Timing Fluctuations In Rb26/30

[Scooby]

Unigroup told me today that there's so much fluctuation in the timing of my 26/30 above about 5500 that it's making tuning very difficult.

Basically no matter what it's set at it'll move plus or minus around that point quite a bit as the relationship between the CAS and crank positions doesn't remain true. Read about this on GTROC UK a while back but there was no real solution, and searching reveals some people here have come across it but again no real solution.

Could be due to belt flop, dodgy CAS (mine's new)or something else. Apparently happens a but with RB26s but not so much with 25s.

Basically it means either tuning it so conservatively on the timing that no matter how much it moves it won't go to det, or modifying the current set up.

Ross have a crank trigger set up that's over $2k, Autronic apparently have a set up that uses the flywheel for about $600 (?), and CRD (who have seen this problem but only over about 8k rpm) claim to have a fix for the CAS that's about $450 but they won't share ANY details eg what it is/does. Understandable but I don't want to get stuck with a proprietary system that only they can fix, and I don't know how fixing the CAS only helps as it has to accurately reference the crank position to fix the problem.

Does anyone have any experience with this or know of a sure fix that's simple and doesn't cost the earth?

[Piggaz]

I had this same problem when mine was getting tuned by Yavuz. I'm pretty sure Unigroup themselves are working on some sort of crank trigger but it is not finished yet. Its a bitch of a problem yet not much has been said about it.

[Scooby]

Hey Paul

That's the Ross kit. Yeah it's interesting alright, there's 100s of RBs running around going to 9k rpm on the standard system, it seems to afflict some but not others. And lots of people know about it but not the cause, and it also doesn't seem to get addressed much.

[R31Nismoid]

Some cars here/there have issues it would seem, but lately it seems everyone posting up coming Unigroup is having this issue almost exclusively

This must be the 6th or 7th person mentioning this since Dec i think.

(i don't mean that in a bad way either, just stating a trend I've noticed)

I wonder what the other big workshops do about this, seems CRD have something but its not commonly required.

A topic for Sat nights dinner with a few people has just been born lol

[paulr33]

never heard of it but what do i know?

if it was belt flop that would make sense

if it was the cas wouldnt it be whacko everywhere in the RPM range?

[Piggaz]

Some cars here/there have issues it would seem, but lately it seems everyone posting up coming Unigroup is having this issue almost exclusively

This must be the 6th or 7th person mentioning this since Dec i think.

(i don't mean that in a bad way either, just stating a trend I've noticed)

I wonder what the other big workshops do about this, seems CRD have something but its not commonly required.

A topic for Sat nights dinner with a few people has just been born lol

Bring the spewbucket hey Ash?

Yeah I have noticed this trend also. Hmmm.

[Aleckr33]

im having the exact same problem mate... going through it right now, CAS was unstable/noisy after 5500rpm. Thats what Yavuz told me. Iv had to take the car home because they didn't have time to really touch the car again for 2 weeks+, so it's only on a half tune and i can't give her a hard time obviously, but will be going back on the 14th of feb.

Edited January 27, 2011 by Aleckr33

[DVS JEZ]

+1 to noticing the trend. Why is it only unigroup though? Hmmm

[Scooby]

Been Googling, seems that Motec know about it and for high rpm use recommend a crank trigger. However there's a lot of chatter about remanufactured CAS trigger wheels also.

http://www.motec.com/forum/viewtopic.php?f=11&t=644

http://www.skylineowners.com/forum/showthread.php?t=69114

The cost of the Ross kit is prob largely due to the cost of the damper. Which is a bugger since I already have an ATI damper. Otherwise it would be tempting. A wheel can't be more than $500 and a trigger the same?

Yavuz was happy for the car to go to CRD to have the CAS done, just need to know more about what they do. There's only so many things you can do to a CAS.

Edited January 27, 2011 by Scooby

[Piggaz]

Ash. Seeing your a Melb/Racepace customer they must have come across this issue in their cars. I knew Steveo asked them but as far as I know they never got back to him.

