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Old 02-20-2014, 05:17 PM   #1
mod maniac
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Default Advancing exhaust cams? HELP PLEASE! The evo's do it!

I was wondering who has advanced the timing on the exhaust cams in a wrx/sti? How much advance? What cams? What was the results? I only have avcs on the intake cams. I am using BC 280 cams on my 04 fxt.
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Last edited by mod maniac; 02-25-2014 at 10:52 PM.
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Old 02-20-2014, 09:36 PM   #2
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You're changing the valve timing so the valves open sooner.
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Old 02-20-2014, 10:27 PM   #3
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^^^ that is the plan. By theory advancing the exhaust cam should make the power band come on sooner but loose some up on top. I have installed bc 280 cams on my 04 forester and want to see if I can get them to work a little lower. Who has done it?
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Old 02-20-2014, 10:44 PM   #4
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Just degree the cams and you'll be happy. Have your cam card?
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Old 02-20-2014, 11:04 PM   #5
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Look I am not just looking to degree my cams. I am looking to tweek on them. I use cams on a lot of my builds. I am looking for someone who has messed with the cam timing on a wrx! I am going to do this and I am sure I wont be the 1st. Looking for insight.
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Old 02-20-2014, 11:10 PM   #6
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Quote:
Originally Posted by mod maniac View Post
Look I am not just looking to degree my cams. I am looking to tweek on them. I use cams on a lot of my builds. I am looking for someone who has messed with the cam timing on a wrx! I am going to do this and I am sure I wont be the 1st. Looking for insight.

Do what you think is right then. I wish you luck my friend!
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Old 02-21-2014, 08:53 AM   #7
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I've done it with DAVCS cams but those have much smaller lift than your 280s. The lift is the thing you're going to be trying to figure out during overlap: valve to valve contact.

Without popping the heads off and claying the tops, it's difficult to say but you can also carefully do it by turning the motor over and trying to feel for contact. Not very scientific but possible with everything bolted together.

These are some of the threads that I researched when I was trying to figure out my situation:

http://forums.nasioc.com/forums/show....php?t=2046298
http://forums.nasioc.com/forums/show...2439060&page=2
http://forums.nasioc.com/forums/show....php?t=1423635
http://forums.nasioc.com/forums/show....php?t=1427706

http://forums.nasioc.com/forums/show....php?t=1475616

That one especially.

The one thing I found is that the cams are designed to work with one another and moving one around independent of the other would show results but the combination of the two showed the best results. I don't know if you're running AVCS but certainly that has a bit to do with it as well.

I would refer to some of the AVCS threads to see where they used advance to fill in the "holes" and then retard the cams for the top end. Subaru has already done the footwork in that regard.

Hope this helps.

BTW: the 19t is still happily chugging along.

-Randy
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Old 02-21-2014, 09:58 AM   #8
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^thats what I tried to tell him in simple terms.
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Old 02-21-2014, 01:46 PM   #9
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Thanks Randy. I have single avcs and so I am just looking for info on advancing the exhaust cams. We can mess with the intake timing while tuning.

Glad you are having fun with that 19t.

Dan
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Old 02-21-2014, 03:18 PM   #10
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Thanks Randy. I have single avcs and so I am just looking for info on advancing the exhaust cams. We can mess with the intake timing while tuning. Glad you are having fun with that 19t. Dan
Genius. Lol
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Old 02-21-2014, 04:22 PM   #11
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Genius. Lol

Spoolinsti don't comment if you don't understand the question.

I see lots of post asking about the avcs and cam advance. I only have avcs on the intake cams. I wish to install tomei adjustable cam gears on the exhaust cams. If I advance the exhaust cam it should make the turbo come in early but i should lose some top end. I am looking for someone who has tried it. I have done this on my toyota 18rg with nos but have not messed with my subi yet.
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Old 02-21-2014, 05:12 PM   #12
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If you have Std. sized valves you should be able to advance the exhaust cams a few degrees with no valve to valve interference.

I'd still want to check how close you are with the heads off.

