Rb25 To Itb's , How Much Real World Difference ?

[discopotato03]

For people who have converted RB25DET's to individual throttles , did this make a huge difference to how your engine drives ?

Also question for RB26 people , RIPS in NZ said when they make their RB25 conversion lower manifold to take the GTR throttles and plenum chamber they don't use the air by-pass valve .

By this I assume they mean the cold start air by-pass valve - he said with the engine management systems they use they don't need it . I'm curious to know if RB26 people have removed it and had no issues .

Lastly I need to know if R33 RB26 idle air control and TPS units are compatible with R33 GTS25T computers - PFC in my case .

Cheers A .

[The Dan]

For people who have converted RB25DET's to individual throttles , did this make a huge difference to how your engine drives ?

Also question for RB26 people , RIPS in NZ said when they make their RB25 conversion lower manifold to take the GTR throttles and plenum chamber they don't use the air by-pass valve .

By this I assume they mean the cold start air by-pass valve - he said with the engine management systems they use they don't need it . I'm curious to know if RB26 people have removed it and had no issues .

Lastly I need to know if R33 RB26 idle air control and TPS units are compatible with R33 GTS25T computers - PFC in my case .

Cheers A .

Rhinorebel had this setup with a highflow on his r33 and was making boost at idle.

We ended up having to change for a 3071 so it would be more practical at making 1 bar 2800rpm. He runs a haltech and uses the IAC but not the AAC from memory.

series 1 r33 uses the same TPS as gtr but his IAC was remote mounted.

Adaptor kit was supplied and designed by Shanef so if you have any questions about the AAC or IAC incorporation, ask him

[Cjmartz2k]

I think I actually used an RB25 IAC with a funky vacuum hose going back into the intake. It doesn't face the right way, but if can be made to work. I think if you use the RB26 IAC, it will fowl on the oil cooler.

As for performance, I noticed better throttle response (it felt very "snappy") but less low end. I changed a lot of other stuff at the same time though to include a bigger turbo, cams, and no VCT. I got the whole intake adapter/surge tank/ITBs/850 injectors/HKS fuel rail for $150, so it was basically my cheapest way to a better intake than the stock RB25 intake.

One big thing I would take away from all that though is don't confuse throttle response with low end power. People often do.

[paulr33]

ill try it if someone pays for it (haha)

ive got ass loads of timing in my tune and the car feels great, but thats on the std throttle body

making boost at idle?

is this even technically possible?

[The Dan]

ill try it if someone pays for it (haha)

ive got ass loads of timing in my tune and the car feels great, but thats on the std throttle body

making boost at idle?

is this even technically possible?

Yeah I didn't believe it either until I saw it with my own eyes.

It made 1psi at 900rpm

[discopotato03]

I'm trying to view it all from a dynamic or actual compression ratio point of view . Obviously ITB's give a far faster pressure rise into the cylinders (off boost) so the dynamic or real world CR gets to be closer to the measured or static CR . I already own an R33 RB26 head and complete inlet so it's just the means to get it on an RB25DET that I need .

Personally I don't like shim under bucket valve trains and since I don't have the need to rev the piss bags out of my car the hydraulic system is fine .

Also I have an ex Woolaf R33 25 head thats been ported/OS exhaust valves/Poncams . Also I'm staying with a single turbo and either a std manifold or the HKS one thats kicking around here . The 33 26 head is staying in storage in case the RB30 ever happens but thats not likley .

I'd like to know more about the differences underneath RB25/RB26 inlet manifolds . By what was mentioned above it sounds like the oil/water heat exchanger is different between R33 RB25DET and RB26 , does this mean that the 33 25 one fouls on the 26 type IAC or its chamber or the AAV valve or plumbing ? I bought all my RB26 stuff from Doughboy some years back and I'm pretty sure there was an RB26 heat exchanger thrown in but don't know if its R32 or R33 era GTR type .

Can I assume that if RIPS modified RB25 lower manifold/adapter places the throttle assemblies in the same place that the RB26's inner manifold section does that basically all the R33 RB26 bits bolt up around it ie the oil cooler/inlet air ducting down to the intercooler etc ?

Also from pics I've seen of the RIPS creation they weld on an RB26 top water outlet which places the hose fitting I suppose where it would be on a GTR , and handily right out of the way of the RB25's cam change actuator solenoid valve . Fingers crossed an R33 GTR top hose completes the picture .

I really have to say the engineer that decided RB26 heads had to have different stud patterns should be shot . Nissan could have sold a lot more spares to many more people if they'd been the same .

Yes I get the picture with power vs throttle response down low , I think if the tuning was right and an educated foot was pushing on the go pedal you shouldn't lose much if any over a GTR because the GTR is heavier and its static CR lower .

If anyone has some answers please sound off !

Cheers and thanks , Adrian .

[Mr GTS4]

here is a pic of the setup i bought off a guy,

its a R33 rb25 bottom runners cut with plates welded to it for the itb's to bolt to. everything bolts up tps, water inlet and standard injector rail.

the only i don't know about is the aac valve.

but yeah the guy i got it off had it on a R33 race car that he had and said it worked fine.

there's one pic i have there that is one with a top feed rail on that suits gtr injectors too.

Curt