Rb26 Fullboost By 5000 Rpm (34 N1 Turbos)

[mr_rbman]

So I've just had my 32 GTR tuned, she made 309 rwkws & 20psi tailing off to 18psi. Basically made the power I was expecting so no dramas there.

The issue of concern is where she's not making full boost til ~5000RPM, reading the RB26 results it would appear virtually everyone with similar mods and power levels are seeing full boost by ~4000RPM.

Below are my mods:

Rebuilt forged RB26

R34 GTR N1 turbos (GT2860-7)

Splitfire Coilpacks

Sard 650cc injectors

Nismo AFM's

Greddy cam gears (2 degrees adv. on inlet, 4 degrees ret. on exhaust)

Nistune ECU

Blitz SBC

Walbro 460lp/h fuel pump (12v direct feed)

Stock airbox with K&N panel filter and CAI

Full custom Exhaust (2.5" twin split dump pipes (350mm separation-1.5" wastegate pipes) into 3" collector into 3.5" decat and all the way to the tip 3.5" with two mufflers)

All intake piping is stock

I did have a boost leak which is now fixed and when doing so and pressurising the system we checked actuators were opening together and they all looked good, the turbos were checked over when exhaust was done and all appeared in good nick <200kms ago.

So any thoughts?! car feels great, mind you I do now have 100+ rwkws more at the wheels so that is to be expected...but on paper it just doesn't seem right.

[Dose Pipe Sutututu]

When does "boost" all come in on the road say in 3rd or 4th gear? sometimes dyno operators don't calibrate the derived RPM vs. road speed properly and it reads off.

[mr_rbman]

mmmm hard to say johnny, can't say I was looking at RPM driving it home

[MrStabby]

So you're getting 10psi at 3800. Should be more like 14 at 3800. What did the tuner say?

I'd be looking at exhaust restriction or boost control setup. Eg. did they wind some preload into the actuators?

I dont think "full boost" is a useful term, better off saying X psi IMO.

[Piggaz]

Crappy HKS style split dumps ain't helping, nor is the 3 inch small point in the exhaust.

[KiwiRS4T]

Get a passenger to watch for you. See at what speed or rpm it hits 20 psi.

BTW boost tails off slowly straight after hitting 20 psi - is this normal for these turbos?

Are the internal wastegates working properly? Not catching anywhere?

Did the tuner spend some time on the adjustable cam gears (I have no idea what the settings should be for your engine)?

If you get the same result as your chart consider changing the boost controller if adjustment doesn't fix it.

[MrStabby]

Crappy HKS style split dumps ain't helping, nor is the 3 inch small point in the exhaust.

How would they slow spool? I thought the argument against these dumps was boost creep. FWIW, i have the xforce knock offs and have neither issue.

[Hadouken]

It's probably in the tune. We need real world not stupid dyno paper

[CEF33Y]

Yeah, I notice a difference in hitting "full boost" on the street compared with my dyno sheet.

The way you load it up makes a big difference, well in my case. But I have a turbo that is too big for the engine.

[mr_rbman]

Pic of my dump/front pipe...

Edited March 11, 2016 by mr_rbman

[mr_rbman]

So you're getting 10psi at 3800. Should be more like 14 at 3800. What did the tuner say?

I'd be looking at exhaust restriction or boost control setup. Eg. did they wind some preload into the actuators?

I dont think "full boost" is a useful term, better off saying X psi IMO.

actuators have the typical 4-5mm preload on them, boost control has been played with (gain etc.)

Crappy HKS style split dumps ain't helping, nor is the 3 inch small point in the exhaust.

I spent quite a bit of time reading the threads on here with bellmouth vs. split dump pipes etc. and came to the conclusion that provided the split was long enough the benefits of either were negligible. I've attached a pic above of my system so that you can see its quite different to the HKS / X-Force style dumps you are referring to.....not saying that my system style still couldn't be the issue...though I thought it would have had an affect on power output too?!

Get a passenger to watch for you. See at what speed or rpm it hits 20 psi.

