[AMC-List] PISTONS: cast or forged

["Brien Tourville" <hh7x@xxxxxxxxxxx>]

LIFTED OFF THE STROKERS LIST:



Re: blower/stroker cast or forged?
Posted by: "Harrel" harrel@xxxxxxxxxxxxxx   pontiacgto71270
Sat Jan 6, 2007 2:34 pm (PST)
7 pounds of boost is OK with a good cast pistons IF NO DETONATION
OCCURS! Also be sure to use a good ductile iron top ring.

>From my engine building experience, audible piston slap will begin
to occur in moderate to long stroke engines once the skirt clearance
is in excess of .006". However, not all forged pistons require that
much skirt clearance. If you look at a custom piston, such as a
Venolia, it will have holes drilled in the oil ring groove, just
above the skirt, and will require a good deal of clearance for
expansion. If a piston has long slots cut into the oil ring grooves
above the skirts instead of holes, that piston has 'thermally
isolated' skirts, and clearance is nearly constant as temperature
fluctuates. However, the slots weaken the piston considerably, so
metal reinforcement is added in a cast piston, which does add more
weight. Most OEM replacement forged pistons have slots and no
metal. They have much more resilient skirts than cast pistons and
can stand extreme loads while running tight clearances. My first
455 race motor was bored to 4.21" and had TRW pistons (slotted), and
I spun it to 6000 rpm with .0015" skirt clearance. Of course the
bore has to be perfectly true in those conditions. The block was
honed with fine stones on a CK-10 and had mirror-finish cylinders.

I hope to be assembling my stroker next week and since it did not
need boring, I will not be putting any type of honing device in the
cylinders. I will use a very fine Scotch Brite pad and lightly
scuff only the very top 2 inches of the cylinders. No use having a
rough cylinder where the rings will never travel. The roughness
will only scratch the skirts from high thrust loads when changing
direction!

--- In strokers@xxxxxxxxxxxxxxx, Fred Rupert <canook2u@...> wrote:

 I just wanted to add my $.02.
 I've run Venolia forged in my stroked Ram-50, (w/ 4.11"
stroke), and have NEVER had
 the piston slap everyone talks about.
 I don't know the tolerance, but the pistons look to be a very
tight fit.
 Since I'm running .100" overbore, I added an oversize
radiator/ HD flex fan, and oil
 cooler w/ remote filter, it can take forever to warm up, but
does not slap.
 Also, I only paid about $60.00 for each slug.
 Just thought I'd mention it, since most people who install
blowers typically continue their
 search for more power, which is easily obtained by more
boost. . .

 Fred


> Dino Savva <dinosavva_no1@...> wrote:
 Go for hypereutectic pistons. Speed Pro and Silvolite
supply hypereutectic
 pistons for the 4.0 and they cost about $130 for a set of 6.
Hypereutectics
 will have no problem handling 7psi and since they don't expand as
much as
 forged pistons, you can run a tighter piston to bore clearance and
avoid
 cold start piston slap.

> Dino
>
 From: "Rich Perry" <rikhard@...>
 Reply-To: strokers@xxxxxxxxxxxxxxx
 To: strokers@xxxxxxxxxxxxxxx
 Subject: [strokers] blower/stroker cast or forged?
 Date: Sat, 06 Jan 2007 02:18:41 -0000

> Hello,

 Do I need forged pistons and rods for my 7psi blower / stroker
build?
 Is there some kind of compromise that will avoid piston slap yet
handle
 the blower and longer stroke? I was thinking of Dino's low
compression
 krawler
 but with the add blower. I like the cost of cast, not sure if I
need
 all the strength of forged. What to do?
 __________________




ain't 'Tech' grand ?

  
        =Bt=
  milnersXcoupe
   "The Heretic"


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