-5's Vs Rs's On A Larger Then Stock Motor

[Piggaz]

This is a thread that I suppose only a few people can really relate or comment on.

N1GTR and myself discuss this all the time. I have a 2.8 and he has a 3.0 both with RS's on it same cams (270 @ 10.25) and both on E85. Now we both make enough grunt (400rwkw+) but I need close to 5K onboard for anything to REALLY happen, with the tallish OS 5 speed this is a pain in the arse! After looking through the results theads quite a few guys are making 400 + on -5's even on pump fuel with one 600 rwhp + (Gav from WA).... but then quite alot of disapointing results. Whats the secret to getting the -5's to work?

Those of you who have gone from the choof choof RS's back to the -5's how do they compare? Do you regret it? Are they big/small enough?

[rockabilly]

i too am curious to know as i am thinking of whipping my gt4094r single of for either, -5, 2860rs,efr 6255 or 6258,s.i too am after responce. its great to have 800 ponies but not so good is a 80bhp car beats you off the line at the lights...lol

[rockabilly]

paul, any idea when steve will swap his -5 on?.

[R31Nismoid]

Friend of mine is doing -5s on a 30DET, heaven knows when it'll be together though lol.

Similar time frame to Steveo "sometime in the future"

[r32-25t]

Just get rid of the 2.8 and put a 3.0 in it

[Piggaz]

Brett you just want me to do that so you can have my 2.8.... It will be my coffee table... a GT blocked 2.8 coffee table.... expensive but nice to look at .

Rockabily. Im 99% sure the -5's are going on the new engine so it wont be for a while...

The only issue is what cams to throw at it? Leave the 270's... Go back to 260's? Or burn it all and buy 997 GT2 RS and forget about it all!

[Gav]

My signature is somewhat deceptive in that the peak power quoted (~600 rwhp) was at an Autosalon event using ~20% toluene when I was still running my GT-RS terbs.

When I got into circuit work some years ago, I headed the advice of Snowman to go to the -5 terbs, fit a smaller IC and install a Nismo plenum. Peak power dropped to "only" ~550 rwhp, but mid range increased out of site. Given the fact that I am running an HKS 2.8 kit with supporting valve train mods etc, a possible 9k redline means that you have the choice for 2 gears in any situation on the track.

The following dyno graph tells most of the story, with the blue line being the GT-RS setup and the red line being the -5 setup:

Recently I converted to E85 (new fuel pumps, lines, injectors, cooler, ethanol content analyser etc) and am seeing 606 rwhp peak. The real benefit is the phenomenal mid range increase achievable given how much timing you can dial in on this fuel. I'll ask my tuner for a new graph overlaying all of the 3 combos.

My overall thoughts on the GT-RS terbs are that they really aren't the best choice for a circuit (or street) oriented GT-R. I really did try to do everything I could to get earlier boost and eliminate the dreaded "choo-choo train" shuffle, but never really succeeded.

[rockabilly]

thanks for that gav, graph looks awesome, my 3.0 has ported head and hks step 2 cams so should spool really well. do the -5,s shuffle?.would you reckon 1.5 bar boost by 4k.

p.s on the bottom scale have you an rpm one instead. here,s my graph to compare with yours.

Edited January 7, 2011 by rockabilly

[R31Nismoid]

I never stop enjoying looking @ that difference

[rockabilly]

well hurry steve and get them -5,s on...lol

p.s what kph is about 2000rpm at the bottom?.

Edited January 7, 2011 by rockabilly

[Piggaz]

Gav that result is just crazy! I dont quite understand how it can make SO much difference.... The hot side is exactly the same size but the cool side is a little smaller...

What cams are you running? How thick is the intercooler and what make is it? I have the Nismo plenum so thats done. Headwork? Bigger valves? Exhaust manifolds?

Sorry for the million and one questions but if I could a curve like that I would be a very happy man!

Having a choice of two gears at any point is awsome... At the moment I have 1 choice.... if im lucky! The RS's just seem really mismatched. This is not the first time I have heard of someone saying that. 2540's anyone?

E85 has made it a little better.... but im still not 100% happy with it.

[R31Nismoid]

I would tend to agree - RE: mismatch. I mean its quite evident with the surge going on that they are quite oversized.

Realistically are not suited to anything other than a 3ltr if you intend to street/circuit and expect decent response.

They do obviously suit their purpose, ok if you are drag racing/top speed runs and after just high end of the graph.

Also remember that your gearset perhaps is accentuating the issue somewhat. Not heaps, but it all has effects in the overall with something like that.

I'm going to get my car and compare with a -5 & -9 racepace cars so near idential - hopefully in the near future (admittedly I don't have stock -9 turbo's lol)

It'll be interesting to see what happens from 2nd/3rd gear 80km rolling runs etc.

Not totally relevant to this i know.

