I’ve done a lot of research into converting my twin Stromberg carbs to triple SU’s. There seems to be a number of different opinions regarding performance improvement. I don’t really “hammer” my ‘70 E Type, but an increase in snap can’t be all bad! Besides, I really like the look…it’s a piece of art! As most know, the conversion kit is really pricey. Taking it to a very competent and experienced Jaguar mechanic, what might I expect timewise, and $’wise for making this conversion a reality?
The time to do the swap, for someone who already knows how, is probably 10-12 hours.
Regards,
Ray L.
If you haven’t already gone with a different distributor with better advance curves, that will give you the most bang for the buck in terms of performance.
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You might want to look at this auction on BaT. It says this engine has an E-type head and photos look like could be Series 1 4.2 manifold and carbs. If so right now the $750 bid for the whole engine is a bunch less than new conversion parts. Please be careful though.
I too have thought about doing the conversion but have decided to stay with the ZS carbs. Removing the secondary butterflies and adding adjustable needles made things much better for me. Next up is the distributor with better advance curve that Bill talks about.
David
68 E-type FHC
I think you’ll find the manifold is from a Mark X - the end on shot clearly shows the manifold slopes up to the carbs, not down. The E-Type manifold has the carbs below the head ports to clear the bonnet. It’s a strange bitsa auction. Block from an S-Type Saloon. Head from a Series 1 E-Type. Manifold from a Mark X. Carbs from who knows where…
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Those carbs won’t fit on an E type.
It looks like the manifold is incorrect but the carbs do appear to have cut down bells, like the E type had.
Sounds about right. I’ve just installed rebuilds from my second set - just the carbs and linkages, saw no sense in replacing the manifold too - and it took probably six hours including tuning.
To do a complete conversion you need to drain the coolant to remove and replace the manifold, salvaging the thermostat housing and extension from the Z-S manifold in the process - the SU housing’s not compatible with the S2 cooling system - the two-piece Z-S housing bolts right up. You also need to replace the two S2 choke cables with a single cable that has a stiff inner wire, and that requires removing the dash top to get access to the lever.
There are more horses on tap with the SUs, but not a whole lot more than what you’d get from taking out the secondary butterflies in the Z-S setup - at least that’s my impression from driving a couple of Es so-configured. No question the bling factor favours the SUs.
Agreed: that, and disconnecting the secondary butterflies will buy you a LOT of performance.
Ive said it before: a properly-set-up set of ZSs, proper advance, and disconnected secondaries will work within a few per cent of a triple-carbed car, up to about 4500 rpm.
You may be right there Bill. Interestingly the choke mechanism looks to be correct for the E as well. So it’s possible the carbs themselves came off an E. The manifold is definitely wrong though.
I have a feeling that Peter Crespin might have some carbs for sale as well.
As others have said: that intake will not work in an E Type, among other things.
The transmission would add value to a pickup truck load of scrap, going to a junk yard…
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Agreed. Mk X manifold. The throttle bodies feature manual choke mechanisms, though, and look to be the same HD8s fitted to E-types. The front and rear float chambers are switched around, or at least the tops. What’s left of the fuel rail is in the wrong place.
Gary, this is what you’re looking for:
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Wow, I didn’t realize there was so much to it, thought it would be undo the Z-S, bolt on the SU”s, tune and go. So…tell me about these “secondary” butterfly’s…where are they located, what do they do, and…how are they removed?
Thanks to all who’ve responded to my posts…I’m new to this, and appreciate all the comments and insight.
This thread describes a quick fix that gets you most of the way there.
Actually removing the butterflies is better.
I drove with the 5-minute fix for years and noted the improvement, when the engine was out & the manifold off I removed them completely,
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If you compare the actual advance curves between the original distributor and the pollution control distributor there is actually very little difference in the lower rpm range - up to 3000 engine rpm (a few degrees only) but after that the pollution distributor continues to advance to 39 degrees BTDC at 4400 rpm whereas the original distributor stopped advancing at 3000 rpm at 32 degrees BTDC. ( Under significant throttle the vacuum advance system is inoperable so it can be disregarded.) Thirty two degrees max advance on a hemi engine is very conservative - most hemis go to 45 degrees, and from dyno experience I’ve had on XK engines, additional advance at higher rpm makes for significant power increases.
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I have the 123distributor with 16 settings. I set static at 10 degrees BTDC.
Which curve would you recommend? Table from the manual.
The secondary butterflies are located in the intake manifold, immediately behind the carburetors. In the closed position, they cause the mixture to take a long path to the intake valves. In the open position, they allow the mixture to take a more direct route. The two paths result in different temperature of the mixture, and consequently different emissions depending on throttle opening.
The “5 Minute modification” involves disconnecting the linkage to the secondary butterflies and holding them in a permanently-open position, but still in the secondary manifold. The fuller modification is to remove the carburetors, to gain access to the butterflies so that they can be removed. The butterflies are brass, secured to a shaft by two small screws each. They can be unscrewed from the horizontal shaft on which they rotate and removed entirely. The shaft itself can be left in place, or removed and the ensuing holes plugged. If you do this modification, keep the parts that you remove.
Any of these modifications result in a faster throttle response, and many of us, me included, believe more horsepower overall.
Note well that these secondary butterflies are not integral to the carbs so they are not to be confused with the primary butterflies in the carbs.
Once you establish an appropriate level of confidence to do one of these mods, you will see why many of us with strombergs choose to keep our money (if we have any) in our back pockets and not spend it on SUs. But there is no doubt that the bling factor mentioned above is a powerful siren call and this post if analyzed by a competent psychologist would show I am merely envious of those with SUs…
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None are an exact match to the curve I use but using curve #5 with a 5° BTDC static would come closest.
That is on a 69 which has no vacuum advance and a 5° static spec.
Is a 10° static advance correct for your engine (a 70)?
What may make comparison harder is that the chart shows advance maxed out at 3000 to 3900 RPM whereas I think the stock distributor continues to advance up to 5000 RPM or thereabouts.