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Spitfire Going up-Engine with my Herald

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Paul Romans

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My '63 Herald 1200 actually has an older 948 engine with the single Solex carb. This must have been retrofitted somewhere in the dim past, and while it's a sweet little unit, I wanted an actual 1200 with a little more pep for mine. Recently picked up a Spitfire Mk2 1147 engine. Compared to the Herald 1200 version, the Spit has higher compression, a hotter cam, dual SU carbs and a factory 4-2-1 header. The 948 engine was rated at 34 hp, with the 1200 Herald leaping all the way up to 39. The Mk2 Spitfire was rated at 67hp, or nearly double the old 948 version. What I've read on the MK2 Spitfire engine says it was the best unit for reliability and cool running, and was the basis for all the factory Spitfire racers of the '60's. Some claim it was a more free revving engine than the 1300 or the emmission-choked 1500.

I'm looking forward to better performance. Any feedback?
 
My Herald had the earlier 1300 small crank engine - free reving like the 1200 supposedly 60hp. The later 1300s had a "big" bearing crank which didn't rev as nicely. If you got the whole 1147 set up it should be a real nice improvement. Around town, it felt peppy enough to keep up with modern cars. On the highway it got a bit buzzy! Just be careful with the rear diff. There were different versions and the earlier ones won't appreciate full blast in 1st gear! The later upgraded ones can handle it.
 
Thanks Luke. The Mk2 engine came with a gearbox, probably the correct one for the engine. On the Herald, I haven't been able to locate the s/n on the diff, but it's pretty leaky so I'll likely have to pull it and install (at least) new seals. I'll clean it up and see what shape it's in. I plan on babying this little beauty, not going to any drag races with it.
 

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Paul, it would be good to confirm what differential you have in the Herald now (just in case it's an earlier 4.55 or 4.875 unit from a 948, rather than the original 4.11). Assuming you have an original 4.11 Herald diff, it's identical to those used in the Spitfires up to the very early Mk3. During the Mk3 run, the diff was strengthened with beefier inner axles due to the increase torque of the 1296 engine.

Beyond that, and other than fabbing up accelerator linkage and exhaust system, everything else is literally "plug and play" and will make for a pretty darned fun car. You'll likely want to upgrade to front discs if your Herald doesn't have them, but that's it. (Oh, the two gearboxes also are essentially identical, down to the same ratios and lack of a synchro 1st gear! :eek: )
 
Terrific info Andrew, many thanks. Looking thru my workshop manual, it looks like any gearbox with a "GA" code should be the 4:11 unit, correct? I don't have any code info on the earlier 948's. I'll scrape off the grease next chance I get and find the S/N.
 
Paul Romans said:
Terrific info Andrew, many thanks. Looking thru my workshop manual, it looks like any gearbox with a "GA" code should be the 4:11 unit, correct? I don't have any code info on the earlier 948's. I'll scrape off the grease next chance I get and find the S/N.
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After all these years, it's wise to "count the turns" just to be sure, as the diffs could have been rebuilt with different ration ring-and-pinion sets, but yes, they should be 4.11 units, as are FC prefix Spitfire diffs up to FC120000.

The 948cc Heralds would have had either a Y prefix on the diff (for a 4.55 ratio) or G (for a 4.875 ratio). Worth making sure regardless, since the housings all look identical otherwise. There was a change in the shape of the bolt-on front mount, though, and that happened at commission number GA80001 and future.
 
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