Been looking at Cranes fast lift rocker arms. Debating on which one to get, the 1.7 or 1.8 or not at all.
Here's what I have. 04 GTO 6-spd. Stock bottom end Ls-1, Dart 225 heads with some minor port work, Comp cam 228/228 .588/.588 114, 918 springs, fast 90/90, SLP long tubes, high flo cats and power flo cat back, RPS clutch, RPM stage V trans, diff tech one piece drive shaft and stub to hub axles, 3:73 gears.
Combo makes 427/389 on motor and has a 100 shot on top.

What is any will I get out of these rockers. With the 1.8's I figure the lift changes to .622. Is my math ok and is the clearance ok on stock pistons with .622.

Thanks for your help!

 

1.8's man. those heads will like the added valve lift, along with giving your cam a little more valve duration and quicker acceleration. just follow adjustment procedure to the dot, or you will have problems.

 

Couple of questions. Are you running the original valve springs that came with the Dart heads? If so, you will be within 0.030" of coil bind and should stick with the 1.7 rockers. When were your heads produced? The early heads had the original rocker boss machining, which was later modified by Dart. Mine are very early Dart heads and I modified them myself. I don't think you will lose much staying with the 1.7's.

Here are my Dart 205's with Crane 1.7 rockers:

 

I bought the heads new about 6 months ago. I swapped my comp 918 springs from the stock heads. Thinking of going with a set of dual springs if I go with the 1.8's.

 

go with crane #144832-16 or #144833-16 springs. make sure the inner spring of the dual springs u use clears and fits around the dart valve seals though.

 

Actually, the Dart's use a one piece seal/seat so he will need new ones. The PAC 1518's will do the lift you need. As for the springs, if you swapped the Dart springs for the Comp 918's, you actually installed an inferior spring. The Dart springs are PSI 1511's and are a nitrided spring that is superior to the Comp.

If you go with the Cranes, I suggest the 833's over the 832's, much better valve control to higher RPM and the first harmonic is quite high as well. If you decide to stay with a beehive design, the PAC 1518's are the right spring but you must measure the installed height to ensure you have enough travel. The Dart's come installed at about 1.765" from Dart if you leave the shims in place.

 

with that cam profile, harmonics should never be an issue.