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Build specs for SC heads in Turbo application

Since their seem to be a lot of fun, but non-turbo related threads, springiing up up recently (due to cabin fever, no doubt), i thought i would re-focus by asking you guys that are experts about the build specs on some heads i will be using for an upcoming turbo project. A recent post by Don regarding the short life of the valve guides on his new top end got me thinking about posting this as well. Also, i just finished reading in Frere's book about the problems the factory encountered with valves and guides in developing the 917/10

Build specs:
-Slightly flowed stock 80 SC heads (Not great, i know, but it's what i have, as the motor will be built using as many of the parts i have in my inventory) twin plugged, ported for use with Carrera manifold
-Standard SC bottom end with usual rebuild goodies
-Low compression 95mm JE pistons and re-using my nickie cylinders (again, for cost reasons).
-Carrera manifold
-Either TEC-Gt or Megasquirt EMS... i am familiar with the MS for N/A, but am still on the learning curve of the TEC, have just installed in the 930
-Twin garret turbos, size appropriate
-Factory WG with .8 spring, boost adjustable

Anyhow, my question is this, what particular areas of concerns are there regarding valve guides as well as valves in building these heads? Are standard sodium filled valves ok for the exhaust, or are inconel valves, like don used necessary? Maganese bronze guides needes?

I guess my main question, is what needs to be done to these heads to make them stand up to use in a turbo motor? BTW, this motor will be going into the 914/6 once the 2.7 expires or i get tired of it... either of which could happen pretty quickly as it will be mostly a DE/track/ hillclimb car. Thanks

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Old 01-24-2009, 01:03 PM
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Should i have started a thread about the favorite color of a 930 driver or something? Anybody?
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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
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Old 01-24-2009, 11:09 PM
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look and my build in my sig I used stock components with good luck so far and use 81sc heads
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Old 01-25-2009, 05:25 AM
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As far as I know, SC heads have larger intake ports so they would flow better than 930 ones right out of the box. I don't think you'll have problems with valve guides or valves as long as standard sodium-filled valves are used.

930 heads are made of slightly different alloy which should tolerate heat better. There are different opinions on this subject, but from limited observations N/A heads doesn't seem to suffer from this even in turbocharged installations.
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Old 01-25-2009, 07:11 AM
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Good question, hopefully members will share their experiences and we can all learn.
I’m new here and no expert, but I’m willing to share my thoughts, in hopes that we might help each other.

As you know Heat is the big enemy, the longevity of valves and guides is directly dependent on cooling the valves.

The exhaust valve in particular, while open and off its seat is exposed to greater heat load from the passing Combustion gases. This means that the exhaust valve needs to transfer this heat primarily through the valve guide interface for cooling. The sodium in the exhaust valves stem turns to liquid and helps transfer the heat from the valve face up through the stem as it is transferred from the valve to the guide on its was to being dissipated through the cyl head. The proper valve stem to guide clearance is critical in this operation, the larger the gap the less surface contact and less heat transfer.

So what can we do to Optimize heat dissipation?

First lets look at our approach. The big picture, everything is interrelated, dependent on each other and needs to be designed as a whole. One component or modification will not compensate for a week link in the chain.

Take advantage of each and every opportunity to contribute to the whole

1: Clean: Everything inside and out. All engine components must be clean to shed heat. Any built covering of external grim or internal pantin acts as an insulating material that will reduce cooling and create potential hot spots.

2: External surface preparation. For a performance motor or one that will be driven hard, I would reframe from top coating with paint or any materials that will encapsulate and retain heat.
Exploring the potential of Increased surface area. The surface area of certain components such as the head fins, engine case, rocker covers etc. can be increased by abrade blasting for further benefits.

3: Insuring minimal and yet proper valve stem clearance when fitting valves to new guides: This is often an issue when reusing old valves as stems tend to wear more from the ends than the middle leaving them barrel shaped. The question of “ what is acceptable” can be debated to application.
For example on my non-racing street motor build, I could not justify replacing all the valves. As A Extreme DYI…. I R&R my own guides, purchased the proper reamer to finish fit them to spec. using my old valves.

4: Choice of Valve Stem Seals: The Pros and Cons of using Teflon seals can be debated.
The extra oiling to the guides might provide extra life and additional heat transfer but at the cost of adding oil to the combustion process and potential increasing detonation.

5: Modifying Cylinder Head : There is an interesting photo on pg 73, 1978 printing of Bruce Andersons Book. It shows a 935 head with an oil passage machined to about half way down exhaust valve guide to supply a constant flow of oil for cooling extra cooling.
Not sure if they supply a return path for the oil or how beneficial this modification might be, but would love to learn more about it.
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Old 01-25-2009, 10:15 AM
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[QUOTE=juicersr;4440131]
-Twin garret turbos, size appropriate...

uh-oh... do I sense a set of particuler 935 headers from ebay making their way to a certain 934?

