Cams = Problems! Help!

[croat]

Hey have recently had a set of tomei 256degree cams and an tomei adjustable cam gear installed. I have a bigger turbo (GTR-S) and all the supporting parts. had someone tuning the car tonight on the dyno and it made 140rwkw on 1 bar. before i had the cams it made 240 on 1.2 bar so something is very wrong. only new parts put on since then are a GReddy plenum and new exhaust manifold.

Now after speaking to the mechanic who was present at the dyno and who put it all together (he said everything was set to 0degrees) so was puzzled as to why the cams were not making any power.

Does anyone know the setting Tomei specify for their cams in a RB25DET. This is really puzzling me and i am trying to sort this out before christmas as i have had a heap of headaches getting the car on the road.

Any help greatly appreciated.. Ta..

[m&m]

I'm having cams fitted at the moment by the guy who is going to dyno tune it.Are you saying one mechanic fitted the cams and someone else is tuning?This situation just leads to finger pointing.

Good luck,but it will just be something simple,like someone forgot to bolt turbo back on with those power readings.

[croat]

ye one mechanic fitted it and the other is doing the tune. nothing wrong with the work that was done just we are unsure of the cam timing that should be set on this application.

Dont worry turbo is bolted on

[The Dan]

Make sure the cam timing is correct. Check all the basics as well like fuel and stuff. If your cam timing is out it will heavily effect your power. Set them up to standard ( 0 ) and then adjust them from there. The Tomei cams are a direct bolt on for that engine so no difference in setup. Also be careful the mechanic didn't stuff the cam timing when fitting the belt up. I bet you'll find your problem there.

[Amaru]

Id also be checking to make sure the cam gears were installed correctly (and the cams...)

[croat]

3lit3 32 yes the cams have been correctly installed as far as i know. no problems. He did set cam timing back to 0 and it made absolute shit power (120rwkw or so). He then advanced timing and ended up getting (140rwkw). there was no more power in them.

Amaru the cams and gears have been installed correctly, i dont think thats the problem. its just the timing. the engine runs fine and all there is just no power in it. Should it make good power on 0 degree's or does it need to be set up differently as 0 didnt seem to work. Is there anywhere i can find this out? anyone installed tomei cams on their RB25?

[Amaru]

It shouldnt lose that much power on 0 degrees (I think the poncams work best on 0 in the RB25 if im not mistaken). If its a timing problem then its one of two things... either the cam gears were not installed correctly, or the camshafts were not installed correctly (well theres a third, being the crank angle sensor wasnt hooked back up correctly... check and make sure its at 15 degrees base timing).

[The Dan]

By 0 degrees I assume you mean the cam gear was set to 0. When they are set at zero degrees on the gear, they are the same as a stock cam but with larger duration and overlap. You will notice an increase in midrange torque and top end will improve/become more smooth. You should not suffer any loss whatsoever, only gains. Then you adjust the exhaust to roughly 2 degrees retarded and inlet to around 4 degrees adv. and you should get a large power increase from before the cams were fitted. Check to make sure the Cam timing is correct. By that I mean, check to make sure the cams both line up with the marks on the back plate and the crank lines up with the mark on the oil pump. If these three marks line up when the gears are set to 0 then the cam timing is correct. look elsewhere for your problem.

Did you remember to unrap the plastic from the inlet plenum....maybe it's blocked.

How did the mechanic install the cams?....did he remove the belt completely to do it?

[croat]

yeah as far as i know he removed the belt completely. From what i have gathered he has set the cam gear to 0 lined it up etc. although it was not tuned it felt very sluggish. The car is running almost no vacuum and hits boost way too early on the dyno. The power and curve is hopeless. I guess all he can do is play around with the cam timing setting to try to find a position which works efficiently.. I thought tomei would have specs on their site for this setup but i have not managed to find anything.

Inlet plenum is fine.

[Amaru]

Then you adjust the exhaust to roughly 2 degrees retarded and inlet to around 4 degrees adv.

<{POST_SNAPBACK}>

From everything I have read on these forums, those settings work well for the RB26, but the best overall gains on the RB25 using poncams are on 0/0.

