[v12-engine] Group A inlet manifolds?

Hi all. Can anyone tell me what physical differences there in in
the Group A inlet versus a pre HE efi version i.e how much larger
were the runners in i.d. / flowrate and also, were the plenums
appreciably larger in volume ?
Recommended for a 5.3 with mild heads, headers, cam & 5 speed ?
Thanks–
Wayne XJC
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I don’t believe there are a lot of differences, other than when carbs
changed to injection.

The carbed cars really have 4 inlet manifolds, on for each carb - which
fet 3 cylinders either on the front or rear of the bank. Also, they had a
fresh air intake system that got cool air from over the top of the
radiator.

Early injected cars - '75 - at least '79 (maybe later) had a mount for a
fuel pressure regulator, and for a cold start injector. If you want to
use these on a later car, you would have to block the cold start injector
hole (not hard - some permatex,and a well designed plate mounted there).
The mount for the pressure regulator can just be ignored. The end caps
may have different vacuum line ports on early injected cars vs. later and
HE cars as well, but as far as basic shape and port size I don’t believe
it ever changed.

Later injected cars, including the HE don’t have those things above, but
they do have a mount on one bank for the ignition amplifier.

Phil Bates
'75 XJ12C - 2 engines, and 3 sets of intake manifolds

Hi all. Can anyone tell me what physical differences there in in
the Group A inlet versus a pre HE efi version i.e how much larger
were the runners in i.d. / flowrate and also, were the plenums
appreciably larger in volume ?
Recommended for a 5.3 with mild heads, headers, cam & 5 speed ?
Thanks


Wayne XJC

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !

Hello Wayne, I’m not sure your intended end result but I found this
product on line and thought I would share the info.

Mike Neal
1987 Ser III V12
1948 3.5 Litre Saloon

At 02:48 a.m. 12/18/2007, you wrote:

Hi all. Can anyone tell me what physical differences there in in
the Group A inlet versus a pre HE efi version i.e how much larger
were the runners in i.d. / flowrate and also, were the plenums
appreciably larger in volume ?
Recommended for a 5.3 with mild heads, headers, cam & 5 speed ?
Thanks


Wayne XJC
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/ Calendar, On Line Books and more !

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In reply to a message from Wayne XJC sent Mon 17 Dec 2007:

Thanks Mike, Phil. Phil. the query was in relation to the Group A
XJS’s ran by TWR rather than carb v’s efi manifolds. The web
alludes to enlarged runner i.d. & plenum volume and I’d like to try
& get a handle on what those differences were - any contributions
re such greatly appreciated.
Second question… anyone know details of the rims these TRW cars
ran, sites with images etc
Regards all. Wayne–
Wayne XJC
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In reply to a message from Wayne XJC sent Tue 18 Dec 2007:

hello
i have no clue to what the twr cars used as inlet manifolds
i do know what they used on the broadspeed cars
and they where bigger and had a similar setup to the carbs
2 butterfly valves each side ( same as on a normal injection but
than 2 of them )
so that would come to a setup per bank of one inlet for 3
cilinders
than the broadspeed car had a fuelinjection system that was
driven by the camshaft (rotary fuelpump like a diesel) with
special injectors
the injectors you can still find if you look realy hard and
they would cost about 50 gbp each
the inlet manifold is harder to find and the injection system
is no where to be found and if you find one it ll be so terible
expensive
if you want a picture of this setup send me an e mail I
have some pictures

about the twr wheels
they look similar to the twr road wheels
that they put on some of the road versions but than without
the center cap
about sizes ? I have no clue but I guess they where 16’’ maybe 17’’

best regards

mitch–
mitch73_nl
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mitch73_nl wrote:

i do
know what they used on the broadspeed cars…

broadspeed car had a fuelinjection system that was driven by the
camshaft (rotary fuelpump like a diesel)

Aha! Injection into the intake manifold or directly into the
cylinders?

Injection directly into the cylinders, once known as “Fuel Injection”
before EFI stole the term to apply to poxy computer-controlled
carburetion, is a serious performance boost. It’s functionally
similar to supercharging. In a normal naturally-aspirated engine,
the intake stroke draws in a fuel/air mixture. All else being equal,
it’s only going to draw so much, limited by the displacement of that
cylinder. But with fuel injection, the intake stroke is drawing in
air only – no fuel. Hence it can draw that much more air, about
1/13 more. Then, after the intake valve is closed, the fuel is
squirted into the cylinder. Equivalent to about a psi of boost.

with special injectors the
injectors you can still find if you look realy hard and they
would cost about 50 gbp each the inlet manifold is harder to
find and the injection system is no where to be found and if you
find one it ll be so terible expensive

Gee, if you really wanted fuel injection, I’d think you could start
by just finding hardware from diesel engines. Dual six-cylinder
injection things, I guess.

I’d still suggest nitrous instead. Of course, that’s for street use;
nitrous isn’t particularly helpful in road racing, you’d be using
more nitrous than gasoline! Probably not legal, either – although
frankly I’m surprised fuel injection was legal on a car in which it
wasn’t available OEM.

– Kirbert

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In reply to a message from Kirbert sent Wed 19 Dec 2007:

Don’t get too excited Kirby, the description doesn’t fit the
picture. Photo’s I’ve seen of the Broadspeed coupes used mechanical
injection similar to a Hilborn set up if your familiar with their
products. One throttle body per inlet manifold with shortish
trumpets and an injector in each throttle body. Belt driven
mechanical fuel pump (or any other suitable drive source like a
cam). In the Hilborn set up overall mixture strength is controlled
by adjusting the diameter of an orifice in the return line. There’s
also a barrel valve connected to the throttle linkage so as the
throttles are opened more air means more fuel. Relatively crude but
none the less effective, especially on a race only application–
The original message included these comments:

Aha! Injection into the intake manifold or directly into the
cylinders?
Injection directly into the cylinders, once known as ‘‘Fuel Injection’’
before EFI stole the term to apply to poxy computer-controlled
carburetion, is a serious performance boost. It’s functionally


Neville S1 XJ12
Christchurch, New Zealand
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In reply to a message from Kirbert sent Wed 19 Dec 2007:

yes its similar to the hilborn system
the injectors scuirt the fuel into the trumpets inside the
inlet manifold so not into the head itself

and no its not as easy as taking some diesel parts
for one using petrol in a diesel pump will kill the pump in no
time

they say its a lucas/bosch system but I couldn t find any propper
markings on the pump when I checked the car out
so I dont know for sure what make the system is
it is a rotary pump with 12 fittings for the fuel pipes
mechanicaly driven by the righthand side cam by a belt
with an adjustment from the trotle tower so it knows when and
how much fuel there should go to the injectors

in basics its an easy system ( no computers )
and with 560/580 bhp who needs NoS

regards mitch–
mitch73_nl
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The rare Group A manifolds are visually similar to the std injection manifolds but clearly different when placed side by side. They are 36mm ID at the head manifolds and 41mm at the larger plenum.
Standard inlets are 33/4mm ID through the runners from head to plenum.

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Like this,


If you want details let me know as I have the original TWR tooling and occasionally get a batch made at the local foundry.

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So yes visually similar to standard from the top, but they are very different.

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