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Q: Hydraulics ( Answered,   4 Comments )
Subject: Hydraulics
Category: Sports and Recreation > Automotive
Asked by: gimmemorepsi-ga
List Price: $5.00
Posted: 13 Dec 2005 12:55 PST
Expires: 12 Jan 2006 12:55 PST
Question ID: 605408
Will a concaved face on a Piston produce more force than a Piston with a flat face?
Subject: Re: Hydraulics
Answered By: redhoss-ga on 13 Dec 2005 13:16 PST
Absolutely not. The pressure acts on what you might call the projected
area of the piston. The projected area being the area that would
project onto a plane perpendicular to the axis of the piston. I don't
have any links to submit as proof, but I do have years of hydraulics
and engineering experience to draw from. You will just have to trust
me on this one.

Subject: Re: Hydraulics
From: markvmd-ga on 13 Dec 2005 15:42 PST
Redhoss, I am speculating that Gimme is wondering why the added
surface area of a concave (or convex, for that matter) piston head
would not produce more force, or same force with less input.

Darn, now I gotta go read up on hemis...
Subject: Re: Hydraulics
From: myoarin-ga on 13 Dec 2005 17:37 PST
I believe a concave face would actually reduce the effective pressure
by increasing the space in the cylinder chamber, thereby reducing the
Subject: Re: Hydraulics
From: brix24-ga on 13 Dec 2005 19:26 PST

I'm commenting on a quote below that mentions extra power produced;
unfortunately, the issue is confused because the quote mentions only
reduced friction and increased charging efficiency explicitly in
connection with increased power. The relation to a concave piston is
more implicit.

Perhaps your question is related to the effect of using a concave
piston as quoted below? If I read the following correctly, a concave
piston can result in more complete lean combustion; if so, this extra
combustion _might_ (I'm extrapolating here since it doesn't say extra
power specifically) produce extra power compared to a flat piston in
the same circumstances. However, as redhoss-ga stated, once a given
amount of pressure is produced, there is no difference between the two
pistons in the total force exerted in the direction the piston moves.

"Nissan Improves Power, Emissions with Effective 
Intake System and Piston Crown Design [Nishizawa 
et al.]:  Nissan?s RB20DE, a 1.998-liter, in-line six 
engine, powerplant of a sport sedan called 
?SkylineTM,? has been revised to consume less fuel 
and produce more power.  Engineers at Nissan de- 
veloped lean-burn technology for a short-stroke en- 
gine which has been known to be difficult compared 
to application in a long-stroke engine.  Tumble air 
motion was effectively generated by the low-restric- 
tion intake system called the ?Air Jet Swirler? (AJS). 
The uniquely configured, concave piston crown re- 
tained turbulence intensity longer near top dead cen- 
ter (TDC).  Both the AJS and the concave piston crown 
successfully increased the burn rate of lean mixture 
in a short-stroke engine.  In addition, engine friction 
was reduced by 20 percent at all engine speeds ..."

"Engine power output was increased by improving charging 
efficiency.  The peak torque increased to 186 Nm at 
4400 rpm, and the maximum power increased to 114 
kW at 6400 rpm compared to those of the previous 
Subject: Re: Hydraulics
From: markvmd-ga on 13 Dec 2005 19:48 PST
Folks, we gotta remember Ginne was asking about hydraulic pistons.

Brix, Nissan's AJS sounds a bit like Honda's Controlled Vortex
Combustion Chamber (CVCC) of the early 70's. It was so efficient it
allowed the Civic and Accord to avoid the need for a catalytic
converter for about a half-dozen years.

And the Skyline-- ah, what a car! I had a '78 or '79 when I lived in
Japan and a colleague had an '87. It was a doozy of a design, flew
like the wind and was a pleasure to drive. It was my first
introduction to heated leather seats.


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