From what you have described it sounds like a timing problem, take it back to the mechanic and make sure everything was installed correctly and check the timing with a timing light. RB25 should be 15 degrees btdc at idle.

[StockyMcStock]

inlet cam and exhaust cam mixed up somehow? though there's a keyway for the CAS in the exhaust cam i guess that would be hard....

[BHDave]

If nothing else has been touched and the install of the cams has netted a gain of -80rwkw then you had better take a look at the cam install. plain and simple, not pointing fingers, pull the front covers off and make sure the base cam timing is correct. My money's on the cam gears being out a few teeth (it won't be the first time), or a massive boost leak second.

The most basic problem solver question in the world: What was the last thing i changed before everything went to shit? It has served me well for the last 29 years

[croat]

BHDave ye i get what your saying. only problem is we did the cams, plenum, piping, cam gears, exhaust manifold all at the same time. But it definately seems like a cam issue. the mechanic has the car now and is retracing his steps to see what could be causing it..

[The Dan]

And a cam that is a couple of teeth out will most definately explain why you have no engine vacuum.

[Cubes]

The car is running almost no vacuum and hits boost way too early on the dyno.

Check the ign. timing has been set correctly. Some RB's double pulse with cheapish timing lights, they may have simply guessed or even worse placed the cas back in its origional position thinking it will be the right ign timing.

Double looping the wire some times gets around the double pulse.

OR it could be just a co-incidence that your CAS has decided to crap its self.

Bl4ck32's recently did this, it wouldn't make any more power than 130rwkw.

After fixing the cas it made 218rwkw.

Edited December 13, 2005 by Cubes

[Sydneykid]

Just need to clarify some points;

1. This is an RB25DET right?

2. With VT on the inlet cam, so it only has an adjustable pullety on the exhaust camshaft?

3. The cams are Tomei 256 degree Poncams?

If the above is correct, all the Poncam equiped RB25's I have seen work best at zero on the exhaust camshaft timing. But every engine is different, so it pays to check.

Make sure the VVT is connected and working, they make little power with poor inlet camshaft timing. Check the inlet camshaft timing, there are marks on the rear cam cover for both the inlet and the exhaust pulley which line up when the crank is at TDC.

Standard pulley, red dots show the camshaft timing marks at TDC

Close up of a HKS pulley show the line up with the rear cam cover mark at TDC;

Check the igntion timing carefully with a timing light that wil tell you if the exhaust camshaft timing is out. The CAS should sit pretty much in the middle of the slots for the ignition timing to be at 15 degrees (BTDC) and with the exhaust camshaft timed at 0.

My guess......inlet camshaft timing

My worry......bent valves from poor camshaft timing set up

My suggestion .....do a leak down test just to be sure

cheers

Edited December 13, 2005 by Sydneykid

[Cubes]

I still think you should definitely look at the CAS.

Looks like what happened to Bl4ck32's anyhow.

His Cas was fine.. pulled the motor out, dropped in the new, bolted everything up and it was a dog.

Replaced cas picked it close to 100rwkw.

It idled fine and appeared to run fine under light load.

Thought the issue was the exhuast, replaced exhaust, nothing.

Then stumbled upon the cas.

He could have stuffed up the cam timing, it sounds as if its been double checked.

Edited December 13, 2005 by Cubes

[Bl4cK32]

Looks to be the same problem i had...

Car started, and idled fine. Light load was fine. Put your foot down and nothing. Cas was farked, and it was running sfa timing under boost.......

People suggested that my cam was off a tooth also when i had the problem, but it wasnt...

[croat]

SK - spoke to the mechanic he is checking the timing over and over making sure everything is correct. Has not found any problems as yet.

Cubes - Yeah sounds like what i have. Only thing is that the car was running fine just before the cams. How could the CAS just stuff up like that?

Anyways anyone near eastern suburbs sydney have a spare CAS i can borrow or try to see if it makes a difference??

[Cubes]

You will never really know of the cas was dropped or just broke once it was touched. Similiar to bl4ck32's.

On one motor its fine, remove it, bolt it on the new motor and its stuffed.

If the tuner deals with skylines he will have a spare cas laying around, possibly on another car.

Edited December 13, 2005 by Cubes