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

http://forums.pelicanparts.com/uploa...1232830817.jpg

Should i have started a thread about the favorite color of a 930 driver or something? :rolleyes: Anybody?

look and my build in my sig I used stock components with good luck so far and use 81sc heads

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.

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.

[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)

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)

make sure the valve to guide clearance is correct, watch the egt, cht, when doing the initial tuning.

Here's the 935 exhaust guide oiling mod on my latest project.
http://forums.pelicanparts.com/uploa...1232924067.jpg
http://forums.pelicanparts.com/uploa...1232924089.jpg

Just make sure you run your exhaust valve clearance (in the guide) about one thousands greater than the stock SC exhaust valve.

Very nice,

Care to share how you came up with the angles?

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.

http://i30.photobucket.com/albums/c3...1/100_7858.jpg
http://i30.photobucket.com/albums/c3...1/100_7859.jpg

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:D Thanks for the info on the turbos.

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.

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

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:D
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&_trksid=p3907.m32&_trkparms =tab%3DWatching&item=160311558101&viewitem=

Sweet deal! That's what I'm going with when I can.

Never heard of this oiling deal, not form any reputable builder, FWTW.

From my understanding this modification was used on later 935 heads, just before they started pumping water. I'm running them on my next build, until then I won't know how effective this mod is. I've been playing with higher boost levels on my current build and monitoring temps, you can't keep the heads cool enough thus my decision to use the 350RR heads, valve guide oiling mod. and 930 sodium filled valves.

Do you plan on running a single wastegate or two? I'm curious as to the pic you posted in the OP.

A930,
What are you going to do with that distributor? I am interested in a twin-plug setup for my 965 also and it would include a JB Racing internally triggered distributor, plus some other components.

(P.S. This could be a thread hijack...)

Mark

Mark, had originally planned on using on my 3.2SS build. However, decided it would be better for the turbo motor, as better flame propagation means both cooler heads and safer (not necessarily more) horsepower. The factory used twin plugging on the 2.1 RSR and other early turbo motors, so figurered if it was good insurance for them, would be for me as well. A lot of guys here (sand_man and others) have gone to twin plug as well.

Lite75, VERY interested in how your oil-modification heads work out. The factory did a lot of cool stuff when reaching the HP limits of the aircooled 935 heads before eventually going to water-cooling them. Please keep us posted on your progress.

Dont worry about hijacking. As someone put it before, these thread have a life of their own, and go whatever way they will.

Nice score! I was planning on bidding at the last minute, but got tied up.

If you use small port SC heads, why not keep the 930 heads?

Craig, i dont have a set of Turbo heads. The 'turbo' motor i'm building is actually based on a spare 3.0 SC motor. The small port heads that are being rebuilt are what i have at moment (gotta draw the line budget-wise on a hobby somewhere). Also, as it is a 'learning engine' in which i plan to eventually put better heads and P/C on it in the future, i want to see how the small port heads work in comparison to later Carrera heads which will eventually be used.

Just use the SC heads and be done with it - with that budget in mind you mentioned.

I have the 935 oiler mods in my heads. I get a little start-up smoke. It oils directly on the center of the exhaust guide and you run no stem seal. The orientation of the guide allows the oil to drain toward the spring ( for the most part) and the exhaust pressure is usually higher than inside the crank case/head.

930turbo,
Thanks for that explanation, it was the missing link for me. Now let me see if I have this right: A 3 x3 mm (?) groove is made from under the edge of intake spring seat on a slight angle (?) and it leads to a 3mm hole (?) that is drilled in the middle of the head but offset to miss the studs and at such an angle that it bisects the exhaust valve guide which has no stem seal because the oil is constantly running out of it due to gravity and the exhaust port pressure.

Is that it? Brilliant! I suppose the flow of oil could be controlled by the size of the groove/hole, but at some point you need flow. And it would be important to keep the cam tower sealant to a minimum in the immediate area of the groove.

Do you mind strenuously if I ask you who did the work and, if outsourced, how much it cost?

I see no reason not to do this mod to every turbo engine. I wonder what Henry would say...?

Mark