well ill start off letting you know what im doing. i have dohc zc that i am putting a golden eagle block guard in tomorro. i have a turbo setup already waiting for this motor. i am going to be getting vitera pistons with fj distributer standar 137mm length i beam rods but i went to google and and found this compression calculator (http://www.zealautowerks.com/dseries.html) that says it would be about 6.55:1 compression ratio. i was wondering if this is first off correct and second if it would still run ok at this low of a ratio? thanks for any help.

 

i would think with that low of a compression you would need alot out of that turbo .. that sounds realy low tho try another calc. and check your numbers . wish i could help more let us know how it goes

 

The reason why it's so low is because the DOHC ZC head has a bigger combustion chamber. Think about it, the PM7/P29 pistons are high compression because of the dome but when they are in a DOHC ZC the compression is about 9.6:1 if I remember correctly. Take that same piston and stick into any other D-Series engine and you jump from 9.0ish:1 up to 11 or so in some combinations. If you feel that the compression calculator is incorrect then do the math on your own and see what you get.

 

Try this one and see if it comes out the same;

http://www.c-speedracing.com/howto/c...c/compcalc.php

I built a DOHC ZC with 8-1 compression and it was a pig to drive on the street. Once the turbo spooled at about 4000 RPM it made good power but you were always down shifting to get the RPMs up to spool the turbo. I rebuilt the motor and went to 10-1 and it was MUCH better to drive on the street.

 

6.55:1 is the correct compression ratio when using the Vitara pistons with the stock DOHC ZC block, head, crankshaft, rods and head gasket

 

yup thats what i keep coming up with for the compression ratio. Sikocivic, what brand of pistons did you use? im still looking for something thatll give me about 9:1. its getting bored out .5 over so the new bore size will be 75.5 now. but i want to find pistons first. thanks!