Packard Forum Index » Modification Discussion

Quote:

Yes and ...

An engine is a system that consists of many parts. To intelligently increase the system performance requires to change more than just one part. The higher pressure impinges on pistons, valves, bearings, head gasket, combustion, ...
If we nevertheless change only one part then this part has to combine two functions: the target improvement and countermeasures to alleviate bad effects.
The Edmunds probably has smaller, more shallow combustion bowls to increase the compression ratio and with that the performance. Increased compression increases the knock susceptibility. Therefore it needs countermeasures.
The improved thermal conductivity (aluminum) and the more simple combustion chamber shape (no hotspot edges) are those measures.




Please compare the Edmunds head above with a --> 288AT combustion chamber.

The center mounted spark plug has a Janus-faced character. It increases the combustion speed to obtain a higher performance yield but reduces the length of the flame front.

What's the meaning of the lengths of the flame front?
Please take a look at the picture:

A - side mounted spark plug with long combustion front
B - center mounted spark plug with short combustion front

A > B and with that it decreases the knock resistance because a long way gives more time for knocking. Therefore the center mounted spark plug doesn't need a countermeasure.

And how about C?

C - a second flame front ("the knock")

To mistake misfire for engine knocking isn't uncommonly. Misfire is a self ignition without ignition spark but engine knocking occurs when:

" ...combustion of the air/fuel mixture in the cylinder starts off correctly in response to ignition by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front ..." [wikipedia]

Ross, the Edmunds makes the combustion more efficient (fuel efficiency).
As you know when we drive more slowly (with less rpm) then the combustion chamber is filled with more residues. That increases the probability of a hot spot occurrence. The Edmunds decreases the knock susceptibility by more efficient combustion. And when we drive faster (with higher rpm) the Edmunds allows higher pressure without knocking.
The improved combustion behavior enables:

1) to use low-octane fuel or
2) to drive longer or
3) to drive faster and
4) to drive cleaner

5) ... to be continued
6) ... to be continued
7) ... to be continued

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Ross, please find attached additional Edmunds effects, tailor-made for your requirements.

Let's have a look at atmospheric conditions. A knock free combustion needs high octan fuel or an Edmunds head when

the atmospheric pressure is higher (5) or
the air temperature is higher (6) or
the atmospheric humidity is lower (7).

You are frequently in Africa. If you are at the coast of East Africa an octane number of 95 is common but if you would drive on its elevated plain 93 octane would be enough (I'm not sure if you have the same system of octane rating like we have in Europe).

A head on a 288 would have lower compression than the same head on a 327 because of the smaller displacement....

Go Away!

Try this site:

http://www.ls1tech.com/forums/generation-iii-internal-engine/1243413-how-calculating-static-compression-ratio-long-post.html

I was doing some digging on Packard performance mods and i found a gentleman making repro Edmunds parts for Packard, his company was called Empire motors he said that the Edmunds head had very high compression close to 11.1 which is way to high for proper flame travel across the top of the piston. He sells as a set an Edmunds head with a revised combustion chamber the Edmunds dual carb intake and a split cast iron exhaust manifold for around $3500

http://www.empiremotorsinc.com/

That company does not have the best reputation on delivering product in a timely manner. I think their actual Terms and Conditions claim they may take up to 36 months (3 years) to fulfill an order. It's a place where you for sure would want to do COD in my opinion.

Wow i was not aware of the 36 month time frame! there products look great though but time frame wise it would probably be better to mod a factory head