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Old 03-01-2007, 01:55 PM   #1
bboy
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Default Analysis of Cosworth AVCS cams vs USDM STI cams

I've asked for detailed data on lift vs degree (duration) but here is the gross comparison.

INTAKE
Stock
Duration at 0.050 lift: 203 degrees
Lobe area: 27
Maximum Lift: 0.378 inches

Cosworth:
Duration at 0.050 lift: 227 degrees
Lobe area: 33
Maximum Lift: 0.431 inches

EXHAUST
Stock:
Duration at 0.050 lift: 207 degrees
Lobe area: 28
Maximum Lift: 0.385 inches

Cosworth:
Duration at 0.050 lift: 231 degrees
Lobe area: 32
Maximum Lift: 0.401inches

LSA on both sets of cams is 110 degrees. These are pretty mild cams, even for a turbo, comparable to other company's Stage 2.

The Cosworth LEFT cams (both intake and exhaust) are retarded by 1 degree compared to stock.
The Cosworth RIGHT cams are retarded by 2 degrees comparded to stock.
It's a "Car Talk" puzzler as to why Cosworth retarded the cams at all, and why the right side is retarded by an extra degree. (I had them measured twice, because I couldn't believe it). **Puzzler Hint: what asymetry is created when you mill your heads?

Some of you know, some of you don't, I have a rather personal reason for such carefulness when if come to cams. The main difference with DPR AVCS cams is that the intake cams are advanced by 4-5 degrees compared to stock, leading to near fatal or fatal valve-piston interference. Cosworth did not make the same mistake, in fact, their differential retarding of the cams demonstrates their astuteness.

It begs the question, why did DPR advance the intake cams by that much when Cosworth was so careful not to advance, and actually retarded them. I'll tell you why. Here is what DPR did and this should be lesson for us all. DPR bought Crower non-AVCS WRX cams, drilled 8 holes in front ends of the intake cams, machined off the other ends and replaced it with a pressed-on piece that had the AVCS notches cut into it. Presto!! 100% mark-up AVCS cams............but NO the original Crower WRX cams have 5 degrees of built-in advance because they lack AVCS. Oops now with the DPR cams AVCS advances by 15 degrees + 5 degrees. Sorry Charlie, your motor is toast, you bent a valve and then dropped it. Caveat Emptor!!!! DPR never tested there cams in an engine, never measured the valve-piston clearance, yet they sell them to the public and YOU are their guinea pig. As you can tell I'm still sizzling about this consumer protection nightmare.

Cosworth has done a much better job. If you own DPR cams, please back off the AVCS advance via tuning if you can.

An interesting design difference with the Cosworth AVCS cams compared to any others is the higher lift of the intake cams (the slightly longer duration has more to do with lash than actual design I suspect). The effect of increasing the lift on the intake cams is debatable, but from my reading, it favors low to mid RPM torque generation because the valves are open at their maximum flow rate lift height or higher. Lifting higher doesn't flow anymore, it just is flowing as much as it can for longer. Longer at max flow means better cylinder filling. At high RPM velocity takes over.

I'll post up the actual cam lobe plots if I can get more detailed numbers and some pics of the cams too.

Note of installation from Cosworth: Billet intake cams, cast exhaust. Cast exhaust require less clearance (lash) than the billet stock exhaust cams (0.010 vs 0.014 inches)
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Old 03-01-2007, 02:10 PM   #2
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Quote:
Originally Posted by bboy View Post
...DPR bought Crower non-AVCS WRX cams, drilled 8 holes in front ends of the intake cams, machined off the other ends and replaced it with a pressed-on piece that had the AVCS notches cut into it. Presto!! 100% mark-up AVCS cams............but NO the original Crower WRX cams have 5 degrees of built-in advance because they lack AVCS. Oops now with the DPR cams AVCS advances by 15 degrees + 5 degrees. Sorry Charlie, your motor is toast, you bent a valve and then dropped it.
Jeeesus, so that's what's been happening. Good detective work, amigo.
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Old 03-01-2007, 02:20 PM   #3
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What stage DPR cams are you refering to? Or is it all of them that are advanced the same ammount? I installed DPR stage 1 cams in a customers STI about a year ago. They have been fine to this day and the car has been raced many times. I was told that the stock valvetrain would be fine to use with these cams by three other shops. My only concern from day one was that the valvetrain is VERY noisy since I have installed these. It has amplified by about 3 times louder than stock. To date this car has never skipped a beat and makes high 400 HP on pump gaas with water injection, GT35R, etc. Thanx for the post.

