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Old 02-11-2007, 01:23 AM   #1
bboy
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Default Anyone comment on Cosworth cams vacuum and onset....

I was speaking to the cosworth rep the other day about their cams and he said they have sold hundreds of sets. Which I found surprising since I haven't seen them on here much.

Any owners care to comment on what your idle vacuum is and how much you estimate the cams hurt boost onset?
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Old 02-11-2007, 04:38 AM   #2
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AVCS or non-AVCS Cosworth cams? I'm running the non-AVCS 275 cams and my vacuum at idle took a big dump. My autometer boost gauge is crap so I can't tell you what the actual value is but I can tell you it dropped by about 9" Hg on my new engine. As for boost onset I'm not sure either, I'm on my break-in tune still with an extra .5L, T518Z turbo, and spring pressure of about 10psi. All in all the car still feels better than the 2.0L on the stock turbo at 16psi across the board and especially up top.

The guys at Harman said the AVCS cams idle better due to the retarded nature of AVCS at idle and low RPMs.
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Old 02-11-2007, 11:34 AM   #3
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Quote:
Originally Posted by kellygnsd View Post

The guys at Harman said the AVCS cams idle better due to the retarded nature of AVCS at idle and low RPMs.
If you retard the cam it will idle worse, not better. What avcs will allow you to do is grind the cam with some advance built in and then take it out using the avcs in the upper rpms.
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Old 02-12-2007, 12:25 AM   #4
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"Hundreds of sets", huh? From the looks of this thread, I'd say that's a little off base...
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Old 02-12-2007, 01:40 AM   #5
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Maybe they mean hundreds of sets worldwide, they are popular in Europe
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Old 02-12-2007, 01:54 AM   #6
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Quote:
Originally Posted by NeilF View Post
Maybe they mean hundreds of sets worldwide, they are popular in Europe
Maybe so, but there sure don't seem to be very many Subarus over there. I spent a month on the Continent recently: we saw 1 (as in ONE) subie the whole time over there...I was kinda surprised.
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Old 02-12-2007, 04:44 AM   #7
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Originally Posted by jabbott View Post
If you retard the cam it will idle worse, not better. What avcs will allow you to do is grind the cam with some advance built in and then take it out using the avcs in the upper rpms.
Not so my brother. The stock STi AVCS cams are the same duration and profile as the WRX with more lift. When used with WRX cam gears you get correct timing, if you were to use STi AVCS cam gears on a non-AVCS car you end up with intake timing that is always retarded. Intake/exhaust overlap is not your friend at idle or low RPM but is up top to an extent on turbo'd cars.
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Old 02-12-2007, 10:11 AM   #8
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i have an ej22t sleeved and bored back to 2.5 and im gonna be using the avcs cosworth cams, i have already bought them. i'll let you know how that goes when i get the heads back.
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Old 02-12-2007, 12:39 PM   #9
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Quote:
Originally Posted by kellygnsd View Post
Not so my brother. The stock STi AVCS cams are the same duration and profile as the WRX with more lift. When used with WRX cam gears you get correct timing, if you were to use STi AVCS cam gears on a non-AVCS car you end up with intake timing that is always retarded. Intake/exhaust overlap is not your friend at idle or low RPM but is up top to an extent on turbo'd cars.
Where did I say anything about using wrx and or sti cam gears?
You said
Quote:
The guys at Harman said the AVCS cams idle better due to the retarded nature of AVCS at idle and low RPMs.
This makes no sense?? When a cam is retarded at idle it will idle worse. Period. This is true for any motor. Be it forced induction or na, 4 cyl or 8.
Retared cam = more power up top Advanced cam = more power down low
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Old 02-12-2007, 01:23 PM   #10
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^^^^
So Subaru is wrong in doing it the way they do?

You do understand that we have DOHC engines right and we are talking about the intake cam only. The exhaust cam is fixed. Changing the relation ship between them varies the intake/exhaust overlap thus changing how well the cylinder fills with air. I think you might be confusing intake and exhaust
cam retard.

With a big overlap at idle its going to be that much harder to draw air in thru the intake valves when the exhaust valves are open also. Minimize the overlap and it has no other place to draw air into the engine than thru the intake valve and the engine gets a better charge of air and maintains higher vacuum at idle.

I'm not making this up man. Contact any tuner and they will tell you for big cams of the same duration, the AVCS ones idle much better than the non-
avcs cams. That's FACT!
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Old 02-12-2007, 01:31 PM   #11
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I'm talking AVCS Cosworth cams. I only know of like two sets on any members' cars.

AVCS has the potential to aid in improving idle since the intake cam can be retard and have less lobe overlap. Then AVCS advances the intake for more overlap and improvement of the dynamic compression at low to mid RPM.

I'm told, but I have never comfirmed that the non-AVCS 2.0L cams are advanced by 4-5 degrees compared to the USDM 2.5 AVCS cams.

-9 inches of vacuum is terrible--must idle at like 2000.

I'll put AVCS in the title.
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Old 02-12-2007, 01:32 PM   #12
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On a stock car, the AVCS advance at warm idle and above 4800-5600 rpm (depending on model) is ZERO. I think you guys are equivocating a different type of motor to ours.
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Old 02-12-2007, 01:35 PM   #13
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And as I said advancing the intake cam will make it idle better. Weather it's a single cam or multiple cam motor. Although it's not actually advance, you can only go to 0. There is no adjustment to go before tap dead center only after tap dead center (retard).

