Reducing lag?

[Phillyb]

K so I finally decided to dump the gtst after a year and get a gtr. The car is dynoed 460 to the wheels but the turbo hits boost at like 6000 rpm and before you know it its smashing the rev limiter. Is there any way to reduce the lag at all? It has a power fc with the commander but im sure these turbos are just overkill. Ill post a pic of the engine and list of mods the car has. Any help is great thanks. PS dont get a triple plate clutch if you daily drive your car...lol

ENGINE:
Wiseco low compression pistons
R33 polished and balanced Crank, rods and bearings
R34 Water pump
Greddy Intake plenum
Greddy adjustable cam gears
Greddy 264 deg intake cams
Greddy 272 deg exhaust cams
Greddy 1.2mm head gasket
Splitfire coilpacks
Risky valve springs
Greddy TD05-18G twin top mount turbo kit
Custom intercooler piping
Greddy external wastegate
Greddy Airinx intakes
4in custom exhaust system with hi flo cat
OS giken triple plate clutch
Radiator with dual electric fans
Trust(Greddy) 4 layer intercooler with piping
Greddy Oil cooler

FUEL SYSTEM
Greddy Fuel rail
Nismo 550 CC injectors
Nismo fuel pump
Sard fuel pressure regulator

ELECTRONICS
Apexi Power FC stand alone engine mgmt with commander
Greddy Full Auto Turbo timer
Greddy Profec type S boost controller
2 Greddy H20 warning gauges
Greddy Fuel pressure warning gauge
Greddy boost pressure warning gauge
Greddy Oil pressure warning gauge

[Skym]

Intercooler could be incorrect for application (too big), wastegate springs might be too soft, boost control part of PowerFC might not be setup correctly, cams are too aggressive (exhaust side), exhaust A/R is too big on turbo's, exhaust is too big in diameter. Or combination of all of them.

Turbo's are not that big, smaller than hybrid RB25 turbo -

http://www.ztechz.net/id1.html

[gtrjon]

something doesnt sound right... with medium sized top mount twins on a built motor with a decent head you should hit full boost way before 6k... might want to check your map on the dated power fc

[Skym]

Thinking about it more, it could be that camtiming was adjusted to shift powerband up rpm (delayed camtiming on intake cam, hard to tell with that photo) -

http://www.tomei-p.co.jp/_2003web-catalogue/e092_adjust-p.html

But I still think intercooler size, etc should be checked to rule them out as part of the cause.

[gezed]

bigger intercooler does increase lag, but the amount if delay introduced by the thicker intercooler is almost negligible

http://www.evo123.net/archive/index.php?t-5549.html

[Super_Dude]

I would double check the part numbers on those turbos. They look a lot bigger than td05's to mee

[r33_gtst]

My stock GTS motor makes 492 rwhp at 4100 rpm....
You should be full boost much sooner, I'm sure it's something small that is making a BIG difference.

[collector240sx]

Hum, what kind of boost or you running ?
I'm wondering if you might have the TD06 compressor housing ?
(Like Super_Dude said, guess I'm not the only one that thinks this)

This would give these turbo more lag then your usual TD05-18G, but if they have that compressor housing they would also flow more (how much more not sure at all) :/

[MarusGTR]

Would the plenum also affect bottom end? I can see it's quite larger than stock and more perpendicular to the ITBs.

[Skym]

bigger intercooler does increase lag, but the amount if delay introduced by the thicker intercooler is almost negligible

http://www.evo123.net/archive/index.php?t-5549.html

Read this (from intercooler specialist) -

http://www.are.com.au/techtalk/intecoolersMR.htm#Turbo Lag

Can be up to 1 second or more difference and note at what rpm it happens. Response, spool are affected by size of intercooler and car can actually be slower on 1/4 mile because of fitting a bigger than needed intercooler.

Dimensions of intercooler core is rated for different hp levels, as shown in this link -

http://www.turbobygarrett.com/turbobygarrett/intercoolers

That hp is engine, turbo combined and as far as I know is at engine.

[gezed]

lol i guess thats gg for me, i got the intercooler rated for 950hp and im only looking to make 550

by the looks of it, and looking at the dimensions of the oem intercooler, it seems that it is rated for ~600hp, would this mean that guys running stock turbos/boost would benefit from a smaller intercooler?

[MarusGTR]

lol i guess thats gg for me, i got the intercooler rated for 950hp and im only looking to make 550

by the looks of it, and looking at the dimensions of the oem intercooler, it seems that it is rated for ~600hp, would this mean that guys running stock turbos/boost would benefit from a smaller intercooler?

You had an OEM one all along!? Hell yeah put it back in! Because of mass conservation, the bigger the cross section for a same flow rate, the lower the speed, the more lag. Go OEM and enjoy.

[Skym]

by the looks of it, and looking at the dimensions of the oem intercooler, it seems that it is rated for ~600hp,

I know of one R33 GTR that achieved around 536awhp with stock R33 GTR intercooler. R34 GTR has the best stock intercooler if you can get hold of one. By changing to tube N fin intercooler (stock intercooler is bar N plate) = +27awhp.

GTR is designed to be at 4000rpm+ on racetrack, so size of intercooler vs lag, response wouldn't be as bad at that rpm band with stock turbo's or N1 turbo's. Just don't let it drop below 4000rpm (drop to a lower gear before corners to keep rpm needle above 4000rpm, just like they did with GTS-R racecars which had to keep above 4800rpm).

would this mean that guys running stock turbos/boost would benefit from a smaller intercooler?

For road use where engine is below 4000rpm most of the time, yes.