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Splitting HEAD'ache - 56K beware.


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68 replies to this topic

#1 Gravityman

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Posted 22 February 2007 - 06:42 PM

Whats up Subaru Freaks!

I have a problem. I pulled my head from the ER27 and found a small crack in the valve. Give me your input as to if it is ok(within limits) and still drivable or I should just junk them?




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This thread is actually dedicated to the full deconstruction of my cracked ER27 cylinder head. I am in the midst of fully cutting the head in half in many different sections to get a full visual of how much meat there actually is in an ER27s exhaust and intake valve ports. This information will be applied to my porting job for the Twin Turbo and how far I can safely and reliably go with them. By doing I hope to gain information that has been missing and has remained a mystery about our cylinder heads.

I do not know how much of this will apply to an EA82 cylinder head but I would imagine that a substantial amount of info could be applied to your cylinder heads as well.


I want anyone and everyones input on this that has input. So what I am going to do is post a see-through FSM pic. If you desire any specific part of then cylinder head to be cut I will try my hardest to do it. Just take the original picture and put a red line through where you would like me to try to cut and a discription if needed and then repost it to this thread. Mind you I am using brut force to cut these heads (HACKSAW) so I wont be cutting the head in half long ways. Praying for a band saw for my birthday!!!

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I am cutting the Right Hand head cyl's 1, 3, 5 I belive, please correct. Here is my first cut.
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#2 Snowman

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Posted 22 February 2007 - 08:43 PM

very cool. I love to see people doing research like this. Perhaps I'll cut apart some EA82 heads next time I have a bad set.

#3 Gravityman

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Posted 22 February 2007 - 09:28 PM

Well the first pics are in!!! It wasnt as hard as i first thought and very fun in a sore arm kinda' way. Now that I have cut from top to bottom on the head I can now cut long ways with less resistance.

Here is something you dont see everyday.!
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The cutaway-- This is cylinder #1's intake and exhaust ports
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One of the reasons I wanted to do this was to see how far(deep) the cracks between the intake and exhause valves actually are. I know a lot of people junk these heads for the cracks but what if we can weld them and reuse them. In 10 years when these cars are around 30 years old we will be mad at our younger self for just tossing out a set of heads that could have been easily fixed. So here are my plans for the next cut.
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#4 Gloyale

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Posted 23 February 2007 - 10:15 AM

Rock on Gravity man:headbang: I think you inspired me to cut up one of my trashed heads. I have one that actally lost a valve seat so it is pretty much toast.

Wait!!! Won't your older self be kickin the younger one for Hacksawing a one of the rarest Subie heads out there?:confused:

#5 Hodaka Rider

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Posted 23 February 2007 - 12:05 PM

I had been thinking of doing this for awhile. Looks like there's not a whole lot of meat in there for contouring the ports. Maybe a bit around the valve guides and under the HLA's

#6 Gloyale

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Posted 23 February 2007 - 04:12 PM

wow, anyone else notice how constricted that coolant passage around the exhaust port is in that one spot?

#7 Gravityman

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Posted 23 February 2007 - 04:27 PM

Rock on Gravity man:headbang: I think you inspired me to cut up one of my trashed heads. I have one that actally lost a valve seat so it is pretty much toast.

Wait!!! Won't your older self be kickin the younger one for Hacksawing a one of the rarest Subie heads out there?:confused:


UUMMMM....:eek: ... I guess your probably right. But I think I have to look at it as something that has to be done to take one for the team. If someone doesnt do it then we will never know. I personally fell better about porting my heads knowing how much meat there is rather then going in blindly, removing too much metal and then totally destroying my head. If I can save a head or 2 by totally destroying 1, I think I can sleep with myself at night, and hopefully you will thank me.

#8 Gravityman

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Posted 24 February 2007 - 01:20 AM

Cut number three complete. Dont try to cut through valve seats, they suck! zzz ALL DAY LONG!!!

Well as I took a long ponder on as to where I should cut I changed my original plan. I instead cut at an angle accross the crack with the cut starting at the edge of one side of the crack. By doing this it would let me actually dissect the crack and find out how far it goes.

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This cut was actually a little harder to keep lined up then the first one because I had to start the cut on a surface that was far away from all the other metal.

Here is a picture of the 2 halfs of the cut. You can see the piece between the 2 halves which is the crack that i removed.
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I took my dremel and cut below the lowest point of the crack that I could see so I could remove the entire cracked piece and to verify how deep the crack runs. Where you see the crack turn sharply to the right is where I intentionally forced it to crack the rest of the way down.

