What? RB25,26,30 all have 86mm bore. Rb20s would be about 78mm or so.

so i've been told......rb20's have smaller bore than rb25, 26, 30.

One important factor to consider when building up a performance motor is to setup the squish properly.. You want around 40thou.

Quote: Originally Posted by 87calais yeah but while 10.5:1 is ok for an N/A engine , its way too high for a turbo application. Special Piston Services in Melbourne (i think) have pistons for RB30/25 head conversions or they will make a custom piston for you. I am using the RB26 head and i just need to supply them with the cc of the combustion chamber and the compression ratio i want to use and they will make a set of forgies for me. Most quotes i got for forgies were around $1800. SPS sell 6cyl piston sets, custom made for $1500. cant beat that for value for money. :mrgreen: how are u mate i thinking about putting a rb26 head on my rb30 block is it match modifactions to fit it i heard it goes on with no probs thanks

non trade price for Forged ARIAS pistons to suite RB26/30 in .020� overbore with 8.5:1. are $1320 with rings.

I will be using the Arias pistons but will be aiming for around 9:1 comp. So machining will required. PS: Arias are $1200 from modyourcar

abit late but quantum racing sell cp forgies for around $1300with gudgens but just remember when your rebuilding you can raise the comp quicker buy skimming the deck

9:1 comp is fine with big boost (1.2+bar) providing the combustion chamber has been polished up nicely and you are running a nice set of cams 260degree+.

Just about to build one using CP's, but u have to buy the rings sepearte, couple hundred is about the going price. These give between 8.3 & 8.5:1 depending how far u deck the block & head. I've also been told by my machineist that CP's are slightly better than Arias.

What deck clearance are you looking at? Having built an engine once I would always set the quench/squish gap to around 40-50thou. Hence have a zero deck clearance and use a 40thou headgasket to give you your 40thou clearance. If you go too large you will loose power, economy and the benifits regarding the 'free' octane boost of a well setup quench/squish.

Quote: Originally Posted by LukeVL My final figure is 8.48:1. Sorry about the confusion. Thats with an Rb25 head (VVT if it makes any difference), nissan gasket and NA psitons. why did u put a vvt head on an rb30 block? i've been told that the vvt wont work so its not worth it, i would go for the non-vvt rb25 head, i've been told it fits straight onto the series 2 rb30 block, which would do gr8 with a blower! also i guess the vvt head might give higher compression than the non-vvt head

Quote: Originally Posted by JuZi why did u put a vvt head on an rb30 block? i've been told that the vvt wont work so its not worth it, i would go for the non-vvt rb25 head, i've been told it fits straight onto the series 2 rb30 block, which would do gr8 with a blower! also i guess the vvt head might give higher compression than the non-vvt head VCT picks up around 10rwkw through the mid range. Its basically giving the cams more overlap at the top end to give the top end performance while minimising the overlap at the bottom and mid range to improve torque. It is most definately worth while for a streeter that is going to see only a mild set of 260 or so duration cams. Tomei/HKS don't make cams that work well with VCT with anything from MEMORY around the 260duration mark. The VCT head also has slightly larger ports, BUT from my measurements it appears the R32 RB25DE Non-VCT head has ever so slightly larger valves. My RB25DE and another friends I have measured up at 35mm for the inlet and 29.5mm for the exhaust. ONE R33 RB25DET I checked out measured up at 34.5mm for the inlet and 29.5mm for the exhaust. Unsure which is better. The larger valve or larger port.

Done some stopwatch testing last night. I done several 3rd gear roll-ons from 2000rpm up to 4500rpm (where VCT switches off). With the VCT plug left connected, i got an average time of 7.6 secs, with the VCT plug off 8.6 secs. So yes VCT is worthwhile. Mind you this is on 5psi, with 15psi the difference should be larger again.

I've seen a stock RB25DET with exhaust, fmic, boost & a microtech (just over 200rwkw) that with the VCT on literally flicks to redline and fry's its 255's through second. Disable the VCT and there is no wheelspin through second. For a mild streeter it is definately worth while. Some original photos have not been recovered yet.

Quote: Originally Posted by R32-Joel What deck clearance are you looking at? Having built an engine once I would always set the quench/squish gap to around 40-50thou. Hence have a zero deck clearance and use a 40thou headgasket to give you your 40thou clearance. If you go too large you will loose power, economy and the benifits regarding the 'free' octane boost of a well setup quench/squish. can you elaborate on the free octane boost theory?

Quote: Originally Posted by duz360 can you elaborate on the free octane boost theory? A good quench improves combustion efficiency. Quote: When properly designed, the quench areas can have a tremendous effect on the quality of combustion, and allow higher compression ratios, and due to this they are considered "artificial octane" by scientific types.

where did you get that from? id like a read of it

hi ya all just a quick question im doing a conversion soon rb25 head on to a rb 30 block now do i have to change the pistons or can i keep the rb 30 pistons and its not a turbo

duz360, google is your friend. vl_86boy, use the N/A pistons, with the dohc head it drops the comp ratio to a nice 8.2-8.3:1.

Quote: Originally Posted by Cubes duz360, google is your friend. vl_86boy, use the N/A pistons, with the dohc head it drops the comp ratio to a nice 8.2-8.3:1. cheers dude