compression ratio RB25DET Comp Ration help

[CenterLink]

Gidday. 

As suggested I require some help in working out my comp ration. I have researched the heck out of this subject and have found some really good posts with very VERY detailed information and processes in order to a quote this information. But nothing about how to adjust the ratio. For instance from what I have found the RB25DET S2 Came out with a 9.0:1 Ratio from factory also here are some other specs I have found for a stock RB25DET. 

SIZES ARE IN MM AND ALL FACTORY. 

BORE SIZE             : 86.0MM

STROKE                 : 71.7MM

DECK HEIGHT      : 188.5MM

HEAD CC              : 66.5MM

COMP HEIGHT   : 31.5MM

So here is my information 

RB25DET S2 Block.      Decked 10 thou

Rb25det S2 Head.        Deckedb10 thou 

Bores.                            +20 thou 

Stroke  (Stock)              71.7mm

I am looking for between  8.5:1 to 8.8 - 9.0:1

I am not as smart as some and cannot seem to figure this calculation method out. The instructions and walk throughs I have seem are really detailed but a little TO detailed to the stage where I am lost and it all starts looking like the matrix wall paper screen saver. 

 

So if someone could help me understand and to figure out what pistons I should her what Head gasket and so I will be forever in your debt. 

I had my rb25det with full stock internals up to 444.4 RWHP @ 19.5 @ 19.5PSI Of boost and snapped piston 1-s Ring Landings.

 

Thank You In Advance. 

[KiwiRS4T]

Stock is fine 9 to 1 is fine ...properly assembled and tuned CR will not be the cause of engine failure.

[CenterLink]

Deleted post. 

Edited November 13, 2017 by CenterLink
Addition of information

[CenterLink]

On 11/11/2017 at 8:34 PM, KiwiRS4T said:

Stock is fine 9 to 1 is fine ...properly assembled and tuned CR will not be the cause of engine failure.

I am trying to ascertain the compression ration I have now as compared to the stock 9 to 1.

9 to 1 i if everything is factory. 

I have a 10 thou decked head

10 though decked block so that would raid my compression to 10 to 1 and over. 

But if I use a 1.3mm gasket it will lower my compression. 

I am guessing lower then 8.5:1 andbdeffinatlu lower then 9.0:1 

If I use a 1mm head gasket it to will lower the comoression ratio but to what I do not know. 

My guesses and assumption are basses upong the given information. 

Standard is 9.0:1. 

Deck head 10thou and block 10thou so if everything else is stock it would mean that my compression height is 20thou or 0.5mm shorter and my piston now comes closer to the valves and the head meaning higher compression.

If I try to compensate for the 20 thou differance and use a 0.5mm or 20 thou head gasket it should in theory bring my compression back to stock (9.0:1) If I use a 1mm or 40 thou head gasket it would mean that my compression height is now lower then 9.0:1 as the pistons are now 20 thou lower at TDC which inturen will lower my comp ratio. 

If I use a 1.3mm or 51.118 thou

Meaning my comp height is now 30+ thou taller meaning my comp is now lower. 

So 

With all this information I still cannot work out my assumed comp ratio. 

I'm guessing that with a 1mm (40 thou) MLS Gasket my comp will be lower then 9.0:1 

And a 1.3mm (51thou) would make it lower. 

But I need to know what it would be lower to.

So if anyone here and I am seriously confident there is. 

Has done this

● what type of pistons were used and

● what size head gasket was used. And 

● Comp ratio was achieved. 

 

Thank You. 

[Dose Pipe Sutututu]

if you are after a cheap rebuild, I have stock RB25DET NEO pistons and rods for sale... with the R33 head you will drop you comp to 8.x:1