Dirty 25 Ideas Based On Oe Block Rods And Headz .

[discopotato03]

Ok this is a spin off from the low mount manifold thread and loosely based around what Mick O did with his GTt .

People continue to get off on R33 and R34 GTS25Ts/GTts and more fun can be had with a few not too expensive mods along the way .

I'll set the bar at a std block and rods because that weeds out RB30s and RB28s - not necessarily 26 cranks because they use the same rods as GTts .

Also a 25 head because that's what you get standard . Also not limited to a factory spec 25 as in can mix any 32 33 34 long engine bits .

That said most people reckon the R34 Neo spec engine is the best out of the box and made the highest factory power level of ~ 206 crank wasps .

Mick got impressive power from his Neo and from memory the engine was never opened up as in factory fitted head and sump . I think it still had std cams as well . In fact engine mods may have only been injectors and the turbocharger itself . Since That engine got 330 plus wheel wasps I'd like this thread to base specs around a factory RB25 exhaust manifold , a factory inlet manifold , and IW turbochargers to make bolt ons straightforward . To make it easy for those with no fabrication skills I'd like to limit welding to a suction/inlet pipe , naturally the dump pipe and a compressor outlet elbow .

Cams pistons injectors turbos fuel take your pick and lets see what you can come up with for a good all round street engine that's still nice to use for daily duties like carting mum in law around ...

I'll put my ideas up for an unopened 33 spec engine and a rebuilt one if it wore out .

Unopened :

If you're going for 260-300 wheel wasps I reckon a GTS25T engine can use mild cam such as Tomeis a keep a quite reasonable idle .

I think one of the modest bolt un GT30IW turbos are good upgrades so something like GTX3067R GT/X3071R GT3076R should work well .

Injectors you are going to need and there is a choice direct fit or top feeds with collars and a different rail , aftermarket or modded GTt .

Budget opened .

A basic freshen up to get good bearings and ring and valve sealing . Maybe direct fit pistons though O/S OE ones should be ok .

Would deck the head and or block to raise the static CR to 9.3 . Wire rings to better seal OE headgasket .

Delux opened .

Obviously more money here with a view to having a Neo built in an R33 block . If the parts could be found cheaply a 26 crank is going to get a few more ccs and use 26/Neo rods - optional . Regardless if intended for E70/85 I'd aim for higher compression pistons because the part throttle lower rev power would be be better . Neo inlet gets you drop in EV14 injectors and the head gets you solid buckets to take better cam profiles such as Tomei type As .

Would anyone like to predict how Mick Os car would have gone with a little more capacity , say 9.6 CR and Type A Poncams ?

If the budget stretched you could swap the GTX3071R for a GT3076HTA and have a pretty impressive RB25DET that looked pretty standard and kept the original block number .

Floors open .

[Piggaz]

Just to clarify, Micks was NOT a NEO, but a normal RB 25 (R33).

As you were .

[iruvyouskyrine]

My budget build was as follows

Engine mods:

RB25DET Neo with 150xxx KM, completely unopened (std EVERYTHING), 1000cc X-Spurt injectors, Hypergear ATR43SS2 internal wastegate.

Supporting mods:
Walbro 400 lp/h fuel pump, R32 GTR standard intercooler, 3" bellmouth dump to leaky 3" exhaust, NIStune ECU, Profec B spec 2, Tuned by Trent from chequered tuning, fuel was pump 98 octane.

literally all that was done to the engine was injectors and turbo, and appropriate supporting mods. It's an awesome example of what can be done if you correctly choose your modifications and don't just have a fistfull of cash you are looking to spend.

Edited May 11, 2014 by iruvyouskyrine

[scotty nm35]

Great result there Josh on a budget build. If it weren't for the dip as the gate opens you would have hit the magical 200kw by 4k.

I bet it feels great on the road...

When is the ethanol tune?

