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Discussion Starter #1
I have been thinking about de-siamesed inlet manifolds for years. But, when I actually got mine and started to think about it, its not as easy as I imagined.

I had imagined that you could use aluminium tube in milled holes that go straight from the carburetor side to the head side. But it looks like that will break into the water jacket and break out of the castings at the ends.

Can anyone help me with more specific tips?

Doug
 

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I completed this exercise for my 2600 Sprint race-car in the 1990s.

Yes, you will break out into the open air - that's the only way to get a straight duct. Having fitted the six tubes into the manifold, I then had it pressure-sealed by a highly recommended company on the Slough, England, Trading Estate, nr London, which had a DoD certification. That sorted out the porosity in the manifold as well as insuring there were no leaks. I fitted Weber 45s : no point in persevering with the totally useless PH44s.
Nick S.
 

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Doug, there are pictures of the Doug Pecchenino conversion (cutting a slot and welding or glueing a separator in place) and a template for the throttle adapter plates by Bob Piacentini in the File section of the Yahoo newsgroup. This AlfaBB thread shows how one owner did the conversion.
 

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BTW, Weber 40s are more than sufficient for street use. The Italian eBay seller "alfa1750" sells bench-tested carbs in sets of 3 for about USD 950 (see here). Although sold as "cleaned and tested", expect that these carbs may need some further work (I recall Don Peterson describing that the carbs he got from alfa1750 seemed to have problems with floats that flooded cylinders so badly that pistons and liners were damaged). According to some German Weber specialists, new made-in-Spain carbs require work as well (because of variations in tolerances and inconsistent setup).
 

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Discussion Starter #5
Thanks.

I do not have Solex's, but do have 3 x 45 DCOE. So that's a simple decision. The advantage of the 45 DCOE is that there is factory jetting available. Although I do agree that the 40 DCOE is probably a better match. The last time I dealt with webers was on a Lotus Twin Cam that i put into a Cortina. It ran better on 40 DCOE than 45 DCOE and the cylinder volumes are not much different between the two engines.

It appears that Doug Pecchenino put tubes in only every second inlet, meaning the airflow on the others will be ordinary.

My next door neighbor at work builds race engines. He'll do the work for me, but he's suggesting it might be easier / better to make a new manifold from scratch. I'm not sure how to handle the water jacket and it wouldn't look original. But I'm tempted by this approach.
 

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You probably would not need to water-jacket the manifold if you convert to Webers. The heated manifold was necessary for the convoluted routing forced by the 44PHH carburetors. When you are using one-throttle per cylinder and a relatively short-straight intake runner, the heat is unnecessary. Just run a pipe from the front to the back to transfer the water between its original source and outlet, and you'd be done.

The 45's will have a slight ridge between the outlet of the carb and the inlet of the stock manifold. 45mm vs 44mm. This can create an interesting reverse rejection wave that won't help things. With a 40 vs 44 you get a wave going the other way that reduced fuel rejection. The original jetting for the 45's was with a factory manifold and air intake plenum system. Bolting 45's onto a Solex manifold, even with it desiamesed, will require different jetting than what is listed for the factory set-up.

Of course, much of this stuff ends up being unimportant so long as you can get acceptable driveability. That should be possible with desiamesed manifold, but the reports on the BB are quite varied on that point.
 

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Discussion Starter #7
Don

Thanks. I might even end up putting it on the dyne next door. I'm planning on grinding the cams too. That will be a separate discussion!!!

By the way, I own a Seneca II and fly some mates aircraft including a 1936 J2 Cub, 1946 Ercoupe, 1955 Auster. I have a couple of hundred hours in Pitts and used to fly competition aerobatics.

Doug
 

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Doug,

There's an excellent chance we know some of the same people.

Helen Going, my fabulous mate, grew up in Melbourne. She and her ex had one of the finer restaurants in town, in Balwyn.

I greatly enjoyed getting to know various members of the Ozian aerobatic team at some of the world competitions I flew in. Richard Wilshire comes to mind. There were several others, all distinct characters, but not surfacing in my aging mind just now. I called it done after the contest in Radom, Poland in 06.

I correspond regularly with a fellow over there restoring a 102/2000. Madman. But then, I'm finding that describes you all.

Cheers,
 
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