Compression Check Results and Plug Read.

[gzig5]

I've got a couple hundred street miles on the car after getting it running with new AVS2 carb. I pulled the plugs to do a compression check and lined them up. They look decent to me but I'm no expert and would like to hear other opinions. Not sure if much can be told from those pics though. #1 at top left has an interesting heat pattern on the threads, not sure what that is about.

I did the compression check hot with the pictured results. Couldn't get the thing hooked up on 5 and 7 because of the header. Will require a different adapter to get around it. Was looking pretty good for the first four and then I was disappointed by the last two. Did them in order. Went back and confirmed #3 at the end. Based on that, any guesses at the static compression?

I don't know anything about the motor other than it is a 71 340 block with J heads and a stock-ish cam that doesn't seem to burn oil. I've added new AVS2 650 carb, RPM Air Gap, new plug wires and the timing was set to 15/16 initial and 36 all in, no vacuum advance. 73 electronic ignition and distributor when pics were taken. Now has an FBO box and limiter plate and I'm starting to work on the spring weights. Car runs pretty good but has lifter noise on 6 and 8.

 

[yellow rose]

You need to take some pictures with the ground strap up. The heat range looks close from that shot, but it's hard to tell. I suspect you are pretty close at idle, a bit rich at cruise and rat at WOT but that's hard to see from those shots. And WOT is hard to do until you get the rest right.

 

[furrystump]

Not happy with 25 lbs different in cranking pressure. Might have just started to push the fire ring towards the lifter valley. Just read the lifter noise on 6 and 8. That could be why they are off.

 

[gzig5]

Not happy with 25 lbs different in cranking pressure.

Nor am I. Hoping it’s in the heads because they are on the list for upgrading.

I’ll get better pics when I get back from my trip

 

[nm9stheham]

Not happy with 25 lbs different in cranking pressure. Might have just started to push the fire ring towards the lifter valley. Just read the lifter noise on 6 and 8. That could be why they are off.

Seems like the lifter noise would more likely be due to leaking or worn drivetrain parts, and that would tend to shorten the timing duration and raise the numbers, not lower them. The numbers are higher that I would expect but who knows what is in the engine, or how accurate the gauge is. Compression gauge accuracy is something none of us ever checks.....

 

[AJ/FormS]

At those pressures, how does that thing not shatter the plug porcelains?

 

[512Stroker]

I've got a couple hundred street miles on the car after getting it running with new AVS2 carb. I pulled the plugs to do a compression check and lined them up. They look decent to me but I'm no expert and would like to hear other opinions. Not sure if much can be told from those pics though. #1 at top left has an interesting heat pattern on the threads, not sure what that is about.

I did the compression check hot with the pictured results. Couldn't get the thing hooked up on 5 and 7 because of the header. Will require a different adapter to get around it. Was looking pretty good for the first four and then I was disappointed by the last two. Did them in order. Went back and confirmed #3 at the end. Based on that, any guesses at the static compression?

I don't know anything about the motor other than it is a 71 340 block with J heads and a stock-ish cam that doesn't seem to burn oil. I've added new AVS2 650 carb, RPM Air Gap, new plug wires and the timing was set to 15/16 initial and 36 all in, no vacuum advance. 73 electronic ignition and distributor when pics were taken. Now has an FBO box and limiter plate and I'm starting to work on the spring weights. Car runs pretty good but has lifter noise on 6 and 8.

View attachment 1715370299

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Looks like No 1 plug may have been loose at some in time, or a bad seal ring allowing combustion gases to get by the threads.
Heat range looks great, would not change it.
Timing marks on the ground strap looks to close to the threads, to much total advance? Did it ping? What rpm at 60mph?

 

[MOPAROFFICIAL]

At those pressures, how does that thing not shatter the plug porcelains?

wth ?

 

[j par]

5&7?

 

[MOPAROFFICIAL]

maybe its just me .. but i see tiny specs on the porceilen .

 

[yellow rose]

maybe its just me .. but i see tiny specs on the porceilen .

I saw those. But without putting a magnifier on there, it's most likely bits of carbon blowing off the shell. That's why reading plugs through pictures on the web is damn tough.

I also see some mixture distribution issues at idle and cruise. It's pretty rare to see them at WOT if things are close, but I'm betting if he cleaned up the idle mixture he'd find some MPG and some driveablity.

 

[famous bob]

At those pressures, how does that thing not shatter the plug porcelains?

You kidding / a friend of mine runs 16 to 1 , no plug trouble .
My first 426 hemi had 203-205 # per cyl the first time I tore it down-from the factory.

I think the timing might be off a hair too -

 

[AJ/FormS]

We're not talking hemi's here, but rather
71 pop-up-piston 340 with a "stockish cam", and; iron, wedge, open-chamber, J-heads.
190psi is a lotta lotta pressure for this combo and pump gas.
I've cracked and broken porcelains with a lot less.

 

[mbaird]

What was the change to the FBO system like ? Did you notice much difference ?

 

[gzig5]

What was the change to the FBO system like ? Did you notice much difference ?

Hard to say at this point because I’ve been playing with timing a bit and the carb idle air adjustments. But it may have a little more grunt in middle and upper range but I’m feeling my way along with the tuning. Didn’t expect much. Stock system worked ok but age/quality were unknown and I wanted a rev limiter. Didn’t go backwards