Query on port-heads

[Nate M]

Thanks for the response as well as the fascinating read and information regarding what Lotus's Colin Chapman did with the Seven engine.

The Big Seven is a very conventional monoblock engine much as established by the Model T and others and very similar the Ford A, 8, copycat morris 8, Austin 10  and very many others. Most cars had the main bearing caps bolted to the crankcase base but the Big Seven has the caps elegantly slotted into an extendedr crankcase. I gather this was carried on into BMC motors where the extra rigidity may have been helpful.
The Seven inlet ports are very large and it would seem practicable to divide, but when is a Seven not a Seven?
While c.r was below 7:1 and bores were small, ohv did not offer much advantage at normal rpm

Would it be accurate to say the Big Seven, Eight and Ten like the copycat Morris 8 all roughly had a similar latent enlargement potential as the Ford Sidevalve later OHV engines (as planned on the pre-war Taunus G93A in 1498cc SV form and later on the post-war Taunus P1/P2/P3 in 1498-1758cc OHV form



It is interesting to see the difference in outputs between the Morris Eight / Minor SV with both the Wolseley Eight OHV and Alta head Morris Minor OHV conversion.

Nate, in 1934 American Austin went belly-up. Bantam, which took over the operation, had the engine (a mirror image of the Austin Seven engine) redesigned. The obvious change was to the main bearings which were changed from ball and rollers to Babbitt.
Perhaps the motivation was to reduce manufacturing costs, perhaps to avoid paying royalties to Sir Herbert.

I gather from posts on here that Reliant, who made a copy of the A7 engine after Austin stopped making it, made a number of improvements before they turned to OHV.

Taken together it would seem a Seven-derived engine that carried over the various improvements from BMW, American Bantam, Nissan D10, Reliant and Lotus, etc would potentially end up being a 860cc OHV unit with 4-to-8 port-heads of indeterminate output, since have seen claims of the SVs from Reliant, Rosengart and others claiming outputs of 20-24 hp when they were in reality only said to be putting out about 16 hp.



Also seem to recall a few Seven-based racers managing to displace as much as 900-950cc though not sure of the specifics companies and teams which did the work let alone would such mods could be productionized or be an improvement over the Big Seven and Eight engines.



Of the understanding the all-alloy Reliant OHV was basically slightly scaled down reverse engineered Standard SC engine used in the Standard Eight. 

I have come to understand that the Mk III as raced by Lotus had a real, 8-port block with round inlet ports, and that Clive Chapman still has the block, which was planned to figure in the Mk V.
However, the Mk III as sold at the end of the 1951 season had indeed a couple of tongues projecting into enlarged inlet ports, as described above. That Australian Derek Jolly also de-siamesed a block seems beyond question, and that block made its way to Hornsey. Now, whether Chapman or Jolly did it first is debatable, we may never know.

There were several de-siamesed cars built after the 750mc relaxed the ban. My father owned one of them for a while, Complexity, whose engine lay almost on its side and had the manifold face of the block machined at an angle, removing metal from the lower edge so as to provide straighter inlet and exhaust ports.

Would have loved to have seen what a Lotus Mark V could have achieved given Chapman's belief a 100-mph road sports car could be developed using an un-supercharged Austin Seven engine that the Mark V was design for, even if it must have presumably laid the groundwork for the Mark VI and Seven.