Xu10J4Rs Compression Info

[Toddy 7]

Following on from the thread below regarding XU7 Info by Sandy. I am assuming the piston crown volume and chamber volume for XU7 AND XU10J4RS to be the same for the calcs below.

 

 

http://forum.205gtid...me&fromsearch=1

 

 

 

 

 

XU7 XU10J4RS

Piston Crown Total volume (dish & Cutouts) 2.0cc 2.0cc

Gasket Volume (1.4 x 84 or 87mm) 7.8cc 8.3cc

Chamber Volume 37.2cc 37.2cc

Swept Volume 440.25cc 499.5cc

 

 

Compression ratio

 

440.25 +(2+7.8+37.2)/47 = 10.4

 

499.5 + (2+8.3+37.2)/47.5= 11.6

 

Working back as we know that the GTI6 ratio is 10.8 gives

 

499.5 +51/51= 10.8

 

Where is the extra 3.5cc? Do the GTI6 pistons rise flush with the block at tdc or are they roughly 0.6/7mm below the deck of the block giving an extra 3.5cc to the piston crown volume (also GTI6 pistons do not have a dome therefore in reality the piston crown volume would be less in the calcs).

 

 

Reading posts on the forum I was lead to believe that a GTI6 Chamber volume was the same as a XU7 and the pistons rise flush with the block at tdc. I am swaying to the conclusion that the pistons are not flush with the block at tdc.

 

I roughly measured a spare GTI6 head I have, although I am unsure whether it has been skimmed ,it had a chamber volume of 38ish cc so that stacks up.

 

Might be being thick but wouldn't be the first time!

[welshpug 1,622]

the RS pistons come flush but have a concave top, J4R have a pronounced circular dish (much like the XU7) and 10.4-1

 

RS gasket is 1.2mm.

Edited March 18, 2012 by welshpug