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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.

Going to get the current motor through this season to stay in my class and do a swap end of year, going from CA to SR, have already started dissembling the SR for a basic forged rebuild - this is not an all out no expense spared deal but "sensible" with some niceties . Dedicate track (grip) car so not after dyno queen performance. The goal is to have the headroom for 300-320rwkw on e85 and whatever it makes on 98. I realise this will mean a box swap as well. Car is highport/redtop so no VCT. Expecting bore to be 86 or 86.5mm. Plan was to base it off the Spool rebuild kit (CP pistons, not Ross) and add ARP main studs to that kit, plus new gaskets,hoses, fresh oem water/oil pump/timing kit/balancer, basic valve spring/cam upgrade and a mild port/cleanup etc etc. Things I'm unsure of. 8.5 or 9:1 compression? Higher = better spool for larger turbo, but more prone to knock or not an issue on e85 and just run less timing? How big to go with Cams, 256-264 range? Will stick with hydraulic lifters but will buy new ones and add rocker are stoppers, plus I don't bounce it off the limiter. Worth bothering with something like this intake manifold? Mazworks claim no lose of response with theirs, awaiting info on this cheaper version. https://otakugarage.com.au/product/otaku-garage-billet-intake-manifold-forward-facing-plenum-sr20det-s13-s14-s15-180sx-240sx/ Can either add wastegate port to stock manifold and give it a basic tidy up or hunt around for second hand 6boost etc if the cost is worth it. Can also ebay something like this - https://www.ebay.com.au/itm/Twin-Scroll-Turbo-Manifold-T3-SCHEDULE40-FOR-Silvia-240SX-S13-S14-S15-SR20DET/192490055785?hash=item2cd14d2869:g:0j0AAOSwnONZBEhW What turbo? Have looked at GTX3067, but I'm not convinced it will get to 300, it might with better intake manifold, gated, etc? Looked at GTX3071, EFR 6758/7163 (bonus of seemingly being able to make the power on IWG setup and does come in T25 config plus everyone ravs about the transient but very expensive. Kinugawa version GTX seems to be in the middle, new for 1400 or so, but then why not Hypergear etc? I ask here as Silvia forums is dead and asking on the Facebook groups is just painful having to deal with the morons.