On Mon, 23 Oct 1995, Greg Meboe wrote:
> John,
> If I remember my specs correctly, the 69 spit (high compression, twin
> carb, vacuum advance dizzy) should be timed dynamically at 13btdc. The 2
> atdc setting would be for the single carburettor, vacuum retarded 1970 model
> car, (timing set with retard connected and functioning).
Well, FWIW, I looked last night at the under-bonnet sticker of my 1969 Mk.3
Spitfire. If I read/remembered correctly -- it's pretty dark in that part
of the barn ;-) -- static timing is 2 deg. BTDC and dynamic timing is 6
deg. ATDC. (It might be the other way 'round, but regardless the dynamic
timing is ATDC.) This is (was/will be again someday) a 68 hp.,
dual-emission-controlled-SU, fairly-high-compression 1296 engine, NOT to
be confused with the 75 hp. version found in the earlier Mk.3!
Interestingly enough, the official factory workshop manual does NOT
indicate timing specs specifically for the USA version; rather, they
show a spec. of something like 6 deg. BTDC for the Mk.3 Spitfire. The 13
deg. BTDC, regardless, I think is for the 1147 dual-carb Spitfire engine.
Of course, much of this information is from the same workshop manual
that shows the capacity of the Vitesse fuel tank at 5 gallons!? Other
manuals or later editions might have addressed this question better?
But back to timing. I DO agree that the dynamic timing of a dual-carb
Mk.3 at anything ATDC might not be optimal; it never was for me. In fact,
that 13 deg. BTDC might be about right!
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