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ModernCamaro.com Founder / Former Camaro Disciple
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Cam upgrades are a bit of a challenge with variable valve timing (VVT) because of the necessities to keep piston-to-valve clearance in check.
Usually this means your options are severely limited.

Here's some info from Comp Cams on their way of addressing this issue:
Comp Cams said:
The 2007 & newer GM L92 engines utilize Variable Valve Timing (VVT) controlled via cam phasers. Cam phasers are computer controlled cam gears that automatically optimize camshaft timing based on the current engine rpm. While this technology provides tremendous efficiency benefits, it presents a challenge when designing performance cams due to the wide range of valve timing movement and constantly changing piston to valve clearance. As a result the COMP Cams® engineers have developed a Cam Phaser Limiter Kit that restricts the range of cam timing movement from 50° to 20°. This modification provides the necessary valve clearance for serious performance camshafts with tighter lobe separations – while still utilizing the benefits of the VVT technology. The resulting upper-rpm gains are some of the largest we’ve ever seen from a camshaft swap without sacrificing any bottom-end or mid-range performance.
Sounds good to me! :thumbsup:

This kit is only about $220 retail too, so it doesn't even add that much expense:
http://www.compperformancegroupstores.com/store/merchant.mvc?Screen=PROD&Store_Code=CC&Product_Code=5456&Category_Code=

This specific information applies to the L92, which is the 403hp truck engine.
But I'm sure they'll have a similar kit soon for the L99.

Here's a PDF file (courtesy of CamaroZ28.com) with some more information, including cam selection.
 

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ModernCamaro.com Founder / Former Camaro Disciple
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Discussion Starter #2
Here's an article from GM High-Tech Performance on installing this cam phaser kit in an L92:

http://www.gmhightechperformance.com/tech/0903gmhtp_l92_comp_cams_vvt_cam_kit_install/index.html

And the engine dyno results after tuning:

218/232 .563/.575 114LSA cam
58hp / 16 lb-ft gain.

222/236 .566/.578 114LSA cam
69hp / 24lb-ft gain!
Dyno Chart:


Note that this was on an engine dyno, so these are all flywheel power numbers.

The bigger cam seems to be at the limits of the stock L92, so nice power gains are seen even from the smaller cam.

Here is a comparison of the two cams:
Only a 13hp / 8lb-ft difference...



And these numbers would only be improved with the addition of a F.A.S.T. intake and/or some ported heads. :)
 

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Is cam advance using real time closed feedback? Meaning, are measurements of manifold air pressure, flow rate, temperature taken and then a decision is made in the ECU to advance the cam? Or, is it open loop and the computer advances the cam X amount vs RPM without computer input.

I would imagine, that cam advance that is built into the L99 does not used closed feedback or else there would be no need for the advance limiter with an aftermarket cam.

It would be neat, if someone could design a closed loop computer that would advance the cam to an optimum position in real time, with an any cam. I would imagine that, if volumetric effeciency is measured in real time that smart cam advance could work out quite well. Unless it already exists?
 

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I'm pretty sure you're right in that it's open loop and sets timing according to RPM.

Closed-loop real time adjustments would be sweet.
I'd bet some aftermarket tuners are working on it. :)
Doh. I wish I knew more about the L99.

Is the cam advance mechanism similar to that on the ford inline 4 (forgot the name of the engine) It's a pretty nifty setup that runs off of oil pressure.

If the L99 cam advance isnt too complex, or if it only involves just a cam gear with a supply of oil pressure, how about we frankenstein the cam advance into the LS3.

Sounds hodgepodge but I bet someone WILL do this and gains will probably be insane. You can go from mild to wild, hell you could even have street and race settings that you could switch from inside the car allowing the user to adjust power output, kinda like a boost controller.

In fact, cams do produce "boost". Thats why VE goes past 100% on big cammed motors. Ahhh, I love this.

:thumbsup:
 

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The Comp Cams kit looks to be a move in the right direction. Eventually technology will allow the VERY best of both worlds.

If I get to he point of changing the cam the "DoD/AFM Delete Kit" looks like the direction I'd go for a "big cam"
 

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Interesting tech, Tim! Love this kind of stuff! If the cam phase limiter reduces cam phasing from 50deg to 20deg, I don't see why the total value couldn't be written out in a custom tune to utilize an even bigger cam!:cool:
 

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Hmmmmm hopefully they have this stuff resolved when it comes time for me to pull the trigger. I would have much preferred the standard LS3 over the L99 for simplicity when the cam change came into play, but did not want another 6M but if they got it sorted out then that would make my decision to get the 6A alot easier to make.
 

