RB25 Rebuid plan: please evaluate/ fill in gaps

[accel junky]

Please evaluate my rb25 rebuild plan and help me fill in the gaps as well.

RB25 Buildup Plan:

-Bottom End:Metal Headgasket: what mm thickness?ARP Head Studs: Same as SR Main Studs?Wiseco RB26 Pistons 86.5mm Comp=8.8:1 or CP Pistons 8.5:1 Pauter RB26 Rods: .827” Pin DiaRod Bearings:?Main Bearings: ?

-MaintenanceOEM Waterpump or N1 Waterpump ?Power Enterprise Timing Belt (or Greddy or whoever)Nismo ThermostatARP Exhaust Manifold Stud SetOEM Full Gasket Kit (already have) Fyi: Motor will be handling 400-500whp

Thanks,Daniel

[gawdzilla]

are the large ends of rb26 rods compatible with rb25 crank? if so, you can probably use rb26 main and rod bearings. i went with oem- they took forever, and ended up going nismo. should be here soon.

"ARP Head Studs: Same as SR Main Studs?" - that seems kind of weird, might want to confirm that.

i know the ARP sr20 ROD bolts are the same as rb26 ROD bolts. I bought 2 sets and had them pressed in no problem.

I got a Cometic MLS gasket through raceeng.com. they had them in stock for $152. They also have the rb25 one according to their website "CM-C4318-051 MLS GASKET:RB25-87mm/.051 $152 "

thickness of the cometic HG is about .1mm thicker than stock (1.2 for rb26). I would get either slightly thicker or equivalent to stock thickness so you dont raise your CR.

good luck w/ the build, mine just got out of the machine shop

[accel junky]

are the large ends of rb26 rods compatible with rb25 crank? if so, you can probably use rb26 main and rod bearings. i went with oem- they took forever, and ended up going nismo. should be here soon.

"ARP Head Studs: Same as SR Main Studs?" - that seems kind of weird, might want to confirm that.

i know the ARP sr20 ROD bolts are the same as rb26 ROD bolts. I bought 2 sets and had them pressed in no problem.

I got a Cometic MLS gasket through raceeng.com. they had them in stock for $152. They also have the rb25 one according to their website "CM-C4318-051 MLS GASKET:RB25-87mm/.051 $152 "

thickness of the cometic HG is about .1mm thicker than stock (1.2 for rb26). I would get either slightly thicker or equivalent to stock thickness so you dont raise your CR.

good luck w/ the build, mine just got out of the machine shop

Did you have the engine builder measure clearances for the bearings....or...how did you know which bearings to buy?

[BoostFab]

go 87mm bore and 1.2mm or standard headgasket, since you already have low CR pistons, you don't need it to be lower.

[BoostFab]

i forgot one thing. the rb26 and rb25 pistons are different....you can't use the rb26 pistons on the rb25 w/o the rb26 crank. the rb25 pistons have a 31.5mm compression height and the rb26 is 30mm. this will cause the squish band (or quench) to be too wide.

[accel junky]

go 87mm bore and 1.2mm or standard headgasket, since you already have low CR pistons, you don't need it to be lower.

What will 87mm bore do for me displacement wise? I can get the CP pistons for the RB25 specifically (from phase2) in 86.5mm.

However, while cruising Nengun and Greenline, the RB25 and RB26 pistons are "compatible" and/or have the same part numbers.

I know the stock rods are the same height, so I can use Rb26 rods I guess...?

[gani]

your science is abit incorrect coz i have run a rb25 with rb26 stock pistons with no problems. the only thing is youll just have abit lower compression.

[BoostFab]

i don't doubt it will work, as it has the same bore. 1.5mm decrease in pistion compression height will reduce overall compression ratio, that's a fact.

the rb26 stock pistions is 8.5:1 compression, put it in the rb25 will make it even lower. either way, since you're going with forged pistions, you have an option for different compression ratio.

just my $0.02

good luck with the build up.

[gawdzilla]

Did you have the engine builder measure clearances for the bearings....or...how did you know which bearings to buy?

machinist measured them and told me which bearing clearances to buy. the mains might stay the same (as written on the crank) if your crank only needs a micropolish. rod clearances will change if you change the rods (duh) or even if you change rod bolts.

[eh?]

why use rb26 pistons? i'm sure wiseco has rb25 pistons. You can use rb26 rods as they are the same. Crower makes them, costs ~$1000. My site as a matrix with what bearing you should use. Just mic and cross reference.

[accel junky]

Ok UPDATE:

I've pretty much confirmed that the Rb26 aftermarket rods are for use in the Rb25, but the pistons need to be specifically for the Rb25 because the Rb26 piston height is different. So.........

Bottom End:Carillo or Pauter RB26 RodsWiseco Rb25 86.5mm Pistons (8.8:1)or CP Rb25 86.5mm Pistons (8:5:1)Nissan Bearings (measured by machine shop)

Maintenance:thinnest metal headgasket (1mm?)aftermarket timing beltnismo thermostatoem waterpumpARP head and main studs

I'd like to modify the head as well, but the price is already going to be f*cking massive.

How's it looking?

[eh?]

keep in mind you're looking at least 1.5k in machine work alone. I mic'd my own parts and it cost me ~1k.

[gani]

you forgot to extend the crank drive for the oil pump and buy an upgraded oil pump or else all the money you dump into the block goes bye bye. and yes you can use rb26 pistons they are usually in stock and cheaper you dont have to wait 2 months for them to make you rb25 ones.

[accel junky]

gani, I thought the crank drive and oil pump problem was only for R32 Rb26 motors?

[BoostFab]

Ok UPDATE:

I've pretty much confirmed that the Rb26 aftermarket rods are for use in the Rb25, but the pistons need to be specifically for the Rb25 because the Rb26 piston height is different. So.........

thank you for listening to what i said earlier about the pistons. hmm.

i believe some earliear models of rb33 rb26 cranks also have a short oil pump drive

everything else looking good....when are you expecting this beast to be rolling?

[StricNyne]

i got pistons,rod, and crank from a 26 to throw in my 25, dont i just need to throw in rods and pistons ? sorry to hijack thread btw hahaha

[gani]

no it affects all rb`s except the r33 and r34 rb26. i have a neo rb25 and still have to extended the crank drive

[gani]

in your case you cant use rb25 pistons coz you are using the rb26 crank.

[StricNyne]

could i just use rb26 rods and pistons ?