Cubes

Decking the block is fine and has been done since the dawn of time. Its most definitely NOT a big no no. However decking too much... I can't see any problems with it UNLESS the blocks design causes problems with quench, water and or oil galleys. So block dependant I would say. I really don't know for sure, which is why I asked some one in the know to clear it up. With regards to the vg30 pistons. I can't see how you have achieved such a high comp raito with a piston that runs a 9cc dish and sits 0.040" down the bore. The CP's run flush with the top of the block, and no dish yet achieve around the 8.2-8.3:1 ratio.

A quick question to those that may know. Is there a problem with decking the block too much? 0.020" may be fine but is 0.040" too much?

I'm unsure exactly where it origionated, but it is fairly close to the mark. Using my 62cc combustion chamber, 86mm pistons, 85mm stroke, 1mm headgasket, 0 deck clearance, -1cc dish - the calc shows a comp ratio of 8.175:1. Same figures with the 55cc rb30 sohc's combustion chamber and I get 8.988:1. Nissan claim 9:1 so close enough for me. If I then directly enter my specs. 87mm pistons 87mm h/gasket bore 1.397mm head gasket 62.2cc comb. chamber 14cc dome 1mm deck clearance = 9.09:1 -- If I were to dial in the stroke, 1mm headgasket and deck clearance those pistons run in the rb25 (according to wiseco) it returns the comp ratio of 8.2:1 as indicated by the wiseco data sheet. So... I must be running a 9:1 comp IF the engine builded did as he said and pulled 0.020" off the block. Even if he didn't I would still be running an 8.7:1 comp ratio. Interesting.... It still returns damn good economy considering it runs such a large quench gap. 'Maybe' the higher comp negates the larger quench area vs a lower comp nice quench. Andrew, you wouldn't have a 240rwkw dyno sheet laying around? I'm interested to see how the low end torque as you initially jump on the throttle responds. Its difficult to compare with a gt35r slapped on the side of yours. If I am indeed running a 9:1 comp ratio it always leaves the door open to drop a 1mm headgasket in there that will bump comp ratio up to 9.4:1 and run a turbo such as the xr6 item. The higher comp will work well with the free flowing hotside, how well. No idea. I'll have to check the deck clearance when the head is off. I have not pulled the head off for the springs and restrictors yet. No time during the semester.

I recently dropped in a s/h wrecker rb20det box. It does EXACTLY this. Its quiet if the clutch is completely out when reversing, if you are rolling back with the clutch in it makes a nasty arsed noise. Oil level is fine. Apart from the strange reverse noise its the quietest rb20 box i've heard, no input shaft noise, no whine through the gears and shifts perfectly. The diff does have a whine. So your not alone.. Its 100% the same problem.

NIB, Be sure to keep the thread posted with how it affects spool and off boost torque.

What pic? Oh.. you mean this one?

Auto's kick arse for straight line acceleration. There's no ifs or buts. If the manuals quicker, well, the auto's stock and or hasn't been setup to suit its application. Do remember we are not talking about a piddly <200rwkw or even worse a 100rwkw family wagon. This thread is a 250rwkw thread. 250rwkw auto with a little stall convertor WILL own a 250rwkw 5speed manual. Hell chances are even a 220rwkw auto will own the 250rwkw 5speed manual. I have seriously considered an auto, I could imagine how well the rb30 would launch as I can drop it in second bring rev's up to 2500rpm, slip the clutch off the line a little to prevent wheel spin, it accelerates quicker and spools the turbo up harder and earlier than using first gear and making 2 changes. For the cost of a decent rb25 box and clutch I can drop a tweaked auto in the car. Full manual (ecu issue) doesn't bother me BUT fuel consumption does. I like my fuel consumption as my car is a daily driver, its one big influencing factor. Maybe Guy can sway me back to the auto option? The auto's are fine for street cornering. I've always been a slow in fast out, I consider it the safe way to drive briskly in the hills. Start pushing hard in to corners in the hills and its a matter of WHEN you will come unstuck, not a matter of IF. If one was a regular track or hill climb user then obviously... A manual.

How is your motor Ash? Had time to get to the bottom of the breathing issue?

