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1956 322 Compression Test Numbers


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I was at a light 5 miles from my house, on the way back from a 30 mile joy ride, when she just died... I knew I was low on gas (right before the red zone), as the sender is new and didn't spend too much time calibrating it, ( I know...). I hit the starter button and she fired right back up, pulled inside a parking lot, where she died again. The rear fuel filter was dry, so was the front. I had a full 5 gal gas can in the trunk and put it in. Waited 5 min, she started but was not idling right and died again. I would crank for 30 sec wait 2 minutes, then 30 sec wait 5 min, till the battery died... Called AAA and had her towed home and put the battery on the charger.

This morning, I got up, hit the starter and she fired right up. Turn her off, hit it again and she fired up again. I wasn't going to risk another mishap, so I let her idle for 30 min, then took the spark plugs out, the coil plug and did a dry compression test with closed throttle. Here are my numbers:

Passenger side starting from the front:

1 130 PSI

3 135 PSI

5 130 PSI

7 135 PSI

Driver side starting from the front:

2 155 PSI

4 150 PSI

6 120 PSI

8 130 PSI

I don't know if it was vapor lock, or what, the fuel line was really hot, as it was 100* here yesterday, (temp gauge was showing 2 clicks before the top) but I have about 80 miles on her so far and not even a single issue, other than this. I should have done a tune up and check plugs, wires, distributor and so forth, but I was so happy to put her on the road, that I didn't...

I ordered a 9 PSI electric fuel pump, a block of plate from Russ, a pertonix igniter kit (as from reading here, it could have been coil, condenser, fuel pimp, not sure...) a new coil, distributor cap, rotor, plugs and wires. I am getting 8 MPG which is not the greatest, but I also ordered a 4 bbl Rochester carb rebuilt kit. All the spark plugs (Autolite 86) were black and dry just like this one from Cyl No 8:

<a href="http://s412.photobucket.com/albums/pp201/2xxnoxy/?action=view&current=IMG_4903.jpg" target="_blank"><img src="http://i412.photobucket.com/albums/pp201/2xxnoxy/IMG_4903.jpg" border="0" alt="Photobucket"></a>

I wasn't able to get to the block number, but the head castings read: R side 1166349-9 and L side reads 1166349-12. The manual that I have shows the compression numbers on a new engine at 170 PSI on a 9.5:1 motor, which is what I have. What do you think?

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The compression numbers might not exactly match what's in the service manual, BUT they are all in the same general area (low to high) so I don't see anything there. Various things can affect the total compression numbers . . . altitude, throttle position, and how oily the compression rings might be.

From the looks of the spark plugs, they are probably the culprit. Getting 8mpg is the reason they are all black. When they get that way, it makes it more difficult for the sparks to happen. Just taking a wire gap gauge and running it between the electrodes will clean them sufficiently in "the spark area" for them to work, from my experiences with my lawn mower.

With the lawn mower, it became an "every use" situation to have to clean the spark plug before use, just to get it to fire off initially. The carb was having issues with the E10 fuels we have in N TX and had gotten a worsening surge, just like the previous one did. I started using some Lucas "green stuff" ethanol fuel additive and it has fixed the surge. First time I put it in the gas, I ended up "over-treating" (which the label says is fine). Initially, it started the first time and ran smoothly. After about 20 minutes of run time, it suddenly started running faster than it ever had and it would not die in "too tall" grass. Almost as if it was possessed! Later times, it ran normally and strong. Always starting on the first pull. When I later pulled the spark plug to see what it looked like, it was looking brand new . . . no deposits or carbon build-up. After I put it in my 'Y2K Impala', no "possession" activities.

There are some small air bleed holes in the top of the venturi area on the primary side of the carburetor. Those also serve as calibration points for the idle and main system in the carburetor. When they get restricted or clogged, it makes the particular system go "full rich", or at least richer than designed, which could definitely relate to the carboned spark plugs. Usually some carb cleaner doused across them or sprayed is all that's needed.

The fuel system's carb floats' needle and seats usually like to see about 5.5psi of fuel pressure. A 9psi pump might overpower them at the 9psi pressure level, so a pressure regulator might be needed, too. I think some of our TX associates use a booster pump of lesser pressure, but as it appears you want to use just the electric pump, a pressure regulator would be a definite consideration.

With respect to vapor lock, you also have to consider that heat radiates upward from the road surface, which can be far hotter than the ambient air temperature, due to solar heating of the roadway. Engine temp can be a lesser consideration considering the exposure of the total fuel line to the roadway's heat radiation. Still, keeping underhood fuel lines away from heat-producing engine parts should be considered.

Adding the Pertronix (or similar) ignition system upgrade can be a plus, but I doubt it'll fix the 8mpg issue . . . unless the stock system just isn't producing enough "juice" to fully fire the plugs. As my old "MOTOR" manual states, fuel system issues and ignition issues can sometimes act the same. If the plugs aren't getting fired well enough, reading them can make it look like a fuel issue (flooding or too rich) when the carb is just fine, but if the carb is running too rich, then it makes the job of the ignition system harder.

Another reason for the Pertronix upgrade to be a good thing is that the cam lobes which the rubbing block of the ignition points rides on, openning the points for each cylinder's firing cycle, can and most probably do have some wear on them. It might not look too bad, but this same situation can also result in the point gap not being the same for each cylinder, which relates to "point dwell" and the time the coil has to saturate before the next cylinder firing. So you get to the situation of whether to go by the "dwell" reading or the "point gap" specification. Going "electronic" with an electronic (or whatever) coil firing trigger system bypasses these distributor cam/rubbing block wear issues in ONE feld swoop. Plus all of the other benefits of these systems.

