An update to our post about mini-tubbing an LS1 Camaro SS, the finished product is finally here!  In the mini-tubbing process, Wizard Racing in Holden, LA shortened the axles and housing on the the Moser 12-bolt rear end, added Wolfe Racecraft spring relocation perches, AFCO springs, custom relocated lower control arms, and a shortened panhard bar.  With the additional clearance, the rear end is now stuffed with massive 17″ x 13″ Fikse FM5 wheels sporting Toyo Proxes TQ P345 40R 17 Drag Radials! The Camaro also sports a Thunder Racing built 410 CID Iron block with custom Diamond pistons, Callies Compstar crank and rods, ETP LS7 cylinder heads, GM LS7 intake manifold, a custom Thunder Racing camshaft, 1-7/8 to 2″ stepped Kooks Headers, and a Meziere electric water pump. As if that weren’t enough to get the convertible moving, a TNT Nitrous 250 dry-shot system tops it all off!

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This past week we had a 2006 GTO in the shop for a dyno tune. After looking at the graphs of the initial pulls, we noticed what appeared to be valvetrain instability beginning around 5500-5600 RPM.

The customer had purchased heads, cam, and valvetrain setup from another vendor. Here’s a breakdown:

2006 GTO w/ 6.0L LS2 Engine
Trick Flow 220 cc Heads (as cast, no additional porting)
Camshaft specs: 23x/23x .61x”/.61x”
Kooks 1-7/8″ Long tube headers
K&N Cold-air induction
Magnaflow catback
Stock LS2 throttle body & intake manifold
Yella Terra Ultra-lite 1.7 Rockers

In order to resolve the valve float issue, we first verified that the Yella Terra’s were properly installed with the correct lifter preload and valvetrain geometry. Next, we swapped the Yella Terra rocker arms for a set of stock rocker arms, along with Manton 7.625” pushrods and the proper rocker arm shims. The swap was completed with the car still strapped down on the dyno, and no other changes were made to the car. The graph shows the results: a much smoother curve with increased horsepower and torque across the band, not just in areas where valve float was apparent.

Why do the stock rocker arms work better in this case?

Using aftermarket roller-tipped rocker arms in LSx applications causes the effective mass over the tip of the valve and entire rocker body to increase. Also, depending on the design of the rocker itself, acceleration and deceleration rates of the valve can be increased.

These factors, coupled with a tall, less secure design of the LSx pedestal mount, contribute to valvetrain instability. This instability causes a variety of problems, including what is seen on the graph in the area marked as “valve float.” During valve float, the valves are bouncing on the seats and not closing properly, therefore bleeding off cylinder pressure and causing a loss of power.

Changing back to the stock rocker arms corrects the valve float issue. The rocker arm shim kit that we installed establishes the proper valvetrain geometry necessary for the stock rocker arms to work with the 13.5 degree valve angle on the Trick Flow heads. The longer 7.625″ Manton pushrods are the proper length to work with stock GM type hydraulic lifters in most applications.

Does this mean that it is always bad to use aftermarket rocker arms?
No; however, it takes a broad knowledge of valvetrain geometry and measurements to ensure that you don’t run into problems such as this. Not only does valve float rob horsepower, it can be hard on your valvetrain and cause premature wear and tear, if not outright breakage.

On Monday we emailed jokes.
On Tuesday we did not.

On Monday we thought that we were secure.
On Tuesday we learned better.

On Monday we were talking about heroes as being athletes.
On Tuesday we relearned who our heroes are.

On Monday we were irritated that our rebate checks had not arrived.
On Tuesday we gave money away to people we had never met.

On Monday there were people fighting against praying in schools.
On Tuesday you would have been hard pressed to find a school where someone was not praying.

On Monday people argued with their kids about picking up their room.
On Tuesday the same people could not get home fast enough to hug their kids.

On Monday people were upset that they had to wait 6 minutes in a fast food drive through line.
On Tuesday people didn’t care about waiting up to 6 hours to give blood for the dying.

On Monday we waved our flags signifying our cultural diversity.
On Tuesday we waved only the American flag.

On Monday there were people trying to separate each other by race, sex, color and creed.
On Tuesday they were all holding hands.

On Monday we were men or women, black or white, old or young, rich or poor, gay or straight, Christian or non-Christian.
On Tuesday we were Americans.

On Monday politicians argued about budget surpluses.
On Tuesday grief stricken they sang ‘God Bless America’.

On Monday the President was going to Florida to read to children.
On Tuesday he returned to Washington to protect our children.

On Monday we had families.
On Tuesday we had orphans.

On Monday people went to work as usual,
On Tuesday they died.

On Monday people were fighting the 10 commandments on government property.
On Tuesday the same people all said ‘God help us all’ while thinking ‘Thou shall not kill’.

It is sadly ironic how it takes horrific events to place things into perspective, but it has. The lessons learned this week, the things we have taken for granted, the things that have been forgotten or overlooked, hopefully will never be forgotten again.

-Author Unknown

This 2002 B4C (Police Package) Camaro recently received an engine and transmission transplant, replacing the stock motor with a freshened-up version, complete with Thunder Racing’s TRak cam and a full complement of bolt-ons.  The 4L60E automatic transmission was also swapped out to a T56 Manual transmission.   Thunder Racing’s Shane Burgess built the custom exhaust, affectionately nicknamed “The Boom Tube,” with a 4″ bullet muffler and turn-down.

And here are the results: