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Morning all - mid way through an engine replacement/rebuild.
got issues with wiring etc but today my question is - were there 2 sizes of downpipe? my donor head came with front and rear Ex manifold - but my car had the front fitted (seized) to the downpipe.
On fitting the rear donor manifold, i cannot seem to get a union with the rear downpipe, so i offered up the olive/seal to the spare front and its way bigger than the hold for the down pipe - am i losing my marbles or is it the wrong manifold?
It's a few decades since I took the downpipes off my Mk2 and it's a bit hard to tell from the pictures. But, apart from needing a good wire brushing, I think you might have the wrong type of seal. I think there are at least three types. There's a long olive like you have and looks way too large a diameter - I think it came later in production and my 420 manifolds would take them. There's a shorter one. And I think that there's a flat one. I can't be certain, hopefully someone will chip in, but you may need he short type. The supplier should be aware of all this and have some to match your photos.
I just took a look at an extra set that I have in storage and the opening appears to be much bigger as compared to what you have. The diameter of the first recess is 2-3/8 inch on my extra set, so it extends nearly to the studs. If I recall correctly, the olive seal fits at least partially into the recess and is crushed into the final shape.
It's hard to tell from the pictures but assuming that you have a 3.4L engine, you should have the "swept back" manifolds. The 3.4 and 3.8 used this style but the 2.4 was more the straight down type like the E-Type. Maybe your replacement head is from another application of the 3.4/3.8 engine? The down pipes are similarly angled to meet the swept back manifolds.
Hope this helps,
Craig
I have a bit of a frankenstein car - Zurich Spec 1962 Auto, imported in 67 by a Jag Dealership in OR and converted to Manual Transmission, sold, took as trade, repeat a few times, then the dealerhsip owner decided to make it his project car... then he died.
I got the car last year with the stick shift and a engine block, since then i have sourced a head, had it skimmed and polished, etc.
so the manifolds that came with the sourced head (and i am told from a 62 3.8) should be a direct fit - but they are not, and i cant tell why, also the studs were shot, i bought new ones but they wouldnt go in straight, so i drilled them and replaced with bolts, TBH i think at this point i should seek a replacement manifold.
The opening appears to be smaller in your manifolds. Here is a picture of my spare set. Note how much less material there appears to be between the opening and the studs.
I would not have guessed that the 3.8S would be different but maybe it is.
Maybe just a different type of seal per Peter's comments above.
Last edited by cdg66mk2; Jan 20, 2026 at 06:15 PM.
Reason: Where is the picture
In my last photo you see the front manifold (came with the car) and the rear manifold (came with the donor head)
the one I measured is the donor front.
You may have mis matched exhaust manifolds. It lookslikethe one in the photos calls for a straight sandwich type of sealing gasket, rather than the olive type seal. Are both manifolds the swept back style, or is one a straight down pipe ? Getting a new manifold that will accept the olive may be your best / only solution. I've had issues myself with manifolds that didn't mate with exhaust pipes, very frustrating !
Good Luck ! keep us posted.
You may have mis matched exhaust manifolds. It lookslikethe one in the photos calls for a straight sandwich type of sealing gasket, rather than the olive type seal. Are both manifolds the swept back style, or is one a straight down pipe ? Getting a new manifold that will accept the olive may be your best / only solution. I've had issues myself with manifolds that didn't mate with exhaust pipes, very frustrating !
Good Luck ! keep us posted.
thanks, I’ll post photos of what I had shortly (just removing the offending article)
one of our members has kindly sold me the correct (hopefully) manifold
Exhaust Manifold/Down Pipe Size Question
