fitting 24v tubular headers to the 12v engine [part 1] - Alfa Romeo Bulletin Board & Forums
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post #1 of 59 (permalink) Old 11-05-2012, 09:29 PM Thread Starter
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fitting 24v tubular headers to the 12v engine [part 1]

Last project of the year before I put the car away for a winter nap. If you are the patient type and don’t mind some hacksawing and grinding this project may appeal to you even if you don’t weld (all welding can be done off vehicle).

As one gazes at our otherwise beautiful 12v engine compartment, don’t you find the clunky cast iron exhaust manifolds somewhat of an eyesore? Besides being ugly and rusted, the flow is restrictive. Alfa redressed the problem on the 24v engine with strikingly beautiful 1-1/2” id tube headers in V2A stainless (a heat shield on the 24v model hides the front headers from plain view). Alfa subcontracted these to Zeuna-Stärker Augsburg which makes exhaust parts for many marks including BMW motorcycles and Ferrari. Although the tubes are not of tuned-length, the workmanship is outstanding. Wouldn’t it be great to graft these beauties onto our 12v engine using the stock 12v flex pipes and cat?

BBer La_strega_nera did exactly this some time ago and this is what inspired me. Others have done the conversion as well. I’d like to share here the steps I took (photos show only front headers but the rear is the same, easier in some respects, but harder to install because of the cramped space).

first some general information:

-id of the 12v head port is approx. 1-3/8” (1.48 sq in)
-the 24v oblong tube measures id 1.04” x 1.92”, reshaped into a round form the id becomes a little bit larger than 1-1/2” (1.77 sq. in, or ca. 20% increase; however the displacement increase (internal size of the whole manifold) is a whopping 60%+)
-id of exit side of headers is 2”; id of stock 24v downpipe is 1.9” while id of stock 12v downpipe is 1.75”


1) purchased a set of second-hand 24v headers from BBer Alfaguy35. They look awfully black but they’re AISI 304 stainless and will clean up nicely.




2) sawed off tubes: on the original design the tubes are set about halfway into the flange and welded from the inside leaving a stepped edge. The first task is to to “skim” the tubes from the outside of the flanges with a thin hacksaw blade.




3) reshaped oblong into round (almost round is fine); beforehand removed the 3 heat shield studs, any extra metal that was an impediment to reshaping, and the reinforcement plates on the cylinder no.6 tube (you will be spared this prep work on the rear headers). (radiator clamps in photo protected “Zeuna” badge from getting accidentally detached)


Last edited by pinino; 04-21-2019 at 05:15 PM. Reason: added: % increase in displacement
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post #2 of 59 (permalink) Old 11-05-2012, 09:32 PM Thread Starter
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fitting 24v tubular headers to the 12v engine [part 2]

4) flanges: spdexhaust.com in California has a CAD file to fabricate these; they offer two possibilities in 304 stainless, one with 1.53” bore, 62mm center-to-center bolt holes and .375” thickness (part# F5512301), and another with 1.5” bore, 62mm center-to-center bolt holes and .28” thickness (FE-1229821S-1)—I chose the .375 version (the FE flange happens to be for Ferrari 365 V12). Made 3 coiled inserts (wound up strips of galvanized sheet) to assist in alignment of the 24v tubes during the welding process.




5) jig: found a suitable piece of metal to use as a jig, then used the old 12v cast iron manifold to mark up the pattern for the 6 bolt holes (my jig consisted of a hunk of u-channel iron that I had sitting around, mounted to a piece of formica-plywood). Carefully punched and drilled the holes, then secured the old manifold to the jig with a couple of bolts. I attached the jig to the plywood base in a ca. 30% tilted position so that the face of the collector flange came out exactly 90° square to the plywood, this way a simple L-square could be used to get the 24v collector flange in the same position. A vertical bracket was added to the plywood so that the collector flange could be bolted down.




Mounted the new individual flanges to the jig using the same holes that were drilled, added the coil inserts, slipped the 24v tubes onto the inserts and bolted down the collector flange to the bracket (beforehand the tubes needed to be ground and shaped so that they mated perfectly with the flanges).

