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Old 08-21-2010, 07:10 PM   #1
Scooby Newbie
Member#: 158449
Join Date: Sep 2007
Chapter/Region: SWIC
Subaru Banner Built motor break in

I just had my motor built with Cosworth pistons, rods, ACL main and rod bearings, and ARP head studs. What oil is recommended and how should I go about breaking it in? I purchased 5W30 NON-synthetic but I was told to go heavier. It hasent been started yet but I'm setting the map to economic to lower the boost for the first 1,000 miles with my acessport.
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Old 08-21-2010, 09:49 PM   #2
Scooby Guru
Member#: 4414
Join Date: Feb 2001
Location: Dublin, CA
2002 WRX Sedan
Midnight Black


Oil viscosity depends on clearances, stock clearances should be fine with 5w30 through 10w40. If larger clearances then 10w40-20w50.

I really don't see a problem with 5w30. Break in oil is only in there for 20-50 miles, so it doesn't really have time to break down and you don't run it very hard. Some will use special break in oil, I'm not sure that's really necessary.

Break in is about getting the rings sealed well, and this happens with cylinder pressure, both positive and negative. Alternate steady moderate boosting (5-10 psi) and decel. If you have a hill nearby, it's really easy, otherwise you have to be a little more cautious for traffic and do accel, decel.

Get some good boosting in the first 20-50 miles and dump the oil. After that first break in, drive like a normal person & change every 500-750 miles until 1500, then switch to your syn and get your real tune.

That's my opinion anyway, I'm sure there are others. I doubt you'll find too many people disagreeing with getting some decently hard running in the first 50 miles though. There's really not any other way to get the rings sealed. You need a large pressure difference between the crankcase and the combustion chamber to really push the rings against the cylinder walls, and you need that to happen before the honed cylinders are worn in to get a good ring seal.
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Old 08-22-2010, 03:41 AM   #3
Scooby Specialist
Member#: 153880
Join Date: Jul 2007
Chapter/Region: RMIC
Location: Western Slope, Colorado
03 Evo VIII
2011 STI


I'd run a thicker oil anyway. 10w30 works good.

Don't baby the motor, beat on it good enough to build enough pressure to seat the rings good so you have a nice sealed motor.

Make sure to let it warm up before driving it and let it cool down after driving it.
Alternate your load/rpms and gears. Don't sit in traffic and don't just cruise down the highway at 70 mph. They main thing is vary the conditions the car sees.
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Old 08-23-2010, 06:13 AM   #4
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Member#: 245786
Join Date: May 2010
Chapter/Region: NWIC
Location: Wenatchee, WA

This: http://www.cobbtuning.com/info/?ID=3475

Although, they say to drive it "easy" and 1-2psi of boost? Im of course a little loose on that as they give good clear directions that go more into detail but mostly they say drive it "easy" during break in.

I have honestly heard more people say drive it "kinda hard" than "easy".
Anyone want to prove cobb tuning wrong?

I need to break my new built motor in here pretty quick aswell.
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Old 08-23-2010, 09:13 AM   #5
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Join Date: Jul 2005
Chapter/Region: SCIC
Location: Tatooine
04 bicycle!


why don't you ask the guy who built it?
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