Lemony midget, and the Unfortunate Series of Events . . . . . . . .Well boys and girls, before descending into a discussion about rod length/ stroke ratio, some background
might be in order . . . .
Astute readers of this Build Diary may have recognized that both of Mr.
midget's engine projects have ventured into the realm of "high" rod length/stroke ratio.
Why is this happening to him? Well, there is an explanation, and possibly a good reason.
Let's start at the beginning . . . . .
In the beginning, the I/GT project required a 1 liter power source. And, after doing a bit of research, the
midget became aware that BMC had already created his dream engine: the XSP Formula Junior engine, based on the 970 cc Cooper S. A big bore, large valve, short stroke, dry sumped racing engine. Only problem was, there were very few produced, even fewer remaining, and therefore: EXPENSIVE. Even the base blocks, a 970 Cooper S or a 1071 Cooper S, even the ones without the dry sump provision, were way overpriced. Based on the demand for replica XSP's prepared for vintage racing.
So, what to do? Well, 1275 Spridget blocks shared the same big bore and they were relatively plentiful and cheap to boot. So it was affordability that determined the direction that the build took. Only problem? 1275 blocks were TALLER than the 970 S and 1071 S blocks. Same height as the 1275 S blocks in fact. Out of the necessity of cramming the 1275 stroke into the big bore block, there was a need to raise the deck height of the 970/1071 series. No problem at the larger displacement, but when used for a short stroke 1000 cc engine, an even longer rod
was required to connect the bits, as it were.
OK, so eventually, the engine got developed enough for Lemony
midget to spend quality time in "Warnerville". Twice, in fact, thereby fulfilling one of
midget's fantasies, one of the ones that did not include Mrs.
midget, Rolling Stones cover bands, cats and/or Stormy Daniels . . . .
Now, jumping ahead to the "current permutation" of power plant, a decision was made to embrace 1980's technology as a replacement for 1930's tech. Undoubtedly, a good decision, as the performance potential for the venerable 'A' series could never hope to rival the performance potential of a short stroke 4 valve DOHC engine. Pure 4 valve racing engines of automotive and motorcycle constructors were extremely powerful.
Yet again, the chosen manufacturer, Rover, had the "dream engine". The 1100cc K16 variant. Only used in the "sportiest" version of the small cars, most of which used the 2v K8's. Several friends in the UK advised that although Rover had indeed produced the 1100 K16, no one had ever seen one, or could procure one. So, what to do? The time honored process. Destroke one of the more common, cheaper, and larger K16 engines. This idea had the merit of being able to use the head designed for the larger engine, at a lower level of modification, to support the higher revving smaller displacement engine. Snap!! Problem solved!! Availability and affordability, both at the same time . . . . .
EXCEPT, the old de-stroking bugaboo resurfaced, only this time with the added complications of an external belt cam drive. What can be done? Well, not all that much really. We can do some "fiddling" with rod length, but not enough to "dramatically" reduce the rod/stroke ratio. We know for certain the 1400/1600/1800 variants all use the same block height. The variations in rod/stroke ratio do not affect those engines, but of course, their output level is much lower. And, as far as we know, even the 1100cc K uses the same block height, giving an even higher R/S ratio. So does it matter? Will it affect this build? I guess we'll see . . . . .
And so, the final thought has to be an homage to one of the greatest engine designers of the 20th, or any other century . . . . .
"Packaging, is everything." K. Duckworth The point being that even the very best engineers and designers are constrained when using the parts produced by others, for purposes not remotely akin to what your bright idea involves.
Duckworthdiscipleboy