Dave
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Old 03-01-2007, 02:34 PM   #4
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fricken amazing bboy.

my hat is off to you *bow*




teh devil inside is gonna grab some cozzies!
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Old 03-01-2007, 02:49 PM   #5
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Very interesting, bboy. Thanks for the post.
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Old 03-01-2007, 03:07 PM   #6
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wow what a refreshing post. thank you.
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Old 03-01-2007, 03:51 PM   #7
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great info.
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Old 03-01-2007, 04:20 PM   #8
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so what is the answer for why one side is retarded more than the other?
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Old 03-01-2007, 05:31 PM   #9
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I cannot tell you how I came to know that DPR cams are "improved" Crower non-AVCS cams, but they are, and they are ALL advanced compared to the USDM STI AVCS cams. Some serious mis-understanding of how AVCS works at all. I'm going to to a post on how AVCS cams work soon too. With pics and diagrams. Let's say I've studied this to death.

Here is the issue: right before TDC the intake cam begins to open the intake valves. The piston is moving UP. The valve is moving DOWN. If you were to look at a cam lobe plot, this is just as you start up the hill, not at peak lift. If the intake cam is advanced, the valve opens earlier, and it is depressed more as the piston comes flying at it.

The valves hit at full AVCS advance. Some piston brands have more clearance than others. So, the DPR cams can work with out issue, but choose the wrong pistons and you too can have a pile of aluminum and steel like I do.

If you deck/grind the heads, the timing belt between the left and right heads is slightly shorter. This means the right cams will be advanced by the total amount of head material removed. Same is true for decking the block, but, a lot less material can be removed (0.004 Subura max, vs 0.012 for the heads). I'm guessing Cosworth wanted to retard the cams by one degree, but knowing that someone might deck/grind the heads, they didn't want the cams to get advanced on the right side too much and cause interference. It's a safe and smart move by Cosworth if you ask me.
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Old 03-01-2007, 05:38 PM   #10
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Do ka mano and the PDXT boys know about this yet?
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Old 03-01-2007, 06:00 PM   #11
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Quote:
Originally Posted by Dizastical View Post
What stage DPR cams are you refering to? Or is it all of them that are advanced the same ammount? I installed DPR stage 1 cams in a customers STI about a year ago. They have been fine to this day and the car has been raced many times. I was told that the stock valvetrain would be fine to use with these cams by three other shops. My only concern from day one was that the valvetrain is VERY noisy since I have installed these. It has amplified by about 3 times louder than stock. To date this car has never skipped a beat and makes high 400 HP on pump gaas with water injection, GT35R, etc. Thanx for the post.

Dave
Did you change all the buckets? What lash did you use, Subaru's rec. One way (a bad way) to keep the valves from hitting is to increase the valve lash, that way the bucket's don't start opening the valves until higher up on the lobes. But you also run into some harsh "accelerations" if the buckets hit high on the lobes.

I'm not saying you can't or shouldn't use DPR cams ever. You can use them, but you should know about the built-in advance, you should have a means of lessening the AVCS additional advance (need to alter AVCS map). Choosing pistons is a bit of a crap shoot, because degreeing the cams with the AVCS sprockets is pretty complicated, the best you can do is use two degree wheels and advance the intake cams by 15 degrees manually, but the timing belt will be "in between" teeth.
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Old 03-01-2007, 06:07 PM   #12
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Are you going to ask DPR for a refund on the cams at least?
I bought a Stg2 set - my motor went toast - but for oiling issues, I would get in on the "give me a refund program"
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Old 03-01-2007, 06:11 PM   #13
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Quote:
Originally Posted by bboy View Post

The valves hit at full AVCS advance. Some piston brands have more clearance than others. So, the DPR cams can work with out issue, but choose the wrong pistons and you too can have a pile of aluminum and steel like I do.
I just wanted to say that FULL advance is a varying degree and will not be set on any ONE engine. correct?

Full advance will have to be judged by things such as your pistons, cam grind, lift, etc.

