballest resistor so the msd coil was getting full 12+ volts

 

[AJ/FormS]

I put it on just to see if maybe my coil was not outputting enough. I bypassed the ballest resistor so the msd coil was getting full 12+ volts

While 12volts is about 60% better than 7.5, it is still just 2% of what the MSD could be firing into it..
Let's say the MSD has a potential to output 40,000volts with a 550v input, that is a ratio of 40,000/550= 72.7 to 1. If you then input 12 volts, I would expect around 72.7 x12=873 volts output. But it's worse. The E-core does not run 550volts into it continuously, but rather, the capacitor unloads everything it's got, everytime it gets triggered,almost instantaneously, and it may not be the same voltage throughout the discharge.
Whereas by comparison, the Kettering is; a lazy-azz, hope it works like it's supposed to system. Which most of the time it does and is fine for my application, probably yours too. But you need the appropriate coil for each system. My best advice is to get a proper, non-CDI,non-Ecore,old-fashioned type HO coil.

 

[Charlesvolare]

Running lean overheats wrong-heatrange plugs, which can then cause pre-ignition which just about instantly causes detonation. At mild detonation, it just causes a rattle. As it it gets worse it begins to crackle and pop as the ignition is now controlled by heat of compression in the 180 psi iron-chambers. So the mixture is now lit before the intake valve closes, and the rising piston sends the fire up into the intake ports and manifold.... and there is your crackling and popping.
If the valve timing is also out, IDK know what will happen. At 180 and more psi, there's a good chance the intakes are closing earlier than the timing card calls for.
To make 180psi @300ft elevation,with a 60*Ica (a 268/110 cam), a 360 would need ~10.5Scr, which is a total chamber volume of 77.6cc @4.00 bore. If the cam is in 4* more advanced, to 102*, then the Scr would need to be reduced to 10.2 to not exceed 180psi.
Some guys get 4* advanced,confused with 4* advance already built in to the keyway. That's not right. If you add 4* and truly have 4* in the keyway, and you install it like that, then you will have 8* advanced, properly called in at 102*. That will mess up your Dcr, and drive your pressure up about 1 to 1.5 psi per degree.
To have a 20 psi difference or more like your results are indicating, something is wrong! It may be the gauge, or it may be your method,IDK, but I'd get a second opinion. And if the results stand, then I would be looking for the why of it. And I'm kindof suspecting some valves are not closing. That kindof points to the 185psi cylinder being correct, and then the others all being leakers..... doesn't it?

As far as the cylinder pressures, I'm gonna take another look at that. The cam has 4* built into it, didn't add any into it.

 

[69FBCuda]

Back to the basics........ I didnt see any mention of the fuel filter being cleaned or replaced

 

[Charlesvolare]

Back to the basics........ I didnt see any mention of the fuel filter being cleaned or replaced

I have a see-through filter after the gauge, it's clean.

I have a secondary metering block conversion kit on the way, that should either let me fix the problem or rule out it being a lean issue. Way easier and cheaper than ordering plates.

If all else fails, I welded an O2 bung into the collector while I had everything apart. I can install a wideband if I need to and see exactly whats going on.

 

[yellow rose]

As far as the cylinder pressures, I'm gonna take another look at that. The cam has 4* built into it, so I installed straight.

But you still have no idea where the cam is timed. There is a thread here where a guy had to move his cam a ton just to get it correct. Dot to dot tell you very little other than its dot to dot.

 

[512Stroker]

But you still have no idea where the cam is timed. There is a thread here where a guy had to move his cam a ton just to get it correct. Dot to dot tell you very little other than its dot to dot.

I am with Yellow Rose on the cam timing.
This may have been covered, but, did you degree the cam?
And if so have you properly done this procedure in the past?

 

[Charlesvolare]

I am with Yellow Rose on the cam timing.
This may have been covered, but, did you degree the cam?
And if so have you properly done this procedure in the past?

I intern in R&D at Comp Cams, most of what I do is install cams and assemble valvetrain for the spintrons and engine dyno. I meant to grab a degree wheel the weekend I installed the cam but forgot, but since I kept an eye on the cam as it was ground and went through insepection I figured I'd risk it. Most of the cams I've degreed have needed only little adjustment, if any. My timing set has 46 teeth on the cam gear. 720 degrees (360*2, crank rotates twice for every cam rotation), 720/46=~15.6 degrees per tooth. So assuming cam was indeed ground correctly (I wasn't there the whole time, but they knew it was mine, I doubt they'd let it slip by), if I was off a tooth it'd be 12 crankshaft degrees retarded or 20 crankshaft degrees advanced.

