Ted
In Mummerts site you will notice that the ECK **** C heads are grouped in with ECL****B and ECL****C units.  All of which are slated for Mercury and T Bird applications.
I have documentation from the "National Service Data" books.

Under the Ford listings and in  the cylinder head section there is no specification or decree for the ECK****C head application used for the 1955 model year.
There is also no listing for head application in the Mercury section.

It does list under Ford as the heads used are ECL****A , ECL****B , ECK****B , ECG****A

In Mummerts listings your ECK****C heads are associated with additional heads speced with the same compression ratings.Those similiar compression heads are cast as  ECL****B and ECL****C .

Now the reason that I mention this is because of a notation in the National Service Data book regarding a differing cylinder head thickness measurements on the ECL****B heads.

It specs two differing  head thickness on the ECL****B heads. 
One is speced as .999 - 1.001 slated for  the 292 Thunderbird engine and the other is speced as .964 - .966 on the 272 Special (early) engines.

I"m thinking that since there was a "pool" of heads  (ECK****C, ECL****B , ECL****C ) , that were compression interchangeable that perhaps a pair of those ECK****C  heads (of yours) were cut to fullfill the ECL****B  -   272 needs but instead got installed onto your 292 engine upping your horsepower rating.

There was also a camshaft change that is noted as a  "material specification change only".
The early cam was cast as ECB and the later cast as ECK.
Might want to see if those cams are actually of the same event timing if they are cast as different critters.

Oldmics

I found this just now. I have also read the same from other sources:

http://www.secondchancegarage.com/public/424.cfm

Charlie.  Thanks for stepping in on this conversation.
 
In 1954, the police engine in the Ford cars was simply the Mercury 256 engine.  I would suspect the police engine for the 1955 Ford cars was the same mentality and that would have been to use the Mercury 292 engine for the Ford police cars.  Part of that assumption is based on the 292 engine not being available to the normal buying public in 1955 which left the top engine for most Ford buyers being the 272 equipped as the 182HP Special.  The Thunderbird engines did have different cylinder heads which may be where the Ford HP number comes from.
 
Assuming the camshafts are the same for both the Ford and Merc 292 engines, then I’m only curious as to why there is what appears to be two different HP ratings for what is essentially two identical engines.  I’ve dynoed the Police engine which was blueprint assembled with NOS parts other than the 0.030” overbore and it does come in at 192HP once the carburetor was rebuilt.  That's close but usually with an overbore, I would have expected just a bit more assuming the factory HP numbers are in the ballpark.  I could also be dealing with some variances in head castings at this point where all the heads simply flowed differently depending upon core shift and machining.

Lorena, Texas (South of Waco)

Ted.  I looked at the cylinder head [6049] listings and camshaft [6250] listings in both of the following...
-  1955-56-57 * Ford * passenger car and Thunderbird * Chassis Parts and Accessories Catalog * Form 7516 * [yellow, white, black, grey cover]
-  1949 - 1957 * Ford * Police Interceptor * Parts List * February 1957 * Supersedes Parts List Dated February, 1956
I don't have Mercury Chassis and Body Catalogs that include the year 1955

I expected to see some 'police special' or 'police interceptor' differentiated performance listing for a camshaft or perhaps modified (broached? higher compression) heads.  To my disappointment the parts listings I had available indicated no special or optional offerings in cylinder head or camshaft listings for Ford passenger cars, 'Birds, or Ford Police Interceptor applications in the two sources I scrutinized.

Based upon numerous past postings on the Forum dealing with camshaft specs, I would recommend your contacting John Harding [Forum handle: 'Oldmics'].  John may have some Mercury camshaft information that would shed light on differences between Ford and Mercury camshafts (IF any) in 1955. 

Felix Natoli, Thunderbird owner and avid 'Bird hobbyist since 1957 here in NY, has shared glimpses he's seen of experimental developments that Mercury division pursued in the mid '50s related to intake manifold development that was separate from Ford Motor Division and apparently pursued with Edelbrock.  Jon Hardgrove, owner of The Carburetor Shop LLC in Eldon, Missouri, has what he believes is a '56 Mercury factory experimental 2x4 set-up with Carter WCFB carburetors.  Mercury's stand alone use of the Carter WCFB on some models of the '56 Mercs was a clear example of their independence and pursuit of engine development apart from Ford Division in that era, too.

Ted, IF your digging for a difference between '55 Ford and Mercury 292 engine offerings yields nothing, we'll be left to assume that their advertised horsepower ratings were another example of advertising / marketing hype that has probably been going on forever throughout the automotive industry.

Wish I could be of more help.  THANKS for ALL the information you're always sharing with us!  -Greatly appreciated!  

Charlie


NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York

The 198 HP version of the Merc engine was installed in Montclair models w/Mercomatic. The lower trim levels got the 188 HP version. I'm guessing your engine came out of a Monterey or Custom. I'm pretty sure the extra 10 HP for the Montclair came from higher compression heads and I believe you're correct with the 8.5:1 figure. 

I have two engines here with ECK-C heads.  Both are 1955 engines with one being out of a 1955 Ford police car with a standard transmission and the other being out of a 1955 Mercury also with a standard transmission.  Both engines are 292 and both have ECK-B blocks.
 
Not really related to the advertised HP numbers but here’s some info on the carbs.  Both have teapot carbs with the police engine having a ECK-T carb while the Mercury had the ECK-G carb.  Date coding both engines finds the Mercury engine being built five months earlier than the police engine so that jives with the carb numbers as both carbs are listed for both the 1955 Ford and Mercury 292’s.  The 1955 Thunderbirds had their own carbs and differed from these.  The difference in the two carbs I’m dealing with is apparently a revision of the main jets and the power valve sizes which was likely a normal deal during the course of production during 1955.  The ‘G’ carb came stock with #51 main jets and a 0.040” power valve while the ‘T’ carb came stock with #50 main jets and a 0.043” power valve.
 
The quandary here (according to what books I have) is the Mercury is rated at 188 HP while the Ford is rated at 193 HP.  The Mummert site lists the ECK-C heads as being 198 HP but I’m inclined to believe that’s the automatic transmission HP rating which should be another set of heads getting the compression ratio up around 8.5:1.  I reverse engineered the static compression ratio for the stock police engine upon disassembly and found it to be 7.6:1.  That comes close to my books saying that both the 188 HP Merc and 193 HP Ford 292 are listed as being 7.5:1 SCR.  I haven’t disassembled the Merc engine yet but will also reverse engineer the SCR and confirm that it’s in the 7.5:1 range as listed in some of my literature for the stick shift cars.
 
So my question is “What’s the correct HP number for a 292 with ECK-C heads?”

Lorena, Texas (South of Waco)