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Old 09-07-2006, 07:38 PM   #1
Kingpin
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Default Assembly: 2.0L Heads on 2.5L block

One of the most popular mods for a non Sti is 2.0 liter heads, be it JDM or USDM, on the 2.5L US Sti block. Here is a basic run down of how to install your heads onto the 2.5L block.

When you get the new block, it will be almost completely bare. Simply set your old block next to the new one and swap everything over, one item at a time (oil pimp, water pump, pulleys, etc….) Just about anybody who is fairly good with cars can easily do this. Just take your time, and pay attention.

Installing the heads, is a bit different of a matter. Due to the fact that the block and heads are both aluminum, extra care must be taken with the install. Also, the install of the heads is one of the most technical and demanding parts of putting a motor together, outside of the short block.

First things, first, you need to get the heads cleaned up. When they come off the old block, they will look a bit like this …



You have two options for cleaning up the head, a machine shop, or do it yourself. A machine shop will completely go thru a head, and check everything and repair any defects for $150-300, depending on what is wrong with them.. The heads will come back in perfect shape, basically like new. The only draw back besides the cash you have to pay, is that machine shops take forever to get anything back to you. If you don’t have the time to wait, you can clean up and check your heads yourself.

Use carburetor cleaner to clean the heads. You will want to buy 2-4 cans of the spray carb cleaner, and I also recommend the good stuff for really stubborn carbon.



The carb cleaner in the bucket is used when you rebuild a carb. You take the carb apart and dip the pieces in the cleaner, and boy does it get things clean. This carb cleaner in a bucket is the good stuff. Be sure to only use this stuff in well ventilated areas, and definitely ware rubber gloves as it will stain your hands.

Spray the heads down with carb cleaner and then use a soft wire brush to scrub them down. Most auto supply stores will carry the carb cleaner, as well as soft brass brushes that will not damage the soft aluminum. Dip the brush in the good carb cleaner and use it to break down stubborn carbon. Once the combustion side of the head is clean, it should look a bit like this …



Now that the combustion side is clean, you’ll want to check two things. 1 the valve seats and 2 the flatness of the head. The flatness of the head is easy, just lay a metal ruler across it and check for any warping. If you see any warping, stop and bring it to a machine shop. They will take the head apart and clean everything and then resurface the head. Unless you over heated the car, warped heads are fairly uncommon.

Next you will want to check the valve seats. Make the head level by placing padding underneath it, then fill the combustion chambers with automatic transmission fluid. Make sure the valves are securely closed, and make sure you have spark plugs in the heads.



Let the heads sit for a while. If the tranny fluid is still there, the seats are good. If the fluid level has dropped, you will be able to see that it has run out of the intake or exhaust port, depending on which valve seat is bad. Either way you will want to clean up the tranny fluid. If a valve seat is bad, you can crack that valve open by twisting the cam wheel, and then spray a bunch of carb cleaner at the valve seat and retest. If cleaning the seat up doesn’t fix the leak, then bring it to a machine shop for re-cutting.

If the valves don’t leak, then flip the head up and clean the matting surface of the intake manifold to the head. The gasket generally leaves a bit of residue, and it is easier to clean it while the head is off the shortblock.

Then flip the head over and clean the cam area. You will want to gently remove the cam caps and cams. NEVER pry or bang on the cams to remove them. If they do not remove easily, then there are coming out crooked. Set them back in and try again. Set the cams aside in a clean and safe area.



Do not mix up the cam caps as they are location specific, but they are marked 1e, 3e, 1i, 3i …. to denote location should they get mixed up. Also, the letters should face up if viewed as if the motor was in the car.

Clean the old gasket maker of the head as well as the actual bucket area. Dry up an extra carb cleaner with a towel, but never tip the heads with the cams out. The buckets will fall out and they are specific to the location they are in.

Once the cam area is all clean, apply a bit of oil to every bucket, as well as to where the cam sits and spins. I spin each bucket after I apply the oil to ensure that it coated the bucket thoroughly. You can also apply engine assembly lube to the top of the buckets as well as the cams if you like.



Now you are ready to bolt the heads to the block. I like to spray the head gaskets with copper spray before I use them. This spray helps seal the oil and water passages, and it also dissipates heat. (Always use a new head gasket.)



Once the gasket is in place, put the head in place. Insert the head bolts and torque to spec, (never re-use head bolts/studs) according to the directions that came with the bolts. Place the cams back in the head, and replace the caps. Take care to ensure the cams are in the right place (intake cam on the intake side) and make sure the caps are all in the correct location. Also, you will want to seal the front most caps will Subaru sealant. Once the cams and caps have been put back in, and torqued to spec, make sure that the cams still spin freely. If the cams do not spin, then they have gone in crooked. Remove the cams and caps and try again.



Replace the valve cover and you are good to go.

As always, keep motoring.

Scotty

Kingpin performance
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Old 09-07-2006, 09:05 PM   #2
Zackbo
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Beautiful, Scotty!