If it was retarded that much, it'd run like crap at any rpm. It doesn't.

If it was advanced, it'd run like hell to a point, then stop. Which is sorta what its doing, BUT, I'm still able to run it through the rpm fine as long as I keep my foot off the floor- ran it to 5500 in first gear a few times yesterday. I was thinking about this last night, and remembered the last test and tune I was at last fall. My trans was going out, so the 2-3 shift terrible and it was popping then at the top of 2nd. It wasn't nearly as bad, but it also wasn't moving as much air. And it could be completely unrelated as well. Just something I remembered.

2-3 shift 0:43-0:50

This run was a 14.0 @ 104 with that bad shift, open diff, stock converter, crap tires

I know the whole debate about the chain tensioner with the double roller chain, but small block mopar chains are 8 miles long and this car isn't going to rack up 30,000 miles a year.

 

[toolmanmike]

I see you have a different carb that needs a kit. It would be so easy to bolt on a known good carb to confirm a lean condition.

 

[Charlesvolare]

That being said, I showed the video of my car popping to a few people at work. The head r&d shop tech, the guy that's ran the engine dyno for the past 10 years, said it definitely sounds like an ignition problem to him and that's when the dug out the msd coil. We were looking for a canister but that's all we had and figured it was better than nothing. But again, he only heard the problem from a video

 

[Charlesvolare]

I see you have a different carb that needs a kit. It would be so easy to bolt on a known good carb to confirm a lean condition.

What's the fun of easy?

No carb is going to be a straight bolt on, perfectly tuned. Both carbs I've had worked good on previous engines. I could borrow a carb that already has that adjustablility but I figured a $40 upgrade kit that will allow me to work with what I have and would just put me in the same spot as borrowing one. If it does work I'd have to get to one anyways and if it doesn't work it's not a bad investment.

I'm a broke college student and with this kit I'm only $150 into this 750 carb. I already have all of the tuning kits and don't mind figuring things out.

I should have the kit tomorrow, but I'll try to grab another carb if I can.

 

[512Stroker]

I intern in R&D at Comp Cams, most of what I do is install cams and assemble valvetrain for the spintrons and engine dyno. I meant to grab a degree wheel the weekend I installed the cam but forgot, but since I kept an eye on the cam as it was ground and went through insepection I figured I'd risk it. Most of the cams I've degreed have needed only little adjustment, if any. My timing set has 46 teeth on the cam gear. 720 degrees (360*2, crank rotates twice for every cam rotation), 720/46=~15.6 degrees per tooth. So assuming cam was indeed ground correctly (I wasn't there the whole time, but they knew it was mine, I doubt they'd let it slip by), if I was off a tooth it'd be 12 crankshaft degrees retarded or 20 crankshaft degrees advanced.

If it was retarded that much, it'd run like crap at any rpm. It doesn't.

If it was advanced, it'd run like hell to a point, then stop. Which is sorta what its doing, BUT, I'm still able to run it through the rpm fine as long as I keep my foot off the floor- ran it to 5500 in first gear a few times yesterday. I was thinking about this last night, and remembered the last test and tune I was at last fall. My trans was going out, so the 2-3 shift terrible and it was popping then at the top of 2nd. It wasn't nearly as bad, but it also wasn't moving as much air. And it could be completely unrelated as well. Just something I remembered.

2-3 shift 0:43-0:50

This run was a 14.0 @ 104 with that bad shift, open diff, stock converter, crap tires
View attachment 1715344738
I know the whole debate about the chain tensioner with the double roller chain, but small block mopar chains are 8 miles long and this car isn't going to rack up 30,000 miles a year.

Well partner I am glad to see you are getting some good experience as I too worked in a Engineering lab as a punk kid right out of school.
A small piece of advice.
Trust no one.
Put a degree wheel on it to check the cam timing .
Good luck

 

[Wyrmrider]

agree with 512
take math EVERY semester
that's where the pay dirt is no matter what your major
I can remember doing custom regrinds with the Late Bill Jenks (Potvin and Moon cams)
frequently had to fudge the centerlines to make it fit
what happens if you make the base circle smaller is that you get a little pointy nose like a stroker chevy kludge then you have to watch your springs and the optimization spirals downhill from there
It is usually better to put the new lobe on the same ICL as the core and fudge the exhaust and then dial in the whole cam to get the intake where you want it
or buy a new core- problem is some cores are not readily available

 

[diymirage]

"also new wire set"

you didnt swap the 5 and 8 wires did you?

