Smitty's '04 GTO

iTrader: (5)

I'm considering a heads/cam swap for the GTO come springtime. I've been taking a long hard look at the Thunder Racing CheaTR camshaft (specs are 214/230 .601/.578 on a 117 LSA) to go along with a set of Stage 2 ported factory casting heads. I understand that dual valvesprings are recommended with this camshaft. My guess is that the .601 lift on a 214* duration @.050 intake lobe is an aggressive enough lobe to require this?

My question is, can I run Comp 918's with Ti Retainers if I'm planning to use the light-weight, hollow stem Z06 valves (approx. 25% lighter than stock), and I don't plan to spin the engine above say 6600rpm (factory LS6 spec)? I already have the valves in-hand.

My thinking here is in going with a lightweight valvetrain, light valves and the lighter single beehive design of the 918's. It doesn't make sense to me to go with lightweight valves, then saddle them with big heavy stiff dual springs. Also, how much valve spring open pressure can the factory lifters handle before failing? Here are some specs comparing three valve springs I'm considering:

Comp 918's Seat:130lbs Open:318lbs Spring Rate:313lbs
Patriot Golds Seat:135lbs Open:385lbs Rate: ??
Comp 921's Seat:135lbs Open:400lbs Rate:408lbs

I should mention that the car is not a daily driver; but a weekend, fair weather, garage queen. It sees about 3-4K miles a summer. It'll make it to the dragstrip about 6 times a season, and to the roadcourse trackday maybe 2-3 times.

Any and all advice/opinions would be appreciated...

Good Day!

PREDATOR-Z

Yes you can, but I would shim the springs to .050 coilbind.

Smitty's '04 GTO

iTrader: (5)

That's funny, I just spent some time in the "shim to .050 coilbind" thread. Yes, I was planning to discuss this with the machine shop when the heads get prepped. PREDATOR, thanks for the comeback, yours is one of the opinions I've come to value on this board...

PREDATOR-Z

This is why the sodium valves are one of the best in conjuction with titanium retainers and 918's for the lighter effective moving valvetrain mass, which in turn is best in controling unwanted harmonics and surge.

mikeith

if your planning on turning those high rpms.... upgrading the rod bolts is a MUST i have heard... better to be safe than sorry

mullenh

iTrader: (1)

same here

Smitty's '04 GTO

iTrader: (5)

Actually, I hadn't planned to change rod bolts. I wouldn't consider 6600 to be high rpm's, afterall, those are factory LS6 specs and the '04 version of the LS1 has the same block / bottom end as the LS6. Some time back, I read an article where Kenny Dutweiler (speed shop out of Southern Cal) says that the Stock LS1 bottom end is good to 6800, and above that, yes it is the rod bolts that are susceptible. The CheaTR is said to peak around 6200, and I may go with an adjustable timing chain to advance timing a degree or two to move power band lower yet. Regardless, I thought I was being safe with a limiter set at 6600.

You're right, it's always better to be safe than sorry! Not sure how far I want to go with that though...

...appreciate your input just the same!

Smitty's '04 GTO

iTrader: (5)

Anybody else care to chime in with opinions on this set-up. Anybody else out there runnin' the CheaTR with 918's? Care to share your results?

Thanx in advance...

Ragtop 99

iTrader: (7)

I'd call Geoff at TR and ask for his opinion. They have a fair amount of experience with that cam.

PREDATOR-Z

Geof will tell you 921's
But with the lighter valves and titanium retainers, i wouldn't think twice to run 918's.