2-1/2 Litre Air Intake Pipe

I have engine L205, and according to the parts book it should take air intake pipe 3072.
The air intake pipe that came to me with the car is marked 3072 (space) 3 (space) A.

Today I tried to fit it on, and found that though the carb-to-carb spacing matches, the stud spacing for each port does not match the carbs.
Stud spacing on the intake pipe ports is 2-9/16" apart.
Flange hole spacing on the carbs is 2-3/8" apart.

Anybody got any ideas, which is wrong, pipe or carbs?
Is this a 3072/A pipe for P engines?

Here is half an idea, which does not answer your overall question. If two of the bolts line up with two of the carb holes then you can assemble and use as is. Either a little permatex or a little hissing in the sides at that mismatch probably won’t trouble the air flow to the carbs much. I have the impression the intake pipe and ancilliaries are mostly for noise reduction and not air filtering?

Given that two of the four studs are missing, maybe that is what some previous owner did.
It was only after spending an hour making two more 5/16-22 BSF studs that I discovered they won’t work.
You may be right about the noise reduction on these filters. Certainly I have read that explanation in regard to the huge filter canister on Mark V, it was called a Helmholz resonator.

The 3073 [ 3073A ] were 3 1/2 litre
They may have used the one casting and drilled it differently for the 2 engine sizes
The bigger size sounds [ without measureing like a 1 1/2 "carb
But as Roger says a nut ateach en d will hld it. The PO may have needed one for one f a dozen reasons s and substituted a3 litre manifold
There’s no reason to make BSF studs. Motalia in UK make them in stainless. Which is excellent for Ex manifolds, and leaves time for important thngs like having a coffee and throwing a ball for the dog.

I see a vacuum unit of the dist which means its a post war unit. Quite a different type Originals were DUH6A A sturdier unit with a cast iron body. Perhaps the carbs and dist together were replaced at some time

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Looks like that’s the explanation, it is marked 3072 but is really drilled as a 3073. With all four studs in place it fits on a 3.5 L engine with H4 carbs.

Although with LHD it will only go on upside down with the dashpots removed. :upside_down_face:

… better breathing. More top end.


Here are a few photos of the 2.5 and 3.5 side-by-side.

The check dimensions are:
2.5L - throat diameter 1-7/16", stud spacing 2-3/8"
3.5L - throat diameter 1-1/2", stud spacing 2-9/16"

The casting part number is the same. It is easy to confuse these two if just glancing as they are so alike but the best way is to recognise the clearance of the studs from the edge of the plinth. This is more obvious than the throat diameter difference of just 1/16".

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Thanks very much for that confirmation and pictures, Peter.
Isn’t this forum terrific?!!
So the casting number is the same for both, as Ed suggested, thus not the sole identifier.
Looks like I have one for a 3.5L. It fits with using only 2 studs, as Roger suggested.
Is the 2.5L version for sale or trade?

You might be in luck. I have a 2.5 plenum similar to that in the photo which I have polished for fitting onto my car eventually, but I can part company from it. I could use a 3.5 spare for my forever renovation work, so a swap is possible.

Using just two studs as you noted would create an induction airflow interference as you will be either using the two front ones or the two back ones, because the c/c of the carburettors is the same, but the offset of the throat to the carbs will be considerable - 3/16" and overlapping at the edges. Message me to follow up.

When I did the last engine , I put afiar bit of effort in to matching ports. Not only the exhaust ports butthe inle t ports on the alloy plenum chamber. Especially I found that the matching between the alloy housing and the canisters was up to 1/4 ''out
Which ever the thing , it certainly runs much better now.

Yes, a little ‘smoothing out’ of the air or gas flow makes a noticable improvement. I am contemplating radiusing the upstream edge of the inlet ports inside the chamber, as that square edge definitely causes considerable turbulence which is very close to the jet.

Well, I wouldn’t want to take the one you have earmarked for your own car. Maybe someone else has an extra, or has a 3.5L car running around with only 2 studs fitted and wondering why. :grinning:
So far I have put only about 5 miles on the road, under 35 miles per hour, so my need is not urgent. I hope to take it to the Chicago British Car Festival next month, 17 miles. :uk:

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You wild man, you.


4 lane Chicago suburban traffic, about 25 stop lights, 2 rail crossings, RHD and trafficators, yep, living dangerously. :grinning:

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Don’t get stuck in da Loop!!!