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The ideal Turbo head? 934? 935? Stock Turbo?

Just curious as to what criteria make for the ideal head for forced induction on the 3.0 or 3.2 engine. Why did the factory have such large I/E ports for the early 934 and 935 engine (41/41), and such smaller ones for the '76 street turbo (32/36), and smaller ones still for the late 70s turbos (32/34)? Furthermore, is there any difference, in either structural casting or metallurgy, which sets the Turbo head apart from say the stock SC or Carrera head? If one is turboing one of these engines (which i am) is it worth it to change to the Turbo head on a top-end rebuild, and if so, which head should be used? Thanks to all and Merry Christmas!
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Old 12-25-2007, 06:58 AM
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All discussed before, at length. Much more information in those threads than I'll give ya

930 heads are a different alloy, withstands higher temperatures better. Many have used N/A heads to avoid massive porting of the 930 heads, but they may not last as long in full-race applications. This may be dependant on proper tuning and sane limits in other areas to control temps.

Small ports are for off-boost torque - irrelevant on a race motor. Depends on your intended use which you choose. Note that Frere says that the 935 "baby" retired on the first outing, at least partly because it was so intractable as to be bordering on undrivable. And that's on a race track.

I've read that the 3.0 930 is a lot "peakier" than the torque monster 3.3's, but I've never driven one...

My $0.02? Whatever heads you use, twin plug them while they're out. That way, you won't regret it later...
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Old 12-25-2007, 07:53 AM
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Thanks spuggy... did a thread search, but may have been impatient as i didn't find the alloy answer you gave. Twin pluggin for sure.
Will do a more thorough search.
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Old 12-25-2007, 08:28 AM
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As spuggy said, big port diameter was chosen on race engines as peak power was important and off-boost driveability wasn't. 3.0L had somewhat choked heads but when diplacement/compression was bumped to 3.3L/7.5:1 Porsche decided to choke ports even further in order to boost gas velocity at lower revs and thus improve VE/torque.

Turbo heads are indeed made of another alloy which is slightly better at withstanding high temperatures (I don't quite remember bu I believe difference was 25 deg. C or so). I believe they quit with this on later 993 heads shich were all made from "hi-temp" alloy.

There are two ways to go. You either use 3.2/3.0 heads and make sure they stay below the limit or use 3.3 heads ported to desired diameter. You never said which kind of engine you are planning to turbocharge as there are additional problems with mating 3.3 heads to Carrera intakes as injector notch doesn't line up.

Personally, I would use Carrera head and Carrera intake and mount slighly smaller pulley for 10% more fan speed. Also, I would move generator out of the fan (and drive it with separate belt) as it loads the belt inertially.
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Old 12-25-2007, 09:53 AM
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If I had to do it I would use 3.3 heads, have them stuffed with slightly larger Ferrara valves, Welded and ported to 3.2, and twin plugged. I have seen a set of 3.2 heads fail (crack) in the area of the secondary spark plug taps. I guess the stronger alloy isnt B.S like I used to think, just had to see it for my self.
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Old 12-25-2007, 10:06 AM
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Thanks Goran, it's a Carrera 3.2, and was having second thoughts about using the stock heads/ port sizes. Looks i will go ahead with them as the car will mostly be street. BTW, my very cool girlfriend got me the IF2 video for Christmas.... great vid!! Are u in it anywhere?

I think Stephen at Imagine Auto is a big believer in seam welding the heads in his rebuilds... is it a big deal to get done?
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'79 930/934 replica
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914/6 2.7 (Projekt 908/3)
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Old 12-25-2007, 10:15 AM
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There's much more info - esp. regarding porting, sometimes in conjunction with EFI - spread over many, many other threads.

