Sanddoc. Trying to help here...
Per John Mummert's web page, ECR whatevers (various suffixes were used depending upon the year) were a '56 and up heavy duty truck or industrial application cylinder head. Cliff just came in with information on that head within the last week in another thread. My understanding is that the intake valve is the ECZ-G, 5752-113, 5750-471 series size of 1.92 inch. The kicker is that the exhaust valve stems have sodium in them and the stem diameter is ~7/16 of an inch compared to the usual y-block stem diameter of 11/32 inch. From what Cliff indicated, the sodium filled exhaust valves can be surplus-ed and passenger car replacement valve guides installed so that the standard diameter y-block exhaust valves can be used.
JM's web page does not indicate the volume of the ECR cylinder head's combustion chambers. Cliff indicated that it was like or equivalent to the 5750-471 heads from JM's listing. Regarding the 5750-471 combustion chamber volume, JM's chart indicates that it is 82 ccs.
You asked about an apparent discrepancy in the compression ratio in JM's chart.
- JM's listing indicates that the advertised compression ratio on the '59 light duty, medium duty, and heavy duty trucks was 8.0:1. All of these vehicle applications had 292 cubic inch displacement engines.
- JM's listing goes on to indicate that the advertised compression ratio on the '59 Mercs was 8.7:1. All of the '59 y-block equipped Mercs had 312 cubic inch engines. The same cylinder head on the larger displacement engine yields a higher compression ratio.
I've been told that some 5750-471 heads used on HD truck applications came equipped with the sodium filled exhaust valve stems. IMO if you're looking at ECR or 5750-471 heads be on the lookout as to whether they have the 7/16 diameter exhaust valve stems. While the large exhaust valve stem heads are use-able, you will experience additional expense in having the valve guides modified so that you can use usual y-block exhaust valves.
From what Cliff reported about the ECRs he has and what I know of 5750-471 heads they are both posted, have the big intake valves, and good porting. The glitch for some applications is that they yield a low static compression ratio when used on a 292 engine with flat top pistons and normally aspiring carburetion. Yes, they could be milled significantly to reduce the combustion chamber volume and therefore increase the static compression ratio for your engine application. Another option would be to use an aftermarket domed piston to increase the static compression ratio. John Mummert has Probe aftermarket domed pistons available off the shelf for y-block bores with domes up to 10ccs.
IF you were building a supercharged or turbocharged engine, the ECR or 5750-471 heads would be desire-able to use because you need a lower static compression ratio for those applications.
Hope this helps.
NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York