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Here is a picture of the crack after it was removed. There are 2 shades on the metal; the lighter part is the part that I forced to break and darker part is the length of the original crack.
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This pic shows you how deep the crack actually went. I would imagine that this crack could go down to the water line but fortunatly it didnt.
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After the dissection of the piece I have noticed that there is actually quite a bit of material that can be removed around the valve guides. I am getting excited to see all my other cuts. It seems that there may be more potential in this head then I originally thought!

#9 Hodaka Rider

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Posted 24 February 2007 - 01:55 PM

The ports look like a really good shape overall just the way they are, but there is a bit of restriction around the valve guide. The main bottleneck in the head itself is where the HLA bucket intrudes. That and right before the valve seat (looks like a factory machined cut there, could be smoothed out a bit.)

#10 Gravityman

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Posted 24 February 2007 - 03:44 PM

Here is a better look on the hla bump on the port side. There are quite a few places that can be ground down to straiten out the ports.
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#11 Frank B

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Posted 24 February 2007 - 08:13 PM

Some engines, like the chevy 2.8,3.1 V6, have bumps like that made into the ports. It's said the they are to increase flow in the port and removing them will hurt performance.

#12 86BRATMAN

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Posted 24 February 2007 - 10:31 PM

I was told the same thing by my machinist a while back. The shape of that area creats a venturi effect similar to a carb's. And removing this, while it would theoreticly increase flow, would hinder more that it would help.

#13 Phizinza

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Posted 24 February 2007 - 11:09 PM

It is hard to know. I have come to the belief now that just because it was put there by "smart" designers doesn't mean it is better or right. Sometimes they do things for profit, fast manufacture, etc. But I also do understand how having a shaped inlet and outlet can make a smoother flow. Experiment is about the only way :-\

#14 Gravityman

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Posted 25 February 2007 - 12:00 AM

Some engines, like the chevy 2.8,3.1 V6, have bumps like that made into the ports. It's said the they are to increase flow in the port and removing them will hurt performance.


This is a very good point but I have 2 things to say about this. Firstly, When you port the head you will not be able to totally remove the bump in the port but decrease the size. By doing this you will still get the venturi effect with a larger capability of flow. It probably is true that the bumps were created for a venturi effect which would benefit a carbed or N/A engine which relies on this effect. A carbed engine would most likely see the most benefit of the venturi effect, where a N/A FI engine would see a little less. A turbocharged or supercharged would probably have a decrease in number because any interferance in the air path of the blower will only increase heat (except intercooler) and cause resistance which will reduce pressure.

Secondly, If you look at the new subaru heads you will see that they are no protrusions into the intake or exhaust paths, the only things are the bend, valves and splitter. I would imagine that if the engineers would have had their way, unlimited budget and time the heads would have looked a lot different, so this is where i am going to have to side with Phizinza. The XTs werent very expensive so not a whole lot after the engineering, casting and machining would be put into them.

EDIT.
One more thing I thought of. If you look at the differences in diameter between the intake manifold runners, the intake ports and the cylinders (the whole picture), you will see that the intake ports will actually act as a venturi for the entire system. The boost will create volume/density and the ports will act to keep the air velocity high.

#15 Gravityman

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Posted 25 February 2007 - 02:19 AM

Well the results on cut number 3 are in! The cut was made exactly between cylinders 3 & 5.
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One thing that was pretty neat to find out on this cut is how thick the metal is between the closest part of the cylinders(where the exhaust and intake ports are the closest to each other. Also look at how far off the casting is where the 2 halves meet.
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I bet you won't be able to guess where my next cut will be...or if you even care. I will try to get the 4th cut done tomorrow.

#16 Gloyale

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Posted 25 February 2007 - 12:37 PM

Well the results on cut number 3 are in! The cut was made exactly between cylinders 3 & 5.
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One thing that was pretty neat to find out on this cut is how thick the metal is between the closest part of the cylinders(where the exhaust and intake ports are the closest to each other. Also look at how far off the casting is where the 2 halves meet.
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I bet you won't be able to guess where my next cut will be...or if you even care. I will try to get the 4th cut done tomorrow.

That seem is rough:-\
Bottom right corner of the last photo, look at the little finger at the bottom of that water passage. it's not on the opposite face. you must have sawn through a tiny little fisure in the metal.

#17 Gravityman

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Posted 25 February 2007 - 06:22 PM

Yea, I see what you are talking about. That where the metal angled eerr where the coolant passage was closing. Once i am finished with all the cuts I would like to go around all the pieces and clean up any extra flashing.