BTW boost tails off slowly straight after hitting 20 psi - is this normal for these turbos?

Are the internal wastegates working properly? Not catching anywhere?

Did the tuner spend some time on the adjustable cam gears (I have no idea what the settings should be for your engine)?

If you get the same result as your chart consider changing the boost controller if adjustment doesn't fix it.

didn't spend a heap of time with cam gears, tuned with them set to '0' and got to around 283kws @ 18psi from memory then from the research I did on here set the cam gears at 2 degrees advanced on the inlet and 4 degrees retard on the exhaust and netted 309kws @ 20psi (went to 20psi and tailed to 18psi without actually touching the boost controller settings.) so I was relatively happy with that change and didn't play around any more...

How would they slow spool? I thought the argument against these dumps was boost creep. FWIW, i have the xforce knock offs and have neither issue.

interested in this too...

It's probably in the tune. We need real world not stupid dyno paper

as I mentioned the car itself feels great.....though I'm not sure if that's because I've been driving it around with <100kws less or if its just the dyno sheet playing funny buggers with my head

Yeah, I notice a difference in hitting "full boost" on the street compared with my dyno sheet.

The way you load it up makes a big difference, well in my case. But I have a turbo that is too big for the engine.

Definitely hear what you're saying, I had an RB30/25 with and XR6T (35/40 - 1.06 e/h) and that was my definition of lag yet that hit full boost around the same as this motor.

Just getting my head around it all I think...and the different types of power and curves....

Edited March 11, 2016 by mr_rbman

[KiwiRS4T]

When the car is on the dyno I think its worth paying the tuner as long as it takes to get the camgears right - makes a huge difference on a 26.

I realise this is a completely different turbo set up (GT 3540 on an RB30) but achieved rock solid boost control with a Link, Mac Valve and a Synapse 50mm wastegate:

[mr_rbman]

That's more like what I expected to see Bob, I know my Blitz SBC unit isn't by any stretch top of the line but from what I'd read before purchasing it was a pretty good electronic unit but the boost curve looks more like one controlled by a bleed valve :-/

[djvoodoo]

I have similar mods to you except on an unopened motor, and on an R34

Did a test just now actually.

On my HKS EVC6 at 3900 rpm (or around 96km/h) I get 13.9 psi of boost in 4th Gear. It's an average mild day in Syd - roughly 22 deg and its not crazy humid.

I adjusted the "offset" map feature in all my RPM ranges on my controller and push a tonne more offset than the default 100% as per HKS.

Tune has a massive influence. My last tune with a different tuner was absolutely shite and was a laggy pos with -7's.

[STATUS]

Can gears are setup for peak not response. There is 500 to 650rpm in fixing the cam timing.

[mr_rbman]

I have similar mods to you except on an unopened motor, and on an R34

Did a test just now actually.

On my HKS EVC6 at 3900 rpm (or around 96km/h) I get 13.9 psi of boost in 4th Gear. It's an average mild day in Syd - roughly 22 deg and its not crazy humid.

I adjusted the "offset" map feature in all my RPM ranges on my controller and push a tonne more offset than the default 100% as per HKS.

Tune has a massive influence. My last tune with a different tuner was absolutely shite and was a laggy pos with -7's.

Thanks for that input.

Can gears are setup for peak not response. There is 500 to 650rpm in fixing the cam timing.

Status, what settings would you suggest for more midrange/earlier boost?

I did search here before having it tuned and the settings I went with were the general consensus for good midrange?!

[Dose Pipe Sutututu]

^ haha.. that's IP man, most tuners won't give that out

but generally advance intake, retard exhaust.. the magically number really needs decent dyno time to overlay the graphs.

[KiwiRS4T]

Thanks for that input.

Status, what settings would you suggest for more midrange/earlier boost?

I did search here before having it tuned and the settings I went with were the general consensus for good midrange?!

Settings can only be determined on the Dyno (or repeated back to back street runs). As always every car is different and a good tune is never cheap if you take the time to do it properly.