I've advanced the ex cams a little (2 degrees) from the cam card for better top end, doesn't hurt midrange much.

But I wouldn't expect massive changes in the powerband by advancing the EX cams a few degrees.

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Old 02-21-2014, 06:48 PM   #13
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I understand. You're trying to reinvent the wheel. Good luck on that long never ending journey.
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Old 02-21-2014, 10:34 PM   #14
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Thank you diso.
Advancing the exhaust cams will give me more valve to valve clearance but I do still need to make sure the piston clears. I do know that the gains won't be great but I am still looking for someone who has advanced the exhaust cam only. Sorry spoolinsti that you think I am trying to reinvent the wheel but this is the way it is done in the race world.

Last edited by mod maniac; 02-21-2014 at 11:14 PM.
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Old 02-22-2014, 09:18 AM   #15
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Subaru thought that advancing the exhaust cams was a good idea so they put AVCS on that side using the same AVCS cams . I'd think about it that way. And yes, it is an old, effective racecar trick to move the power around.

Advancing the cams will bring the onset of boost sooner. It raises the dynamic compression and the additional overlap will help the intake charge. Obviously there is a no free lunch and the top end which doesn't like overlap will suffer a bit but the low and mid will benefit: ie: where you spend most of your time anyway.

It's a better option versus shelling out more money for a smaller set of cams and pulling the motor. Degreeing the cams to spec is all fine and good but that is just a starting point really. Adjustable sprockets will allow you to move the curve to where you need at the expense of taking it away from somewhere else.

With autocross, obviously moving the curve to the left will help out of corners and the start. You would set the cams up differently for drag or road racing. That much is obvious.

In my limited experience with this with Subarus, I found the biggest results advancing the intakes but with AVCS, the computer can take care of that. By moving the exhausts around, you can take more advantage and tailor accordingly.

I personally don't see any negative in trying. Beats pulling a motor.

-Randy
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Old 02-22-2014, 08:20 PM   #16
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Yes but with avcs you can have your cake and eat it to. So to speak!
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Old 02-23-2014, 11:09 AM   #17
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^^^Yes the avcs is nice but I only have that on the intake cams. Still looking for more info on setting the exhaust cams advanced. I am trying to get the benefit of big cams while using a td05-20g for early spool. I may be dreaming but who knows?

Last edited by mod maniac; 02-23-2014 at 11:34 AM.
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Old 02-23-2014, 04:27 PM   #18
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Yes I can read previous posts and remember them with no issues lol good luck on your research and testing
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Old 02-23-2014, 09:25 PM   #19
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Quote:
Originally Posted by spoolinsti05 View Post
Yes I can read previous posts and remember them with no issues lol good luck on your research and testing
For someone who has absolutely nothing to add to this thread, you sure seem to be posting in it a lot!
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Old 02-23-2014, 10:26 PM   #20
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Originally Posted by Patrick Olsen View Post
For someone who has absolutely nothing to add to this thread, you sure seem to be posting in it a lot!
I'm not in favor. I have my reasons. Those reasons are beyond a google search. Yah!
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Old 02-24-2014, 10:30 AM   #21
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Still looking for info.
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Old 02-24-2014, 12:41 PM   #22
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I've advanced and retarded the intake and exhaust cams on the dyno, these engines do not have avcs. Advancing both gears moved the power band to the left, for pulling hills or corners. With your avcs heads the intake cams are retarded more than non-avcs, i'd have to look at my notes for the exact amount. First off you will need to degree the cam gears on the engine, do not assume that the zero on the gears are zero. If you change head gasket thickness or deck the block/heads, this will change cam timing. I have a video on you tube on Subaru cam degreeing that might help you on the process.
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Old 02-24-2014, 12:45 PM   #23
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Old 02-24-2014, 02:11 PM   #24
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Thanks hooper. I know how to degree and have the equipment. If you could check your notes and let me know how much advance worked for you that would be great. What cams were you using? Dan
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Old 02-24-2014, 04:55 PM   #25
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Lmfao
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