Hello everyone been busy year for me at work hope everyone had a great thanks giving… I noticed on the uk models the carbs are different set up then the north American cars. I also noticed that extra box that the ZCarbs are attached to, could some one explain the difference to me, and what the benefits would be to take of the box and change the carbs to those uk models, and also that black heat channel that attaches to exhaust heat riser that comes across both valve covers. I would like to be educated on this topic. cheers
The US versions of the S1 had Stromberg carbs (low emissions), a secondary manifold (for emissions) and a provision for hot air from the exhaust manifold on warmup. I think that most agree that the rest-of-word version (SU carbs, no secondary manifold, etc) is better. You can remove the exhaust crossover, and block open the secondary manifold throttle butterflies to good effect. Better yet is to source a single manifold. This can be European, or a later manifold from Canada that used SU carbs that were different from the European ones. Or a Mark X manifold with triple SU carbs. Cheapest, (and with arguably little loss in performance) would be to keep it as it is, except block open the secondary butterflies.
The same situation pertained to Series 2 E-types, and there is much discussion in their archives, as well as in the XJ archives. Have a look!
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I ‘think’ the US set-up might be considered part of the emission control items, Sawyer. If emission is part of ‘Warrant of fitness’ testing; visibly removing something might fail tests…?
The main difference between US and ‘European’ was that the latter did not, at the time, test emissions - which simplified matters; they went for power. It doesn’t immediately follow that the ‘European’ set-up will fail US testing if properly tuned, but formalities may intervene as said…
In short; adopting European will increase power - but it is more to the US versions than plain carb changes. But Bob’s points are well taken…
Frank
xj6 85 Sov Europe (UK/NZ)
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Most points have been argued: The ROW twin SU HD8 (later HS8) are two inch carbs, while the Strombergs are only 1 3/4 inch carbs. Gas flows seem to be better with those two inch carbs. I’m fairly sure though that the intakes are different as well.
The hot air duct running from a stainless heat shield over the exhaust to the air filter housing has little to do with emissions: There is a t-stat at the air filter housing making sure that right after being started the carbs are fed with air at 40°C - no matter whether ambient air is cold or hot. It makes tuning easier and thereby may add to control emissions, but there is no ill effect on performance, except maybe from reducing the amount of oxygen available in the combustion chamber at cold temperatures.
The cold start and running device is different as well: HD8 and HS8 make use of ASD/AED, while the Strombergs have manual chokes. If you want to run the AED system, you’ll need the hot air duct necessary to control the bimetal strip in the AED as well - many owners have resorted to manual operation anyhow, so this might not be an issue.
SU HS8 are quite readily available at UK ebay motors; overhaul and manual choke conversion kits are distributed by Burlen, NAYY. The biggest issue might be to find an intake manifold. Parts from Euro SII cars (till 1979) should interchange with your setup.
Good luck
Jochen
75 XJ6L 4.2 auto (UK spec)
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Before cross-flow heads the inlet manifolds were heated by the surrounding exhaust manifold - offering also a modicum of carb heating to prevent carb icing, Jochen. Some carbs were actually fitted with electric heating - anybody having experienced carb icing appreciated that…
Carbs generally works on air volume, but as cold air is more dense it contains more oxygen - hence the intercooling on compressors. Advances in carb technology included air temp compensation to maintain the proper air/fuel mixture 14,7/1 - measured by weight. Such air temp compensation are standard for all EFI systems - and is part of attempts to reach emission standards without compromising engine performance…
Frank
xj6 85 Sov Europe (UK/NZ)
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The problem was of course that exhaust heating only works after some delay
Sure, Frank,
what I wanted to say is that the hot air pick up may reduce emissions by actually improving efficiency of combustion, but doesn’t sacrifice output as e.g. air pumps do.
Best
Jochen
75 XJ6L 4.2 auto (UK spec)
Thanks lads sounds like a lot of work to change over! plus I have a air rail with smog pump but no emmisions testing, I guess I could take smog pump off and block air rail ports in the head…but will it make car run better? or just leave it alone? I’m not looking for a faster car. just less maintenance. cheers
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The air pump has no effect on engine performance, Jochen - air is injected after the combustion process…
However, the air pump itself does draw some power from the engine - a parasite. The main effect of the heated inlet air is to stabilise the inlet temps - which does stabilize the mixture, which is beneficial for emission control. However, refrigerated air would actually improve power…
Frank
xj6 85 Sov Europe (UK/NZ)
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