Same as any rebuild. Your best bet is to drop in to your local performance workshop that deals with such motors/cars.

joe2548, Dropping an rb30 in is suprisingly straight forward. The only mods required are engine mounts, dump pipe and power steer bracket. + the vvt if you go the rb25 route. I would have to say the vvt is the most indepth and most fiddly to do. The way I look at it. R32 - R32 RB25DE or RB26. R33 - R33 RB25DE/T or RB26. Unless you struggle to find an R32 rb25de head then I wouldn't bother with the r33 rb25de/t head UNLESS you simply wanted to. R32 RB25DE head in an R33.... You would have to have rocks in your head. RB26 is obviously the best option in all cases. With regards to buying items... It is cheaper to buy a complete rebuild 'kit' rather than buying individual parts. The same goes for rebuilding your head, grab the VRS kit that contains all top end gaskets/seals and valve stem seals for around $280 odd. Try to buy the valve stem seals on their own and you are up for $330. Go figure. The RB30DET thread really is a too large. It contains a LOT of inaccurate information that only confuses one. When it first started out almost nothing was known on the build up so some recommendations are obviously not 'the best' that could be offered. Hell we are even still learning now... i.e CP pistons being an almost perfect choice for the RB30DET. The rb30 guide that has been collated is still updated. It covers what I consider to be the most important to you and even an engine builder that hasn't done such a build before.

JetR-32, Have a read of the guide the answers to your questions are in there.

One more reason to measure everything up with the motor you have on hand. As should be done anyway.

Here's a little quote from the calaisturbo bloke that did a little measuring.

The RB30 does suck a little more IF you are stuck in to it constantly as it comes on boost and starts hauling off idle vs the rb20's 3000rpm+. Drive it around normally with the odd squirt and I average around 11L/100km's. Drive it really nice and it WILL nudge the same as my rb20det was getting. ~10.5L/100km's. All my driving is local short trip 60km/h stuff to uni/shops and back, no peak hour and no open road. The worse I have seen after a shade over 1/4 tank on the dyno and a lot of hard driving that followed was 380km's to a tank ~50l. My fuel economy did go to the crap for a little while there. I replaced the o2 sensor. No difference. Replaced injectors. Problem solved. + had a little tune that picked up a little better fuel economy again. There's still more left in it with regards to economy tuning, as soon as I get my hands on a wideband I will be tuning up to around 3psi with an afr of 14.7:1 vs the current 12:1 once it sees any boost. So I may pick up a little again.

Foolboost is running the motor in a GTS4 so as I remember Sky30 saying the only way it can be done is by lowering the subframe some how. I envy the Attessa + rb30 package. I don't know the particulars. Sky30.... The 1cc dish measurement was by some bloke on calaisturbo.com. I do see it as being feasible as sure they are slightly domed looking BUT they have quite large valve reliefs. + it works out when you do the comp calcs. The CP pistons as stated have NO valve reliefs so they are a true flat top. The RB30e piston with a 53cc sohc head, 1cc dish (due to valve reliefs) and 0.020" deck clearance (1.280" same as CP) is required to achieve its factory 9:1 compression. Thats taking in to account the std headgasket squashing .2 of a mm.. I have no idea if this is correct but its the value that returns a 9:1 comp ratio. IF the std headgasket doesn't squish by .2 of a mm then if you remove the 1cc dish from the piston it drops the comp ratio smack on 9:1. Any one know how much the std headgaskets squash by? Either way.. its very close. If I change the heads cc from 53cc (SOHC) to the DET head of (62.2cc in my case) the std comp ratio 'should' be 7.98:1. A little lower than the expected 8.2-8.3:1. Then if I dial in my piston specs, deck clearance and headgasket it shows myself as running an 8.9:1 comp ratio. wtf. I have NFI.. its too hard. Here's a good little Java calculator if any one wants a fiddle. http://www.csgnetwork.com/compcalc.html A quick run down on the specs for those that are unsure. Bore - 86mm Stroke - 85mm Headgasket Bore - 86mm (same as bore) Compressed headgasket thickness - 1mm (headgasket thickness once torqued up.. what does the std squish?) Piston dome - std RB30e (0cc to -1cc), rb30et (-11cc), CP (0cc), Wiseco rb25 (14cc), Wiseco rb30 (-11.1cc) Deck clearance - std rb30e (possible .5mm), CP (.5mm), Wiseco rb25 with decked block (1mm)

I've updated the origional Post. I received a call early this morning.