Just do like Tim B. said in the other thread....tune until you heard the bad noises, and back her off a little

just poking Tim
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Old 03-01-2007, 06:13 PM   #14
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I passed the info on to Ka Mano a couple months ago. He's running WRX heads without AVCS so he's fine, but he could have bought cams from Crower. Enough about DPR.

These Cosworth cams look like something that will boost the top end becuase of about 25% more duration, but will retain the low end because of the atypical higher lift intake cam.

The 1.5 degree retard was smart, but they did it on both cams. Maybe someday well see some cams with a greater LSA. You can have the benefits of low overlap during idle and while cruising, but then use the high advance AVCS to help with the dynamic compression and turbo spool at mid RPM and load, and low AVCS advance to increase gas velocity at high RPM and load. Suffice it to say, Subaru did not implement AVCS for making power, but it can be used for it. I believe we could see broader torque curves with wider LSA and AVCS tuning as outlined.

Camshafts are very cool. It's quite simply amazing the amount of thought that has gone into designing them and controlling them. Eventually we'll see something more VTEC like from Subaru (the EZ30R already has it). If some cam gurus get in there with sophisticated flow analysis software I think they could come up with some good approximations great cams for power that merely harness the control mechanisms that Subaru has put in place for mainly emissions. In the mean time, Cosworth has made a worthy intermediate.

Now to get the things in my car and see what they can do.......I hate shimless buckets!!.....but they are what Subaru uses and probably a good idea for high revs.
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Old 03-01-2007, 06:29 PM   #15
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What cam part number did you have examined?

What are 'advertised' durations? something like a 272, 276, 280+?

just curious...
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Old 03-01-2007, 06:29 PM   #16
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Quote:
Originally Posted by modaddict View Post
I just wanted to say that FULL advance is a varying degree and will not be set on any ONE engine. correct?

Full advance will have to be judged by things such as your pistons, cam grind, lift, etc.

Just do like Tim B. said in the other thread....tune until you heard the bad noises, and back her off a little

just poking Tim
By full advance I mean in the AVCS map you enter the maximum duty cycle that will rotate the sprocket until it hits. You have to look at the trifoil shape of the AVCS sproket to see how it's limited. It's not infinite. USDM advances the intake by 15 cam degrees, some JDMs have the possibility of 20 cam degrees.

Tim B knows better. The valves are incredibly fragile compared to the piston that is slamming into them. One hit, and it's just a matter of time before the valve drops. The valve doesn't break as a result of the hit, it breaks becuase everytime a bent valve tries to re-seat it fatigues the stem.

DPR has never offered my money back. I sent my cams back in October. Dan wants to remake my cams without the advance, will admit no fault to smoking my engine and heads, and I've never heard an thing from him since. I know he's going to have a hard time remaking my cams since I found out he buys them from Crower. He'll have to get them custom made. Maybe I should call him again, but I'm still pretty .

This is the last I'm saying, at least in this thread, about DPR cams. I have heard of three engines that imploded as a result of valve-piston contact due to DPR cams: Mine. One was a Cobb built engine. One was a Godspeed (or whatever they are called now). I'd be interested in hearing from the owners of those engines or anyone else that has had problems with the DPR AVCS cams now or when their engines eventually self destruct.
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Old 03-01-2007, 06:35 PM   #17
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IB all the PR guys come screaming in here, raving about DPR cams
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Old 03-01-2007, 06:39 PM   #18
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Quote:
Originally Posted by bboy View Post
By full advance I mean in the AVCS map you enter the maximum duty cycle that will rotate the sprocket until it hits. You have to look at the trifoil shape of the AVCS sproket to see how it's limited. It's not infinite. USDM advances the intake by 15 cam degrees, some JDMs have the possibility of 20 cam degrees.
I guess what i was saying was that depending on your pistons, cams etc. full advance could be say 12* and not the full 15*.

Because at 12* you could be ok and not hitting pistons, but at 15* you will be. Thus, you would have to adjust your duty cycle in a way that your maximum advance is NOT the maximum the cams will take, but the max your pistons and valves will take
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Old 03-01-2007, 06:48 PM   #19
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KK3766
278 duration, 10.9 mm lift, INTAKE
272 duration, 10.3 mm lift, EXHAUST

I've heard the Cosworth cams are made by Kelford. After seeing them in person, I'm suspicious that this is true. The intake cams are billet like stock STI cams. The look very different. I'll snap a pic to show you.

