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1428Re: The '49-'62 V8... anything out there?

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  • david brode
    Dec 12, 2004
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      I've only seen a few late 500s apart, but they all were pretty decent
      as far as deck to piston. Assuming you have eom pistons and they're
      good shape, and a 40-50 thou gasket is used, a .020" to *maybe .025"
      deck cut will give you a nice tight assembled quench. El-cheapo cast
      replacement pistons are often 20+ thou shorter than oem. I would
      shoot for 040" assembled quench, regardless. Experts use either
      Felpro of Corteco gaskets. The Coretcos are a little better, but
      thicker, btw. .044"-.048" installed, iirc. You may need to stick the
      piston out of the hole a bit wioth those. The 472/500 heads can be
      cut way down. 050" is nothing on those, afaik. The 425 heads' deck
      isn't as thick, and experts say not to cut them much over 040".

      As far as rocker geometry, you can use shorter pushrods. You can also
      have a good stock cam re-ground, and that'll reduce the base circle a
      bit. Maybe enough to make up for the head/block cut. Most of the
      caddy parts vendors offer re-ground cams, btw, but most grinders will
      do one for you if you have a decent stock core. A note on that; most
      grinders want to use profiles with 10+ extra exhaust duration. Afaik,
      it's not needed on a caddy, esp with the 76cc heads. Even the 120cc
      heads' stock exhaust port flows well enough to allow same duration on
      intake and exh. Some experts even say that when ported, the caddy
      heads flow so well on exhaust side that they use a little less
      exhaust duration!

      As far as higher lift cams, you may need to snip a little from the
      top of the guides for clearance there. The '68 up seals are a joke.
      You can use the normal old umbrella valve seals from the '67 429
      caddys. SBchevy springs can be used, but you'll need to get creative
      with shimming. The caddy springs are very tall. The new behive
      springs offered for fords and LS1 chevs work better, with a retainer
      change, as they fit the caddy spring pad, and are taller than std sbc
      springs. If you have a freindly machine shop, they'll probably have
      some larger diameter used retainers from something that'll fit the
      behive springs. Just make sure they fit with the 11/32" valve
      keepers. Unlike the sbc or behive springs, larger o.d. springs will
      require pricey spring seats and more machine work. If you don't have
      a machine shop that you can trust, you might want to buy a spring
      package from one of the vendors. If you use stock rockers, choose a
      cam grind with nice slow ramps, as quick ramps are hard on the stock
      stuff. When cam shopping, make sure to tell them that you want slooow
      ramps. Fast ramps are hard on the stock T pedistals and rockers.

      Brown" <jerome@p...> wrote:
      > Actually I was speculating about just milling the 500 heads to get
      > increased compression ratio. Since the engine would be out of the
      car its no
      > big deal to pull the heads and have a valve job done and to mill
      them for
      > increased compression...So long as you don't booger up the valve
      > ratios. It seems to me that if you mill the heads, say .040, that
      it would
      > drop the head lower with respect to the valve train i.e., closer to
      > center of the camshaft, and might result in any of a number of
      > results.
      > In order to keep everything in the same ratio you would have to
      account for
      > being .040 closer. Seems to me that pushrods that are .040 shorter
      > compensate or taking .040 off the top of the valve stem might as
      long as the
      > keepers would still fit. Doesn't seem right that you wouldn't have
      to do
      > anything but mill to do the job right. Likewise decking the block
      would have
      > the same result of moving the head closer to the center of the cam.
      I guess
      > the right question is can milling or decking be done without
      > catastrophic consequences and if so how should one compensate for
      > changes.
      > Jerry Brown
      > -----Original Message-----
      > From: jvandecreek25 [mailto:jvandecreek@c...]
      > Sent: Sunday, December 12, 2004 1:15 PM
      > To: Cadillac_Performance_Association@yahoogroups.com
      > Subject: [Cadillac_Performance_Association] Re: The '49-'62 V8...
      > anything out there?
      > --- In Cadillac_Performance_Association@yahoogroups.com, "david
      > brode" <dbrode@h...> wrote:
      > >
      > > Jerry,
      > >
      > > The '74-'76 500s have 120+ cc chambers and a very small dish. If
      > the
      > > bores look good, you could just deck the block for a .040" or so
      > > assembled quench, and whack the heads to get to *maybe* 9.5-1.
      > Fyi -
      > > KB makes no dish flat tops for it if it needs bored [which I doubt
      > it
      > > will].
      > >
      > > Another option would be dished KB designed for the early heads.
      > They
      > > give 10-2-1 or so with the '68-'73 heads [76cc]. Another option is
      > to
      > > use 107cc 425 heads on your shortblock. They'll put you a little
      > over
      > > 9.5-1. The 425 heads don't flow as well as yours, but a little
      > work
      > > and they'll do ok. The 76cc heads flow better than yours, btw, but
      > > not much in stock form. More fyi - 2.11"/1.66&1.77" pontiac valves
      > > fit the 107 and 120cc heads perfectly. For larger valves on the
      > 76cc,
      > > aftermarket valves are available from the caddy
      > > parts vendors.
      > > Dave
      > I'm looking for about 9.5:1 CR to help out performance. I know the
      > best way to go is usually different pistons but I'm trying to keep
      > the costs reasonable.
      > Jerry Brown
      > Jerry wanted to keep the costs reasonable, to "deck the block "
      > will require a complete disassembly, and is hardly a way to keep the
      > cost down, and as he stated he did not want to get into piston
      > changes.
      > I made my recommendation based on the premise that he wanted an
      > inexpensive power increase for a engine that was going into a street
      > rod, no it is not the 'ultimate' performance build up, but if it is
      > not being used as a race car, there is no need to pursue a lot of
      > expensive modifications that are unnecessary for strong street
      > performance. Jessie
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