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Old 05-17-2012, 02:36 PM   #1
wrxsubiemod
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This thread’s purpose is to show how the combustion chamber is reworked and measured. It is also meant to show the end user how to do it themselves, if the need presents itself. This thread is NOT meant to discuss the right or wrong way to build an engine or, “you HAVE to do this on all hybrid builds.” That will just dirty up this thread rather quickly.
First you will have to know where you want your compression ratio to be. Everything including piston ring placement, re-decking, spark plugs and lapped valves will affect CR. This thread would literally be 4 pages long if I were to get into how to measure for CR so I will skip that for now and leave you with some facts borrowed from Maxwell’s thread LOL. link here http://forums.nasioc.com/forums/show....php?t=1667168
and here http://forums.nasioc.com/forums/show....php?t=2393037

06wrx heads (D25 casting): 50cc
04-07 STi (B25/V25 casting): 55.5cc (used for calculations, but they're actually 56)
02-05wrx (S20 casting): 49 cc

Factory compressed HG thickness .0236"

EJ257 block on B/V25 STi head: 8.28:1
EJ257 block on D25 WRX head: 8.78:1
EJ257 block on S20 WRX head: 8.88:1

EJ255 block on B/V25 STi head: 8.11:1
EJ255 block on D25 WRX head: 8.55:1
EJ255 block on S20 WRX head: 8.68:1


Tools needed

- Head cc’ing kit which is basically a Graduated cylinder that measures in CC or ML. “1cc = 1ml” and Plexiglass plate to cover combustion chamber
- Tube of grease
- 4 valves
- 1 spark plug when measuring cc use the spark plug you’ll be running
- die grinder with porting bits
- water or Alcohol “not the drinking kind”
- liquid food coloring
- masking tape
- Vernier calipers
- ej25 head gasket or better yet a piston installation tool. I use both
- dykem marker or sharpie
- green scotch brite



My customer gave me a set of EJ2.0 S20 cylinder heads that are going to be paired to an EJ255 short block. I was specifically told to try to get as close as I can to stock STi CR while removing the head overlap. My first order of business was to measure what the cylinder head currently was.



I measured twice and I was getting about 49.8cc with valves that were previously re-lapped. These heads still needed a re-deck and valve job. I also needed to take into consideration that the short block was re-decked. We came to the conclusion that we needed to remove at least 4cc’s totaling to 54cc to be able to remove the overlap and bring the compression down to STI spec which is lower than that of the WRX.

Let’s get started. I first use an OEM head gasket as a template. The OEM head gasket measured out to about 101mm, too big to use on stock bore 99.5mm. I put a piston installation tool on top, used to install 99.75mm pistons and traced it to give me a better idea of how much material I would need to remove.

Once everything is traced out, I find my end point then radius into the quench pad, making sure that my outline does not go over 99.5mm or the combustion chamber will be bigger than the actual bore. At this point it would be a great idea to tape up every coolant passage along with the head surface to reduce scratches and to avoid any metal from getting into places it does not belong.



Now we get to the fun part! Install a used spark plug and the valves into the cylinder you are going to be working on. Grab your die grinder with single cut or double cut carbide bit, (use what your more comfortable with) and start grinding from the center of the combustion chamber working your way slowly towards the valves. Start at a 45 degree angle and try to remove the overlap first. Leave about 1mm of material when you are using the carbide bits and you can finish porting the rest using your sanding bits.



I stopped after I was done with my first cut of the overlap, making sure I was not going to go over 4cc’s of material. Notice that I am working at a 45 degree angle trying to remove the least amount of material while also removing the overlap.



Before CC’ing, install the valves with a little bit of grease on the seats to prevent any liquid from seeping out. Install the spark plug you’ll be running and torque it down. Next you will need to install your CC’ing plate with a little bit of grease around the combustion chamber to seal in the liquid. Press down around the edges so you can get a good seal and to eliminate false readings. For this next step I added 60cc’s of liquid into my graduated cylinder with a drop of blue food coloring. Pour in the liquid SLOWLY, (some graduated cylinders have a valve you can adjust flow) make sure that you do not have any air bubbles trapped inside of the combustion chamber. If you do give it a few taps and they’ll usually come out.


This head measured out to 52CC’s, 60cc-8cc remaining. Remember to measure twice.

So now I’m left with having to remove 2 more CC’s. At this point I finished porting the remaining edges around the valves, blending the combustion chamber into the quench pads and tapering out the overlap. Once all the cuttings done, I move onto my heavy sanding bits and smooth out the grinding marks left by the carbide bits and finish porting the rest of the overlap.

Measure again double checking you are not going over.