Paul - you and Steve should do the same before he pulls it apart. Just to see what its like for before/after.

Also dyno as well, two differences of the scale

[NYTSKY]

Big single time

GTX35R!

[Gav]

Gav that result is just crazy! I dont quite understand how it can make SO much difference.... The hot side is exactly the same size but the cool side is a little smaller...

What cams are you running? How thick is the intercooler and what make is it? I have the Nismo plenum so thats done. Headwork? Bigger valves? Exhaust manifolds?

Sorry for the million and one questions but if I could a curve like that I would be a very happy man!

Having a choice of two gears at any point is awsome... At the moment I have 1 choice.... if im lucky! The RS's just seem really mismatched. This is not the first time I have heard of someone saying that. 2540's anyone?

E85 has made it a little better.... but im still not 100% happy with it.

Terbs sit on Tomei manifolds and exhaust is Mines dumps, HKS front pipes and HKS Hi Power exhaust without a cat.

Intercooler is an HKS 100mm thick unit.

I have oversize Supertech valves fitted (inlet and exhaust), a LOT of head porting, HKS step 2 272 IN and EX cams.

ECU is PFC D-Jetro running Twin Power CDI, Splitfire coils and plain old copper plugs.

Fuel system is 1 Nismo intank pump feeding surge tank with 2 x Tomei (Walbro) pumps in parallel. 1000 cc HKS injectors mounted on an HKS fuel rail. Fuel flows back via a boot mounted fuel cooler (thermo fan radiator type).

Other mods aren't really relevant to the power curve.

Out of interest my mate here in Perth (R32TT) is just finishing a rebuild on his RB30 that also has -5 terbs. Hopefully he'll have a dyno graph to compare in the next month or 2. This was no slouch before the latest rebuild, so I expect it will be verry impressive in the latest guise.

[R32 TT]

Out of interest my mate here in Perth (R32TT) is just finishing a rebuild on his RB30 that also has -5 terbs. Hopefully he'll have a dyno graph to compare in the next month or 2. This was no slouch before the latest rebuild, so I expect it will be verry impressive in the latest guise.

Speaking of which - getting closer now...

-5's, 3L. 8.8:1 comp, HKS 264 Step2 (10mm lift), headwork but standard valves, Motec ECU and CDI.

Hopefully will have a good result - assuming Gav was joking today when he said he loosened some bolts....!@

Edited January 8, 2011 by R32 TT

[Simonster]

My 3 litre with -5's should be back running after an oil pump fail, yes N1- by the end of the month. 260x9.1 cams, stock cooler ex manifolds plenum but some headwork.

I'm replacing the Powerfc with an SM4 and running around 19psi, so it should be a reasonable indication

[HYPED6]

Here is my little story. I have been wondering the same thing the last 6 months or so. This is what I have found.

I bought my gtr with plain bearing -5's. Now with

Cams, 10.25 @ 292

Good after market front mount

Very good fuel

Stock dumps

Stock but ported exhaust manifolds

After market exhaust

After market ECU

Fuel systems to support anything I threw at it

Made around 490 rwhp on around 20 psi. Boost control was rubbish. Needed one solenoid per turbo and a 32x32 table just to get any descent control.

If I rung its neck.... (shut the wastegates) it would spike to 2 bar as it came on to boost and 22 psi at 850rpm it would make 530 rwhp. Rubbish.

Now I thought that this was under powered. So made some 2.5inch dumps. No difference

Shortly after one turbo died.

I bought some shiny new -10's.

Made some 3 inch dump pipes. Twin 3 inch front pipe to single 4 inch system.

Engine now makes 400rwhp on 10psi. Much better

Bloody thing hits another brick wall at 480 rwhp!!!! Regardless of boost levels. Regardless of ignition timing or fueling etc.

Now. I believe its the standard exhaust manifolds. I really do believe that is the key to making big power out of these turbos.

At the moment I am currently fitting a single turbo charger. Its the only thing I am changing so it will be a reasonable back to back.

Has any one else seen anything else similar?

Edited January 8, 2011 by HYPED6

[rockabilly]

32tt, thats almost my set up on a single though. i have hks step 2 272/280 10.25mm on a fully ported head. forged everything. cant wait till i hear from you or simon... i wonder what they are like at 1.7 bar..uuuuuuummmmmmmmmmmm we like big boost here in the uk.lol get them wound up boys,, 580bhp @ the hubs...lol

Edited January 8, 2011 by rockabilly

[rockabilly]

hyped6, i would be checking you have not got a collapsed silencer. we have a 33gtr here making 500bhp @ the hubs on std manifolds. its not the manifolds thats the problem. do you still have a cat fitted. if yes check its not collapsed.

[paulr33]

RPM = (SPEED / 28) * 1000

to work out RPM from a speed based dyno plot, assumes 4th gear with 4.11 diff gears