[iruvyouskyrine]

It did feel amazing, was super stoked with it. But when i had to remove the turbo to replace exhaust manifold studs (for unrelated reasons) i forgot to hook the wastegate actuator up. Drove it for a few days without giving it much then when i did hit it, i saw the boost gauge read past 2.5 BAR, lifted the head, bent #6 rod, scored the block, game over! Was my own mistake no blaming anyone so i just have to learn from it haha. New build is completely standard RB30 wrecker bottom end and slap the NEO head on and see how we go. Same turbo just external gate and E85 now, should be good

Sorry for the off topic-ness Disco.

All in all, it was amazing to drive and looked completely standard, as i kept standard neo top feed fuel rail. I would gladly recommend it to anyone as a cheap way to get very good results.

[skylinecouple]

If least spent and best results are what really matters here then I am happy with my little 3071R .82 IW. 550cc Nizmo injectors, 3.5" dump, Tomei 256deg cams. This is a really great street car with a lot of work on tuning to get smooth responsive power. Fuel economy should also be a player in this thread as there is already a thread on results but not driving experience or fuel economy. This car is, and always was what I believe Nissan should have done.

Economy at 480-500k for a trip and 400-430k's for town. Love it. Having said that there is a second engine in the build. Have sold the 25/30 and going to rebuild the original engine. Rb26 crank, rods, cams & GTX.

[discopotato03]

Thanks guys , the idea of mostly factory RB25 parts was to show what can be done with usually readily available and affordable parts . The welded bits are really just to do with plumbing a bolt on style turbo .

Sorry my bad about Micks engine , don't know why I though it was a Neo though it gives me a bit more faith in my 33 engine .

And yes fuel consumption is part of the fun since it's an ongoing cost that's always going to increase . I'm trying to get ~ 10/100 with mine atm but I really need those EV14 injectors , very next mod hopefully with doctored Neo rail . Will report when its done . Gut feeling is that fast accurate injector control will make a noticeable difference to drivability and consumption .

A .

[jet_r31]

Ill take a stock bottom end rb30 with a Neo head on E85. Would have the fullest power curve and be the most fun. Can't say im a Rb25 fan at all

woudn't waste my money on one unless i had to.

cheers

darren

Edited May 11, 2014 by jet_r31

[owen1r]

My budget build was as follows

Engine mods:

RB25DET Neo with 150xxx KM, completely unopened (std EVERYTHING), 1000cc X-Spurt injectors, Hypergear ATR43SS2 internal wastegate.

Do you think for this build it would be highly beneficial to get the external wastegated version and run a gate off the exhaust housing, it's a budget option I guess? Only a couple of hundred dollars more, earlier boost and hold boost till redline?

Awesome result regardless, I will probably be doing this exact setup with perhaps some smaller injectors. People buy forward facing plenums, bigger turbos, 6boost manis and get the same result.

Edited May 11, 2014 by owen1r

[zebra]

I'm always a big fan of building a car like the factory should have

[skylinecouple]

True, the external waste-gate is always a better option. There are of course other things to think about. If the car makes the numbers and still looks stock, well, that for me is a very important consideration when somebody opens your bonnet. Besides, if you add a waste-gate and piping you may as well get a GTR and have no room to work. It all comes down to that perfect choice of parts for minimal cost, fuel economy, standard looks, maximum strength. Though I do like the RB25/30 I decided in the end that with good tuning and the right turbo a 25 is more than enough for a street car.

You know, I haven't seen anybody do a RB25 with 26 crank and rods. You could pick up a set cheap or at least the crank and get forged pistons. Anybody done this before I start mine ?

[75coupe]

Whats all this std look thing? Sure im in nsw but ive never had an issue and never looked std in any aspect body or engine bay... Is std look really a benefit if it has never been an issue?

[Piggaz]

Whats all this std look thing? Sure im in nsw but ive never had an issue and never looked std in any aspect body or engine bay... Is std look really a benefit if it has never been an issue?

Only takes one angry cop to make your life hell.

[Blackkers]

I'm another one who drools over the idea of a factory RB30e bottom end put together with a 25 neo head. A bit of a freshen up and throw the original pistons back in with a new set of rings. If the bearings look okay then re-use them too! Probably use a twin cam oil pump and bump up oil pressure slightly by shimming the relief valve if bearings have decent mileage.