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hey guys,

We spent some time with the guys from Comp at the PRI show last December and got a good taste of the VVT system. The VVT is a dream of a setup. The system utilizes oil from the #2 cam journal to feed back towards the front timing cover. The phaser has two vaned areas that receive oil that is controlled by the main camshaft bolt. This bolt has a check valve at one end and when commanded from the actuator can control oil to appropriate cavity. The cam is in a retarded state and the phaser advances it from there. The reason for the "lock out" limiters is that when using a higher lift and longer duration camshaft you obviously getting closer to piston to valve clearances. The PCM can can control the amount if advance but the limiters ensure that even if the motor over revs OR your tuner gets a little nuts with the advance values...........you can't biff the piston.

Working with the phaser is a bit tricky and parts can go flying if you are not careful! LOL! There is also some tricks when dialing in the advance to get the most power from the package. They haven't even scratched the surface of what is to come!

We have a couple in the shop right now that we are testing some neat stuff with.

Howard
 

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The PCM can can control the amount if advance but the limiters ensure that even if the motor over revs OR your tuner gets a little nuts with the advance values...........you can't biff the piston.

Heh I know this quite intimately!!! I'm kind of wondering now that you state this though. I didn't know you could advance a standard cam enough to have PTV clearance issues.

case in point, my 00 Z28. Put in a MS3 on a 112+2 cam kit from texas speed. Dual valve springs etc. I did the research and though that the PTV clearance issues were safe enough without flycutting. I had an over rev incident where my car got downshifted into second (A4 with 4.11 gears) at about 80 MPH pegging the 6800 rev limiter and chirping the back tires. Each of the exhaust valves hit the pistons (unbeknowest to me at the time as it ran fine and didn't make any noises). One valve finally broke shattering the piston and toasting the block and that head.

I always attributed it to the over rev but I did notice when I glanced at the timing specs that they were retarded high. I cannot remember the number but like 36 or more at idle or something like that. You think that could have contributed to my PTV contact as well as I never explored that option?
 

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Heh I know this quite intimately!!! I'm kind of wondering now that you state this though. I didn't know you could advance a standard cam enough to have PTV clearance issues.

case in point, my 00 Z28. Put in a MS3 on a 112+2 cam kit from texas speed. Dual valve springs etc. I did the research and though that the PTV clearance issues were safe enough without flycutting. I had an over rev incident where my car got downshifted into second (A4 with 4.11 gears) at about 80 MPH pegging the 6800 rev limiter and chirping the back tires. Each of the exhaust valves hit the pistons (unbeknowest to me at the time as it ran fine and didn't make any noises). One valve finally broke shattering the piston and toasting the block and that head.

I always attributed it to the over rev but I did notice when I glanced at the timing specs that they were retarded high. I cannot remember the number but like 36 or more at idle or something like that. You think that could have contributed to my PTV contact as well as I never explored that option?
Lets make sure we are talking apples to apples! I am refering to cam degree advancement not ignition timing advancement. Comp was very concerned about one; too much programming control and two; mechanically over revving the engine and causing a "encounter".

Your situation was a mechancial situation where the valve spring lost control and piston speed rapidly increased.

Ignition timing advance was not the issue in your situation. We have seen quite a few guys come in with the same issue. By limiting the cam advance to 20 degrees, Comp has left some margin to avoid this issue.

Howard
 

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Hey, Howard.....glad to see you stepped on board....congrats! :thumbsup:

My question is this: what's the most lift capable with an aftermarket cam with a 20deg cam phase limit setpoint?
 

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VVT is an engine builders dream....to some extent. Advancing camshaft timing will increase low end power and retarding the cam timing will increase top end performance. If you can advance a cam at lower rpms and retard it at higher rpms with the same camshaft you can produce very good power everywhere in the curve. As anyone who has installed a "larger" camshaft in an engine has found; the bigger the cam the more the engine looses low speed power and gains at the top. VVT allows the best of both worlds. Two cams in one!

I am not sure exactly how much lift the engine will tolerate with a full 20 degrees in the calibration. This is a tough question to answer regardless as there are many variables that effect piston to valve clearance. Different ramp rates may hang the valve open longer in the cycle and limit PTV clearances. The camshafts that Comp has marketed is well within the safety range of the mechanics and PCM controls.......as long as the phaser limiter is used. I'm sure many of us have not found the limits as of yet but the L99 using the VVT this limit will be pressed on!

Howard
 
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