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post #3 of 59 (permalink) Old 11-05-2012, 09:37 PM Thread Starter
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fitting 24v tubular headers to the 12v engine [part 3]

6) TIG welding*: the tubes were then butt welded to the new flanges on the jig (left coiled inserts in place until each tube was tacked). After tacking, wedged a big screwdriver between the flat of each nut and the tube to pry the tube away to give adequate clearance for the fillet. Tubes had a tendency to wander during welding so the screwdriver trick is important. After polishing mounted headers on car with new exhaust gaskets, part# 60506636 (when doing the rear headers you can dispense with the polishing as no one will appreciate your labors). *(welding by Chris Bernard, West Hurley, NY—”good welding is not any more difficult than knitting or darning, you need to have good eyesight”)




reworked top flange of the stock 12v downpipe to match the collector of the 24v headers. I bought a set of junk 24v downpipes from BBer jrowan just to salvage the top flanges along with 3/4” of tube. Next sawed off the top flange of the existing 12v downpipe without damaging the pipe itself. Slipped the 24v flange nub right over the 12v tube. Did a final run-through on the car to be sure everything lined up and that the angle was right, then removed downpipe (without disturbing the position of the nub flange) and had it welded; before final installation filed off any sharp edges on the inside of the smaller 12v pipe within the 24v flange. Installed with new gaskets, part# 60654239.







8) finished, with twofold results: the ca. 20% increase in the id of the 24v headers and collector will result in a definite boost in torque and horsepower, and in the case of the front headers the polished stainless tubes create a nice visual balance with the intake runners. (By the way the really really hard part of this project was having to drop the the catalytic converter: all 12 bolts had frozen in place and had to be cut or ground off in order to install new gaskets)





Click this link to see pictures of the rear header :

http://www.alfabb.com/bb/forums/1223002-post31.html

Last edited by pinino; 09-05-2016 at 06:59 PM.
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post #4 of 59 (permalink) Old 11-05-2012, 09:57 PM
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Beautiful, just beautiful.

1987 Milano Gold 3.2 24V + JK Cams
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post #5 of 59 (permalink) Old 11-06-2012, 05:26 AM
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Great job. Did not know that the headers can be polished up to that degree.

Will the loss of the heat shield be a problem?
Frank

1994 164 LS 5 Speed
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1959 Giulietta Sprint

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post #6 of 59 (permalink) Old 11-06-2012, 07:47 AM
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Admirable effort! They certainly look nicer when peeking in the bay.

I truly hope, given all that expense and work, you have a dyno comparison (before and after) to illustrate actual changes...

I am very curious because I had considered picking up a set of 24V manifolds to modify (much like you have) to use on a GTV6/ Milano fitment, but I found a set of rather nice SZ manifolds to replace the 3.0 cast iron units from the Verde (yes, I put the car on they dyno with the iron manifolds! )

Rob
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post #7 of 59 (permalink) Old 11-06-2012, 08:26 AM Thread Starter
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I think I see where you are coming from (noting the list of cars you have among them a 24v). Why the heat shield on the 24v and not on the 12v I cannot not say, as the cast iron of the 12v (w/o shield) definitely generates more heat. But if you are possibly thinking of "uncovering" your Zeunas, I really can't imagine how that would be a problem. Of course I envy you, to be able to expose the beautiful Zeunas without much sweat.

P.S. You probably should look at the thread "Alternative to the Bosch Coil Packs", particularly this post.

http://www.alfabb.com/bb/forums/225610-post11.html

Heat is the enemy of the coil packs but there are a number of measures you can take.


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Originally Posted by multicam View Post
Great job. Did not know that the headers can be polished up to that degree.

Will the loss of the heat shield be a problem?
Frank

Last edited by pinino; 11-09-2012 at 03:38 PM. Reason: added PS
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post #8 of 59 (permalink) Old 11-06-2012, 08:39 AM
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Very cool to have the "designer" tag showing!
I will try next summer on and then off and report my findings.

