Rb20 Not Sure Anymore

[D-limo]

(edit)

Head is off. Bores measured at close to 83mm. Bores seem to be in quite good condition.

Please any of the RB guru's I'm looking for any recommendations for the rebuild to suit drift applications with regular street use.. The engine was run with no oil to the extent of the exhaust cam ceasing.

At this stage I'm looking at-

Fresh rebuilt stock de-burred head

Retaining the east bear 1.8mm HG

Power enterprises F1 black metal bottom end bearings

100k service kit

Rear oil seal

Oil restricter/s (what size/type?)

Bolts/studs - which of these need replacing?

Edited July 11, 2007 by Drift_Limo

[Bl4cK32]

seriously why would u want to? I mean the cyliners are 78mm vs the 86mm (or something way off as im not familiar with rb25 specs)

The cylinder size difference, let alone the valve sizing (29 vs 36?) would be enough to make anyone not want to do it. Boost is a measure of resistance to airflow so if u have smaller ports/valves then u need to cram more air in (more boost) to get the same number as u would using a 25 head.

If i were u id be slapping the 25 head on and enjoy a lower boost level for the same power u had before.

Cubes and i had our heads mildly ported before doing the 3lt and i can tell u we dont have to push as much air in as some to make some good power.

[D-limo]

Turns out it's a RB20 bottom end. Measured bores at around 83mm. Suspecting stroker of some variety.

Too be continued..

[R31Nismoid]

83mm.. that isnt much meat left there!

[limpus]

Bores at 83mm? hmmm...seems like you have a rb23 there...interesting...

[D-limo]

Well I'm hoping for 82mm Tomei pistons, which should mean a full RB24 kit..? Will be pulling down the bottom end in the next few days. What is the easiest way to identify RB26 rods and crank?

Was a big surprise, as the auction details from j-spec said the car was fitted with an RB25 engine and transmission!

Edited June 27, 2007 by Drift_Limo

[Roy]

What engine number is stamped on the block? Should be a dead give away! But sounds like you have an RB20 which has been bored. Interesting to see if its running std crank or RB26

[Roy]

Boost is a measure of resistance to airflow so if u have smaller ports/valves then u need to cram more air in (more boost) to get the same number as u would using a 25 head.

But something to remember. Is whilst you say small valves, for the 2L displacement they are not a abd thing. Consider the swept volume of each cylinder, then compare it to the surface area of inlet valve and then exhaust valve. The ratio of valve area to displacement for an RB20 is better then an SR20, and not far off an RB26. When you consider the valve size of an RB25/26 head on an RB30 bottom end then the ratio is worse then it is on an RB20, its about the same as the SR20.

So obviouly more displacement and valve area means more power...but looking at it in isolation as a ratio, the valves in the RB20 arent really small for their application.

[Adriano]

Just measure the stroke without pulling the motor down, measure form the deck to the crown at BDC

[Bl4cK32]

but looking at it in isolation as a ratio, the valves in the RB20 arent really small for their application.

Are the 20 valves undersized for the 25 though...? An extra 25% of displacement would mean a need for larger valves. I dont see any advantage of running a 20t head on a 2.5 or 3lt block, but ppl still think its a good idea?

[Roy]

With you there...but it has an 83mm bore so its an RB20 block, so no real alternative?

Though i would love to throw an RB20 crank and rods into an RB25 block with custom 86mm pistons. That would be a rev crazy 2.4L with a good flowing head

[robots]

Why do u need custom 86mm pistons ?

Also I got an RB20 in car right now. I also got and RB24S seating in the garage. I was thinking about putting a 25DE/DET head on and turboing it.

Hmmm, but it wasn't really rev happy before. Like 6000rpm redline. Don't know if the head and electronic fuel/ignition management would help with higher redline http://www.answers.com/topic/nissan-rb-engine

Thanks! ))

[D-limo]

First post updated. Please can we stay on topic from here on. There are plenty of RB22/23/24 threads open for discussion

Edited June 29, 2007 by Drift_Limo

[D-limo]

Ok will measure stroke tomorrow, also dropping the sump and have a mechanic friend inspecting what bearings will need replacing.

Will Nismo bearings suit my application? RB20 or RB26 bearings?

What bolts should be replaced?

Edited July 2, 2007 by Drift_Limo

[Bl4cK32]

Think ive come across on here somewhere that nismo bearings are rebranded Nissan ones. King bearings ftw.

[D-limo]

And is there any special machining needed on the new head to accommodate the larger piston/bore size?

Edited July 2, 2007 by Drift_Limo

[Cubes]

Throw King bimetals at it.

There's a lot of highpowered rb25/26 and 30's getting around with absolutely no issues.

They are a tad more expensive but worth it.

http://www.kingbearings.com/

As its a stroker of sorts it you may be worth while picking up a set of cheap gtr cams for $50-$100 and have Tighe Cams in QLD regrind them for a hair over $200 a pair.

You get around 8.5mm lift and 252-254 duration. So nice and mild.

[D-limo]

Well the pistons are cast and seem to be of Nissan origin. Only visible markings on them were '08U'

Crown to deck height was around 53.5mm (ruler measurement so not exact on this)

Markings on rods were 20-3 05U41-1

Crank '08U'

Edited July 3, 2007 by Drift_Limo

[abu]

Throw King bimetals at it.

There's a lot of highpowered rb25/26 and 30's getting around with absolutely no issues.

They are a tad more expensive but worth it.

http://www.kingbearings.com/

As its a stroker of sorts it you may be worth while picking up a set of cheap gtr cams for $50-$100 and have Tighe Cams in QLD regrind them for a hair over $200 a pair.

You get around 8.5mm lift and 252-254 duration. So nice and mild.

Hi

I can also confirm that.

KING's make some quallity parts, and your right in saying there is a lot of RB's running them with huge power.

Very popular with the Rb30s, I had them in my forged RB30 bottom end and they were fine! Available at a good price from VPW, Melbourne.

Good luck with the project.

Thanks,

Abu

[Roy]

83mm bores with std pistons??????? Strange, perhaps they are the Toyota pistons that ppl speak of being able to use?!?!?!

An option, maybe havent considered....

If you are going to be retaining the 2530 you run (memory?) then i would grab a std short motor and just rebuild your head in your own time. Maybe play with porting and some cheap cam grinds then when the heads ready throw it on and retune with new head gasket. The std bottom end will put up with the power ad boost you will run with a 2530

Cars that only owe you 2k to get back to the track are far more fun then ones that cost far more to repair and keep you away from the track