What don't you understand??

Maybe somebody else can chime in and explain it.
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Old 02-12-2007, 02:27 PM   #14
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Good idle requires good vacuum (i.e. vacuum leak idle is terrible). Advancing the intake cams means more overlap with the exhaust cams. When the intake opens early, part of the "suction" that could be used to pull a vacuum on the manifold is missing. Less suction=less vacuum.

Intake cams open the valves Before Top Dead Center by about 30 crankshaft degrees. When AVCS is active, the intake cams can open an additional 30 crankshaft degrees (15 cam degrees) earlier for a total of ~60 BTDC.
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Old 02-12-2007, 05:30 PM   #15
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Quote:
Originally Posted by bboy View Post
Intake cams open the valves Before Top Dead Center by about 30 crankshaft degrees. When AVCS is active, the intake cams can open an additional 30 crankshaft degrees (15 cam degrees) earlier for a total of ~60 BTDC.
with avcs active there is not 60 degrgrees of total advance. There is about 30 and it goes from 0 to 30 atdc (retarded). With the the avcs not hooked up it will be stuck at the most retarded postiion which is about 30 degrees atdc. If you put wrx gears on it, it will put the cam back to 0 degrees.
This is what I've been trying to say.
You wrote "the retarded nature of avcs cam" there is no retarded nature of avcs cams. Your just don't have the avcs hooked up, which will cause the cam gear to stay locked at 30 degrees retarded.
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Old 02-12-2007, 06:27 PM   #16
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What I meant by retarded nature of AVCS cams what I meant was if you have two cars side by side, on a WRX, on an STi at idle the STi intake cam will be retarded more than the WRX intake cam. You will have less overlap between intake and exhaust valves and therefore you draw better vaccum with big cams and idle is improved. Did you even look at that link I PM's you? If even had pictures to explain for those who don't read to well. Maybe you have your advance/retard terms mixed up.

If the intake valves normally open 15 degrees BTDC and now the open at TDC, that is retard
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Old 02-12-2007, 08:17 PM   #17
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I wish I knew where the stock STI cams opened the intake valves. Cosworth spec is 29.5 degrees BTDC. I can find no such specs for the stock subaru cams.

jabbott,
30 BTDC + 30 more degrees BTDC is 60 degrees BTDC that the valve is opening. The AVCS cams are "retarded" compared to the non-AVCS cams I'm told and the cams "start" in a retarded position compared to when AVCS advances them.
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Old 02-13-2007, 01:23 PM   #18
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USDM Stock Camshaft ift: IN 0.378 EX 0.386
Cosworth Camshaft Lift: IN 0.425 EX 0.406

If I find our when the stock USDM cams open and close and thus their duration, I'll post it back here.

My take on this thread is no one has the AVCS Cosworth cams.
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Old 02-13-2007, 03:15 PM   #19
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Quote:
Originally Posted by bboy View Post
...My take on this thread is no one has the AVCS Cosworth cams.
So it would appear. Why not call Cosworth back and tell them you're unable to find anyone on the boards who is using them and you want to speak directly with a couple of buyers to ask them some questions. Since they've sold so many sets, it shouldn't be any problem whatsoever to provide you with a few references, right?
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Old 02-13-2007, 03:18 PM   #20
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They are the same as Kelfords. I have tuned many. They work fine. Axis sold the kelfords first and thus are grandfathered in. The Axis cams are more agro and are made to Rons specs. If I keep this car and pull the motor its going to Ron for heads and cams.

Clark
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Old 02-13-2007, 03:23 PM   #21
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Quote:
Originally Posted by bboy View Post
My take on this thread is no one has the AVCS Cosworth cams.
That would be an incorrect assumption.

I personally know of them in 2 different cars, mine being one of them.

I can't tell you the vacuum at idle because I simply don't remember.

Right now the car is in the middle of a turbo swap and waiting on parts to get back from ceramic coating.

Thanks for the specs on the stock cams.

-D
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Old 02-13-2007, 03:46 PM   #22
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People.. There is Life outside Nasioc!

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Old 02-13-2007, 04:41 PM   #23
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Quote:
Originally Posted by bboy View Post
USDM Stock Camshaft ift: IN 0.378 EX 0.386
Cosworth Camshaft Lift: IN 0.425 EX 0.406

If I find our when the stock USDM cams open and close and thus their duration, I'll post it back here.

My take on this thread is no one has the AVCS Cosworth cams.
I have a set along with the heads, I'll check the vac. at idle next time I'm out.
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Old 02-13-2007, 07:58 PM   #24
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Vacuum and an estimate of how much the boost onset was affected.

I'm most curious about the boost onset. The Cosworth cams have very high lift and the duration is, I would say, moderate. I think, but don't know, that that higher lift may actually preserve the spool/onset better than some of the other cams.

Another way of saying what I'm talking about is that the increased lift is the source of greater duration, and in fact these cams don't have a whole lot more overlap than the stock cams (vacuum is preserved closer to stock of -21 inches).

NASIOC is life Clark.........artificial life.

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Old 02-13-2007, 08:00 PM   #25
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I'm going to try to get more detail and take them to Delta Cams and have the stock and Cos' measured.
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