Thanks for supporting the community
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Old 09-07-2006, 10:03 PM   #3
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Very very nice write-up. However, I don't think the Subaru factory service manual never mentions getting new head bolts (although it's good practice).
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Old 09-07-2006, 10:41 PM   #4
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Good work! This needs to be sticky!
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Old 09-07-2006, 11:03 PM   #5
NITROS
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i wish this was around when i was putting my hybrid together.
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Old 09-07-2006, 11:16 PM   #6
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Sticky?
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Old 09-07-2006, 11:20 PM   #7
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Quote:
Originally Posted by Bolster View Post
Good work! This needs to be sticky!
+1. Excellent write-up.
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Old 09-07-2006, 11:36 PM   #8
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Sticky this for sure, you just helped me out a ton! Thank you.
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Old 09-08-2006, 08:54 AM   #9
rebos123
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Awesome post! Thanks for taking all the mystery out of performing this kind of swap!!!!
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Old 09-08-2006, 10:35 AM   #10
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thanks for the write up. doing this right now.
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Old 09-08-2006, 10:52 AM   #11
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Well done
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Old 09-08-2006, 11:41 AM   #12
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Thanks to all for the support. If you ever have any questions, don't hesitate to call or email. We here at kingpin have a very informative staff, and information is always free.

InfamousDX- i belive you are right, i don't think the manual specifically states to use new head bolts, but we always do.

thanks again,

scotty
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Old 09-08-2006, 12:49 PM   #13
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Awesome write up, I will most definitely be referencing this when I swap in a 2.5.
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Old 09-08-2006, 01:00 PM   #14
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can you give us an answer to what the CR is with this setup and STI headgaskets? I've seen numbers ranging from 8.6-9.1
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Old 09-08-2006, 01:12 PM   #15
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thank you. and subscribed bc when i get back from iraq the parts will be sitting im my garage waiting on me.
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Old 09-09-2006, 11:12 AM   #16
Kingpin
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To be honest, I couldn’t say with 100% accuracy what the compression ratios is, as i have never run the numbers myself. It does go up a bit, and I have most often been quoted 8.8.
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Old 09-09-2006, 12:17 PM   #17
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when adding this shortblock, how much power wise will you be behind a a 2.5L sti when reaching larger power levels around 400whp due to wrx head restriction?

would adding a v7-v8 intake manifold help?
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Old 09-09-2006, 12:53 PM   #18
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One thing to add. Always check for cracks between the valve and spark plug hole. The cracks usually start in the threads for the spark plugs and work there way out toward the valve seat. Seems A LOT of scooby heads are prone to crack there.
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Old 09-09-2006, 04:55 PM   #19
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Sticky
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Old 09-13-2006, 11:11 AM   #20
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Quote:
Originally Posted by bren wrx View Post
when adding this shortblock, how much power wise will you be behind a a 2.5L sti when reaching larger power levels around 400whp due to wrx head restriction?

would adding a v7-v8 intake manifold help?
What head restriction? The heads are nearly identical flow wise. The limit will be the cams. Upgrade those while you have it out and hang on.
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Old 09-14-2006, 01:02 AM   #21
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Default WRX cams/valves in STI heads?

I know it might sound silly, but in the money crunch that exists in reality it might be a possibility. I have not seen used STI heads running around for sale, but you can buy new STI head castings from a dealership. Does anyone know if the WRX cams/valves fit in the STI heads? You might ask what the benefit doing this instead of just using the WRX heads is. The STI heads have the proper design for the 2.5l, as opposed to the WRX heads, I think that it will make a difference in engine efficiancy/operation. I do not have the money to buy a shortblock, heads, cams/valves, and all the other crap needed to do the work, but I might be able to do a little more than just the shortblock (which I need because my 2.0 has a bad rod bearing), so I am exploring possibilities.
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Old 09-14-2006, 10:23 AM   #22
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it really seems bad rod bearings/spun rod bearings are becoming more common these days. myself included.
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Old 09-14-2006, 10:33 AM   #23
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Is it true that 2.5 hybrids are very prone to knocking and all? According to Clark they are and they are a major pain to tune. I just may opt out of doing this swap and go JDM.
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Old 09-14-2006, 10:39 AM   #24
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Quote:
Originally Posted by Kingpin View Post
InfamousDX- i belive you are right, i don't think the manual specifically states to use new head bolts, but we always do.
Yea... It's only good practice. Any idea how much a set of new head bolts costs from Subaru?
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Old 09-14-2006, 10:43 AM   #25
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Quote:
Originally Posted by Kingpin View Post
You have two options for cleaning up the head, a machine shop, or do it yourself. A machine shop will completely go thru a head, and check everything and repair any defects for $150-300, depending on what is wrong with them.. The heads will come back in perfect shape, basically like new. The only draw back besides the cash you have to pay, is that machine shops take forever to get anything back to you. If you don’t have the time to wait, you can clean up and check your heads yourself.
Machine shops are like anything else... There are good ones and bad ones. However, most will also do partials. The machine shop I use will bake parts for me. Price depends on size, but I would guess $30-40 for a pair of Subaru heads. This will get them clean in places I can not see. And my shop will do it same day or next day when very busy. You can then self port them, and send them back for a valve job and final build, or DIY.
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