 

[Charlesvolare]

I got my secondary metering block kit in yesterday, threw in a set of 78 jets and put it together. Couldn't find the specs on my metering plate but then again I didn't look too hard either. Not much difference so that should pretty much rule out it being a lean issue.

After that my thought is coil or detonation. Your compression is really high for iron heads, so the next test would be to take out at least 6 degrees of power-timing. I've never seen detonation that far up the rpm band in a streeter, but you gotta rule it out. If it's still there at minus6* then it's not likely to be detonation.
Next would be an open air spark gap test off the coil-wire.
If you have a multi-strike; skip this paragraph. I'd wanna see how far that coil will cast a spark, looking for .375 inch or more. Yeah I know everybody says .25, but not everybody has cylinder pressure as high as your engine does (which IMO is a different problem by itself). Try not to set the car on fire. Before you throw the coil away check your ballast resistor specs. I run my Accell on about 8 volts on the run circuit.

After that, I pulled a plug to check spark gap, about ~.388" (I tried to be as accurate as possible but I used a metal caliper and did my best not to electrocute myself. 0.388" should be pretty close though). I then turn my timing down. I loosened the clamp and the made sure the distributor was still tight enough to hold but loose enough to turn and I didn't verify I was at 36 total before I did that. I turned it down to 30 total. It seemed to idle higher at that too, but then again I haven't touched the timing since before I made a bunch of carb changes. Taking timing out helped a lot! I can floor it and it doesn't fall on it's face anymore! It's still cutting up on the top end and other things that are just tuning issues, but I can put the pedal on the floor and she doesn't complain nearly at all. So I think the issue has been found, now it's the issue of getting things squared away.

I have a few pictures of the spark plug I'll upload when I get a chance.

 

[yellow rose]

I got my secondary metering block kit in yesterday, threw in a set of 78 jets and put it together. Couldn't find the specs on my metering plate but then again I didn't look too hard either. Not much difference so that should pretty much rule out it being a lean issue.

After that, I pulled a plug to check spark gap, about ~.388" (I tried to be as accurate as possible but I used a metal caliper and did my best not to electrocute myself. 0.388" should be pretty close though). I then turn my timing down. I loosened the clamp and the made sure the distributor was still tight enough to hold but loose enough to turn and I didn't verify I was at 36 total before I did that. I turned it down to 30 total. It seemed to idle higher at that too, but then again I haven't touched the timing since before I made a bunch of carb changes. Taking timing out helped a lot! I can floor it and it doesn't fall on it's face anymore! It's still cutting up on the top end and other things that are just tuning issues, but I can put the pedal on the floor and she doesn't complain nearly at all. So I think the issue has been found, now it's the issue of getting things squared away.

I have a few pictures of the spark plug I'll upload when I get a chance.

So you have a 3/8 inch gap? It should be .038ish not .388 as you have posted

I'd love to see a plug.

 

[Charlesvolare]

So you have a 3/8 inch gap? It should be .038ish not .388 as you have posted

I'd love to see a plug.

Holding the plug away from the block, the coil will cast a spark the gap of .388", from the plug to the block, which is what I'm assuming AJ was talking about. The plug gap itself (electrode to strap) is at .040". I quoted his earlier reply as to not confused anyone

 

[MopaR&D]

Interesting, glad you found the issue. How new is the harmonic damper, you sure it hasn't slipped at all? 36 degrees total is a tad much for an SBM but I wouldn't think it would cause it to run like that.

 

[Charlesvolare]

Interesting, glad you found the issue. How new is the harmonic damper, you sure it hasn't slipped at all? 36 degrees total is a tad much for an SBM but I wouldn't think it would cause it to run like that.

It's an aftermarket balancer, I've had it about three years. There's only a few thousand miles on it so I wouldn't expect it to have slipped, but it's possible.

Next steps will probably be checking the balancer and colder plugs, anyone have any recommendations? Magnum heads, Autolite 5224 at the moment. They've only been in a few days and have probably seen at most an hour of run time

 

[nm9stheham]

Both cams have the same duration, I'd need to look up the specs and do the math for the rockers, but old cam was about .500/.510 lift and new is .536/.544. Thethe roller cam probably has a bit more aggressive ramp to it. I guess about .030" more lift to it at the valve.

The heads weren't really set up well for the old cam before, now they are. Springs match the cam, .060 from bind.

See if you can find the .200" lift specs. The new cam may just be faster ramps plus lift, so better cylinder filling, and so more DCR that pushed your motor into detonation.

Nice call on AJ's part to point that out!