How to bring boost on quicker on GTR with big low mounts

[Mik]

I have an R33 GTR with a pair of GT-RS's. What can be done to bring boost on a little quicker? The car has good top end power now (obviously), it is currently making about 340rwkw on 1.3 bar.

Target boost is currently reached at about 5800RPM in the higher gears.

The car has adjustable cam gears, but they are set to zero degrees on both sides as we found this to be the best.

All internals are stock, but other mods are:

550 injectors

HKS dumps

NISMO tuned length front pipes

Trust MX 80mm exhaust

Power FC and boost control kit

I have been told that the exhaust is choking it, hence spool up is slow. I tried dropping off the exhaust from the front pipes and going for a run, things improved VERY slightly (like 100RPM), so I don't think this is a problem.

The wastegate actuators are adjusted to be quite hard (crack at about 1 bar)

I don't want to pull the engine out of the car, as the engine is still very healthy (perfect compression and leakdown), so oversize pistons and higher compression is not an option.

The only other option is a pair of drop in cams. What sort of difference would a pair of say Tomei PONCAMS make to midrange power? They make two types, both with 260 intake and one with either 256 or 260 exhaust duration. I'm assuming the pair of 260s would be best for the big turbines?

Are there any other better cams that will fit straight in using standard valve springs and without machining the head?

I would be over the moon to have target boost at 5000RPM. Is this possible, or should I just swap the turbos for a pair of 2530s or N1s? I know these will be on full song at 4500RPM.

Also, I'm getting compressor surge at low RPM in high gears, I'm assuming the extra air flow form a pair of cams will stop this. Is this wishfull thinking?

Thanks in advance

[R31 POWER]

Also, I'm getting compressor surge at low RPM in high gears

I'm no expert so I'll leave it to them but do you have a balance pipe between each pipe before the turbos? I'm sure I read in another thread this can cause probs if it does'nt.

[Sydneykid]

Hi Mik, the general consensus from GTR owners around the world is that GTRS's are too big for 2.6 litres. A set of camshafts would help, as would a light port of the cylinder head and an increase in compression ratio. As for cams, 256/260/264 would be OK, keep the lift under 9 mm. I haven't found any particular brand which outshines the others when used in GTR's. Personally I find the 256/260 Poncams are superior in GTST's, but that has not, to date, been the case in GTR's.

Hope that helps

[Mik]

Hi Mik, the general consensus from GTR owners around the world is that GTRS's are too big for 2.6 litres.  A set of camshafts would help, as would a light port of the cylinder head and an increase in compression ratio.  As for cams, 256/260/264 would be OK, keep the lift under 9 mm.  I haven't found any particular brand which outshines the others when used in GTR's.  Personally I find the 256/260 Poncams are superior in GTST's, but that has not, to date, been the case in GTR's.

Hope that helps

Thanks SK. Are you saying the poncams haven't been good in GTRs or that you havent tried them? I think the poncam's lift is about 9.2mm. Do you think that's too much lift for the standard valvetrain, or will it be okay?

I guess there's not that much else I can do is there? Without taking the eninge out that is. But if I were to do that, I'd sooner swap the turbos for a pair of 2530s or N1s.

[meshmesh]

markr34gtr is running these in his gtr... making around the 440rwkw and boost is coming around 5ish... do a search he just ran a 10.9 qtr

[Sydneykid]

Thanks SK. Are you saying the poncams haven't been good in GTRs or that you havent tried them? I think the poncam's lift is about 9.2mm. Do you think that's too much lift for the standard valvetrain, or will it be okay?

I guess there's not that much else I can do is there? Without taking the eninge out that is. But if I were to do that, I'd sooner swap the turbos for a pair of 2530s or N1s.

Tomei call them Poncams because they are bolt in (no other mods). If they say 9.2 mm is OK with standard everything else then it must be OK. Tomei do make cams that are not Poncams ie; they need mods to fit.

When I have used the 256/260 's in RB25DET's they are demonstrably superior to any others I have tried or see the results of. I have not seen this same superiority in their GTR cams. They are as good as the others, but not better.

I suggest you give the cam upgrade a try before you swap out the turbos, you might find that it is enough for your tastes.

Hi meshmesh, Mark has spoken to me a number of times about his set up. :wavey:

[T517zGTR]

Mik, Your not alone. I have a pair of Trust T517z in my R33, not sure how these compare to GT - Rs, I think they are close in term of total output power (330 - 360kw at 4 wheels on 22psi). I also have a susbtantial amount of lag over the stock items - to be expected. I seem to have full boost at about 4800 - 5000. I have done many of the other mods you mentioned and have been brainstorming ideas to lower my lag time with little success - came to a similar conclusion cams, cam gears, etc. Wonder how quick a pair of 2510s spool up? - pity it would be a massive top end sacrifice!

