DIY: Engine Building: EJ251 with STI Rods/Pistons and Head Work - Page 34 - Subaru Impreza GC8 & RS Forum & Community: RS25.com
 
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DIY: Engine Building: EJ251 with STI Rods/Pistons and Head Work
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Old 08-06-2017, 03:14 PM   #331
boycotshirts
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Quote:
Originally Posted by nepbug View Post
The adjustable cam pulleys will allow you to "degree" the cams in respect to the piston position. In this case, you would use them to advance the cams. This will mean that the valves will open (and also close) earlier in the piston stroke.

Advancing a SOHC cam will do several things:
-Increase low end power, but reduce top-end power
-Spool the turbo faster, the exhaust valve will open earlier in the power stroke and send the hot expanding gases to spin up the turbo.
-It also increases the piston to valve clearance of the intake valves, but decreases the clearance of the exhaust valves.
-Advancing the cams will also reduce the exhaust gas scavenging effect, but that is more of a concern in NA engines than boosted ones because the turbo will still be able to fill up the cylinder without the scavenging effect.

Turbo motors would prefer less overlap in the cam profile actually. More overlap means that the intake and exhaust valves are open at the same time for longer. That then means that the hot exhaust gases (which are great for spooling a turbo) are being mixed with cool intake gases (which are not good for spooling a turbo). So, limiting the overlap limits the amount of cooling of the exhaust gases that occurs.

So you can see that an NA cam profile is probably more setup for ideal scavenging, while a turbo might be for better spool characteristics. DOHC heads with new grinds/cams or adjustable pulleys will allow you to dial in the NA to turbo change a bit more, but advancing the SOHC cams is a good compromise and should net better results than not advancing them.

Writing this out makes me realize I need to call Delta and really get the specs of their re-grinds.
I have been trying to find the cam spec sheets for the 2000 grind for a little while now. Let me know if you find anything.
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Old 08-06-2017, 03:50 PM   #332
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Wish I could find a set of adjustable cam pulleys for the SOHC.
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Old 08-06-2017, 08:26 PM   #333
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Quote:
Originally Posted by FryphaX View Post
Wish I could find a set of adjustable cam pulleys for the SOHC.
You should be able to use a set designed for an ej20k, id believe theres some out there for those. Ive test fit ej25d cam gears onto a ej251 and as far as I can remember they fit, I know the overall mounting is the same but not so sure on the offset. The ej25d/k has a thicker belt than the 251 so the 251 belt will just have a little extra room.
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Old 07-30-2018, 02:54 PM   #334
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Bump because I'm in the process of building my ej253 and this is a god send. Anyone have an requests for pictures? i have 1 MY00 ej251 torn down, 1 MY07 ej253 w/acvs, and 1 MY09 ej253 w/acvs.



thank you OP!
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Old 09-16-2019, 11:27 AM   #335
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new to the forums. how come I can see the pictures on my phone but not on my computer?
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