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Difference between RB20 and RB25 ECU/harness?


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#1 GMMTC

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Posted 26 January 2010 - 10:57 AM

I have a line on a cheap RB25 engine with no turbo/tranny. I have a turbo for it and would use a Z32 n/a tranny with a rb25/26 bellhousing.

Can I get a RB20DET harness/ecu and be in business?

#2 240z!!!

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Posted 26 January 2010 - 11:42 AM

is the rb25 a s1 or a s2...if its a s1 you should be able to use a rb20's harness with some modifications...but the cheapest route to go is probably the z32 harness and z32 ecu...you can modify the z32 harness to work and if you get nistune(if you wanted the chance to tune) for the z32 ecu it will work for the rb25

nistune's cheap like 250 bucks plus a z32 harness is maybe 200 so 450...thats cheaper than purchasing just the wiring harness for a rb25...

but (someone correct me if im wrong) im pretty sure the ecu connecter's for the rb25 and rb20 and if you used the rb20 ecu you'd have to get a tune for it to run the rb25...

but either way there is wiring to be done with any harness other than using the rb25 harness

#3 GMMTC

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Posted 26 January 2010 - 01:17 PM

is the rb25 a s1 or a s2...if its a s1 you should be able to use a rb20's harness with some modifications...but the cheapest route to go is probably the z32 harness and z32 ecu...you can modify the z32 harness to work and if you get nistune(if you wanted the chance to tune) for the z32 ecu it will work for the rb25

nistune's cheap like 250 bucks plus a z32 harness is maybe 200 so 450...thats cheaper than purchasing just the wiring harness for a rb25...

but (someone correct me if im wrong) im pretty sure the ecu connecter's for the rb25 and rb20 and if you used the rb20 ecu you'd have to get a tune for it to run the rb25...

but either way there is wiring to be done with any harness other than using the rb25 harness


It's from my buddy's '93 R33 so I'm assuming it's an S1.

Would I need a Z32 TT ECU or would a N/A ECU do? Does the harness have to be for a manual or can an auto harness be modified to work pretty easily?

#4 macr32

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Posted 26 January 2010 - 01:37 PM

You can use a RB20 harness and ecu on a RB25, but it will be more than just a harness and ecu. RB25 has nvcs, vvt or whatever nissan calls there variable cam stuff, which the RB20 does not. So to make it work you will also have to change the intake cam and cam gear to a rb20 or RB25 N/A intake cam to get rid of the vvt stuff, exhaust cam can stay the same. once all of that has been changed then you will need a means of tuning the RB20 ecu, flash/ rom tuning.

Using the above mentioned RB20 Harness, will work on both s1 and s2 RB25's but there might be issues with the s2 ignition preamp box( can't remember the real name) and the coil harness, also with the connectors on the alternator. I am sure someone else will chime in with exactly what the differences all are.

If i were in your situation (depending on budget and plans for the motor of course) i would look at something like electromotive's Tec3, that comes with its own ecu harness and wire and the entire engine with that.

#5 GMMTC

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Posted 26 January 2010 - 03:29 PM

If i were in your situation (depending on budget and plans for the motor of course) i would look at something like electromotive's Tec3, that comes with its own ecu harness and wire and the entire engine with that.


That's way over budget for tuning, I always prefer to socket my own ECU and go that route. My plans aren't much, upgrade injectors, put a decent sized turbo on and get a decent power figure, nothing fancy or crazy. My whole budget is about $1k-1500 for the engine, tranny, bellhousing, ecu, harness and tuning depending on if the Z32 stuff will work or if I have to go the RB25 route.

The Z32 seems to have NVTC, so maybe that idea will work good?

#6 Canadianz

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Posted 26 January 2010 - 04:57 PM

I am looking at a similar route.The RB20/25/26 ecu's all have the same connectors. What is different about them is the pin outs obviously and that the 25 series one uses an external ignitor for the ignition. Basically Nissan built a bunch of boards, and just added components to them. Unfortunately the RB25det ecu's can't be chipped due to onboard memory which contains also the processor, or something to that effect

What is interesting is that the signal sent to the ignitor from the RB20 ecu or 25 series one ecu is the same. So basically on the ignitor engines the signal hits the ignitor box then fires the plugs. On non ingnitor engines, like the series 2 the same signal is sent to the coil on plug units.

