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View Full Version : how do you tell the compression of a piston ?

no_sir
07-31-2008, 10:40 PM
id like to get my motor build on its way and the pistons are the only thing holding me up before going to lht to sleeve the block , i just like to know how i can tell what the compression of the pistons that i have are ? i know sounds crazy but i was under the impression they were higher then what they really are in other words i was lied to from the person i bought them from .

thanks in advance

justin
MrLHT
07-31-2008, 11:07 PM
Most low compression pistons will be either a flat top or they will have a slight dish to them. If you post a picture of them I will be able to give you an idea.
no_sir
08-01-2008, 08:18 PM
http://i51.photobucket.com/albums/f366/bonkrokz/festivilleofspeed038.jpg
MrLHT
08-02-2008, 09:43 AM
They look like Wiseco pistons, With that done in 81mm I would say the compression will be around 10 to 1. 84mm they will be 11 to 1 +.
This is just a guess, either way I wouldn't re-use those rings and locks.
no_sir
08-02-2008, 06:23 PM
there stamped je 85mm underneth....
MrLHT
08-03-2008, 01:19 AM
It's hard to tell, with them being 85mm I would say there close to 11 to 1 comp.
no_sir
08-03-2008, 09:21 AM
hmm.. so how do i tell exactly i would like to use them with the jrsc ?
MrLHT
08-03-2008, 02:18 PM
I would contact JE and see if they can give you some exact specs on them. We only use CP Pistons so I can't get you any numbers on those.
no_sir
08-03-2008, 09:27 PM
oh ok ill get with je and find out .. were you driven down 49th st today in a red s2000 ?
no_sir
08-04-2008, 04:08 PM
ok i just called je directly and they confirmed its 11-1 so now the question is can i use these with the jrsc or is it to high ?
MrLHT
08-04-2008, 06:29 PM
I think that was me in the S.

I have built 11to 1 motors with the JRSCs but it's pushing it, It's on the high side of safety. I would really like to see the compression to be around 10 to 1 for blower motors, It's not like a turbo that builds boost later and allows for a little over lap in the higher RPMs. Blowers make boost the second you crack the throttle.
no_sir
08-04-2008, 07:05 PM
ill give you a call tomm .. thanks
MrLHT
08-04-2008, 07:30 PM
Please give us a call at the shop, it will be much faster.

727 344 1800
I_C_Sharp
08-04-2008, 07:40 PM
if your putting a jrsc on get lower compression and run more boost
DAMPACHI
08-04-2008, 11:43 PM
if your putting a jrsc on get lower compression and run more boost

Thats not the way to go...Call us at the shop and we will point you in the right direction.