Duplex manifold

As Dick said and Mike Frank's pictures shows - the system routes mixture over the engine and back, to bypass the closed secondaries. The bulge plate does not stop this like a flat plate would, it merely short-circuits the route across the engine but you still need flow as long as you have the secondaries. You swap the exhaust manifold just because it looks odd - there is nothing that needs to be blanked off. A flat alloy plate would mean the engine would be strangled until the secondaries opened so to use one yu have to jam the secondaries open. Removing them requires dismantling the intake system and means the spindles can now slide sideways and come a bit loose.

Assuming your secondaries still have a return spring around the spindles you can get most of the benefit by just disconnecting the linkage at the little retaining washers and turning the link forward to jam the secondaries fully open against the manifold. No wire, no nothing, takes five minutes, max. Car accelerates much better and I probably won't bother fitting triple SUs to a Federal S2 from now on.

Dick, what did you to the rear exhaust manifold when the crossover is removed?

Edited on 2013-02-26 2:48:28

Edited on 2013-02-26 2:43:15

Edited on 2013-02-26 1:25:44

Edited on 2013-02-26 1:24:19

Dick, what part is fitted for the rear exhaust manifold when the crossover is removed?

Why does your plate have a bulge per photo?
-- why is it not flat?

Why don't you give me a call. 800-331-2193 ext.210 if you are interested in the part?

Dick Maury, stated 2012-05-30 15:07:20
"Jaguar has a cast aluminum piece that fits on the later cars, no use fabricating one. However, if you remove and blank off this piece with a flat plate, you will have to remove the secondary butterflies or you will have severe driveability problems. The Jaguar piece will work as it is not a plate but a pass through."

Is this part in photo still available to buy?
-- if so where?

Is there a similiar shaped piece to cover exhaust manifold opening after removing the cross-over? Alternative is to replace the rear exhaust manifold.

Dick Maury, stated 2012-05-30 15:07:20
"Jaguar has a cast aluminum piece that fits on the later cars, no use fabricating one. However, if you remove and blank off this piece with a flat plate, you will have to remove the secondary butterflies or you will have severe driveability problems. The Jaguar piece will work as it is not a plate but a pass through."

Is this part in photo still available to buy?
-- if so where?

Is there a similiar shaped piece to cover exhaust manifold opening after removing the cross-over? Alternative is to replace the rear exhaust manifold.

Dick Maury, stated 2012-05-30 15:07:20
"Jaguar has a cast aluminum piece that fits on the later cars, no use fabricating one. However, if you remove and blank off this piece with a flat plate, you will have to remove the secondary butterflies or you will have severe driveability problems. The Jaguar piece will work as it is not a plate but a pass through."

Is this part in photo still available to buy?
-- if so where?

Is there a similiar shaped piece to cover exhaust manifold opening after removing the cross-over? Alternative is to replace the rear exhaust manifold.

That was version two of the Ex/Em engine--see the Judging guide for the S2 cars!

I have a 1969 E-Type that does not have the crossover to the Exhaust. Was this an "improvement"? I am considering eliminating the secondary butterfly maninfold either by removing it, wireing them open, or just removing the butterfly plates themselves. Obviously removing the secondary manifold affect the intake port length. Is this shortening a good thing or not?

Will eliminating the additional intake heating that the car gets from this secondary manifold hurt the performance?

The easiest thing to do is to simply disconnect the secondary linkage and wire them open.

Cool air is "better" if you can control the fuel charge to match air density. Cars, especially older cars, heat the intake charge to a relatively constant temperature by circulating coolant through the intake manifold. This is in part because carburetors can't be precisely regulated to temperature. The second benefit is that the fuel vaporizes. Vaporization not only gives smoother operation, it requires a great deal of energy. The energy comes from the hot coolant, and has a measurable impact on cooling system efficiency. The point is that some heat helps.

I removed the secondary butterflies from my '68 FHC several years ago but left everything else ( cross over pipe, rear exhaust manifold etc) intact. I am delighted with the improved throttle response with only the secondary butterflies deleted. Is there additional advantage by removing the crossover pipe and changing over to the Series II '69 configuration with the blank off piece and one piece rear exhaust manifold ?

David Barnes

Not sure of the part number as this is used. Last one I have also. But then, who knows what the future holds.

Dick,
That is pretty cool. What is it called, part number, etc. I may want to buy one in future, as a just in case.

Here is a shot of the factory piece. If you use flat stock, the secondary butterflies must be removed. You should also consider replacing the rear exhaust manifold with the earlier style as the flat boss where the crossover bolted on will still be there. You can call 800-331-2193 ext.210 if you want any of these pieces.

Edited on 2012-05-30 14:57:53

Sorry, the photo did not upload.

I fabricated mine from aluminum stock, and removed the secondary butterfly plates. I put headers on the motor. The "Jaguar" emblem is a key chain that I glued to the plate.

Would you happen to know where one can be found? I have searched online for this cast alluminum piece and have found nothing.

Jaguar has a cast aluminum piece that fits on the later cars, no use fabricating one. However, if you remove and blank off this piece with a flat plate, you will have to remove the secondary butterflies or you will have severe driveability problems. The Jaguar piece will work as it is not a plate but a pass through.