Seeing that they are the king dick of street/track orientated GTR's you would think they might have a solution for this?

Its a very annoying problem on a big built engine. Not only because you cant get 100% power out of it but also what if its out THAT much that it pop's the engine. There goes ALOT of cash!

[STATUS]

could the trend be the ecu thats being used?

Most of the trigger issues are with particular ecu's not liking the nissan pattern.

Maybe post the ecu's (and engine combo) that are having the issues?

I can say its not inherent in nissan CAS's especially in these cars which are being mentioned.

[JAGR33]

could the trend be the ecu thats being used?

Most of the trigger issues are with particular ecu's not liking the nissan pattern.

Maybe post the ecu's (and engine combo) that are having the issues?

I can say its not inherent in nissan CAS's especially in these cars which are being mentioned.

Bingo.

Seems like some ecus don't like the factory cas/crank trigger.

I'm sure that's why Racepace recommend using Powerfc, problems in this regard are very rare.

What ecu's are you guys using???

[Scooby]

Could be specific ecus not liking the CAS signal, otherwise presumably it'd be present in all other set ups including stock and there'd be grenaded RB26s everwhere due to this. Googling suggests that makers of aftermarket CAS discs do it for reasons of a mismatch between aftermarket ecus and the CAS, and that's why I suspect CRD is using a different CAS wheel.

Trent when you say 'most of the trigger issues' have you come across the problem and fixed it?

I'm running a Vipec V44 plug in but would rather shell out for another ecu in preference to getting a crank trigger set up, if that'll fix the problem. But then there's probably a lot of big rpm engines using a Vipec with the stock CAS, not sure how they do it.

Also not sure why mine has started having the problem suddenly. Paul did yours have it from the start or did it just appear?

Edited January 27, 2011 by Scooby

[R31Nismoid]

Ash. Seeing your a Melb/Racepace customer they must have come across this issue in their cars. I knew Steveo asked them but as far as I know they never got back to him.

A topic for Sat nights dinner with a few people has just been born lol

It's a long time mates pre-wedding on Sat night, and Chris will be there

[Piggaz]

Bingo.

Seems like some ecus don't like the factory cas/crank trigger.

I'm sure that's why Racepace recommend using Powerfc, problems in this regard are very rare.

What ecu's are you guys using???

Im running a Power FC and Steve is running a.... ummm... haltech? Motec? either way it is not a power fc.

[JAGR33]

Im running a Power FC and Steve is running a.... ummm... haltech? Motec? either way it is not a power fc.

hmmm, seems strange then, I remember having a chat with Ben a while back and he said that he had experienced these problems with Motec and Autronic, but never Powerfc.

Do you have a new CAS?

[RRob]

Iv'e only ever come across this issue with motec. Due to the processors in the ecu being so fast they pick up any deflection in the timing belt (usually on a hard ramp and at around 8500rpm). Fixed it by running a crank mount pick up and using the cas for sync purposes only. PFC never have this issue due to slower processing.

[Piggaz]

hmmm, seems strange then, I remember having a chat with Ben a while back and he said that he had experienced these problems with Motec and Autronic, but never Powerfc.

Do you have a new CAS?

I 99% sure when the previous owner built the engine he chucked a new CAS at it. Maybe I should replace it and see what happens? Is there any way of insulating the CAS from 'noise'?

[Piggaz]

Iv'e only ever come across this issue with motec. Due to the processors in the ecu being so fast they pick up any deflection in the timing belt (usually on a hard ramp and at around 8500rpm). Fixed it by running a crank mount pick up and using the cas for sync purposes only. PFC never have this issue due to slower processing.

Whats the damage for the crank mount pick up? Do they run off all balancers or is it off the flywheel?

[RRob]

Cant remember prices. All the cars havn't had A/C so mounting is off the A/C holes in the block. Then a trigger disc onto the harmonic balancer and a GT101 sensor. In the logging when the issue occurred there was a 550rpm fluctuation.. Afterwards about a 20rpm fluctuation and all the issues where gone.