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Old 01-11-2010, 04:24 PM
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1956 nailhead 322, compression test

Hello, I am a new member and wanted to introduce myself and post a quick question.

I picked up a 1956 Buick Special with a 322 nailhead and did a compression test on it. I got about 115 to 120 consistently on all 8 cylinders. The engine is bone stock with a 2 barrel carb. The google results state a ratio of about 8:1 to 9:1 depending on the year. I could not find a psi to ratio converter so does anyone know if this is a decent compression for this stock engine?

I did the test by disconnecting most of the spark wire cables, coil cable and the engine was warm. The only thing I did not do was force the carb open.

If the psi is good, can anyone recommend a decent/affordable manifold and carburetor combo so I can upgrade it to a 4 barrel?

Thanks in advanced!

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Old 01-11-2010, 07:50 PM
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The compression is ok...as long as its consistent no worries unless you want to rebuild it. I looked on ebay, theres usually a few things there for the nailhead family. Found 1- stock 322 intake, the dreamer wants $395 for it and around $600 for the stock carb!! You'll just have to hit the bone yards, look on craigs list. The 322 4 bbl casting numbers are...'53 1162286 '54-'55 1163206, '55 1165384 and '56 1170625. Also see www.buick.net, lots of stuff
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Old 01-11-2010, 10:27 PM
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I have not seen a compression pressure to compression ratio converter, but the math is simple.

Formula:
Compression Pressure = (Compression Ratio minus one) to the 1.1 to 1.2 power multiplied by Atmospheric Pressure (14.7 psi at sea level)

8:1 ratio example
Compression psi = ((8-1)^1.1)*14.7 = 125 psi
Repeat with 1.2 for a range.

So in your case 8.0-9.0:1 has compression pressure range of 125-178 psi.
That is IF you are located at sea level. 14.7 can be substituted with the psi at your elevation for a theoretical range closer to the results you will get with your compression tester. (For every additional 1,000 feet above sea level the atmospheric pressure decreases 4%.)



You do not say if you removed the spark plugs, just the wires. This along with the closed throttle may have invalidated the results you have found.
In other words, your compression pressure maybe better than you think.

Remember, compression pressure is checked with the engine warm, throttle open, all plugs out, gauge in plug seat and engine turned by starter.
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Old 01-12-2010, 04:41 PM
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Quote:
Originally Posted by hackery
Hello, I am a new member and wanted to introduce myself and post a quick question.

I picked up a 1956 Buick Special with a 322 nailhead and did a compression test on it. I got about 115 to 120 consistently on all 8 cylinders. The engine is bone stock with a 2 barrel carb. The google results state a ratio of about 8:1 to 9:1 depending on the year. I could not find a psi to ratio converter so does anyone know if this is a decent compression for this stock engine?

I did the test by disconnecting most of the spark wire cables, coil cable and the engine was warm. The only thing I did not do was force the carb open.

If the psi is good, can anyone recommend a decent/affordable manifold and carburetor combo so I can upgrade it to a 4 barrel?

Thanks in advanced!
This is very much appropriate for an engine close to 8.0:1. The consistency is a really good sign. There really isn't a perfect conversion for cranking pressure into compression ratio. The camshaft has big effect as the intake closes after bottom dead center which bleeds some amount of cylinder volume back into the intake so the actual compressed volume is less than cylinder volume at the low RPMs at which the starter can spin an engine. Plus at cranking speeds compression loss around the rings and past valves far exceeds what these looses are at operating speeds as then events are happening faster than the "normal" leakages past these parts. Adding oil to the cylinder helps bring the compression towards that of operating as is slows the loss past the rings as would happen in an operating engine since the piston and bores are absolutely swimming in oil when the engine is running.

The problem with a 4 barrel carb is that there isn't much effect without more cam and higher compression. For the period you'd want a Rochester 4GC not a Holley or Quadra-jet.

Try here for parts http://www.oldbuickparts.com/index.html
Another good one was Poston Buick but they seem to have been absorbed into something else.



Bogie
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Old 01-13-2010, 12:14 PM
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The information you all have provided has been outstanding! From the results it does seem like my engine is in decent shape with regards to pistons,rings,etc. I wanted to make it a bit more responsive by adding a 4 barrel carburetor but from what "Oldbogie" says, it will not make much of difference unless I get a performance cam. I am up against the fence now. I don't want to race anybody with this car just want it to be snappier when I do punch it.

Thanks!
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Old 01-13-2010, 05:26 PM
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You could always bolt on 1.6 stock aluminum rockers from a 364 or a 401 on to the 322 (1.5 is stock). I haven't heard of people changing out the cam too often.

IMO the largest limitation to performance are the heads as they have small valves at an odd angle and the ports are rather restricting. Do not use a 364/401 head ('57-'66) on a 322 as you will lower the compression quite a bit (larger chambers) and the only way to get it back up is with custom dome pistons.

If you still want to go with a four barrel then find a stock one and cut out the partition between the FRONT and REAR barrels of the factory intake manifold, leaving the partition between the two sides.


Here are some sites you might want to check out
http://www.secondchancegarage.com/public/358.cfm
http://www.v8buick.com/
http://www.buicks.net/shop/reference/blown_buick.html
http://www.buickpartsdirectory.com/

The differences in compression ratio between the special with a manual transmission and Dynaflow are due to a difference in head gasket thickness.
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