Hot Rod Forum : Hotrodders Bulletin Board - View Single Post - 1968 gto 400 build questions
View Single Post
  #26 (permalink)  
Old 02-28-2013, 08:54 PM
cobalt327's Avatar
cobalt327 cobalt327 is offline
WFO
 
Last wiki edit: Intake manifold
Last journal entry: 1980 Malibu Wagon
Last photo:
Join Date: Mar 2009
Location: Atlanta
Age: 59
Posts: 5,037
Wiki Edits: 1616

Thanks: 128
Thanked 595 Times in 545 Posts
Quote:
Originally Posted by actmobmar View Post
would the additional lift be of any benefit? also, what is an easy way to check how far the pistons are down in the bores(deck height), as i've never checked that, w/ the chevies the machinist always checked. i have dial indicators and calipers, i was thinking a straight edge over the deck w/ a depth caliper over it, get the number, subtract the thickness of the straightedge and that would be my measurement?
I have found that unported D-port Pontiac heads (like your #48's) work well w/around 0.480"-0.500" lift. If the heads were ported you would see more benefit from more lift.

What rockers are on it now? The stock Pontiac rockers will spec slightly less ratio than advertised, but aren't as bad as most stock Chevy rockers. If you have stock rockers you'll pick up a little lift just having an accurate 1.5:1 ratio.

Using higher ratio rockers will require the springs be checked for coil bind, along w/the other clearances mentioned in the previous links like piston to valve clearance, rocker to retainer, retainer to seal/valve guide boss, etc. Good pushrods should be used.

Even w/stock rocker arms/ratio you should use straight wall studs (as opposed to the stock bottleneck studs). ARP p/n 190-4003 or BBC studs will work.

You can use a straightedge like you described. Measure to the piston's 'quench band' (top image) if the piston has a dish or dome. Do not measure to the bottom of the dish/valve relief or the top of the dome, in other words. Take the measurement directly over the wrist pin (red arrows bottom image). Measuring over the wrist pin will keep the piston rocking in the bore from skewing the measurement.



Reply With Quote