Rb30/25 Question

[mr30_2.4e]

Ive been thinking and heard alot of good things about puting a r33 RB25DE or T on my RB30ET block and selling my intake and exhaust manifolds 4 rb25 items.

Ive been doing alot of searching and reading about it on here and on the skyline forums.

Is it possible to have the RB25 head shaven to bring compression up to 8.5:1 on my standard rb30et block ?? (I no i could use the NA block but dont really wanna pull motor out as its fairly fresh).

Cheers

[Adriano]

Basically no, without measuring, i would guess you would have to deck the head about 2-3mm.

[mr30_2.4e]

ok anyone else tried this or messured it??

What about the na boys putting rb25 heads on there na rb30 blocks??

How much can u deck the head of a rb25??

[infamous_t]

RB30ET standard compression with DOHC head will give a poor ~7.1:1 CR

Other than the conversion sticky at top of forum, there is a 'summary pdf' which has lots of good info Guide to building an RB30DET.pdf

[Adriano]

If you have to put the head straigt on a stock bottom end, you are far better using an RB30e bottom end, as the c.r. doesnt end up so bad

[nismomiles33]

RB30E I heard is the better option. The block I used was a N/A block that had done around 400,000klms , machined up and did the job perfectly. I'm not sure of compression ratio though, but wasn't too high or low took lots of boost without detonating or troubles we guess-timated around 8.5:1. Plus they are initially cheap to buy.

Edited April 24, 2008 by nismomiles33

[nizmonut]

why raise the compression.....just stick a big turbo on it and go for 10 second qautermiles,

young fella here n nz has done exactley that. twin cam turbo head on his auto vl commie, changed the loom n ecu, fitted and front mount, stucks sum 265's on the rear, wound the boost up to 14 psi and ran a 10.4 on his first run.

my first conversion was a rb30/R33 25de striaght swap, the only new thing i bought was a head gasket and head bolts ...the only work done to it was to face it and weld up the oil gallery to the hydralic lifters. stuck it straight on, bolted on a idleler pulley for the cam belt and reassembled it.

i then drilled and tapped a qauter inch fitting into the intake side of the head back into the gallery that had been welded up, fitted a brass t piece behind the oil pressure sensor and connected the two with a hose. ran 13.2 exactly as described above, no extra go fast bits or engine work done.

the way to do it would be use your et block a na twin cam head and then turbo it.

Edited April 24, 2008 by nizmonut

[infamous_t]

why raise the compression.....

Because the car will drive like a piece of shit with compression that low (30ET + 25/26 head)

Mate I think your best option is to sell your current package and buy a RB30E, or rebuild with correct compression pistons.

[mr30_2.4e]

Thanks everyone for all the responces,

I have kinda Been going through the 300+ page thread for info.

Thanks for the pdf doc f*kin unreal..... exactly what i was after (Legend the person that wrote it)

Ive just got and bought a rb30e block from the wreaks for 100 bucks lol started to strip it down last night but mates came around.....

Im gunna use standard rods but give them a polish maybe send them away for shotpeening??

I also donno wether to do Forged pistions or us NA standard pistons (over size if the bore needs machining)

Ive heared alot of people dont bother about using the piston oil squirters from the rb25 block? R they really that nessecery?

Sounds tricky and im gunna be doing the full build myself in my old mans smash repair shed.

Also will be using standard rb25de head with heavy duty valve springs.

I would like between 300rwkw maybe a little more but i want fast spool for the street. was thinking of using a hypergear TR44

they seem like a decent budget turbo made and balanced in Melbourne Australia.

Edited April 25, 2008 by mr30_2.4e

[SirRacer]

apparently you can use a rb25de neo head (99+ i think) which due to the different amount of cc's in the head will let you run your bottom end