Re: stroker cranks

[Dan Bubb <jdbubb@ix.netcom.com>]

Well, aside from the fact that the engine wouldn't turn more than 1/2
revolution before a piston would cream the cylinder head...
Cr assuming the piston was moving further up the bore would be 12.8.
Dan

"Fry, Larry" wrote:
> 
> Ah, your computations were assuming a change in pistons or rods as well.
>   So...if the ONLY change to the engine was a stroker crank, then the CR
> would, indeed, skyrocket.  thanks for clearing that up...
> Enjoy the ride.
> 
> Larry  sandiego16V
> 
> -----Original Message-----
> From: Dan Bubb [mailto:jdbubb@ix.netcom.com]
> Sent: Thursday, November 08, 2001 11:27 AM
> To: Fry, Larry; scirocco-l@scirocco.org
> Subject: Re: stroker cranks
> 
> Cr=(D+V)/V
> Where Cr = compression ratio
> D=cylinder SWEPT volume (displacement of one cylinder, e.g 496cc for a
> VW 2.0)
> V=volume of the combustion chamber with the piston at TDC. This includes
> volume in the head, volume of any cutouts in the piston and volume due
> to gasket thickness.
> Rearranging the above equation we get:
> V=D/(Cr-1)
> 
> So, if a 2.0 has a Cr of 10.8 then V=496/(10.8-1)=50.61cc
> 
> If the displacement is increased to 2042cc then D=2042/4=510.5cc
> Then Cr=(510.5+50.61)/50.61=11.09Cr
> 
> As I said this assumes the piston height is unchanged at TDC after
> stroking either by using a shorter rod or raising the pin height in the
> piston and that the piston crown shape does not change.
> Dan
> 
> "Fry, Larry" wrote:
> >
> > Dan-
> >   I haven't done the calculations, but only .3 increase in CR doesn't
> sound
> > right.  Are you sure?
> > How did you calculate?
> >
> > Larry
> >
> > -----Original Message-----
> > From: Dan Bubb [mailto:jdbubb@ix.netcom.com]
> > Sent: Thursday, November 08, 2001 10:11 AM
> > To: Fry, Larry
> > Cc: Jonathan Pack; Randy B
> > Subject: Re: stroker cranks
> >
> > There is no doubt that stroking a VW engine without changing rod length
> > or piston pin height will NOT work. The piston comes within .040" of the
> > head on an 8V engine. Accounting for rod and piston stretch at 6500 RPM
> > will take  this down to about ZERO. Having a minimal piston to head
> > clearance is generally a good idea if your combustion chamber has squish
> > bands (and both 8V and 16V do) or the squish bands will not work to
> > promote turbulence.
> > So, you will have to get shorter rods (standard length is 146 I believe,
> > so length would need to be 144.65) and make sure the bottom of the
> > piston clears the counterweights at BDC, or raise the pin height in the
> > piston by 1.35mm. With no changes in deck clearance or piston crown
> > shape and assuming the CR is 10.8 stock, the CR strictly due to change
> > in displacement will be 11.1.
> > Dan
> >
> > "Fry, Larry" wrote:
> > >
> > > Jonathon's method is the most correct.  Potterman's doesn't factor in
> > number
> > > of cylinders, so you couldn't use it universally.
> > > And, yes, Scott, stroking an other-wise-unchanged engine will most
> > > definately increase the compression ratio, probably to right up there
> with
> > > the diesels IF, IF, IF the pistons don't hit the head.
> > >
> > > Larry  sandiego16V
> > >
> > > -----Original Message-----
> > > From: Jonathan Pack [mailto:pack.39@osu.edu]
> > > Sent: Wednesday, November 07, 2001 9:36 PM
> > > To: Randy B; Scott F. Williams
> > > Cc: scirocco-l@scirocco.org
> > > Subject: Re: stroker cranks
> > >
> > > First, I would be afraid of piston-to-head interference.  The stock
> > pistons
> > > come all the way to the top of the cylinders with 92.8 stroke.  Once
> they
> > go
> > > 1.15mm farther...I don't know.
> > >
> > > Second, this would substantially increase CR.  If you know chamber size
> > and
> > > the volume of the cutouts for the valves on the pistons, you can
> calculate
> > > how much defference it will make.
> > >
> > > Third, the formula for volume of a cylinder is pi*h*r^2.  In engine
> terms,
> > > this means pi*stroke*(bore/2)^2 is displacement of each cylinder in
> mm^3.
> > > Divide that by 1000 to get displacement in cm^3.  Multiply by number of
> > > cylinders and you've got it.  Somebody else posted a formula that
> squared
> > > bore (diameter) instead of (bore/2), which is the radius, and what you
> > > square to find area of a circle.
> > >
> > > Fourth, TDI cranks are pretty spendy.  Kudos to you if you have the
> money
> > to
> > > buy one.
> > >
> > > Jonathan
> > >
> >
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> representation or warranty as to the accuracy or completeness of the
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