However, these two threads are worth a read regarding the two specific questions you asked - port sizing and the composition and characteristics of the alloy used in the 930, 935 and all 993 heads:

head for a turbo
Truth or Rumor: 930 vs. 3.2 heads
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Old 12-25-2007, 10:25 AM
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Thanks spug. Good threads.
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'79 930/934 replica
80 RSR-look(Now in Sicily)
914/6 2.7 (Projekt 908/3)
1965 Karman Ghia-Class winner 2007 Carrera Panamericana/Ducati 900ss/GhezziBrian STW
D-Zug Produkte/D-Zug.com
Old 12-25-2007, 12:00 PM
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I have a blown 3.2 Carrera with stock heads (only twin plugged) and they have held up fine @ 1.25bar of boost quite happily. It's pretty rare to see these crack in a forced induction application... many guys running around with them with over 600+HP (Mike, Juan, Glenn etc). Unless you plan to run crazy levels of boost over 30-40psi, they're fine.
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Old 12-25-2007, 01:57 PM
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Merv, have you dyno'd that beast?
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'79 930/934 replica
80 RSR-look(Now in Sicily)
914/6 2.7 (Projekt 908/3)
1965 Karman Ghia-Class winner 2007 Carrera Panamericana/Ducati 900ss/GhezziBrian STW
D-Zug Produkte/D-Zug.com
Old 12-25-2007, 06:23 PM
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No I haven't as yet. I'm going to experiment with a TT setup shortly, so once I get that sorted out I'll get it on a dyno. Not really after big numbers, just trying to get it as snappy as possible
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Old 12-26-2007, 05:05 PM
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SC heads make a big difference on a 930 - and the composition difference in a non-issue.
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Old 12-27-2007, 09:10 AM
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Quote:
Originally Posted by juicersr View Post
Thanks Goran, it's a Carrera 3.2, and was having second thoughts about using the stock heads/ port sizes. Looks i will go ahead with them as the car will mostly be street. BTW, my very cool girlfriend got me the IF2 video for Christmas.... great vid!! Are u in it anywhere?

I think Stephen at Imagine Auto is a big believer in seam welding the heads in his rebuilds... is it a big deal to get done?
Seam weld as in weld heds to jugs? Dunno, don't have any expirience with that. Factory used to do it on 4-valve watercooled race engines (beam welded) but it seems a tad too much for a street driven car, don't you think? It would solve leak issues though and maybe relieve some strain on the studs but such engine would be "fire and forget". Never saw welded 2-valve aircooled head though...

But as I said earlier, 930 vs. Carrera plastic heat deformation issue is maybe 20-30 degrees apart. Nothing big. As long as head temps are kept in check, I don't see the reason why Carrera heads wouldn't stand up to occasional stresses. If such car would expirience prolonged boost time, I believe overdriving the fan would be prudent thing to do. Also, CHT gauge would be a good thing (just like on old recip airplane engines). It saves the hassle with porting out 930 heads...

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Old 12-27-2007, 12:43 PM
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RE: Welding.

They may of meant welding the top fin to the one below it for more sealing strength to the cylinder head.
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Last edited by NathanUK; 12-28-2007 at 09:50 AM..
Old 12-27-2007, 02:03 PM
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Quote:
Originally Posted by beepbeep View Post
Seam weld as in weld heds to jugs? Dunno, don't have any expirience with that. Factory used to do it on 4-valve watercooled race engines (beam welded) but it seems a tad too much for a street driven car, don't you think? It would solve leak issues though and maybe relieve some strain on the studs but such engine would be "fire and forget". Never saw welded 2-valve aircooled head though...
According to Frere "This was impossible with the two-valve heads as the larger and more inclined valves cannot be inserted after welding" "Porsche 911 Story" p199.