[meshmesh]

T517zGTR, a couple of sau members have these turbos, JAGR33 & Ph1, I've for a drive with JAGR33, and yes they're alot laggier than the 2530's, but damn they hit hard. I have a comparison thread somewhere in one of my threads. JAGR33 ended up getting Ben from Racepace in Melbourne to sort the lag out, and so far seems alot happier. Perhaps give Ben a call, a see what he suggest, Ben also built Ph1's car..

[R32-GTS]

As far as bolt in cams for gtr's go HKS Step1's have longer duration with 272 been the biggest bolt in with 8.5mm lift . The tomei poncams have a higher lift of 9.1mm but the duration is smaller with 260 been the biggest you can go . Im probably gonna use HKS 264 inlet 272 exhaust with 8.5mm lift to try bring the single turbo on a bit sooner.

[Sydneykid]

As far as bolt in cams for gtr's go HKS Step1's have longer duration with 272 been the biggest bolt in with 8.5mm lift . The tomei poncams have a higher lift of 9.1mm but the duration is smaller with 260 been the biggest you can go . Im probably gonna use HKS 264  inlet 272 exhaust with 8.5mm lift to try bring the single turbo  on a bit sooner.

It has been my experience that higher lift will help more than longer duration.

[R32-GTS]

Yeh i was interested to know this. But from 8.5 to 9.1 would that be a noticable difference ?

[Sydneykid]

Yeh i was interested to know this. But from 8.5 to 9.1 would that be a noticable difference ?

Yes :Pimp:

[R32-GTS]

tomei poncams seem to be cheaper than the HKS As well.

[Mik]

Yeh i was interested to know this. But from 8.5 to 9.1 would that be a noticable difference ?

That is a massive difference.

I think 272s would kill the idle a little too much for my liking.

SK,

Do you think the 260s would be better than the 256/260 for my application? I think I will drop in a set of cams and keep the GT-RSs for now. If it doesn't work out, the cams won't be wasted with smaller turbines anyway.

I have attatched the GTRS graph from the HKS website. I would love to know what has been done to that engine, because it looks like the engine is making 1.8kg boost at about 5000RPM. I guess the Jap fuel helps because you can run heaps of timing on spoolup.

Is the R34 RB26 a bit better than the R33 version? Or is the extra torque on the R34 over the R33 just due to ECU mapping?

[R32-GTS]

I think the 256 cam would be a bit small for a rb26 but thats only my opinion . I dont mind the lumpy idle of a 272

[pnblight]

ha I GOT A GTR RUN 260 DEG PONCAM STD INTERNVALS WITH BALL BEARING GARRETS RUN 518HP AT THE WHEELS ON 18 PSI AND WE PICK UP OVER 100 HP WITH THE CAMS AND ADJUSTABLE CAM WHEELS SO I THINK THE PONCAMS WORK JUST FINE

[discopotato03]

Mick just my two paseos worth not from experience . I think Nissan intended the RB26DETT to run like two 1300cc' engines on a common crank . I look at them as three 430 odd cc cylinders feeding each turbo on seperate manifolds . It looks to me like the GTRS (Garrett GT2871R) was intended for 2 to 2.5L engines in road tune . These turbos use compressor wheels a significant amount larger than the turbine ie 71 and 54mm . The GT2530's use 60mm diameter compressor wheels better suited to turbine (same) . While the GTRS's work better than the 2540's I see them as a compromise just less than the 2540's . I'm not sure what your power and drivability expectations are but its questionable if the GTRS's can deliver . If not you may be able to sell them and fit something that suits you better .

cheers A .

[R32-GTS]

ha I GOT A GTR RUN 260 DEG PONCAM STD INTERNVALS WITH BALL BEARING GARRETS RUN 518HP AT THE WHEELS ON 18 PSI AND WE PICK UP OVER 100 HP WITH THE CAMS AND ADJUSTABLE CAM WHEELS SO I THINK THE PONCAMS WORK JUST FINE

Did they bolt straight in or did u have to setup the shims again ? Also what did u set the cams too ? HKS seem to work best set on zero.

[blk180]

Yer i think cams(264in264ex is what hks were using in there dyno graph) and i think a set of aftermarket mainfolds to increase air flow would be good :headbang:

[rev210]

the 260deg poncams have 9.15mm of lift. I'd say they are a good option, you will have plenty more airflow room at 4000rpm onwards.

You want the turbo's to come in 'faster' ie; take less 'time' to hit power. This is appart from the rpm issue. Things like a set of lightened greddy pulleys and the replacement of the factory fan with a davies craig 16inch thermo will reduce the 'time' for the engine to reach revs. As will a good lightweight flywheel and even (if you have $4k or so) a single peice carbon fibre tail shaft (they weight about half the factory one).

A higher flowing intercooler might be the go as well.