Rb26 Cam Timing Adjustment To Reduce Lag

[chrisking666]

Hi guys and gals, so I have built a new forged RB26, with 270 10.8mm tomei cams and a 70mm billet turbo (slightly bigger than a t04Z), problem is its very laggy, it starts to make boost around 3500 1-2 psi but takes till about 5700 to get up to even 8-9 psi and then full boost of 19 at about 6500. I have adjustable cam gears and want some info on how advancing or retarding inlet/exhaust mght help my lag problem to make the car more responsive.

Im quiet aware that big turbo = lag, but this is a bit frustrating.

I had an rb30 with t04z and it would not come on boost with your foot on the brake and flat out on the gas standing still. We went drag racing and it ran a 13.6, spoke to a guy in the pits who said to roll the cam 1 whole tooth to advance the cam timing, next pass was an 11.1!!! It came on boost at least 1000 rpm earlier!

So just want to know if it might work the same way with this engine. Any opinions would be appreciated..

Thanks Christian

[chrisking666]

So I just tried retarding the exhaust cam only, took it to 4 degrees on the cam so 8 at the crank, it definatly makes it boost earlier i'd say 500rpm and much more driveable down low like from a stand still.

I should have the inlet cam gear tomorrow so i'll try advancing that gear a couple of degrees and see if that brings the midrange on harder and boost earlier again.

Cheers

[chrisking666]

Edit on the first post, ment to say retarded the cam timing on the rb30!! not advanced it 1 tooth

[Moodles2]

These changes are best done on the dyno to actually confirm the changes aren't causing harm, and making sure with each change you make sure every fastener on both in&ex cam gears are locked down or pistons will be meeting the valves.

[doo doo]

Yep best done on dyno to check gains and also to adjust tune for new settings. If your tuner is switched on he'll already know what settings will work best for your setup and get there without to much mucking about. (I have my Tomei type B's dialled in with 4 degrees retard on ex and 2 degrees advanced in intake, for the best result with my setup) There are a couple of other little tricks to get the boost up a bit earlier, (by retarding timing a bit and going slightly richer just as boost starts), plus a well designed dump with minimal restriction and good wastegate integration will be beneficial. If you haven't already got an electronic boost controller (dual solenoid) with a gain function then this could also help. With this you can adjust wastegate creep to keep the wastegate closed longer which can help boost build quicker (but doesn't bring it on sooner).

Edited March 23, 2011 by doo doo

[GTScotT]

Is the motor tuned etc? How much power did it make? How high are you revving it?

You have described cams and a lag time expected on a 1000hp 10,000rpm motor.

Prepare to have everyone with a reasonable understanding of turbos tell you to buy a smaller turbo. Best to state your aims for the car in preparation of the same.

[Dose Pipe Sutututu]

I would personally go lower duration cams.. the longer the duration the more laggier it's going to be.

[chrisking666]

Ok so the motor has ross pistons, spool rods, main studs, head studs, steel head gasket, 4 inch dump pipe, profec b boost control, tuned two days ago by Matt at PITS, made 400 rwhp on 20 psi.

Should make 650 -700 quiet comfortably when the cooler is changed.

Reving it to 8500 as it only has a N1 oil pump.

The biggest downfall i think is the standard intercooler atm.

The other thing that needs to be changed it the rear half of the exhaust as it is only 3" but I dont think that is the cause of the lag.

The turbo has a 0.81 exhaust housing aswell to try to keep lag to a minimum.

If I cant get much of an imporvement with cam gear adjustment and cooler I think i'll have to go for a stroked rb30. But i'd like to try to improve this setup as its all brand new!

Im also very aware of piston to valve clearances and retarding exhaust timing will only give the valves more clearance if anything.

Thanks for everyones feedback

[DVS JEZ]

what boost controller, what rear housing on the T04z?

[GTRNUR]

Its either got a boost or exhaust leak somewhere on the pressure side, or something is massively wrong. Only 400hp from 20psi with a monster turbo that should make near on 800+ flywheel hp just isnt right.

Pressure test the intake from the compressor housing intake and check for air leaks.

Examine the exhaust manifold with a microscope looking for signs of carbon. A leak between the head and the turbine housing will cause this. Also check the wastegate-manifold gasket, and make sure the gate is actually closing properly.

Pull the radiator and re-set your timing to 0-0. A full tooth out is something like 14 degrees from memory, which is FAR too much of a change. Your luckly you havent killed/bent something already.

