BwalterChevrolet

building a 5.3l for my 99 1500 silverado
need some help with picking rocker arms
hydraulic roller lifters comp cam
.515 ,.522 duration 259 265 xr259hr-12 comp cam
timing chain and gear comp cam
need some advice, thanks!

Jeebalow

iTrader: (3)

Stock with comp trunnion bearing upgrade is what I am running with a 215/223 .604/.610 112+5 cam (and most people run them). You can use LS6 springs with the xr259hr cam as well they were used with .551" of lift stock I believe.

(Yep, Just checked. LS6 cam specs are:

204/218 0.551/0.547 117 LSA

Here is the link to the LS6 cam specs and others as well: LS Engine Performance - Exhaust - Super Chevy Magazine Page 5).

Oh and the duration you posted is the duration at the seat. The duration at 0.050" is 206/212 on the xr259hr.

craigsix

im running yella terra 1.8 non adjustable ultralite rockers. they can add op to 20 hp.

sprayed99

iTrader: (16)

That is because you took the bait and were sold. You would be surprised how little you would gain or even lose with those rockers.

There is no replacement for stock rockers with the trunion upgrade until you get into the high dollar shaft mounted systems. The only time you should really change the rocker arm is if the head manufacturer specifies it.

craigsix

i could feel th differece with stock cam. how can 36 lift and a couple degrees duration full oller shaft mounted rockers loose horsepower?

Jeebalow

iTrader: (3)

The 20 hp increase is on a stock motor only. With an aftermarket cam, those increases will likely be less. The reason for that is that stock heads only benefit from more lift up to a certain point. AFAIK it's usually up to ABOUT .550" of lift depending on the heads. So with a cam that already has around .550" of lift with stock 1.7:1 rockers and stock heads; add 1.8:1 rockers. Now the same cam gives.583" of lift. That extra lift did nothing for power because the stock heads do not flow more with more lift past .550". Now add that fact that spring force increases with higher spring displacement and you can see that it will take more force to open the valves the extra .033". This extra force to open the valves takes more power, resulting in an overall loss of power.

And with higher ratio rockers you do not change the duration. The cam has the exact same lobes so the valves open and close at the exact same time. They just open and close more aggressively.

BwalterChevrolet

im not lookin for any upgrade or anything like that. i need a solid recommendation on some good rocker arms that will work well with this cam xr259hr, prefer some rollers to cut down on friction

BwalterChevrolet

What kind of a ratio rocker arm should is use with my cam

Jeebalow

iTrader: (3)

I would run the stock rocker arms. Like I said in post #2,
that is what I'm running. If you're worried you can buy a new set from GM the bearings were redesigned or changed in 2004 IIRC. Or just upgrade the bearings in the ones you have now. That's what I did. The comp upgrade isn't much money and proven to work. Your cam is mild and doesn't need anything other than stock.

spent21

iTrader: (3)

Casting Number 706 and 862
Head: 1999+ 4.8L / 5.3 Liter Truck
Material: Aluminimum
Part Number:
12559862
12561706
Combustion Chamber Volume: 61.15cc
Compression Ratio: 9.5:1
Intake Port Volume: 200cc
Exhaust Port Volume: 70cc
Intake Valve Diameter: 1.89 inches
Exhaust Valve Diameter: 1.55 inches

Stock Head Flow Numbers
Chamber 61.15 cc----0.100--0.200--0.300-- 0.400--0.500---0.550---0.600
Intake 200 cc----------63 ---128----179-----210----218----221-----226
Exhaust 70 cc----------54 -- 93 ----121----145-----163----168----174