Semi-Sprint S2?

[RotoFlexible]

I am in the early stages of an engine rebuild. If I fit a pair of Sprint cams, what sort of performance gain (and what driveability loss, if any) can I expect if I fit a tubular header (already planned), the appropriate distributor, and 32mm chokes and correct jets? I wouldn't be shaving the head all the way to the Sprint spec, but it is already slightly shaved and may need to be shaved again for flatness. I probably wouldn't fit big valves. I would also like to stick with the stock S2 exhaust (or rather, the new SS system that I've already purchased).

Does this seem worthwhile, or would I be better sticking with the standard cams or trying to find some S/E cams?

[tower of strength]

I'm reading Miles Wilkins excellent book on the TwinCam engine, according to this tome, there was a "super S/E spec engine that was basically a Sprint spec, ie cams and compression that produced Sprint power with standard valves, on Strombergs and webbers!!
I will try and post the suitable carb details and timing settings when I get time.

Regards

Mark

(I may have miss read this though!!)

[bcmc33]

In a previous lifetime I improved my 65 S2 in 1969 by flowing the head, changing the cams and opening-up and jetting the Webers to 45. I have no memory of exactly what the cams were apart from them being re-profiled standards. I obtained the complete kit from a well known London tune-up shop that advertised in Autosport.
The outcome was 105bhp at the rear wheels, and traction in traffic was no different to standard.
The car was my daily work transport, and the improved power was aimed purely at improving performance at weekend hill climbs and sprints.


Brian Clarke

[steveww]

IIRC the Sprint cams are 272 degrees duration with 0.36" of lift. This profile is not too wild and will provide good traction form around 2000rpm through to 6500rpm (aprox).

While the head is off it is well worth flowing it and opening up the ports a bit. The big valves do not make much difference as they are only 1mm bigger. I think the Big Valve engine was more marketing than engineering.

[tower of strength]

Having perused the book again last night, the "Super S/E" spec engine didn't officially exist, howerver it is believed that a few of them ended up in press demonstrators!! The spec was, 10.3-1 compression ratio, sprint cams, sprint carburettor settings and the result 125-127BHP. On standard valves but with a bit of port work. The "big Valve was a marketing ploy, rather like the "silver roof +2" and was worth at best 1bhp (again according to Miles Wilkins book)
The reason given for not using the Super S/E spec engine 2 years earlier was due to the lack of availability of interleaved rotoflexes.

Again according to the book, Autocars Sprint was slower accelerating than thier Earlier plus 2, despite the shorter gearing and lighter weight!!

I think you will end up with a slightly pokier engine with the power and torque moving up the rev range, with a slightly lumpier idle.

Hope this helps

regards

Mark

[trw99]

The Autocar road test car was faulty and had to be returned to the factory during their test. When they re-ran the acceleration times, they were more in line with expectations.

Tim

[richardcox_lotus]

Also, IIRC, the earlier +2 Road Test car was fitted, on the sly, by Graham Arnold with a demon hillclimb engine, thus producing the most impressive performance figures, and presenting Lotus with lots of trouble in trying to always match it in future tests.

[RotoFlexible]

Thanks for the replies. I have the Miles Wilkins book and reviewed the section on the "Super S/E" setup - it sounds encouraging. Between that book and the Dave Bean catalog, I should be able to work out the jets.

Thanks to ebay, I am now the proud soon-to-be owner of a set of 125E con rods (to replace the original 116E rods) and a pair of Sprint cams, so this project can go forward. Next big hurdle is the block, which is already .040 over and is graded "LB" (meaning that it shouldn't be bored any larger).

[tower of strength]

If you raise the compression to 10-1 you should find sprint carb settings will be ideal

Mark

[rgh0]

At plus 0.040 inch (83.5 mm) the bore is going to be close to the limits as you say but not necessarily impossible to go further. Find a good engine shop that can measure the bore wall thicknesses and offset the boring of each cylinder slightly if necessary to maximise available wall thickness. If wall thicknesses are really too thin even with offset boring then you may need to sleeve one or more of the bores to recover the block. If your not after the last few CC's it may be worth sleeving all 4 bores and returning the block to standard bore of 82.5mm given the low cost of standard pistons and starting its life all over again.

regards
Rohan