3L, VCT, E85. SS1.5/SS2 ~ish sized turbo externally gated on E85. Boost the shit out of it. mid 300's KW with full boost around 3250RPM in 5th? yes please.

Not sure if a set of mild duration-moderate lift cams would do much at this point; might make better use of the 30 bottom end

[Manuel Kasko]

How much does it normally cost to chuck together a neo head and 30 bottom end?

Not planning on doing it but it would be interesting if you were on a budget how much the roll in roll out price would be.

Do many parts have to be modded to fit the 30 bottom end into say a r34 GTT? Or is it as simple as take the bottom end off your neo and bolt on a 30 bottom end?

[iruvyouskyrine]

I'm another one who drools over the idea of a factory RB30e bottom end put together with a 25 neo head. A bit of a freshen up and throw the original pistons back in with a new set of rings. If the bearings look okay then re-use them too! Probably use a twin cam oil pump and bump up oil pressure slightly by shimming the relief valve if bearings have decent mileage.

3L, VCT, E85. SS1.5/SS2 ~ish sized turbo externally gated on E85. Boost the shit out of it. mid 300's KW with full boost around 3250RPM in 5th? yes please.

Not sure if a set of mild duration-moderate lift cams would do much at this point; might make better use of the 30 bottom end

That is exactly the setup I am going to be running with the new engine, and the Neo head has the added benefit of 9.5:1 CR

[Blackkers]

The neo head has a smaller combustion chamber right?

What's the ETA on completion? Sounds like a killer project.

Also where did you get the rb30e and how much did you pay for it? Most of them have a zillion kms on them

Edited May 12, 2014 by Blackkers

[jet_r31]

The Rb30 woudn't cost anymore..Only if its 4wd you have headaches...if your after a peak power you just have to remember that due to higher capacity there will be more backpressure

and the turbo flow will be capped a bit with the turbo stuff thats smaller on the exhaust size. but midrange would be epic..

I thought with the thinnest headgasket comp ends up in the low 10's from memory. My mate built one a while ago for a customer

cheers

darrenr

[discopotato03]

Guys the idea was to keep the original RB25 block because you don't get the legal dramas and not everyone wants to go through emissions testing .

AFAIK no one has run a significantly higher static compression ratio on an RB25 using E70/E85 and the extra compression pressure is what gives an engine better part throttle torque .

Standard Neo turbo RB25s are 9.0 : 1 static CR from Nissans specs and same as R33s but , smaller capacity chambers with a lower plateau on their piston crowns .

What they would have gotten is shorter flame paths and better quench so they could run slightly leaner mixtures , emissions , without detonation . Pretty sure they were made in the ULEV or Ultra Low Emissions era where R33s were not .

I remember SK telling me that in the 93-97 (R33 era) there were changes with computers and coils and the later ones were cleaner than the earlier ones . The factory Neo revisions wouldn't have been cheap and you'd think they were forced to by tightening emissions regs .

Obviously the hydraulic buckets didn't like fast lifting short duration cams and a slight shrinking of the inlet manifold and or plenum chamber gave slightly higher gas speeds for better part throttle torque .

BTW my calcs show the RB26 stroke plus 1mm overbore to 87 works out to 2628cc which is 323cc short of a std RB30 . That's is about 11% .

If you went 87.5 bore that's 2659cc or 293cc short , within 10% . What this says is that you can halve the capacity difference between an RB25 and an RB 30 and the only aftermarket parts needed are the pistons , aftermarket 26 pistons that is . Maybe not the cheapest option but it looks factory and if you scored the right crank takes the good oil pumps . You get to keep the piston oil squirters as well .

A .

Edited May 12, 2014 by discopotato03

[Manuel Kasko]

My budget RB25 build was as follows using a hypergear SS1PU on 98.

Nistune, HKS 555cc Injectors, Z32 AFM, Walbro 255 Pump, 3" Intake, 3" Exhaust, Blitz Super Flow Pod, Hybrid Intercooler, KB Heavy Duty Clutch and Profec B Spec 2 Controller

This turned into a clean 250rwkw with 20psi tapering down to 16

I’ll see if I can dig up a dyno graph