PRW Roller Rockers - RPM Loss
09-15-2013, 12:41 PM
#1
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PRW Roller Rockers - RPM Loss Looking to free up a little friction from my LS1 valve train, I decided recently to upgrade the stock rockers to a full roller rocker. Due to the high cost of the top brands, I decided to gamble with the PQ (PRW) shaft mount rockers http://www.prw-usa.com/2834.
These rockers are not something you can just bolt on out of the box, but need a fair bit of additional attention to cleanup and prepare for the detailed installation. The finish machining of this product is not top quality, so deburing of bolts, thread chasing of rocker stands and cleanup were required before the final oil soak in preparation for the install.
The instructions provided are well detailed, with measurements needed to get the correct stand height and rocker arm alignment with valve stem. After reading them very carefully and completing every step of the install, I ended up with a 7.100" pushrod length requirement. As the rocker arms are adjustable, I set the valve lash at approximately 0.080" as determined by zero lash + 1 3/4 turns. (adjuster threads are 24UNF)
My issue now is that with only this rocker change, I have lost 700 RPM, with the engine now losing power at 6500 RPM, where it seems to start breaking up. (Rev limiter remains set at 7200 RPM) The engine is a 2001 LS1, which I rebuilt with forged pistons, Vindicator cam, rebuilt Patriot 243 heads, etc. Prior to this rocker change the engine has been running flawlessly with 7k+ pulls continuously.
Has anyone run into this issue with these rockers? Is the extra rocker weight over the stem preventing the additional RPM? (valve float?) Am I running too much or little valve lash? (I believe 0.100" is stock requirement) Thoughts?
These rockers are not something you can just bolt on out of the box, but need a fair bit of additional attention to cleanup and prepare for the detailed installation. The finish machining of this product is not top quality, so deburing of bolts, thread chasing of rocker stands and cleanup were required before the final oil soak in preparation for the install.
The instructions provided are well detailed, with measurements needed to get the correct stand height and rocker arm alignment with valve stem. After reading them very carefully and completing every step of the install, I ended up with a 7.100" pushrod length requirement. As the rocker arms are adjustable, I set the valve lash at approximately 0.080" as determined by zero lash + 1 3/4 turns. (adjuster threads are 24UNF)
My issue now is that with only this rocker change, I have lost 700 RPM, with the engine now losing power at 6500 RPM, where it seems to start breaking up. (Rev limiter remains set at 7200 RPM) The engine is a 2001 LS1, which I rebuilt with forged pistons, Vindicator cam, rebuilt Patriot 243 heads, etc. Prior to this rocker change the engine has been running flawlessly with 7k+ pulls continuously.
Has anyone run into this issue with these rockers? Is the extra rocker weight over the stem preventing the additional RPM? (valve float?) Am I running too much or little valve lash? (I believe 0.100" is stock requirement) Thoughts?
Last edited by HP52TA; 09-15-2013 at 12:47 PM.
09-15-2013, 03:00 PM
#3
I would say you made a rather ignorant choice is wanting to put full rollers on an LS when the stock rockers are so good with a trunnion upgrade, then made it worse buying bottom of the barrel parts which are heavy.
IMO you have a bit too much preload and too heavy a rocker and need to start doing research before you buy things like this rather than trying to fix it after you make mistakes.
IMO you have a bit too much preload and too heavy a rocker and need to start doing research before you buy things like this rather than trying to fix it after you make mistakes.
09-15-2013, 03:33 PM
#4
Yea even though they are shaft mount I really don't see the need for those...while the roller tips may have decreased friction the added weight is probably your downfall like others have mentioned...the pushrod length seems super short by Ls standards...maybe start there
09-16-2013, 01:37 PM
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I would say you made a rather ignorant choice is wanting to put full rollers on an LS when the stock rockers are so good with a trunnion upgrade, then made it worse buying bottom of the barrel parts which are heavy.
IMO you have a bit too much preload and too heavy a rocker and need to start doing research before you buy things like this rather than trying to fix it after you make mistakes.
IMO you have a bit too much preload and too heavy a rocker and need to start doing research before you buy things like this rather than trying to fix it after you make mistakes.
If you spin an LS1 over without plugs with stock rockers, then roller rockers, you will be surprised by the load on the engine that the stock rocker arms produce.
In your opinion, what research can be done ahead of time here?
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09-16-2013, 07:04 PM
#8
It is really common knowledge that roller rockers are a lot of trouble and excess weight on a LS engine, hell the need for roller rockers with aftermarket heads bronze guides is usually consider a big downside of aftermarket heads prompting some vendors to offer PM guides for use with stock rockers as upgrades to aftermarket heads.
Just because full roller rockers is considered a standard mod on gen 1 and gen 2 motors that came with stamped ball fulcrum rockers doesn't automatically mean full rollers are a blindly good idea on a motor that already came with roller fulcrum.
09-17-2013, 12:07 AM
#10
96capricemgr is right. It's fairly common knowledge here that the roller rockers aren't necessarily an upgrade.
The weight can be overcome by throwing a lot more spring pressure at the problem. And when I say a lot, I mean so much so that it's simply not worth the wear and tear on other components to try and get the rocker weight under control.
Also, I'll say this: that the roller fulcrum provides less friction and is therefore good for more power or RPM is a horrible internet myth that needs to die.
The weight can be overcome by throwing a lot more spring pressure at the problem. And when I say a lot, I mean so much so that it's simply not worth the wear and tear on other components to try and get the rocker weight under control.
Also, I'll say this: that the roller fulcrum provides less friction and is therefore good for more power or RPM is a horrible internet myth that needs to die.
09-17-2013, 03:54 AM
#11
Sounds like the additional rotary inertia is not being controlled by the springs. Therefore, more spring is required. However, this leads to more pushrod deflection and so stiffer pushrods may be required as well at that RPM.
Unfortunately, it sounds like the rockers are the issue here and you need to return to the lighter stock rockers. Having said that, not sure what your heads or cam is, but stock rockers and bronze guides don't get along well. I have found unacceptable bronze guide wear in as little as 8,000 miles and that was with a rather low lift cam compared to what is available for these motors today.
Unfortunately, it sounds like the rockers are the issue here and you need to return to the lighter stock rockers. Having said that, not sure what your heads or cam is, but stock rockers and bronze guides don't get along well. I have found unacceptable bronze guide wear in as little as 8,000 miles and that was with a rather low lift cam compared to what is available for these motors today.