Just about 54cc’s, a little bit of elbow grease and polishing will get these right on the money. You can move on to the rest of the combustion chambers at this point or finish the fine polishing to get the heads right. I usually use some green Scotch brite to do the finishing which removes little amounts of material while leaving a nice polish


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Last edited by wrxsubiemod; 08-15-2012 at 08:54 PM.
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Old 05-17-2012, 02:36 PM   #2
wrxsubiemod
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heads being double checked


some finished pics








I did a little bit of port and polishing of the runners. Just got enough to remove some of the left over castings and did a bowl blend.

Last edited by wrxsubiemod; 05-17-2012 at 02:43 PM.
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Old 05-17-2012, 02:37 PM   #3
wrxsubiemod
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reserved..
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Old 05-17-2012, 03:07 PM   #4
sorrowfulkiller
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Got any first hand info on smoothing the combustion chambers? I smoothed my 205 chambers for my hybrid 2.35 build since the ej257 has a mucher smoother chamber and as many people know smoother = less det.

How much would you charge for this? Pm me please.
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Old 05-18-2012, 12:47 AM   #5
Bishop
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Nice work man!
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Old 05-18-2012, 12:51 AM   #6
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sweet post ruben! i can really appreciate your contribution to those who are perhaps more technically inclined. for the time being i'll just have you keep doing all my porting work!

i'll always refer you to customer and friends. amazing quality, prices that can't be beat, and stellar service. you people need to PM this guy, haha!

ruben, i don't know if you remember but i took some pictures of the runners of the jdm long runner you did for me.

before:



after your touch:



thanks again - getting the whole TS setup tuned this weekend!
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Old 05-18-2012, 02:35 AM   #7
ronzogonzo
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Nice write up, DIY FTW!

I may need to go buy a few more hand tools to keep me busy when I'm slow. I always have my stuff sent out, but stuff gets backed up, specially right now -till late october.

Nice write up, I have a few spare sets of heads I can play with and see what i'm getting myself into.

more of an excuse to fix the flowbench...The pet Blackwidow needs a new loving and bitey home.



-Phil
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Old 05-18-2012, 03:43 AM   #8
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looks good sir!
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Old 05-18-2012, 08:15 PM   #9
wrxsubiemod
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Quote:
Originally Posted by Bishop View Post
Nice work man!
Thanks bro

Quote:
Originally Posted by monkiboy View Post
sweet post ruben! i can really appreciate your contribution to those who are perhaps more technically inclined. for the time being i'll just have you keep doing all my porting work!

i'll always refer you to customer and friends. amazing quality, prices that can't be beat, and stellar service. you people need to PM this guy, haha!

ruben, i don't know if you remember but i took some pictures of the runners of the jdm long runner you did for me.

thanks again - getting the whole TS setup tuned this weekend!
sweet deal, i should have the turbo and mani shipped out Monday

Quote:
Originally Posted by ronzogonzo View Post
Nice write up, DIY FTW!

I may need to go buy a few more hand tools to keep me busy when I'm slow. I always have my stuff sent out, but stuff gets backed up, specially right now -till late october.

Nice write up, I have a few spare sets of heads I can play with and see what i'm getting myself into.

more of an excuse to fix the flowbench...The pet Blackwidow needs a new loving and bitey home.
-Phil
Im loving the flow bench! If had one of those I would be in heaven about now. I could only image the Sleepless nights id spend on that thing trying to get the right head combination

-Phil[/quote]

Quote:
Originally Posted by FuJi K View Post
looks good sir!
Thank you, that means a lot to me coming from someone with your talent

Quote:
Originally Posted by sorrowfulkiller View Post
Got any first hand info on smoothing the combustion chambers? I smoothed my 205 chambers for my hybrid 2.35 build since the ej257 has a mucher smoother chamber and as many people know smoother = less det.

How much would you charge for this? Pm me please.
Yeah I do have some first hand experience smoothing them out but you would really need to know how much you will need to remove and where to remove it. On these heads I had to stop short but if i had more room i would have de-shrouded the valve area alittle more.

You can always remove but you cant add PM'd you sir
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Old 05-18-2012, 10:53 PM   #10
ronzogonzo
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I wish it was my flow bench, its the shops.

I would have had it fixed a long time ago.
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Old 06-02-2012, 07:30 PM   #11
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Very Nice!!!
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Old 08-15-2012, 08:51 PM   #12
wrxsubiemod
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Almost thought this thread was lost.

Here's a nice link to a spread sheet calculating compression ratios and such

http://forums.nasioc.com/forums/show....php?t=2393037
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Old 01-29-2013, 02:24 PM   #13
tomtom84
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good info. thanks.
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Old 02-07-2014, 04:14 PM   #14
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After having done this recently I would like to say firstly well done, good post.
Also the bore is tapered /chamfered at the top to out to nearly 101mm depending on block decking which leaves a little more room to deshroud the valves.
If you drop down from a die grinder to a lower speed dremmel for the last 1/2mm or so you get a bit better control so you don't end up with that lumpy sort of texture on the walls.

Last edited by ripman; 02-08-2014 at 04:54 AM.
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