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Old 11-14-2018, 03:15 PM   #1
azak907
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Member#: 432487
Join Date: Oct 2015
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2013 WRX STI Hatch

Default Winter driving with cams

I live up in Alaska with a 13í sti hatchback and Iím think of going down the route of doing cams (Kelford 272ís) and I was wondering if anyone knows how winter driving with a cammed Subaru is? Mostly like cold starts and such. I park the car in a garage at night but when Iím at work itís a cold start. Thanks in advance
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Old 11-15-2018, 01:35 AM   #2
NSFW
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Chapter/Region: NWIC
Location: Near Seattle, WA
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05 Stage Free LGT
ATP 3076, 6MT, AVO FMIC

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That's a dual-AVCS motor, isn't it? That helps a lot with your scenario, because it moves both cams away from each other during idle and warmup.

Disclaimers: I'm in Seattle not Alaska, and I have BC 272s not Kelford 272s. Kelford and BC make their duration measurements at different lift specs, so it's hard to compare the numbers directly, but Kelfords seem just a little bigger in duration. The lobe center angles are the same though.

But, just in case nobody steps up from Alaska with Kelford 272s...

My 05 LGT has an 08 STI engine with BC 272s (dual AVCS), and if I'd known a couple years ago what I know now about cams, I would have gone with 280s. At 1000 RPM it idles dead smooth. It can drive little rough after a cold start but that's minor if I'm careful with the throttle. Once it's warm you'd never guess the cams aren't stock.

If you look at the valve timing at 0.050 lift, BC 272 dual-AVCS cams have the same "overlap" at rest as stock single-AVCS cams. "Overlap" in quotes because there isn't any, the math works out to -34 degrees. The stock cams do have less overlap at 0.006 (stock: 0, BC272: 16), but there isn't a lot of airflow at such low lift anyway.
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Old 11-16-2018, 12:59 AM   #3
azak907
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Thatís very helpful thanks! And yes itís a dual AVCS motor. So you donít think I would have any issue cold starting my car in 0įF with BC272 cams?
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Old 11-16-2018, 01:35 AM   #4
NSFW
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Location: Near Seattle, WA
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05 Stage Free LGT
ATP 3076, 6MT, AVO FMIC

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I think you'll be fine, but I have to admit I haven't actually tested mine below about 40F yet. If you can wait a few weeks I'll probably know what they're like in the 20s, maybe teens, but it rarely gets colder here.

34 degrees really is a lot of non-overlap though. The factory cam in my Corvette has -23, and while those engines don't have much in common, you could kinda look at it as a pair of 2.85L four-cylinders.

The problems that people associate with big cams come from overlap, and when the engine is cold, AVCS advances the exhaust cam and retards the intake cam, both of which reduce overlap and the problems associated with it.

But that's a lot of theory... It would still be great to have someone from a colder climate chime in to confirm that reality actually matches the theory at 0F.
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