The other day I was reading an article about an LS1 making over 500hp with just bolt ons... Of course, one of the key elements was a pretty big cam swap. They said with this cam going in, they needed to replace the rocker arms with some adjustable units because of the stock LS1 valvetrain's inability to retain proper geometry with cams that have over .530 lift. What would happen if I swapped in a .551 lift cam? I dont fully understand yet what "retaining proper geometry" means... Dont mean to sound stupid, but I'm still kind of a noob at the LS1 engines. Does this just mean that the valvetrain flexes a little at the higher rpms? I've heard of quite a few cam swaps done with .550 and higher lift cams, and no valvetrain mods except for springs... Never heard of any problems, but that may be just because no one said anything... Any input would be very much appreciated. Thanks.

 

the article was full of BS.

stock rockers are perfectly fine for cams with .600" lift and higher. i'm sure there is some amount of flex, but not enough to warrant new rockers.

some of the highest hp LSx motors are still running stock rockers.

only reason i changed mine out was because i got a KILLER deal on the HS rockers.

 

More proof that they're full of BS.
Since when was a cam change considered "bolt-on?" Must be like "bolt-on" forged pistons.

The valvetrain geometry gets messed up with the weak stock pushrods even at stock lift. Thats a simple fix. Just get some hardened pushrods, good springs, and don't worry about the rockers. I'm running .590 lift on a daily driver.

 

Heads/Supercharger/Nitrous it all bolts on in the end.

 

Yeah, IF you're to do a cam, I mind as well say upgrade the push rods while you're in there. THe stock rockers already have a roller fulcrum. Valve springs too, BTW.

 

Don't jump to conclusions about the bs factor. When they talk about valvetrain geometry, they're refering to the fact that the stock valvetrain is non-adjustable. In other words, the only way to adjust the geometry & lifter preload is by using shims and changing the length of the pushrods. It has nothing to do with the weakness of the stock pushrods or flex in anything. It's about lining the rocker up so that it properly opens/closes the valve as it travels along its normal path of operation while keeping the right amount of preload on the lifters. This is part of the reason why LS1's sound like a sowing machine after a cam swap. You can quiet them down with the right adjustments from what I'm told.

 

Ok a quick tech lesson for those who don't know and need to.

Valve train geometry refers to the angle that the pushrod hits the rocker, the angle of the rocker it self and the way that the tip of the rocker sweeps the valve stem during the full travel of the valve.

Most high lift cams have a smaller base circle diameter (the part of the cam that the lifter rides on when it's closed) than stock because if they just added lift the cam would be too big to install thru the bearings. The base circle being smaller causes the lifter to sit lower in the block and may require longer pushrods to put the upper tip back to the same height where it contacts the rocker.
The roller rocker also needs to work in the proper range of motion. Being a rocker it doesn't just push straight down. It sweeps from out side to inside during travel.The right length pushrod will make the rocker tip, during it's trip down and up, start out side of center then hit the center of the valve stem at mid lift and end inside of center the same amount off center as it started.

Then you throw in milled heads and it gets more complicated. That's why a good engine builder will use an adjustable pushrod to get the goemetry right then measure it and buy pushrods of that length. And to get things perfect a stationary pedestal mount rocker may not work.

 

Thanks guys, this was a lot of help. I'm looking at several different cams for a swap... The most lift I will probably go with will be around .560 or so... How much lift can a camshaft have and still keep the stock base circle? Even if I need to change pushrods, it's not really that big of a deal to do that, since they have to come out anyway. The thing I'd be worried about is getting the right length. The LSx engines use zero lash, correct? If this is the case, I could probably just talk with the cam manufacturer and see what length of pushrod they recommend for a certain camshaft... I installed the LS1 Hot Cam kit in a 2001 chevy truck and used stock pushrods and rockers, but swapped in some LS6 valvesprings... I just snugged up the rocker arms, ran the engine for a bit, and then tightened them down again, and never had a problem one with any of it. Of course, the LS1 Hot Cam is only .525 lift and probably still uses the stock base circle. I guess I should find some literature on the LSx engines and read up on how to figure all this huh... Hehe

 

Thanks guys, this was a lot of help. I'm looking at several different cams for a swap... The most lift I will probably go with will be around .560 or so... How much lift can a camshaft have and still keep the stock base circle? Even if I need to change pushrods, it's not really that big of a deal to do that, since they have to come out anyway. The thing I'd be worried about is getting the right length. The LSx engines use zero lash, correct? If this is the case, I could probably just talk with the cam manufacturer and see what length of pushrod they recommend for a certain camshaft... I installed the LS1 Hot Cam kit in a 2001 chevy truck and used stock pushrods and rockers, but swapped in some LS6 valvesprings... I just snugged up the rocker arms, ran the engine for a bit, and then tightened them down again, and never had a problem one with any of it. Of course, the LS1 Hot Cam is only .525 lift and probably still uses the stock base circle. I guess I should find some literature on the LSx engines and read up on how to figure all this huh... Hehe

 

you tighten the rockers down to 22#s of torque...not sure if that's called zero lash or not