Well stated ! That was a collage course in two paragraphs.
Rule of thumb was for every 1lb before ignition you get 10lbs after. That
is why ignition timing is more critical when you start adding compression.
Doug
At 02:08 PM 1/21/00 -0600, Ronak, TP (Timothy) wrote:
>Alex,
>To determine compression it depends on whether you talk about static
>compression or Dynamic compression.
>Static Compression
> i.e.: the compression based on the swept volume of the cylinder bore that
>is displaced by the engine as it moves the piston. You simply take the bore
>say 4" an put it into the formula for area of a cylinder lets presume the
>stroke is say 3.48 (Chevy 350 sorry guys) for (4/2)squared X pi X Length of
>the cylinder 3.48" for 43.7485 cubic inches or X 8 = 349.988 ci (small block
>350) . or in Metric 4" = 10.16 cm and 3.48" = 8.8392 cm the formula then
>gives roughly 25.8064cm X 3.14285714285 X 8.8392 = 716.9106 cc.
>
>If we assume zero deck height no valve relief or dome and no gasket the
>ratio would be ((716.9106 swept volume + 54cc Head volume)/54cc) : 1 or
>13.276:1 compression.
>
>To do your computation we would need Bore size, dome and piston valve
>relief, volume and thickness of the compressed head gasket and piston to
>deck height.
>
>That gives you static compression.
>
>Dynamic compression
>What you really want is dynamic compression and get it around 195lbs of
>compression for pump gas. And you can do this with a 10:1 or a 11:1 or a
>12:1 or a 13:1 compression ratio depending on when you choose to close the
>intake valve in relation to the position of the piston in the bore. It
>depends what you plan to use the engine for but I have seen 10.5:1 motors
>perform significantly better than 11.8:1 motors because the produced more
>cranking cylinder pressure.
>
>I hope that helps,
>Tim Ronak
>B382000680
>A Canadian forced to stay indoors while it is cold out.
>
>
> -----Original Message-----
> From: Alex MacLaurin [mailto:Alex_MacLaurin@telus.net]
> Sent: Friday, January 21, 2000 12:11 PM
> To: Ronak, TP (Timothy); 'Bob Palmer'
> Cc: 'Tiger News Group List'
> Subject: Re: Performance Tuning the Tiger
>
> With all this talk about compression,I have a question: if a
>motor has 11:1
> compession with a 54cc chamber and all variables stay the
>same, how much
> compression does the engine have with a 64cc chamber?
>
>
> ----- Original Message -----
> From: Ronak, TP (Timothy) <Timothy.P.Ronak@akzo-nobel.com>
> To: 'Bob Palmer' <rpalmer@ames.ucsd.edu>
> Cc: 'Tiger News Group List' <tigers@autox.team.net>
> Sent: Friday, January 21, 2000 10:14 AM
> Subject: RE: Performance Tuning the Tiger
>
>
> > Bob,
> > 195 ....so I was told ... is about the optimal pressure to
>avoid excessive
> > heat generation on the compression stroke and not use too
>much power to
> > compress the next charge when running pump gas. If you
>were to optimally
> > tune your engine you could probably retard the cam 1
>degree close the
> > intakes a little later drop the cylinder pressure for an
>average of 195
> > (190-200 range between cylinders) and get a little more
>power out and it
> > might even run slightly cooler. IMHO This explains why you
>do not have
> > detonation. But didn't you run the car at 60 degrees
>advance. I hope now
> you
> > are around 36-38 Total at 5000+ RPM. I hope someday I can
>go for a ride.
> > Regards,
> > Tim Ronak
> >
> > -----Original Message-----
> > From: Bob Palmer [mailto:rpalmer@ames.ucsd.edu]
> > Sent: Friday, January 21, 2000 8:57 AM
> > To: Ronak, TP (Timothy); MWood24020@aol.com;
> > TSMIT@isotel.com; rdmallory@earthling.net; Ronak, Timothy
>P;
> > tigers@autox.team.net
> > Subject: RE: Performance Tuning the Tiger
> >
> > Tim,
> >
> > After you guys taught me the proper way to do a
>compression
> > test (plugs
> > pulled, WOT) I get 195-205 psig depending on which
>cylinder
> > and which day.
> > I'm at sea level here, but of course that doesn't affect
> > psig, just psia.
> >
> > Bob
> >
> > At 07:57 AM 1/21/00 -0600, Ronak, TP (Timothy) wrote:
> > >Bob,
> > >I have to agree with you about the effect removing and
> > sharp spots from the
> > >combustion area will have on detonation. The key to
> > avoiding the excessive
> > >pressures is by changing where the Intake valve closes in
> > relation to the
> > >piston traveling up on the compression stroke. What is
>your
> > cylinder
> > >pressure warm with all of the plugs out ... or have you
> > tested it? The
> > >method I will use on y 302 will be to chose the desired
>cam
> > profile and then
> > >increase compression (or advance the cam) until I obtain
> > about 195 lbs
> > >cylinder pressure cranking. My experience is similar to
> > yours in that
> > >compression is fine provided that the combination once
> > assembled gives you a
> > >usable cylinder pressure. It may be that the guy who has
>to
> > run race gas
> > >needs to install a cam with a little more overlap or one
> > that closes the
> > >intake valve a little later reducing the amount of
>cylinder
> > pressure the
> > >piston can build. I do know that back in the race car
>days
> > we had an engine
> > >that was 14:1 (remember that car Theo .. it was blue and
> > yellow) it made
> > >over 220 cranking cylinder pressure and we had to run
>C-14
> > and methanol in a
> > >15% and 85% ratio respectively or it detonated like
>crazy.
> > >My 2 cents too,
> > >Tim Ronak
> > >B382000680
> > >PS: It is amazing how a well placed email gets us back on
> > the performance
> > >topic....YEEHaaaww!
> >
> > Robert L. Palmer
> > UCSD, Dept. of AMES
> > 619-822-1037 (o)
> > 760-599-9927 (h)
> > rpalmer@ucsd.edu
> > rpalmer@cts.com
> >
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