I have run my RB25det series 2 for a short time on an rb20gtst ecu, with zero modifications. It started up and ran just fine, I didn't rev it or do anything else knowing the maps are totally different. As you know you can socket and tune the Rb20 ecu's, which is the reason to go to them. What I think you need to use is the GTST ecu if you want to run the stock injectors on your 25det as they have the same injector drivers. Also something to keep in mind is that a RB25det MAF will only support something like 300 hp before maxing, so its best to wire in a q45 or big Maf while your at it, or go blow through.

The 300zx ecu does support dual Maf's the same as the Rb26det ecu, giving a higher potential in that area, however the 300zx ecu does have a slower processor.

So the best solution is to run an Rb20 GTST ecu, it will run and hook right up to your RB wiring harness with little or no mods, then set up a blow through Maf and big injectors.

This with a good tune should be the way to go, I have collected just about all the parts and am doing this swap in the spring !


If you look at the pinouts that AEM uses it might help...
AEM PINOUT RB Series

I wish I could remember better, I did a ton of research on this exact issue.

Cheers

Chris Crombie
I forgot about the vvc system so if you find something on that give me a shout. I know there are a couple guys running the Nistune or chipped RB's on here ..

#7 GMMTC

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Posted 26 January 2010 - 05:19 PM

So the best solution is to run an Rb20 GTST ecu, it will run and hook right up to your RB wiring harness with little or no mods, then set up a blow through Maf and big injectors.


What's the downside of a slower ecu? I'm not going to be going for mega hp and I'm trying to stay on budget. Chipped Z32 ecus are plentiful for ~$50 and if it'll work good with the vvt it seems like the easier/cheaper/better choice?

#8 macr32

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Posted 26 January 2010 - 06:20 PM

Before i went to power fc i also was using a chiped rb20 gtst 5speed ecu. It works great. On the Z32 ecu controlling the vvt on a rb25, i am waiting on a answer on it from a friend of mine.

Now that i am thinking about it i will no use for the cams i used with the rb20 ecu in my rb25 head, since i now have a complete tomei valve train with 270 dur. cams going in. so depending on if you can wait till march for me to get back from the work trip I am on, and to pull the cam outs of my head, I might be able to work something out with you. Should you decide to use a rb20 ecu.

#9 240z!!!

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Posted 26 January 2010 - 09:39 PM

either ecu you use will need a tune to run the rb right...i actually had a friend that had a rb25 running off of a z32tt ecu and it ran fine without a tune(not great just fine)....

z32tt and na ecu's are the same just different maps
z32 ecu will support the vvt on the rb25
early z32 ecu's are 8 bit later are 16 bit...you want to get the earlier one

really the only thing to get it to work with a rb25 is
put a resistor where the z32's fuel temp sensor was or it will run rich
the z32 uses 2 02 sensors while the rb uses 1 so you'll have to figure out how to send 2 signals to the ecu or splice the 1 o2 to send both signals
and of coarse you'll have to repin a few wires

either way these somewhat of a tune required and the rb series dont have much support for cheap and reliable tuning like the z32 has...

and you could probably use a automatic z32 harness but it will have heavy wiring modifications...id stick with the 5 speed harness for ease

#10 Canadianz

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Posted 29 January 2010 - 04:02 AM

I think RS Speed on this forum is using a chipped ECU on his car, its a flat black flared 280z I think (used to be white and black). Might be worth pm'ing him about it.

#11 GMMTC

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Posted 30 January 2010 - 04:40 AM

I think RS Speed on this forum is using a chipped ECU on his car, its a flat black flared 280z I think (used to be white and black). Might be worth pm'ing him about it.


Thanks for the tip, his insight has been very helpful




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