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Rb25 Neo Exhaust Cam Gear Question

Shoujiki

By Shoujiki,
in Engines & Forced Induction

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Shoujiki Proficient

Shoujiki

Posted
Posted

Hey guys,

I know this has been said to death about how to setup timing and all that, searched around and found a lot of info, but nothing definitive to this question i have.

Doing a 100k service, timing belt etc on my RB25 NEO. Upon taking the covers off and winding the engine over clockwise many times and double, triple and quadruple checking the timing marks, it would seem the exhaust cam gear is out by 1 tooth in the clockwise direction (i think advanced?).

I haven't taken the belt off or anything as yet, trying to make sure I get it all spot on when putting back together.

Is this a trick that some tuner has done for more power? The car has some odd daughter board in the ECU and was "tuned" by Dr Drift. Could they have done this to improve something? Should i put it back the same way?

Thanks, Kurt.

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Shoujiki Proficient

Shoujiki

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Here are some close up images with the stock belt still on. Haven't removed tensioner at all, this is how it was when I took the timing cover off.

Surely this isn't the right thing to have done, every thread i read suggests that 1 tooth is far to much to be of use and actually will kill engine power.

Inlet and Crank line up perfectly.

post-89402-0-76445100-1432224396_thumb.jpg

post-89402-0-55244800-1432224398_thumb.jpg

post-89402-0-01492000-1432224400_thumb.jpg

hardsteppa Grand Master

hardsteppa

Posted
Posted

I suggest - buy ebay adjustable cam gear, the type with the steel outer gear not aluminium, install on exhaust cam. Adjust to stock position, see if it runs better or worser. Move back to 1 degree out if needed, or tune further to get max power. Problem solved for $80-90 and tuneability of engine increased.

jiffo Mentor

jiffo

Posted
Posted

One tooth on a cam wheel equates to 15 degrees on the crank.

Usual IGN static timing is 15 degree BTDC and has the CAS sitting pretty central in the slots.

Yours looks slightly retarded, perhaps compensating for the advance on the exhaust cam but one would need a timing light on it to be positive.

If the cam wheel had been set up a tooth retarded, there may have been a plan to bring boost on earlier or such, but set up a tooth advanced looks like a mistake to me.

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Shoujiki Proficient

Shoujiki

Posted
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Posted

Yeah it's a real strange one. I have a timing light so that is no problem to check after. I've sourced an adjustable cam gear so i'll pop that in with it set to 0.. install the CAS at the same mark and see what it times at and adjust to 15 degrees if it's out. Would still love to know if it was a mistake or not... as you said, everything points to retarding it for any purpose.. but not advancing.

jiffo Mentor

jiffo

Posted
Posted

Unless you're going to degree the cam wheel I wouldn't bother with an adjustable wheel.

There's not much chance the marks on the adjustable wheel are going to be accurate enough to prove the point.

Handy if you decide to play with exhaust valve timing but you've also got the inlet to think about….too much hassle for me.

Shoujiki Proficient

Shoujiki

Posted
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Well you have a point. We know that the timing should be on the mark, so really, i should just put it back on that marker. Also most people suggest that the NEO doesn't do much outside of the 0 mark anyway, so having the gear would be pointless? Ahh I dunno what to do now haha! I don't think the adjustable gear (Tomei) would give me enough adjustment anyway to go back to "one tooth out" would it?

Shoujiki Proficient

Shoujiki

Posted
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Well i don't know what to do. The right thing to do is put it at the right marker. It is supposed to be on that really. From what i've read, i cannot see why anyone would want to advance the exhaust on a NEO by that much. Most say they lost significant power when adjusted outside of 0.

Shoujiki Proficient

Shoujiki

Posted
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Posted

Completely stock. This looks like the first major service it's had in a long time. Certainly hasn't had any "engine work" as such. I just hope there hasn't been some drastic adjustments made in the ECU with the daughter board it has. Doubtful though as it seems to be a pretty basic chip anyway.

  • 5 months later...
mick-r34gtt- Proficient

mick-r34gtt-

Posted
Posted

Hi bro, just seeing how things went and did u need to set it out by 1 tooth again as I'very just changed all mine and yep 1 out so I set it all up correct and now runs like a bitch. Did yours do same thing? Cheers and I will look forward to your reply. Mick.

Shoujiki Proficient

Shoujiki

Posted
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Posted

Hey Mick,

I haven't got around to getting the car finished yet, still waiting on a new CAS and then it should be good to go.

Strange that your having issues. What exactly is yours doing that is bad? The service manual suggests having the gear line up dead on the marks, and so do the opinions here, makes sense really, i don't know why it would ever need to be 1 tooth more and that info is not in the service manuals.

mick-r34gtt- Proficient

mick-r34gtt-

Posted
Posted

Hi bro, yeah mine was 1 tooth out on the exhaust side and now that I've lined all timing marks and put new belt on its holding back power a he'll of a lot and when I change into second gear it shoots a flame and just wants to die at times. I have a nistune board on the ecu (daughter board) like you. I'm thinking of putting it back to a tooth out again or leave it and see if a shop can fix it on a dyno tune and remap ect. It's doing my head in bad. Hopefully someone can help.. I will let ya know how things pan out. cheers talk soon.

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