Inserting the valves is one thing, I have no idea how they compressed the springs to put the collets on those suckers afterwards

Quote:
But as I said earlier, 930 vs. Carrera plastic heat deformation issue is maybe 20-30 degrees apart.
If the alloy used in standard air-cooled heads is really AMS4220 as Bill V suspects in the thread I linked in earlier, then the difference in rating betweem RR350 (aka AMS225B) and AMS4220D is the difference between 600F and 400F according to the specification:

http://www.haley.on.ca/images/Alloy%20Spec%20Sheet.pdf

Which does raise the question as to why, if there were so little difference, did the factory start using RR350 for all 993 heads? Given that it's so much more exotic, expensive to produce and requires special production controls?

RR350 also seems to be specified for use for bearing support housings and other internal parts in more than one gas turbine engine.

And you know those guys would save money if they could use something cheaper.
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Old 12-28-2007, 11:48 AM
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Good point Spuggy about saving money, the 993 sure did have the bean counters on it. The shocks for example.
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Fitting - New service kit.
Needs Fitting - Innovate XD-16 Kit, Kokeln IC. Stephen's K27 HFS, EVO Intake Assy & his Modded USA Fuel Head.

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Needs Fitting - K&N CO Sensor, Round A/F Dial Gauge, Factory Short Shift Kit.

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Old 12-28-2007, 01:49 PM
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Quote:
Originally Posted by spuggy View Post
Which does raise the question as to why, if there were so little difference, did the factory start using RR350 for all 993 heads? Given that it's so much more exotic, expensive to produce and requires special production controls?


And you know those guys would save money if they could use something cheaper.
I suspect it may have been for longevity purposes with the new emission standards coming out in that time period. Emissions were tightening up and with that, EGT's must have gone up quite a bit. They also produced ceramic coated exhaust ports to help save the heads.
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Old 12-30-2007, 06:34 AM
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Don't forget that warranty plays a big part in the selection of materials, boost levels, ect.
The factory will always seek to strike a balance between regulations, performance and warranty concerns.
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Old 12-30-2007, 07:01 AM
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Good point Spuggy about saving money, the 993 sure did have the bean counters on it. The shocks for example.
I'm sure you're right about the pressures to reduce production costs at Porsche, although the later cars aren't something I know much about - heck, half the time, I don't even recognise them on the road, if they're coming towards me...

The comment about "those guys would save money if they could" was actually related to people designing mass-production jet turbine engines - every dollar there adds up over the production run, and there would be a huge incentive to use materials which were as cheap as possible - or as easy to work with as possible - because difficulty in machining/working or any additional production controls etc. all translate directly into production cost.

Just Alan Shephard's quote about the safety factory being determined by the lowest bidder. It makes me happier not to think about this stuff when flying commercially...
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Old 12-30-2007, 07:19 AM
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Quote:
Originally Posted by spuggy View Post


If the alloy used in standard air-cooled heads is really AMS4220 as Bill V suspects in the thread I linked in earlier, then the difference in rating betweem RR350 (aka AMS225B) and AMS4220D is the difference between 600F and 400F according to the specification:

http://www.haley.on.ca/images/Alloy%20Spec%20Sheet.pdf

Which does raise the question as to why, if there were so little difference, did the factory start using RR350 for all 993 heads? Given that it's so much more exotic, expensive to produce and requires special production controls?

RR350 also seems to be specified for use for bearing support housings and other internal parts in more than one gas turbine engine.

And you know those guys would save money if they could use something cheaper.
Hmm...this is outside of my domain. I got temperature information "ad hoc" and it was more like "don't run the CHT above 220 deg. C on Carrera alloy or 240 deg. C on 930 alloy or you might bugger up the heads" I guess somebody had to test this experimentally

I believe there are also issues of thermal contraction/elongation as well which might influence the longevity.

Why factory decided to use same alloy for all heads? It's hard to say but I suspect economies of scale and common parts had something to do with it. They might have saved money by ordering only one type of heads from subconctractor.

Same happened to SAAB:s. They used to differ slightly in first years but later on turbocharged and N/A engines were almost identical save for pistons/rods.

Regards.
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Old 12-30-2007, 11:43 AM
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