That is a very good question. Certainly one would gain a few net HP by
removing the drag of the air pump from the system. But there probably are
changes in the carburetor needles, advance curves, and/or timing that
account for a portion of the loss, as well. One could compare the specs
for the various years in the manual to get an idea of what one would have
to change to achieve parity with the 1966 and earlier models. I am not
sure what the functional distinctions are between the HS-4 and HIF SUs,
other than the butterflies, but presumably they contribute something. I
am afraid I don't know much about most of the incarnations of the
Spridget, although I replaced the clutch, generator, steering wheel and
brake light switch at various times on a 1967 Midget.
BTW, here are the R&T figures on the Spridget:
1958 Sprite (948) - 48HP @ 5000
1961 Sprite (948) - 50 @ 5500
1963 Sprite (1098) - 55 @ 5500
1967 Midget (1275) - 65 @ 6000
1973 Midget (1275) - 55 @ 5500
1976 Midget (1500) - 55.5 @ 5000 (where'd they get the 1/2 HP?)
1979 Midget (1500) - 50 @ 5000
It looks like the 1967 tuning would be your target. Too bad they didn't
give the 1968 figures for comparison.
Charles D. Sorkin had this to say:
>>These data seem to indicate that, while emissions equipment certainly had
>>a deleterious effect on HP, the big drop came with the substitution of
>>the single Z-S carburetor for the twin SUs.
>
>Does this imply that the effect of plugging the air injection manifold (and
>removing the thus useless airpump) is an immediate raising of HP?
>Substantially?
>
>Or were there alterations in the cylinder / exhaust system that also must be
>fixed in order to turn a later engine into an earlier setup? My interest is
>for my '68 Sprite, which has been desmogged (but not yet restarted. #:-< )
>I have a set of set screws to seal up the injection ports, but I am not
>certain if there are other small modifications that were made between the
>earlier and later A-series 1275s.
--
===============================
Max Heim
mvheim@studiolimage.com
Studio L'Image/San Francisco
415 643 9309 : 415 643 9307 fax
Studio L'Image/New York
212 242 3366 : 212 242 3399 fax
www.studiolimage.com
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