V12 XJ6 Conversion Build

Yea, I assumed that it would be pretty bad down low. What do you think of my idea to chop off the plenum on the factory intake and put the ITB’s on each runner? that way you get good torque and more room for air filters and velocity stacks/horns.

That’d work, especially if you make sure they’re all the same length; the outer end runners are a tad longer on the OEM intakes. Still, I wouldn’t go that way because it’d look too much like the stock setup and would probably perform pretty much the same as well.

Yea, I really like the look of vertical ITB’s kinda like webers. Unless I did something like this Toyota V12 https://www.youtube.com/watch?v=Iyw20RCk8Yo that looks pretty cool imho.

Thats where I fell off on the Porsche dipper at .31in my XJR its a circuit called Hampton Downs just south of Auckland

or maybe a single large TB, each bank with long runners, and large plenums to give it easier tuning, more low /mid range torque!jag%20pix%20%2Cmodel%20cars%20005 .

or this setup worked well at Daytona 24 hr races, SLIDE Plate throttles, made of Magniseum weight saving!002 .

or this setup.


Those last 2 look great!.. But they cant fit under the hood which is a requirement for me. Thanks for the suggestions though!

Have you considered how to provide vacuum to the brake booster with the ITB’s?

Bill White put together a similar setup, and he connected a tiny tube – looked almost capillary, like 1/16" or so – at the base of each ITB. Connected all 12 to a vacuum storage tank, making sure all 12 tubes were the same length. Ran everything that needed vacuum from the tank. He noted that you cannot just pull vacuum from one of those intakes because it’ll screw up its resonance and that cylinder will run completely differently than the other 11.

Might be easier just to buy a 12V vacuum pump.

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Yup I was going to do exactly that. I’ll probably add another set for idle control or i’ll just adjust it like bikes do a physically open the throttle bodies a little like a Carb.

On DKW’s, at least the cars, it would not have worked to have it on the tranny, and the 4-speed on the tree worked pretty well.

On the MUNGA–4WD–the same tranny was close enough tot the floorboard, they did put a shifter on the 'box: unfortunately, the gate near the 'box was about 2 square inches, and by the time it translated up to the shift knob, it was about like the Volvos!

Yes Kirby, i use a Vac. pump , my cams dont have enough vac at idle in traffic, brakes hard to push!
pump cured it, and made driving smoother with better feel!

I learned to drive on a 1961 Impala with a 348, 3X2bbls, and a three speed on the column. Fun times!

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Wordman: nice car!

i had a 1960 Impala , 348 ,3 dueces, but 4 speed in floor!
the engine was different than most 348s, seems Chevy made 4 types of 348s, one with single 4 barrel carby, hydraulic cam, low compression!
2nd was with 3 two barrel carbs, hydrualic cam!
3rd 3 two barrel, with solid lifter cam hi compression pistons 10-1 pistons, gettin serious now,
called " HI Performance engine"!
4th last the one i ordered Called “Special Hi Performance engine”.

3 two barrels, special exhaust manifolds, the unheard of 11.5-1 pistons(100octane and up only ).
soild lifter cam!
heads had much bigger valves & dual springs, course a 4 speed close ratio box!
head cast numbers did not match any other 348s as far as i could find!

well by a few months with it, 409s were showin up, i seen one and thought that twin -4 Barrel manifold could fit my 348, so bought new 1962 409 manifold and two AFBs carbs to fit!
YES magic, that engine must have developed at least 25/30HP more than the 3 dueces!
Ohboy you said it “Fun times”

Yeah it was pretty fast

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William, email me at nalutz@hotmail.com

William, yes the rope seal is impregnated and it’s the correct length. DO NOT TRIM or it will leak.

Email sent! Thanks in advance.

Mail](https://go.microsoft.com/fwlink/?LinkId=550986) for Windows 10

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I later swapped it for a bored and stroked 409 (482 cubes) with 2 4 bbls and an M21 4-speed. Jerked second gear one day and ripped the rear, right, lower control arm mount off the frame (bad weld from the factory).

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Little update/sneak peek. Now to make the linkages and other little things that will probably take forever. This is just the plate at the end of the Intake runners not going straight onto the head. Still trying to decide whether to bend them over the valve covers for OEM-ish runner lengths or go full “race car” and have the standing up with short intake runners.