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While a 2bbl downdraft manifold for the Opel ohv can be hard to find, there are new manifolds for Vauxhalls ohv available that can be modified to fit on an Opel:
DGV Weber Aussiespeed manifold HB Torana Vauxhall Viva AS0710 | Aussiespeed Street & Racing Products Australia
The distance between the outer bolt holes on the flange facing the head is slightly wider on the Vauxhall ohv manifold
Cool thanks wasn't sure what all was involved in making them fit the opel
 

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That downdraft manifold sure looks nice ! Those are hard as hell to find for the opel 1.1
Both the weber downdraft and the factory single barrel sidedraft manifold are actually Viva parts; I'll try to remember to take a picture of the gasket vs manifold to show the difference. My second Opel, back in 1989, had a manifold that fit a single Weber IDA or similar downdraft and I really wish I could find one of those manifolds now.
 

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Both the weber downdraft and the factory single barrel sidedraft manifold are actually Viva parts; I'll try to remember to take a picture of the gasket vs manifold to show the difference. My second Opel, back in 1989, had a manifold that fit a single Weber IDA or similar downdraft and I really wish I could find one of those manifolds now.
The Weber IDA manifold was originally from Jetten Conversions in Holland Europe, just like the Weber 2bbl downdraft manifold for Opel ohvs. There can of course have been others too, but Jettens manifolds are the best known here in Europe.
There were also Opel ohv manifolds for Strombergs and SU's made in the UK, this is an Alexander manifold with Strombergs.
 

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Is that a Judson or Shorrock supercharger?
It's an Eaton M45, originally modified for use on an MG. I have the custom intake for it about 30% done, and it's going to definitely be different. I'm taking advantage of the valve cover and intake ports all being in the same plane and making one large aluminum block that replaces both and uses all their attachment bolts. A smaller aluminum cover will sit on top for access to the valve train.
 

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Sounds a little bit like the original Vauxhall SSD intake from Blydenstein.
Scroll down to the bottom of the page in this link:
 

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Hi-

Yes, you want to base model Mini pistons like this one:


You'll have to bore the block to 77mm and cut the crank journals for the Mini sized bearings. It's not a big change to the crank but make sure your machine shop makes a generous radius at the ends of the journals for maximum strength. The Mini rods are a tiny bit narrower than the Opel ones so they float a bit on the crank journal. I was concerned about this when I built the engine but now that I've run it for months including a full 24 Hours Of Lemons race with this setup I can say it doesn't matter. The pistons sit a tiny bit above the block deck and with a stock 1mm head gasket you end up with a zero squish engine. Perfect fit. Do not deck the block.

As for the head, take a look at Honda K series valves. They are even bigger than the ones I used and can be modified to fit by a good machine shop. Depending on how much you cut down the head for compression you might have to notch the pistons a bit for valve clearance. With the Honda B valves I did not have to notch with a stock cam even after cutting 1.5mm off the head but the K valves are bigger.

Keep us posted on how you do. Just doing the Mini pistons alone will get you solid gains because of their lighter weight and lower friction design. If you can stand to look at a programmable ignition I would use one because once I figured ot out on my car it really helped.
I got my self a row Keihins 37 mm today; Will adjust them to use on the 1200 engine which I plan to bore 82.5 ... Tell me if that bore will not be possible; Pistons suited to Kadett 1500 ... The 1200 will be a "old scool" / low cost before even more exciting upgrades on the 1100SR ... Porting on both cylinderheads these days ... Lot of fun !!!
 

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I wouldn't go much larger than 81mm. The 15S Kadett pistons have a compression height of 45mm, which is significantly more than the 38mm on the 12S pistons. Not to mention the piston pins.
 

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1971 1100SR 75 bore ... 2 seized pistons ... The Mini Cooper pistons and conrods will be used ...
Some improvement ... One cylinderhead + intake + exhaust manifold is ported ... Conrods + pistons from Mini Cooper received today; First unit cleaned this evening ... Keihin 37 mm will also be adapted to one of my two OHV - engines ...
 

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Some improvement ... One cylinderhead + intake + exhaust manifold is ported ... Conrods + pistons from Mini Cooper received today; First unit cleaned this evening ... Keihin 37 mm will also be adapted to one of my two OHV - engines ...
Cleans up nicely !!!
 

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