As you probably know, Duration figures are pretty meaningless unless you know the lift or have comparisons at the same lift as stock (like I gave up top).

Here are the various INTAKE cam "durations" at different lifts:

Lift Cosworth STI stock
0.003 inch 334 degrees 298 degrees
0.004 inch 326 degrees 293 degrees
0.006 inch 309 degrees 284 degrees
0.015 inch 260 degrees 245 degrees
0.020 inch 251 degrees 231 degrees
0.040 inch 234 degrees 209 degrees
0.050 inch 227 degrees 203 degrees

Cosworth seems to have used the valve lash setting "opening" as there start of duration measurement. Intake lash is 0.008. Exhaust lash is 0.010. The intake and exhaust lobe are nearly the same, the small difference in duration (278 vs 272) is probably due to the different lash. That said, the intake cam lobe's initial acceleration and velocity are steeper on the intake side. If you want to get really deep into camology, this fact is important because it is occuring during overlap. Essentially the intake cam is allowing the piston of "suck harder" (sorry) on the intake ports than the exhaust ports. That will help to prevent exhaust "reversion" in theory--in practice, you've got me.
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Old 03-01-2007, 06:50 PM   #20
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Quote:
Originally Posted by modaddict View Post
I guess what i was saying was that depending on your pistons, cams etc. full advance could be say 12* and not the full 15*.

Because at 12* you could be ok and not hitting pistons, but at 15* you will be. Thus, you would have to adjust your duty cycle in a way that your maximum advance is NOT the maximum the cams will take, but the max your pistons and valves will take
Exactly, if DPR, then 11-12 not 15.
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Old 03-01-2007, 06:59 PM   #21
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IB all the PR guys come screaming in here, raving about DPR cams
Let them come. The cams can/do make power. They can also demolish your engine. Both are true.

If you go back to why the WRX cams are advanced, it's because it will improve low-end torque. It's a perfectly reasonable reason to advance the the intake cams, people do this in the NA world all the time. On a turbo car with boost, it make a little less sense.

What is unreasonable, is to use intake cam advance in conjunction with with AVCS--and with certain pistons. It is also quite unreasonable is to not inform the buyer that the cams are completely experimental and have not been tested for basic engine-worthiness or that they are advanced by 5 degrees at an extremely critical valve timing point, namely TDC between 'blow' and 'suck' on the suck, squish, bang, blow strokes.
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Old 03-01-2007, 07:23 PM   #22
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I passed the info on to Ka Mano a couple months ago. He's running WRX heads without AVCS...
Ah, that's right. I forgot he was still using WRX heads on top of his new 2.5 block. Memory, what a wonderful thing to loose.
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Old 03-01-2007, 07:47 PM   #23
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so i was looking at the brian crower sti stage 2 cams...im guessing these cams are non avcs??? anyone know if this is true
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Old 03-01-2007, 10:32 PM   #24
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It seems in my limited research that the EVO guys like the 272's. These are 278/274 I too, would be concerned with idle vacuum/quality.

Someone has to take the plunge!

http://www.cosworth.com/uploads/1143850103.pdf

Here's the cosworth specs page:

Cosworth, Inc. Torrance California. USA
310 534 1390
cosincsales@cosworth.com
PERFORMANCE CAMSHAFT DATA
Manufacturer Subaru
Model WRX STI
Engine Type EJ25 AVCS
Cosworth Part Number KK3766
Checking Height .010"
Intake Exhaust
Valve Clearance .008" .010"
Peak Cam Lift 10.9mm 10.28MM
Rocker Ratio 1 1
Peak Valve Lift 10.71mm 10.03mm
Centerline 107deg. 113deg.
Open 29.5BTDC 70.9BBDC
Close 69.3ABDC 23.4ATDC
Degrees Duration 278 274
Special Notes:
For WRX EJ25 solid tappet With AVCS (North America)
Complete set of 4 cams
Strong mid to high RPM performance
Works well with bigger turbo
Notice: Performance camshafts may require improved valve train for proper operation.
Always check for spring coil bind. Cam followers should be in good condition or replaced
with new parts. Follow proper break-in procedure for maximum cam life.
For off-road racing use only.
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Old 03-02-2007, 05:56 AM   #25
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i would never trust dpr.
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