2006 LS2 I would like to use crane cams quick lift rocker arms. can I use the 1.8's or do I have to stay with the 1.7's with stock springs- stock motor??

 

Quinn,
I know very little about LS-x engines but I will offer my honest opinion based on what I do know. A rocker arm swap to higher ratios with no other changes to a stock engine will generaly not make any noticeable improvement. I suspect that in many cases a rocker swap is a lot more attractive to some people when compared to digging deeper into the engine. The swap looks good to someone who wants to do an upgrade but does not want to do a more involved and costly tear down in order to go faster. JMO here. If you have performance modeling software you can approximate the HP gain by altering the cam lift to account for the rocker arm change. The gain is very small.

One of the theoretical downsides of higher ratios with the rest remaining the same is somewhat reduced RPM potential. The valve train limiting speed will be lower but this is probably splitting hairs.

Bottom line - a little extra lift is not going to do much. If you compare that to the gains made from a full cam swap or an exhaust system mod you will find much more bang for the buck there. Add some compression with the above and then you can get some much more significant improvements.

-Mark.

 

seems like no one else want to wade in on this, what you say is very true, but what crane has done is changed the geometry{ I also found this in an eng. builders man} what the builders book said to do was , move the push rod toword the intake side of the engine, as the rod moves up it goes out {ext. side} actually decreaseing lift 1.7 coming off the seat 1.6 in the middle{decreaseing duration}1.7 back on. follow me? now move the rod in and below the center of fulcrum. what happens is that the valve comes off the seat at 1.8, 1.7 in the middle, 1.8 back on. going off and on faster actually increase's duration. computer controlled engines run on seat to seat timing, the old motors they used to "overlap" in hi-hp apps.{crank timing} valve timing, fire the cyl.before the valve completely closed, I've seen the crane "quick-lifts" bolted on a LS2 GTO nothing else done and produce 17HP more. not bad for $700.00. more than a $2-3000.00 set of headers! I was going to put them on anyway I just wondered if anybody was using them, don't new springs, they like low spring pressure when you put the 1.85 SLP's on all you do is put the lift back to 1.7 in the middle and actually make the duration longer which screws the timing upand you need better springs, and a cam to get the timing back, IMHO Quinn