Frank

1994 164 LS 5 Speed
1988 Milano Verde 5 Speed
1960 Giulietta Spider
1959 Giulietta Sprint

1965 Giulia Spider [parts car now]

Last edited by multicam; 11-06-2012 at 11:32 AM.
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post #9 of 59 (permalink) Old 11-06-2012, 08:55 AM
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Well how does the car feel now? Did the power band shift up a bit?

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post #10 of 59 (permalink) Old 11-06-2012, 08:58 AM
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I think the cast headers are restrictive. I imagine about 5 hp from 4K upwards.

And modify the down pipe to equal length ones. The sound will be superb, even with the stock exhaust (more GTV6 like)


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Last edited by 75evo; 11-06-2012 at 09:31 AM.
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post #11 of 59 (permalink) Old 11-09-2012, 08:47 AM Thread Starter
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75evo, racingswim, you make me blush because you are the guys who really know this stuff well. I think a 5hp boost is about right, with stock downpipes. The restrictive design of the cast iron manifolds is quite evident. Besides that strange upward bend that the hot gases have to take as soon as they leave the head, the internal dimensions of the cast iron duct narrows perhaps to as little as 1 1/4" id maybe even less; finally the "collector" of the cast iron manifold is a joke. The 24v headers are full 1 1/2"+ id the whole way, and the collector is a work of art. Sorry to disappoint you racingswim that I did not have the luxury of dyno testing. This is not a racing vehicle for me in any sense of the word (I have another car that provides my adrenalin boost), I just enjoy little improvements here and there on the Alfa, and that monstrosity rust heap really bothered me, especially having noticed that the studs on the lower flange had lost much of their strength due to rusting. By the way I did my best grafting on the 24v "nub" to the 12v downpipes: after welding it was easy to ream the inside edge of the 1 3/4 pipe, then with a hammer to mushroom it out so there was no "edge" to create turbulence. As students of header design you probably picked up on the "step-up" at the head of my conversion, i.e., going from a 1.375" exhaust port to 1.53" flanges to 1.5"+ tubes. It really made welding and line up a breeze and many designers find this amount of "step-up" desirable.

The SZ headers sound like a nice way to go racingswim, I assume that they look the photo below. We look forward to the results of your before and after dyno tests.
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Last edited by pinino; 11-10-2012 at 09:24 PM.
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post #12 of 59 (permalink) Old 11-09-2012, 02:26 PM
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I don't see the advantage other than weight?? They are the same length primaries as the cast ones so ... ?

Modifying to equal lengths as you say would make sense. BTW, nice work though.
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post #13 of 59 (permalink) Old 11-09-2012, 03:33 PM Thread Starter
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I'm no expert but when I do a search "horsepower gain tubular header" there seems to be ample (dyno-tested) evidence out there that replacing rough small-bore cast-iron manifolds with smooth larger-bore tubular headers (even of unequal length) has distinct hp advantages somewhere in the power band. I'm totally aware that improving the downpipes and other things further downstream would produce even better results. Racingswim is right, only a dyno test before and after would prove anything. But an the other hand it's just logical that the stock Alfa cast iron manifold restricts airflow and saps power. (don't take my word for it, if you have one off the car, just look at its intestines). Ah, that's an idea, I will fill one up with water and see how many cc's it contains, then I'll do the same with the tubular—will report back.
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post #14 of 59 (permalink) Old 11-09-2012, 04:15 PM
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I understand where PSK is coming from, but until you see the original 12 valve manifolds in the metal, you don't really see the weird kink that Alfa had in the runners just after the head flange.
Still, it would have been nice to see more even lengths, especially more length added to the rear runners (runners closest to the flywheel).

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post #15 of 59 (permalink) Old 11-09-2012, 07:38 PM Thread Starter
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Quote:
Originally Posted by 75evo View Post
...
And modify the down pipe to equal length ones...
I'm trying to visualize how this would be possible on a transverse mounted engine with limited space and the added problem that there needs to be a flex section in the run because the engine is constantly flexing as you accelerate and deaccelerate. Is it possible that the 164 simply doesn't lend itself to equal-tube downpipes when running a street legal cat?
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