Check your cat for blockages and upgrade that exhaust. You should have at least a 3.5" on it, but it will need a 4" to come close to reaching the potential of the rest of the setup. And definatly upgrade that intercooler too.

While its all apart, compression test it as well, just to get a picture of what the ring seal is like.

Edited March 24, 2011 by GTRNUR

[chrisking666]

Its either got a boost or exhaust leak somewhere on the pressure side, or something is massively wrong. Only 400hp from 20psi with a monster turbo that should make near on 800+ flywheel hp just isnt right.

Pressure test the intake from the compressor housing intake and check for air leaks.

Examine the exhaust manifold with a microscope looking for signs of carbon. A leak between the head and the turbine housing will cause this. Also check the wastegate-manifold gasket, and make sure the gate is actually closing properly.

Pull the radiator and re-set your timing to 0-0. A full tooth out is something like 14 degrees from memory, which is FAR too much of a change. Your luckly you havent killed/bent something already.

Check your cat for blockages and upgrade that exhaust. You should have at least a 3.5" on it, but it will need a 4" to come close to reaching the potential of the rest of the setup. And definatly upgrade that intercooler too.

While its all apart, compression test it as well, just to get a picture of what the ring seal is like.

Im new to GTR's and RB26's and ive followed some of your posts and know you know your shi't so i'll go and check the cam timing, i was quiet dissapointed with the power output myself as I have spent quiet a bit on a combo that i thought would make alot more HP. Im sure its not just in the tune and I agreee that in must have a problem somewhere hence asking on SAU.

Cheers for your input, get back to you soon!

[chrisking666]

no cat either

[chrisking666]

what boost controller, what rear housing on the T04z?

Hi mate its not a t04z its a little bigger, its a 70mm billet which i think is getting close to a t51r kai the ex housing is a 0.81. and the boost controller is a Greddy profec B spec 2.

Cheers

[R31Nismoid]

As Ian said... you've several issues. main two being that exhaust and the timing. A whole tooth has all sorts of wrong going on mate.

When the tuner only managed 300rwkw at 20... what was discussed? What areas did he say needed attention?

[chrisking666]

As Ian said... you've several issues. main two being that exhaust and the timing. A whole tooth has all sorts of wrong going on mate.

When the tuner only managed 300rwkw at 20... what was discussed? What areas did he say needed attention?

To be honest we didn't discuss it, like i said im new to rb26's and was not sure to expect but its obvious from the replys that there s something wrong.

I will check timing etc and make sure its all ok but if anyone can advise of anything else to look for that'd be great!

[R31Nismoid]

By rights it probably should've been explained too you, or at least your attention brought to it etc.

See how you go, but with the exhaust etc, its gonna be kinda hard as even if you fix one... you still have the other(s) so its a case of overall package needs sorting.

[chrisking666]

Cam timing is spot on, TDC on crank lines to both marks on cams and cam plate.....The only thing I havnt pulled off this car since I brought it blown up is the I/C, any chance it could be partially blocked, can this even happen?? last motor was over boosted, melted 5 pistons and broke the rear turbo. Well at least thats what I think happened as I brought it blown up.

[R31Nismoid]

A GTR cooler will flow 360-400rwkw without a problem

Wouldnt hurt to measure the pressure drop across the core (pre and post reading). Still exhaust is prime candidate still.

I've seen cars go from 3" to 3.5" and pickup 20-40rwkw instantly. (when making over 300rwkw)

[Tangles]

Take off the intercooler, clean it out with 50/50 mix metho/kerosene, it'll be gunked up with old oily deposits.

Get that crystal clean inside, make sure there are no intake leaks throughout the system, and work on that 'zaust.

[chrisking666]

Take off the intercooler, clean it out with 50/50 mix metho/kerosene, it'll be gunked up with old oily deposits.

Get that crystal clean inside, make sure there are no intake leaks throughout the system, and work on that 'zaust.

Im thinking i'll just go and get a 4" cooler with 100mm plumbing from turbo to plenum and be done with it. Rolin Imports down the road do a 4" cooler for about $475 and pipeing I can source easily shouldn't be a problem.

I'll do the rest of the exhaust as soon as im back from Thailand and get some more money together. Leaving to Thailand on Thursday next week so im runnng out of time and missus will kill me if I spend to much more on this car!!

Looked at the muffler today and it turns out to be 2 1/2 inch ID so that would have definatly been causing some serious back pressure.

Thanks