The GTR diffs are a clutch type mechanical LSD Diff.. That is what makes it better over the GTST's VLSD. http://en.wikipedia.org/wiki/Limited_slip_differential Good ol' Wiki.

The CP Pistons. Run a 1.280" compression height. I've double checked the wiseco catalog and it states with a comp height of 1.260" you will achieve a deck clearance of 0.040". The 1.260" piston will sit 0.040" down the bore. + the headgasket it will give you a sloppy 2mm (0.040") quench. The CP 1.280" comp height piston will sit 0.020" down the bore. So what does this mean.. The STOCK RB30 N/A piston must run a 1.260" compression height (piston sits 0.040" down the bore) to achieve its 9:1 compression with the sohc head. I swear the rb30 block in the shed 'looks' as if it has zero deck clearance. hrmm maybe not. Does any one have a picture of the top of a CP RB30 flat top piston or know if they run valve reliefs, I would assume so. If so does any one have their spec sheet laying around on the dish cc? Providing the CP has no valve reliefs they will achieve a comp ratio of 7.9:1. Should you deck the block 0.020" for that 0 deck clearance it will raise the comp to around 8.2-8.3:1. Thats using my head cc measurements of 62.2cc's and a gasket thickness of 0.040". Wish I knew this earlier... Looks as if the CP's specs are the better suited pistons that I know of. Nice comp ratio for some good boost + a really nice quench. 8.2-8.3:1 ... As Mr. NIB said.

My calcs show 8.07:1 comp ratio running the 86mm n/a rb30e -1cc dished pistons (due to valve reliefs), 85mm stroke, stock headgsaket, 63cc combustion chamber. According to a bloke on ct.com who measured the n/a and t pistons, the stock n/a pistons are 1cc dished due to the valve reliefs Doing the calcs they do appear to return roughly the expected comp ratio. Maybe mine is running more comp and the measurements were stuffed up. I do doubt it though as Ash's R32 runs the same ignition timing as I and had an almost identical power curve (except for top end where his developed a strange power loss). He runs the n/a pistons, so the 14cc dome pistons I run MUST be damn close to the same sized dome as the rb30e pistons. I have done a comp test BUT the motor was cold, I had the injectors out so I thought I would check for variation. All cylinders were suprisingly exact apart from number 3 that was from memory 1 psi down. I think from memory they came up around 158psi. I made a post when I did the comp ratio, I should dig it up. Either way ~158psi with the cams and head I'm running is what the n/a piston rb30det's achieve. *According to RIPS in NZ (SDU)*

The discussion is piston selection for the rb30det. First thing we need to do is select a suitable compression height which is 1.260". THEN we worry about the dome or negative done to achieve the comp ratio we are after. Without a dome and zero deck clearance you will be running some where around a 7:1 comp ratio. :

That is so tempting to get just a little more life out of my diff. 7yphon, as your in the circle, how would this shim help an almost completely stuffed vlsd diff? As a rough description of its condition it will spin one wheel through first and some times twin up second in a straight line without any nasty clutch dumps/gear slaps. All though clutch dumps/gear slaps do tend to have it twin up more often than throttle roll ons. Hot 35+degree weather after driving on it for a while has the diff locking up almost perfectly.

Mine is connected via the std r32 way.. Directly to the comp cover. I get half of a psi spike. A friend of mine is running the same boost controller on the same motor/turbo setup and has exactly the same tinny little spike. Both setups drop boost. To prevent boost drop in my own and his case the only way around it is either an adjustable actuator OR good ebc. Not a manual ebc where you simply dial in a fixed gain and duty cycle. I consider a good ebc one where you dial in the boost you want and it will learn the duty cycle required at certian rpms in order to achieve the boost level you are after.

Newkeeler, A boost source closest to the turbo is the best way to avoid boost spike. According to Corky Bell's Maximum Boost.

I am not 100% sure what the std rb30 comp height is to achieve a zero deck clearance. The best way to know what comp ratio you will have is to buy your pistons last. Measure everything up then select what pin height etc you require.

Cillham, What tyres/brake pads are you using? How did they hold up?