Re: [Amc-list] Compression Ratio: Static, Dynamic

[Wrambler242@xxxxxxxxxxx]

All your really doing is changing the cylinder pressures, not changing the actual compression ratio.
   The cam just gets used to bleed or lower pressure to make it act like a lower compression ratio.
You can't use the cam to raise the pressure above a certain level.
Compression ratio is calculated by the piston travel, bore size etc;

Way back in the 70's or 80's Hotrod built a circle track type tow rig box van with about 12-1 static compression and bled the pressure off with some "high tech" cam etc to supposedly get optimum whos-is and what-is out of the SBC. They succeeded in getting a decnet amount of power and about 14-15mpg IIRC.
  That was many years ago and that's about all I remember about that specific experiment. Whoever was making the cams, Crane?, was trying to create a "new" niche during the fuel crunch of the 70's IIRC. Don't think that idea went far.
I have no idea of what may or may not have been the limiting factors in the idea.
  
  Guys over on the stroker list have been using the cam design to make th elowbuck strokers more driveable by bleeding off some of the pressue for less ping. Since the engine is stroked the cubic inches make up for the drop caused by cam overlap.
   In a perfect world the fuel would have enough octane that the overlap could be cut back, pressures raised and more power would be the result.

   Now, I'll shut up. I've probably posted just enough stuff on this to look like an idiot... :]

--
Mark Price
Morgantown, WV
1969 AMC Rambler, 4.0L, EFI, T-5
2004 Grand Cherokee Laredo, 4.7L, Quadratrac II
" I realize that death is inevitable.
I just don't want to be around when it happens! "

 -------------- Original message ----------------------
From: Greg Taylor <amundaza@xxxxxxxxx>
> Dave,
> You can see the difference the cam timing makes on dynamic compression by 
> inputing your engine specs at http://kb-silvolite.com/calc.php?action=comp ;... 
> shows the static vs. dynamic compression ratios.  This has been helpful in using 
> it to determine the camshaft I'll us in my 304 stroker build, so that I can make 
> an 10.25:1 (now 11:1) motor run like a 12:1 motor on E85.  E85 can run a much 
> milder cam than gas, which allows the dynamic ratio to be brought up higher.
> 
> Sincerely, 
> Greg Taylor :) <>< 
> Rochester Hills, MI
> 1989 Jeep Grand Wagoneer "TRMN8R2"
> 
> And the testimony is this, that God has given us eternal life, and this life is 
> in His Son. He who has the Son has the life; he who does not have the Son of God 
> does not have the life. - 1 John 5:11-12
> 
> 
> --- On Tue, 10/7/08, David Crooks <david.crooks@xxxxxxxxxxxx> wrote:
> 
> From: David Crooks <david.crooks@xxxxxxxxxxxx>
> Subject: [Amc-list] Compression Ratio: Static, Dynamic
> To: amc-list@xxxxxxxxxxxx
> Date: Tuesday, October 7, 2008, 7:43 PM
> 
>  > I'm not arguing that the 4.0 head isn't a good swap,
>  > just that without changing the cylinder volume, you are not
>  > altering the engine's compression ratio.
> 
>  > Compression ratio is a measurement comparing the cylinder
>  > volume with the piston at BDC vs TDC. The only way to change
>  > that is to physically alter the size of the cylinder.
> 
> Static compression ratio is the ratio between total volume at BDC
> and TDC as you say, but Dynamic compression ratio is a bit different,
> and much harder to calculate...  For one thing, you have to take
> valve timing into account.  If the intake valve is still open after
> BDC (which it commonly is) then you need to consider
> where the piston actually is when the valve closes.
> 
> I thought that Dynamic compression also included Volumetric
> Efficiency, making it a comparison between cylinder pressure
> just as the Intake closes, and at TDC.  This would make it a
> really good indicator of power potential.  After all, an engine
> with a higher VE will achieve higher final cylinder pressures,
> for a given compression ratio.
> 
> Unfortunately, I can't find a reference to back up my
> understanding!  and when I think of it some more, it occurs
> to me that the same argument could be made to say a
> turbo motor has a really high compression ratio...  So
> I guess VE doesn't actually enter into the dynamic
> compression ratio calculation, even though it does have
> a big influence on final cylinder pressures.....
> 
> Cheers,   Dave
> _______________________________________________
> Amc-list mailing list
> Amc-list@xxxxxxxxxxxx
> http://splatter.wps.com/cgi-bin/mailman/listinfo/amc-list
> 
> 
> 
>       
> -------------- next part --------------
> An HTML attachment was scrubbed...
> URL: 
> http://splatter.wps.com/pipermail/amc-list/attachments/20081008/45c75ac6/attachm
> ent.htm 
> _______________________________________________
> Amc-list mailing list
> Amc-list@xxxxxxxxxxxx
> http://splatter.wps.com/cgi-bin/mailman/listinfo/amc-list

_______________________________________________
Amc-list mailing list
Amc-list@xxxxxxxxxxxx
http://splatter.wps.com/cgi-bin/mailman/listinfo/amc-list