Hello all, Regarding the Series 1.5 E type, I'm wondering if by swapping the existing two Zenith-Stromberg carburettors for the three SUs (including manifold and linkages etc) used on the Series one, one can achieve exactly the same performance from the 4.2 engine as the earlier cars had?

Apologies if this has been discussed before but I'm having trouble finding a definitive answer as to whether swapping the hardware is enough, or whether there is other work one must do to achieve the same hp etc.

 

It is quite expensive to swap out Strombergs to triple SUs. Almost as much HP improvement is possible by doing a "Crespin mod" to the existing Strombergs. This bypasses most of the strangulation needed to pass US emissions back in the 60's . And really, the HP and performance of a modern car outclasses most e-types anyway. I tried the mod last fall and it improved the HP enough that I will keep the Strongbergs and spend on other Jag maintenance instead.

 

Interesting, thanks I'll research this mod.

 

The 'Crespin mod'(?) just needs you to disconnect the secondary
throttle link at the carb end and leave it dangling attached to the
secondary plate quadrant. The secondary throttle plate (on E-types
at least) is spring-loaded to close. If you wriggle the link
around, you can jam it against the engine side of the manifold (for
which you need to open the secondary plate to make room) and the
return spring holds it tight against the manifold.

In doing so. the secondary closes a very slight amount, so it's not
as good as complete removal, although it does jam the secondary
almost totally open. It therefore eliminates the major obstruction
that causes the mixture to divert at lower revs and messes up gas
flow at medium revs too. It also avoids all possible secondary
throttle mis-timing (which is pretty common), be it from
maladjustment or due to incorrect carb spacer thickness that messes
up the opening geometry.

Offered in case it helps you overcome those terrible power-sapping
intake arrangements Jag were forced to inflict on you. Doing it by
sleeving, or total removal and plugging is better, but you have to
love that five-minute timescale as an interim step. Many will
settle for it as final choice.''

 

Thanks for the explanation Alfred. I wonder what hp the engine gets on the dyno with this mod compared to with the triple su's. Sounds like a good interim fix though...

 

Yes, but I much prefer the look of the triple SU's. Also my 68 is a series 1.5 and has the funky crossover pipe and odd exhaust manifold, so I am trading over for the 3 SU's!

 

I think that's the direction I'd go ultimately too. To realise the engine's full original potential. Now all I have to do is find the right car!

 

Personally, the triple Webers would be my ultimate swap for the SUs but for now I'm happy with what I've got.