Neo Vrs R33 Rb25 Piston And Rod Comparo With Pics.

[Simon-S14]

so much talk lately of neos having this or that... i thought while my neo was apart i'll take pics of it. if anyone wants pics of anything neo spesific youve got a week to let me know before it goes back together.

heres a neo piston vrs a 33 piston and rod combo... the neo is the clean one and the 33 one is the dirty one with the oil soaked fly lol. some very interesting differences!

[GTSBoy]

Good work. Piston differences are about what you'd expect.

BUT! Look at how chunky the rods are. nice.

[Simon-S14]

biggest thing that suprised me is that the crown on the neo piston is hollowed out and on the under side there are two large opposing holes which allow oil to channel thro the crown via rod oil squirter and the main block oil squirter... pretty decent stuff from OEM

[tridentt150v]

pics of the head side by side showing valves would be good, get to visual the valve size and squish area.

[discopotato03]

Yes thats what I was going to say the R34 Neo chambers to compare with the R33 ones .

Too late for me now because I have a ported R33 head on my R33 engine but if I had my time over I would have looked for a Neo head to modify .

Usually manufacturers don't change things like pistons and head details for the same engine without good reasons because its expensive .

From memory in the late 90s emissions and fuel consumption were , and still are , big issues and it would be interesting to know exactly what Nissan gained from the last revision of the RB25DET - over the R33 version .

From memory Nissan claimed 206Kw for the Neo where I think the later R33 ones were 184kw ?

Correct me if I'm wrong but the notable changes were turbine housing/injectors/cams+actuator/intercooler and probably lower load PS pumps etc externally .

The things you can't see are the chambers and pistons and I suspect that Nissan was working hard to keep the performance of these engines acceptable with lean AFRs for light load and cold start . It would have been an opportunity to rejig water cooling jackets around the hot sides of the chambers and possibly exhaust ports as well .

A REAL interesting thing to know is if the tuners here have noticed Neo engines being less detonation prone than the R33 one allowing a bit more ignition advance which pays off in many cases .

Yeah I like those rods too , reminds me of the later intercooled FJ turbo ones but shorter and not as wide across the big ends .

A .

[MrStabby]

From memory in the late 90s emissions and fuel consumption were , and still are , big issues and it would be interesting to know exactly what Nissan gained from the last revision of the RB25DET - over the R33 version .

From memory Nissan claimed 206Kw for the Neo where I think the later R33 ones were 184kw ?

Correct me if I'm wrong but the notable changes were turbine housing/injectors/cams+actuator/intercooler and probably lower load PS pumps etc externally .

I've wondered if they went back to the solid cam setup to allow them to run higher lift/shorter duration (so high ramp rate) cams, as part of emissions management work.

The coilpacks are different and neo specific. Series 1.5/2 gtsts and R34 gtrs didnt get them. I would love to know if the primary winding on a neo coil has a lower resistance, and therefore pulls more amps for a bigger spark.

[GTSBoy]

Disco & Stabby,

The Neo engine gained LEV rating from the changes, so it was all about reducing fuel consumption and improving the breathing, mixing and combustion behaviour. The reduced combustion chamber volume (in the head) coupled with a flatter piston crown reduces the surface area of the combustion chamber for the same volume (and hence compression ratio) so reducing thermal losses to the cooling system - which helps to make it more efficient. But increased combustion chamber temperatures can also lead to more NOx, and make it more detonation prone too, so I'm sure that they spent a lot of time on the squish design.

The rods are basically RB26 rods, hence the extra bulk around the bottom of the webbing.

There's another thread around here somewhere where comparison pics of the combustion chambers are already posted, if you want to dig around. I can't remember where though.

[Simon-S14]

Few other differences I noticed while cleaning my engine. The neo oil pumps are different. Gear profile is different then that of a 33 item. On the crank the oil holes are far more chamfered then a 33 one. Will get pics

[discopotato03]

The other thread was here http://www.skylinesaustralia.com/forums/topic/370688-what-differences-internally-r33r34det-short-blocks/page__p__5908942__hl__r34+rb25+differences__fromsearch__1#entry5908942

Still looking for the chamber pics one .

A .

[Simon-S14]

i can take pics and measurements of the neo chanbers but i dont have a spare 33 head lying around

[KiwiRS4T]

.

The rods are basically RB26 rods, hence the extra bulk around the bottom of the webbing.

^^^ Rods are GTR items - same part number

[JonnoHR31]

i can take pics and measurements of the neo chanbers but i dont have a spare 33 head lying around

i have one sitting outside i can take pics of. just of the chamber?

[discopotato03]

Yes the chambers would be interesting to compare .

Out of interest what does a factory standard R34GTt feel like to drive compared to a standard S2 R33GTS25T ? Also for those that have tuned engine management systems on both versions is the R34 type any more or less detonation prone than the R33 type ?

I'm curious to know so that others can seek any advantages going if they chose to rebuild their RB25 engines . If for example someone had access to both heads and was replacing std pistons anyway does the Neo offer anything worthwhile over the late R33 version .

Cheers A .

[045HOW]

I can buy a set of neo pistons and rods for 300 bucks.

im guessing i can't use the pistons in my 33 block? Would the compression be stuffed?

Or would this work?

Cheers.

[Simon-S14]

You could use them in the block no worries but not with your head I wouldn't think

[GTSBoy]

Neo pistons and rods will go into your block OK, but they won't work with an older head. Yes, compression will go through the floor.

[045HOW]

Neo pistons and rods will go into your block OK, but they won't work with an older head. Yes, compression will go through the floor.

interesting.

this deal is through a major performance workshop and they reckon compression will be fine.

is it those valve spots on the top of the piston that muck around with compression if i were to put them in my 33 engine?

Edited August 15, 2011 by 045HOW

[MrStabby]

interesting.

this deal is through a major performance workshop and they reckon compression will be fine.

is it those valve spots on the top of the piston that muck around with compression if i were to put them in my 33 engine?

Check the second photo that shows the pistons together. The pins are at the same height and you can see 33 crown has more bulk on the top, so will produce higher compression than the neo piston. Think about how much space will be left when the piston is at TDC.

[045HOW]

just awwwwwwsome when a BIG name company lies to you just to make a buck!

[666DAN]

Would be good to see what the 25DE is actually equipped with as well