ONE issue, though . . . battery voltage. The electronic control boxes usually have a minimum voltage they need to fire the plugs. A point system will fire the plugs as long as there's enough spark energy for the spark to jump the gap in the points and then the spark plug. For the record, the Chrysle "Orange Box" (their higher-performance control box) needs a solid 12 volts to fire the plugs, which makes it look like the non-start condition (with the engine spinning over just fine, but "no start"!) look like a fuel supply issue, but as soon as a jumper cable to another vehicle is attached, it fires off immediately. As if it needs 13.5+ volts to work! Chrysler Mopar Perf also sells a replacement electronic regulator which keeps the system at about 14 volts all of the time, probably to keep the Orange Box working, BUT with some advisories about that higher voltage level.

Just some thoughts . . .


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Thank you... In regards to this:

"The fuel system's carb floats' needle and seats usually like to see about 5.5psi of fuel pressure. A 9psi pump might overpower them at the 9psi pressure level, so a pressure regulator might be needed, too. I think some of our TX associates use a booster pump of lesser pressure, but as it appears you want to use just the electric pump, a pressure regulator would be a definite consideration."

The only reason I got the 5-9PSI Airtex E8012S pump was because from what I have read here, the 9 PSI at the tank, will be 4-5 PSI at the carb due to losses... I might be mistaken, but I will read up again...

Thanks for the reply, lot's of things to digest...

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You mention that a full ignition tune up was not done.... and fully agree that problems of

heat/ethanol can manifest themselves as you experienced, but,

Not to complicate things,

sometimes condensers and coils intermittently fail; esp. with high

heat conditions. Even old style wires can crystallize inside and fail with high heat.

Since you have to do this anyway, Perhaps first, do

a full ignition tune with new coil and new low resistance plug wires. Then set the dwell and timing; and check the vacuum

as part of the tune up.

Relatively cheap stuff and can be quickly done, before modifying the fuel delivery system with the electric pump, regulator, etc ....

my 2 cents


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Your main problem that resulted in a tow was most likely vapor lock. Install a 7-9# pump as close to the tank as possible and that will give you 5-6# at the carb. If you eliminate the mechanical pump and use the electric full time consider a collision interrupt device. This combination has served me well most of the time, but I had some vapor lock even with the electric fuel pump...may have been the volatile fuel, 105* temps, low gas or the fact that my inline filter is before the electric pump (I crawled under to check if it was dirty and the gas was boiling --- I'm going to put it after the pump)

Your engine is not new and those are not unexpected readings.


see post #2 for my rant on Pertronix

Autolite 75 or 85 is the correct plug, but your 86 being one notch hotter should be OK.

Black on the plugs is not unexpected if the engine has been idling cold.

Get the ignition in top shape before messing with the carb.

The Rochester 4GC is junk! Our currently available ethanol laced fuel will dissolve the cement on the bowl plugs which can leak and catch fire. Also the ethanol fuel when it dries in a carb will leave a white powdery residue. That is what seems to clog the 4GC: rebuild it, install and it performs just fine; let it sit for a week and you will have poor idle, stumble, surging until you disassemble and clean again. The Carter WCFB seems to tolerate drying much better.

8mpg is not bad if city driving or romping on it a lot...15mpg on the road 65-70mph is likely.


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Heres a thread with some data and advice you can use for comparison on your compression numbers:


Everything else you mention sounds very familiar. Your plugs are sooty like mine were also - its running rich or not running enough. I had R46 ACs in the car. I switched to NGK B6S plugs, which I think are hotter and are non-resistor, made sure the choke was properly set (at cold I adjusted it toward lean until the butterfly just starts to move). Also made sure the fast idle was set high enough so the plugs would not load up at rich mixture and low idle (thats important). Added seafoam in the carb - ran thru two tankfuls. And then just ran it - more. Lots more. Highway speeds for 50-75 mile jaunts. Most of my build up on my plugs, and am betting varnish and junk in the carb, was just from not running the car enough and letting it idle in the garage without a good highway run. I also reset the mixture, although I think it is out an extra 1/2 or 3/4 turn than originally set. The car idles smoother and it can get down to a lower idle speed (475 in Drive) using todays ethanol gas. Another change, not sure what effect it had, was upping the thermostat from 160 to a 180.

The stalling is vapor lock. Alot of us with 55s that exhibit this have fixed the hot stalling and surging with a 7-9# pump with inline filter mounted on the crossmember back by the tank exactly as Willie suggests. With my car, flipping the pump switch, hidden under the dash, at a critical time (like going through an intersection - ugh!) brings the engine right back to life. Fills the glass filter bowl by the carb back up too. And I can swear by the electric pump because the stumbling/hesitation/stalling only happens when the outside temp goes over 90 deg and the car has been idling, and the engine recovers about 5 seconds after the pump comes on.

The engine also retains its original points/condenser, and they have given me no issues and my plan is to stick with them. My timing is set at the high end - 7.5 deg, and while I put 93 octane in it, I've had 89 unleaded in it with no pinging (prob since compression is so low).

Coils and condensers can act up when hot also. Take notice how consistent your condition is vs outside temperature before you condemn either part.

So ==> choke, plugs, electric pump, timing, mixture, 180 thermostat, fuel system cleaner - and - RUN IT! ON THE HIGHWAY! ALOT! Thats the fun part! The more you drive it the better it will run. Good luck!

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