compression question?
05-22-2006, 08:50 PM
#3
Moderator
Join Date: Dec 1969
Location: Buffalo, New York
Posts: 10,745
Re: compression question?
Originally Posted by jerminator96
If you changed the rod length without changing pistons then yes, it would. But that is not really possible unless the rod lengths are very close to one another.
Rich
05-24-2006, 04:34 PM
#4
Registered User
Join Date: May 2006
Location: Round Rock, TX
Posts: 52
Re: compression question?
Doesn't it matter if the pin bore is moved up on the piston? I would think that the piston for a 6" rod is different than a piston for a 5.7" rod, otherwise they would not list a different part# piston for each rod length. It does change the piston dwell at the top, which is what produces more power. Incidentally, depending on the application, a 5.7 rod is better than a 6" rod for short track use. At least, that is the experience from the local builders.
05-24-2006, 07:00 PM
#5
Banned
Join Date: May 2003
Location: LA (lower Alabama)
Posts: 6,661
Re: compression question?
Originally Posted by String
Doesn't it matter if the pin bore is moved up on the piston? I would think that the piston for a 6" rod is different than a piston for a 5.7" rod, otherwise they would not list a different part# piston for each rod length. It does change the piston dwell at the top, which is what produces more power. Incidentally, depending on the application, a 5.7 rod is better than a 6" rod for short track use. At least, that is the experience from the local builders.
There is NOT a nickle's worth of difference in either. Ya can't see it on the dyno or feel it at the track.
A rod is a good thing to connect the piston to the crank.
There is some advantage when using rod length to influence the intake port,that's a whole 'nuther book.
05-24-2006, 11:03 PM
#6
Registered User
Join Date: Nov 2005
Location: WI
Posts: 268
Re: compression question?
yea use longer rods if you have issues with the piston skirt hitting the crank counterweights, lol. the main thing is the piston still goes up and down your crankshaft's stroke and the rod doesnt affect that.
05-25-2006, 05:47 PM
#8
Banned
Join Date: May 2003
Location: LA (lower Alabama)
Posts: 6,661
Re: compression question?
Originally Posted by JohnnyPappis
Thanks gusy so it really has little affect on compression
If ya use 5.7" ya have to get the crank with smaller weights to clear the pistons.
05-25-2006, 07:01 PM
#9
Moderator
Join Date: Dec 1969
Location: Buffalo, New York
Posts: 10,745
Re: compression question?
Originally Posted by mgray
Would someone please explain to me how three-tenths of an inch makes no change in compression with the same piston? 
The compression height of a piston is resultant of the desired compression ratio, quench or squish, deck height, stroke, and rod length. A piston designed for a 5.7" rod will not work on a 6.0" rod, all else being equal.
Mike
The compression height of a piston is resultant of the desired compression ratio, quench or squish, deck height, stroke, and rod length. A piston designed for a 5.7" rod will not work on a 6.0" rod, all else being equal.
Mike
05-25-2006, 10:17 PM
#10
Moderator
Join Date: Dec 1969
Location: Buffalo, New York
Posts: 10,745
Re: compression question?
Just for purposes of illustration, ignoring mechanical interference.
CR with zero deck, flat tops = 12.5:1
CR with -0.3" deck = 6.77:1 (piston for 6" rod on a 5.7" rod)
CR with +0.3" deck (piston for 6" rod on a 5.7" rod = infinite?)
Rich
CR with zero deck, flat tops = 12.5:1
CR with -0.3" deck = 6.77:1 (piston for 6" rod on a 5.7" rod)
CR with +0.3" deck (piston for 6" rod on a 5.7" rod = infinite?)
Rich
Last edited by rskrause; 05-25-2006 at 10:27 PM.
05-26-2006, 01:54 PM
#11
Registered User
Thread Starter
Join Date: Jan 2006
Posts: 291
Re: compression question?
Originally Posted by mgray
Are you aware that you use a different piston when you change rod length to adjust for the increase or decrease, thus preserving the static compression ratio?
I rember that being brought up.....well anyways thanks alot guys i let him know whats up
05-27-2006, 02:30 PM
#12
Registered User
Join Date: May 2006
Location: Round Rock, TX
Posts: 52
Re: compression question?
There is NOT a nickle's worth of difference in either. Ya can't see it on the dyno or feel it at the track.
A rod is a good thing to connect the piston to the crank.
A rod is a good thing to connect the piston to the crank.
Thread
Thread Starter
Forum
Replies
Last Post
Henson071
Parts For Sale
6
05-04-2015 12:23 PM
Carogna'sZ-28
Suspension, Chassis, and Brakes
0
02-03-2015 07:04 PM