Re: [FWDLK] 290HP FURY ENGINE AND "DOMED PISTONS'

[Eastern Sierra Adjustment Svc <esierraadj@xxxxxxxxxxx>]

Not to say that I told-you-so, because I didn't, here, but
over on the FWDLK website a similar question arose about
the D500 pistons -vs-Poly pistons, and how/why their compression
ratios were different.

I don't have the Good (Parts-)Book in front of me, now, but
the D500 pistons are physically taller than the Poly pistons
(which even, IIRC, are of negative-deck-height), which produced
their lower compression ratio---despite the larger volume of
the domed Hemi heads--which would tend to decrease an
over-all  c.r. .

The Hemi pistons even feature valve-reliefs in them; the Polys are
not 'notched'.

There are different P/N's for the Dodge Pistons, and, I'll bet different
P/N's for the PLY's, too.

BTW, it has been a common practice (deception) to install Hemi heads
onto a Poly engine block.

The Poly's compression ratio was 8.5:1; the D500's: 9.25:1 (even with its
'domed' combustion chamber, and, with its 'tall' pistons).....

Installing the 'domed' Hemi heads onto the negative-deck-piston-topped
Poly engine probably REDUCES the c.r. to something like 8.0:1 !!!

Neil Vedder




DOLORES ECKERSON wrote:
> Hello Members
>
> After much time and searching I finally can CONCLUDE the 'domed 
> piston' questions involving the 'higher compression' pistons 
> supposedly in the 290Hp engines.
>
> I HAVE A TRUE ORIG FP31 MOPAR PISTON,,,along side a regular 318 9/1 
> compression piston of about 1960 vintage.
> ALL POLY 318s were 9/1 compression except for of course the 290HP 
> engine (supposedly)
>
> I am able to use a common wrist pin to locate both pistons at the same 
> point that they would be on the same connecting rod.
>
> GUESS WHAT--The FURY piston is higher by .010 to .015 (depending on 
> how and where you measure it.)
> SURE DOESNT SOUND LIKE MUCH DOES IT??
>
>
> ANYWAY---A little math based on 9/1 compression for the stock piston 
> and using a .012 average higher FURY piston YIELDS-------------------
> 9.23/1 for the FURY PISTON!!!
>
> So the FURY piston WAS A SPECIAL PISTON,,,yielding approx 9.25/1
>
> ED ECKERSON
> LI  NY
>
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