Ace with alloy head

[Jam2]

https://www.carandclassic.com/magazine/1960-ac-ace-classified-of-the-week-2/?bsft_aaid=a5ce63ed-6419-48b8-adb6-8692f74daf04&bsft_eid=ae06d53d-78ac-3b0c-13b5-f18ace78e54a&utm_campaign=broadcast-i-saturday-uk-email-i-0-90-days-i-25-05-24&utm_source=blueshift&utm_medium=email&utm_content=saturday-newsletter-25-05-24&bsft_clkid=4631e629-7f13-4487-81e9-01e6695f4913&bsft_uid=8694d51e-d8c4-44ad-9406-e7ccd1d27dc9&bsft_mid=c7c79605-01af-4ea1-91e2-b7c023a9ce9b&bsft_txnid=0d5b6987-1b42-469c-a153-0b55a2cf6564&bsft_mime_type=html&bsft_ek=2024-05-25T09%3A00%3A51Z&bsft_lx=16&bsft_tv=13
I thought the above car interesting. In particular the alloy head, does an alloy head confer many benefits?  Who made the heads and if only three, were they not very successful?

[Robin A Woolmer]

they saved significant weight

[Flyinghorse]

A flat configuration ---horizontal rods, but engine is vertical. Someone who wrote the add has verbal diarrhea, plagiarism at its best (revealing utter crap)

I do believe that AC built a flat six but its not in this car.

Surprised I don't see Subaru in engine bay. Lightbulb moment-,may be a good aftermarket swap or a lexus V8.

[James Eastwood]

I'll add to Robin's weight note, that aluminim alloys also having better heat transfer and with a manufacturing hat on, they are faster to machine.

[Brackers]

As a new member of the club, I have only just come across this post. I am also new to AC ownership, so my knowledge of the marque is limited, but I would like to comment as follows:

I am the new owner of the Ace with the alloy head. I am aware that AC employed Zdziswlaw Marczewski after WW2 to develop flat 4, then flat 6 engines. The December 2024 edition of "The Automobile" magazine has an article on the AC Greyhound, which touches on the subject of the flat 4 and 6 engines and is my source of information on this.

I can, however, confirm that the engine in my car is not one of those engines; neither is it out of a Subaru (?????). It is a 1991cc "Weller" straight six. I can also confirm that the engine in the car has an aluminium cylinder head.

Those are the facts. Additionally, I have spent some time researching this car, and have come across the following statements regarding the aluminium cylinder head, which I would be interested to either confirm or, if incorrect, establish the correct information regarding these heads.

1) Only three aluminium heads were produced by the factory, the whereabouts of two of these heads being unknown with the third being on my car.
2) The cylinder head on my car was originally fitted to Ace AE01, which was raced in period by Bob "Sideways" Staples. He returned the head to the works when it broke a valve spring. I presume he replaced the aluminium head with a standard cast iron item.
3) The Aluminium cylinder head is approximately 1mm longer than the cast iron heads, which alters the rocker arm spacing slightly (could this be a possible cause of the valve spring breakage experienced by Bob Staples?)

With respect to item 3) above, the history file which came with my car contains a beautiful sketch, prepared by Rod Briggs (who rebuilt the engine in my Ace before my ownership, in 2019) for correctly establishing shimming of the rockers to accomodate the extra 1mm or so additional length of the head.

As to why only 3 of the aluminium heads were made (if that statement is correct), I can only speculate. Was it's use for racing by Bob Staples part of the factory's testing and development program for these heads? Was the valve spring breakage the reason AC didn't continue with these heads? AC had clearly made a new pattern for casting aluminium heads (aluminium has a much greater shrinkage rate than cast iron, so using the patterns for cast iron heads to cast heads in aluminium would result in a casting shorter, rather than longer than standard) and these patterns were expensive to make. Bearing in mind that the Weller engine had pretty much reached the end of it's development potential by this time, did AC management take the decision that continuing development of these heads would not provide sufficient benefits to justify the costs?

As I said, I am new to the marque and am interested in establishing the facts, as best as we can after this length of time, regarding these heads. I would be very interested in reading any comments on this subject by those more qualified, and with far greater knowledge, than me.

[3andahalfpints]

Welcome to the club! There is an article about the history of the AC engine in the 1975 annual review mag of the ACOC. This mentions the 3 alloys heads which were all pre-WW2. Apparently, one was scrapped due to defects, one went into a company car, and one had been left unmachined. That last one was bought in 1943, by E. A. Stafford-East to go into an FN/GN racing car project. He had a special milling tool made to complete the head. The car was not complete by the time of that 1975 article.

Contrary to some forum posters (on other car forums), alloy improves volumetric efficiency. The heat passed to the inlet tracts, increases vapourisation of fuel, and thus latent-heat of evaporation cools the charge as it reaches the cylinders.