2600 Intake De-siamizing - Alfa Romeo Bulletin Board & Forums

 
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post #1 of 8 (permalink) Old 12-03-2016, 07:05 AM Thread Starter
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2600 Intake De-siamizing

Well I've finally decided to pull my old oil burning engine and put my rebuilt one in. Now the problem is I want to fully convert to the modified Webber (or in my case Delorto) set up. With the stock intake - I had great performance until 5000 rpm - then nothing.

Does anyone know of a fab source that has successfully done the intake modifications in the US? I'm in Eastern Washington, so closer the better. Idle hands in winter really are the devils work! Thanks for any help. Brian
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post #2 of 8 (permalink) Old 12-03-2016, 10:13 AM
Richard Jemison
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Manifold

Send me pics from top & bottom of the manifold and I`ll give you an estimate of the modification.
I built mant totally custom aluminum manifolds and these should be relatively simple to modify. However work & fitting aluminum and matching inside walls require accurate work.
Send pics to alfar7@aol.com.

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RJR Racing

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post #3 of 8 (permalink) Old 12-03-2016, 11:05 AM
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Brian, It is quite possible to de-siamese your intake manifold by having simple plates cut and welded into slots cut into the manifold. I had this done by Roberto Piacentini many years ago. I have printed explanations from his website somewhere that show how it is done. He and Jay aka Two Liter Lover are in your area I believe.

It is not necessary to cut up your manifold and weld tubes into the intake path; I have heard first hand that this method can result in many problems from coolant jacket water leaks from the manifold.

Try this search for more information:

de-siamesing intake manifold site:1900, 2000 & 2600 (1950-1968) - Alfa Romeo Bulletin Board & Forums

You may need to cut the above search and paste it into your browser window.

Here are a couple of samples:
Webers and then some

alfa romeo 2600 weber conversion infos

Mark

Last edited by IRONBLOCK; 12-03-2016 at 11:14 AM.
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post #4 of 8 (permalink) Old 12-03-2016, 01:19 PM
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I agree with mark, it is very simple to do it. I have done it very simply (see my threat) :

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post #5 of 8 (permalink) Old 12-04-2016, 12:52 PM
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Venturi size?

I run an original weber manifold ( ie de-siamised ) with triple Dellorto 40's.

I had no power above 5,000 rpm when using 32 mm venturis - moving up to 36 mm gave great power at the top end . I have now moved back to 35 to give a little more power lower down . Any size 34 or below gives a high rpm power loss

Current best
Venturi 35
Main 130
Emulsion 7772.5
air corrector 210
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post #6 of 8 (permalink) Old 12-04-2016, 03:50 PM
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Quote:
Originally Posted by Redmerlin View Post
I run an original weber manifold ( ie de-siamised ) with triple Dellorto 40's.

I had no power above 5,000 rpm when using 32 mm venturis - moving up to 36 mm gave great power at the top end . I have now moved back to 35 to give a little more power lower down . Any size 34 or below gives a high rpm power loss

Current best
Venturi 35
Main 130
Emulsion 7772.5
air corrector 210
I wonder if there is a cam timing and/or lift issue with your engine? My 2300 is using 35mm venturies, and with the revised RJ cams, I have a very strong and flat torque curve all the way to 6,500. I've also got the same or more low RPM torque as I did with the original cams using 33 mm chokes.

The 2300 has a 575cc per cylinder displacement, whereas the 2600 has 433 cc per cylinder (very close to a 1750 4-cyl). That's 25% less displacement per cylinder. A 25% smaller choke (by area) would be somewhere between 30-31 mm.

It sounds to me like your upper RPM power loss is being caused by a restriction other than the venturies.

Don P
Carson City, NV

Past Alfas...
59 102 Touring (first Alfa $500 running)
65 Sprint GT (2nd Alfa, $500 daily driver)
102 Sprint (never did anything with it, but wish I had)
74 Berlina (first new car - now certainly rusted into oblivion)
61 Giulietta Spider G-Prod Race Car (where is it now?)
84 Spider Veloce (rarely drove it, so sold it)
86 Quadrifoglio (Dull car - no more 115s for me)
1971 Montreal "The Full Monty". Fair winds and following seas

Current Alfas
59 102 Touring Roadster - restoration complete, enough Alfa for any rational man. Or irrational, for that matter
And past...
Two 1946 Stampe SV4C (c/n 294 "Rocinante" - wife's favorite airplane. RIP), and c/n 235 "La Bon Temps Femme" (gone to a new home, but never forgotten)
Zlin 50LA (+9 -6 gees, titanium spar, 1200 lbs, 260HP rumored to now be in Brazil)
1946 Luscombe 8A
Starduster Too (recently spotted at the Nevada City, CA airport - over 20 years and an entire continent separating it from our stewardship in Binghamton, NY)
1955 Cessna 170B (wife taught me to fly tailwheel in this)

And present...
64 Mooney M20E ("Rambo". My faithful steed for over 30 years) Nearly 50 years old, and just returned from a trip to Argentina in him
Newest in the fleet
1967 Piper Super Cub on Wipline amphibious floats (a true "all terrain vehicle")
2010 Triumph Thunderbird


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post #7 of 8 (permalink) Old 02-28-2017, 09:57 AM
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Quote:
Originally Posted by brianmathis View Post
Well I've finally decided to pull my old oil burning engine and put my rebuilt one in. Now the problem is I want to fully convert to the modified Webber (or in my case Delorto) set up. With the stock intake - I had great performance until 5000 rpm - then nothing.

Does anyone know of a fab source that has successfully done the intake modifications in the US? I'm in Eastern Washington, so closer the better. Idle hands in winter really are the devils work! Thanks for any help. Brian
Mike Pierce at Pierce Manifolds in Gilroy California has just de-siamesed the stock 2600 manifold on my Spider with Solexes. He has a website, and knows a lot about Weber carbs and manifolds. My engine is not yet running with its newly rebuilt Bologna-made 45DCOE's, as I just got the manifold back a few days ago, but I am going to put it on the same chassis dyno after it's running, and compare it to the miserable specs from it's pre-conversion run. I'll keep you posted....
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post #8 of 8 (permalink) Old 02-28-2017, 10:27 AM
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Hi Brian,

I can't 'speak' to your 2600 issues but I'd be sure to check that the intake system does not have any restrictions like the Old Two-Liter has.

Two Liter Air Filter Options...

With this simple mod, that Don suggested, the Two-Liter is now running better than it has in years!

Mark
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