How to calculate CR? just got my new rods/pistons :D :D :D
06-01-2006, 12:09 PM
#1
How to calculate CR? just got my new rods/pistons :D :D :D
is it possible to work it out from the rod length, bore and piston height?
its all going into a 2.0l zetec with std throw crank
reason im asking is cos the piston has a flat top, i assumed it would be dished as i wanted a CR of 7.8:1
Rods are Carrillo, pistons Wiseco
Rods:
centre to centre 5.362
P.E bore 0.8132 (little end?)
B.E bore 1.9645 (big end?)
pistons:
comp height 1.181 (from centre of pin to top of piston??)
bore size 3.3660
Stroke:
88.0mm
compressed head gasket thickness is 0.5mm
only thing i dont know is the cc of the combustion chambers in the head
cheers anyone lol
its all going into a 2.0l zetec with std throw crank
reason im asking is cos the piston has a flat top, i assumed it would be dished as i wanted a CR of 7.8:1
Rods are Carrillo, pistons Wiseco
Rods:
centre to centre 5.362
P.E bore 0.8132 (little end?)
B.E bore 1.9645 (big end?)
pistons:
comp height 1.181 (from centre of pin to top of piston??)
bore size 3.3660
Stroke:
88.0mm
compressed head gasket thickness is 0.5mm
only thing i dont know is the cc of the combustion chambers in the head
cheers anyone lol
06-01-2006, 12:35 PM
#2
PassionFord Post Troll
Dan,
If you have the original zetec rod length and comp height i should be able to work back from the original CR and give you a figure.
PE will stand for (wrist) pin end or piston end which is yank speak for little end.
If you have the original zetec rod length and comp height i should be able to work back from the original CR and give you a figure.
PE will stand for (wrist) pin end or piston end which is yank speak for little end.
06-01-2006, 12:41 PM
#3
the pistons are flat top?
I dont see how they can lower the CR then without causing horrible issues with having no squish bands on them
what is the deck height of the piston in the bore?
there isnt enough information above to work out the CR
head volume is an important one for a start, although if you know what hte standard quoted head volume is you could use that to get a guess at approx cr
I dont see how they can lower the CR then without causing horrible issues with having no squish bands on them
what is the deck height of the piston in the bore?
there isnt enough information above to work out the CR
head volume is an important one for a start, although if you know what hte standard quoted head volume is you could use that to get a guess at approx cr
06-01-2006, 12:42 PM
#4
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06-01-2006, 12:48 PM
#9
PassionFord Post Troll
Chip,
Because of its under square bore stroke ratio, i fear that a really low comp zetec (<8:1) will be very hard with out loosing the squish band on the piston or shortening the rod length to enable thicker crowns/deeper dishes on the pistons.
Because of its under square bore stroke ratio, i fear that a really low comp zetec (<8:1) will be very hard with out loosing the squish band on the piston or shortening the rod length to enable thicker crowns/deeper dishes on the pistons.
06-01-2006, 12:51 PM
#12
Originally Posted by fudgeass
Originally Posted by Stu @ M Developments
If you dont know the clearance volume there is little you can do without measuring it.
it says on the spec sheet: suggested clearance 0.0030 if thats it?
that will be the piston to bore clearance needs setting at 3 thou
06-01-2006, 12:53 PM
#14
Dan, are you building this yourself, or are you going to get someone who has at least a vague idea about engines to lend a hand 
Cause if its DIY, i reckon you should start ordering some spare bits
Cause if its DIY, i reckon you should start ordering some spare bits
06-01-2006, 01:23 PM
#17
ah fair enough lol
i also emailed the guy at wiseco, as the pistons were done ages ago but turned out to be for e a n/a zetec, he got these back on xmas eve and date on info sheet with em is from 08/12/05 then shipped from the US so i guess they are the right ones lol
i also emailed the guy at wiseco, as the pistons were done ages ago but turned out to be for e a n/a zetec, he got these back on xmas eve and date on info sheet with em is from 08/12/05 then shipped from the US so i guess they are the right ones lol
06-01-2006, 01:30 PM
#18
Sounds like the shape of them is dicated by the internal geometry of the stnadard engine as Doug mentions above.
I guess to get really decent power from a zetec then you will need to shorten the crank throw slightly in order to allow you to maintain rod length whilst also moving the centre of the piston down so it can be dished with raised sides.
Obviously not the sort of thing you are trying to do, but thats probably the way to go for BIG power.
I guess to get really decent power from a zetec then you will need to shorten the crank throw slightly in order to allow you to maintain rod length whilst also moving the centre of the piston down so it can be dished with raised sides.
Obviously not the sort of thing you are trying to do, but thats probably the way to go for BIG power.
06-01-2006, 05:24 PM
#22
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