As far as the valves go- yes sodium filled valves will work- maybe stock 930 exhaust valves (not sure if they are the same size) and if not, you could do a set of cut Ferrera blanks (8 mm stem for high rpm)

For you I think a set of Garret Gt-30r's with .63 hot housings or Gt-28rs's with .81 hot housings (if they make that size for 28 based turbos)
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Old 01-25-2009, 11:27 AM
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Quote:
Originally Posted by beepbeep View Post
..but from limited observations N/A heads doesn't seem to suffer from this even in turbocharged installations.
I agree with this statement- but I have seen what happens when the n/a heads don't hold up and it sux- I think tuning has a bunch to do with it.
If the turbo hot housings, primaries/secondaries on headers, and ignition/fuel maps are conducive to keeping the heat out of the cylinders, you should be just fine as many people are on this forum (Craig tracks the hell out of his with no problems)
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Old 01-25-2009, 11:32 AM
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make sure the valve to guide clearance is correct, watch the egt, cht, when doing the initial tuning.
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Old 01-25-2009, 01:32 PM
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Here's the 935 exhaust guide oiling mod on my latest project.

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Old 01-25-2009, 02:59 PM
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Just make sure you run your exhaust valve clearance (in the guide) about one thousands greater than the stock SC exhaust valve.
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Last edited by cgarr; 01-25-2009 at 04:00 PM..
Old 01-25-2009, 03:09 PM
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Quote:
Originally Posted by lite75 View Post
Here's the 935 exhaust guide oiling mod on my latest project.

Very nice,

Care to share how you came up with the angles?
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Old 01-25-2009, 03:24 PM
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I think the angles are there to clear the studs, then a passage is drilled to intersect the exhaust guide about mid point for direct oiling.


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Last edited by cgarr; 01-25-2009 at 03:57 PM..
Old 01-25-2009, 03:38 PM
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Great, thanks for the input

Craig, i was actually planning on sending my heads to you guys, as Danny (bahnzai) and other have spoken highly of your work. If you use valves such as inconel, or Nimonic, or chromium plated, does that obviate the need to increase the clearances? Does the material used in the guides (such as manganese bronze) make any difference?

Lite, what type of heads are u using? What build specs/ hp are u aiming for? Definately would like to 'overkill' these heads with that oiling system.

Kris, while i am itching to pull the trigger on those 935 twin headers, i am going to use the existing dual header system on the 914/6 (as the engine is mounted fan forward in the 914/6) and fab up a custom system. For a future project tho....tasty Thanks for the info on the turbos.
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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 01-25-2009, 06:44 PM
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Data point:

****Not just "SC heads", 78/79 SC heads are specifically better****
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"930 is the wild slut you sleep with who tries to kill you every time you "get it on" - Quote by Gabe
Movie: 930 on the dyno
Old 01-25-2009, 06:49 PM
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Quote:
Originally Posted by Craig 930 RS View Post
Data point:

****Not just "SC heads", 78/79 SC heads are specifically better****
Craig, i know, but my set of large port heads are currently going into the 3.2SS build. This is my first turbo build, so i can live with losing a little breathability as i am not going for gonzo hp.
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'79 930/934 replica
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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 01-25-2009, 06:58 PM
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If your using the 3.2 intake, I would go with the 3.2 heads. best port sizes avail without touching them. 40I 38E
The heads I have are 930 RR350 alloy modified to 935 specs. Very little gain for way more $$$ 43I 41E
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Old 01-25-2009, 10:51 PM
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I was always curious about that 935 exhaust guide oiling mod. Is it just a gravity feed down to the exhaust valve? Any change to the valve stem seal? Is there any downside to this mod? Increased oil usage? Smoking out the exhaust pipe? I remember a different type of valve guide with a lip, maybe just to mark the difference in clearance.

It would seem that the oil would end up in the exhaust port, could that cause a carbon build-up issue? What is the recommended hole size to control the flow of oil?

Mark
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Old 01-26-2009, 08:56 AM
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Quote:
Originally Posted by lucittm View Post
I was always curious about that 935 exhaust guide oiling mod. Is it just a gravity feed down to the exhaust valve? Any change to the valve stem seal? Is there any downside to this mod? Increased oil usage? Smoking out the exhaust pipe? I remember a different type of valve guide with a lip, maybe just to mark the difference in clearance.

It would seem that the oil would end up in the exhaust port, could that cause a carbon build-up issue? What is the recommended hole size to control the flow of oil?

Mark
I'm curious about this as well.

Also, will smaller port SC heads, such as the ones i'm using, allow for an increase low end torque, as in the N/A motor (in comparison to the bigger port 78/79 heads)?

Gotta luv ebay... scored a twin plug distributor for the motor today. Brand new JB Racing unit, half-off
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&_trksid=p3907.m32&_trkparms=tab%3DWatching&item=160311558101&viewitem=
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'79 930/934 replica
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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 01-27-2009, 05:36 PM
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Sweet deal! That's what I'm going with when I can.

Quote:
Gotta luv ebay... scored a twin plug distributor for the motor today. Brand new JB Racing unit, half-off.
Old 01-27-2009, 05:50 PM
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Never heard of this oiling deal, not form any reputable builder, FWTW.
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"930 is the wild slut you sleep with who tries to kill you every time you "get it on" - Quote by Gabe
Movie: 930 on the dyno
Old 01-27-2009, 07:52 PM
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