#18 970subaru

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Posted 25 February 2007 - 06:49 PM

all this talk of changing shapes of ports is pure speculation until you have them on a flow bench. for instance on my motorcycle, a gn400(400cc thumper), the shortside exhaust radius has a square edge on it. that must suck for flow right? well a guy I know that road races them smoothed that edge to maybe 1/8" radius and it killed all the low end and he didnt see any increase in power. we are going to
those bumps in the chevy 2.8 are most likely a feature to improve swirl for fuel atomization ie emissions. they are in lots of american heads. that 2.8 is a dog tho, cant believe people are even trying to hot rod them.

gravityman, are you planning on trying to unshroud those valves any? those seats look pretty sunk in. looks like youve got a decent amount of meat to work with there. also can you cut the valve guides back any?

#19 Caboobaroo

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Posted 25 February 2007 - 07:11 PM

all this talk of changing shapes of ports is pure speculation until you have them on a flow bench. for instance on my motorcycle, a gn400(400cc thumper), the shortside exhaust radius has a square edge on it. that must suck for flow right? well a guy I know that road races them smoothed that edge to maybe 1/8" radius and it killed all the low end and he didnt see any increase in power. we are going to
those bumps in the chevy 2.8 are most likely a feature to improve swirl for fuel atomization ie emissions. they are in lots of american heads. that 2.8 is a dog tho, cant believe people are even trying to hot rod them.

gravityman, are you planning on trying to unshroud those valves any? those seats look pretty sunk in. looks like youve got a decent amount of meat to work with there. also can you cut the valve guides back any?


I have a 2.8 but its in my Camaro and it hauled butt! I actually got a set of Trickflow twisted wedge aluminum heads for it though:-p

I can't wait to see how this turns out!!

#20 Gravityman

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Posted 25 February 2007 - 10:11 PM

gravityman, are you planning on trying to unshroud those valves any? those seats look pretty sunk in. looks like youve got a decent amount of meat to work with there. also can you cut the valve guides back any?


I was wondering about the valve seats and if i could grind some of the pearch that it sits on away as long as I dont remove the entire pearch. I am going to show my machinest and see how much I can cut from it. I want to make the area between the valve seat and valve guide as smooth as possible and I will be grinding the guides down a alot. Something like this.
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#21 Gravityman

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Posted 25 February 2007 - 10:23 PM

Well here it is... CUT #4 !!!
This one was really neat minus my arm getting really tired!! Look hard you might miss the cut.

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Well If you need any help figureing this one out I cut cylinder #3's ports directly down the casting line. I am glad to say that there is plenty of metal between the siameased exhaust ports, about .3+ inches in some areas. Man I wish you guys could see these in person. This is so cool.

It kinda looks like voltron...eerrr ROOTRON :lol:
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Here is another pic looking down into the exhaust ports.
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Any ideas on the next cut? I have a few in mind but I would like to keep the cuts I have already completed intact. Any measurements that you would like me to make, just let me know.

#22 Gloyale

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Posted 28 February 2007 - 12:39 PM

I'd like to know how much meat is between the deck and the passages behind. I have been curious about using 9.5:1 NA pistons in a turbo motor. Then "domeing" the heads above the cylinder to bring the compression back down slightly. How thick are those shoulders around the valve recess. Seems like you could mill a nice dome out and smooth out those angles at the edge. I hope I am being clear or that you get what I'm saying even If i'm not:lol:

#23 Gravityman

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Posted 28 February 2007 - 08:37 PM

I'd like to know how much meat is between the deck and the passages behind. I have been curious about using 9.5:1 NA pistons in a turbo motor. Then "domeing" the heads above the cylinder to bring the compression back down slightly. How thick are those shoulders around the valve recess. Seems like you could mill a nice dome out and smooth out those angles at the edge. I hope I am being clear or that you get what I'm saying even If i'm not:lol:


I think i am following you, take one of the pics i posted and photoshop or draw a line on where you want a cut.

#24 Gloyale

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Posted 01 March 2007 - 11:04 AM

I just went back and looked at you're first and second cuts. They show what I want pretty well. It looks like those shoulders are pretty thick. I think the dome idea will work great. I just have to calculate the volume difference between Turbo and NA pistons, then remove about half that volume from each cylinder head. I want to end up around 8.5:1 compression.

#25 Gravityman

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Posted 01 March 2007 - 12:50 PM

You are looking at "about" 1.2 cubic inches of material differance between the N/A pistons and the turbo piston, turbo pistons with the lesser of the two of course.




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