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Old 03-10-2009, 10:58 PM   #1
vanillajuice
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Default BC 272 cams....pronounced lope

so a local guy has the same cams as me BC 272/272....his idle sounds stock as where mine has a very pronounced lope, think this could just be due to the need to tune? or something else? of course hes on 2.5 litre heads and im on the 2 litre heads....any ideas?
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Old 03-10-2009, 11:34 PM   #2
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Quote:
Originally Posted by vanillajuice View Post
so a local guy has the same cams as me BC 272/272....his idle sounds stock as where mine has a very pronounced lope, think this could just be due to the need to tune? or something else? of course hes on 2.5 litre heads and im on the 2 litre heads....any ideas?
Got my 04 WRX back today with a new rebuilt motor! Yes it has the BC stage II cams, my car sounds stock and it has a tune installed from PDX, can't really hear the lope, but still runs great and has pleanty of power! My new motor has only 74 miles on it!!!!!!!!!!!!!!!!!!!!!!!!
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Old 03-11-2009, 01:42 AM   #3
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hmm...ya what the heck is goin on with mine?
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Old 03-11-2009, 01:56 AM   #4
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Quote:
Originally Posted by vanillajuice View Post
hmm...ya what the heck is goin on with mine?
You said he has 2.5 heads, does he have AVCS? If he does that could have something to do with it.
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Old 03-11-2009, 11:19 AM   #5
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Quote:
Originally Posted by vanillajuice View Post
hmm...ya what the heck is goin on with mine?
the heads I don't think are making the difference...and shouldn't. the lope on your setup could very well be from cam timing being off. Who did the install?
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Old 03-11-2009, 11:20 AM   #6
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Could also be due to differences in engine speed at idle.

-Duncan
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Old 03-11-2009, 11:26 AM   #7
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Could also be due to differences in engine speed at idle.

-Duncan
very true...I would assume they'd have check that though...fuel and ignition can change the sound too.
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Old 03-11-2009, 11:34 AM   #8
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the heads I don't think are making the difference...and shouldn't. the lope on your setup could very well be from cam timing being off. Who did the install?
I did... Things not mentioned..
1: Ultra light aluminum flywheel
2: 2.5l hybrid from a 2l
3: Base map guess
4: port work not optimum for low end (knife edge runners)
Rich idle mix... runs decent off idle.
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Old 03-11-2009, 02:30 PM   #9
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Originally Posted by Homemade WRX View Post
the heads I don't think are making the difference...and shouldn't. the lope on your setup could very well be from cam timing being off. Who did the install?
With AVCS heads (and active AVCS) you have less overlap at idle. That will affect lope to some extent wouldn't it? That's the reason I've been told STi always idle better with identical cams than non-AVCS cars do.
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Old 03-11-2009, 02:43 PM   #10
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AVCS are 0 at idle
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Old 03-11-2009, 02:51 PM   #11
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AVCS are 0 at idle
That's a relative number. Compared to non-AVCS cams the centerline of the intake cam will be different at idle
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Old 03-11-2009, 03:09 PM   #12
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That's a relative number. Compared to non-AVCS cams the centerline of the intake cam will be different at idle
TRUE ^
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Old 03-11-2009, 03:23 PM   #13
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its probably just where your idle is set... i have BC 280's in my car and at idle they sound more like 264's by my car idles at 1200rpm... if i bump it down to 700-800rpm is becomes VERY rough to the point where the car shakes pretty bad
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Old 03-11-2009, 05:37 PM   #14
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yea mine is set at 800rpm, and yes it shakes and sounds rough, idle is no longer rich tho, still does it, guess its just too low of an idle?
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Old 03-13-2009, 12:48 AM   #15
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In my experience, cammed 2.0L cars tend to idle a little lumpier than cammed 2.5L Subarus. I tuned a couple hybrids in the past couple weeks, one with BC 280 cams and another with Kelford 272. Both needed a 1000-1050 rpm idle to have good albeit still lopey idles. In comparison all the 2.5L Subarus with Cosworth and Kelford cams that I have tuned all idle near stock with no notable lope even with idle set at 850-900 rpm.
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Old 03-13-2009, 01:03 AM   #16
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Thanks for the heads up socal... I wondered about that because the 2.5l has the intakes retarded which reduces valve overlap hence a smoother idle.
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Old 03-13-2009, 09:50 AM   #17
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Quote:
Originally Posted by kellygnsd View Post
With AVCS heads (and active AVCS) you have less overlap at idle. That will affect lope to some extent wouldn't it? That's the reason I've been told STi always idle better with identical cams than non-AVCS cars do.
sorry, I wasn't even thinking about the actual AVCS function but just head differences...knife edging could effect it however.

the BC cams have the same lob whether its wrx or STi however I don't recall the difference in LSA/LCA


which brings the question; did you get ej20 cams or ej25 sti cams for the hydrid build? if the wrx, did you change the LSA so it would be corrected for the 2.5L bottom end?
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Old 03-13-2009, 11:07 AM   #18
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I'm the local guy. I think it could be related to the tune since the OP's car is using a email base tune and I have been working on mine and constantly tweaking it from the get-go, and the car idles smoothly at 700-800 RPM. There is really not a pronounced lope. However, when you take the car above 4000RPM it begins to sound very mean and way different than a stock STI.

Just for grins, I upped the idle to 850, 950, and 1050 RPM and did not notice any positive benefits whatsoever, so I left it at stock. Car pulls 19 in/hg at hot idle like that.
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Old 03-13-2009, 10:11 PM   #19
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Quote:
Originally Posted by Homemade WRX View Post
sorry, I wasn't even thinking about the actual AVCS function but just head differences...knife edging could effect it however.

the BC cams have the same lob whether its wrx or STi however I don't recall the difference in LSA/LCA


which brings the question; did you get ej20 cams or ej25 sti cams for the hydrid build? if the wrx, did you change the LSA so it would be corrected for the 2.5L bottom end?
My Cosworth 275 cams(Kelford 199-E equivalent) have a centerline of 113 for intake and exhaust, the AVCS versions list centerline as variable on intake and 113 for the exhaust.

Remember AVCS was designed for emissions as well as performance and excessive overlap does not equal good emissions. Excessive overlap isn't good for fast low end turbo spool either but for some reason tuners can increase spool by fiddling with the AVCS maps and comparatively true STi long-blocks tend to spool turbos better than hybrid 2.5L motors.

If you run AVCS cam gears with non-AVCS cams you end up with an intake cam that's retarded ~5 degrees. I'm running 2.0L cams on my hybrid BTW.
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Old 03-13-2009, 11:23 PM   #20
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Here's a video showing different idles with diffrent air-fuel ratios.
http://www.youtube.com/watch?v=CPNM5S9CxBA

Idle speed will determine how ROUGH it is. The lower the rougher, the leaner the rougher.
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Old 03-14-2009, 12:25 AM   #21
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ya i have the 2 litre cams also....as i have 2 litre heads
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Old 03-14-2009, 01:18 AM   #22
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Thicker head gaskets? The thicker cometics that so many people use throw cam timing off just ever so slightly (by moving the heads out away from each other just a touch, not nearly enough to equal a full tooth, just enough to make a big lope on a mild cam. My 2.0/2.5 hybrid WRX sounded like a V8 with a HUGE cam.
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Old 03-14-2009, 10:13 AM   #23
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My bc 272 sound almost stock on my 07 sti idle set at 900 rpms
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Old 03-14-2009, 11:00 PM   #24
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im on sti head gaskets
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Old 03-15-2009, 12:41 AM   #25
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any misfires with those cams?
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