R34 Gtr Garrett -5 Turbo Lag, Need Advise

[baicai]

Hi Guys

I recently had Garrett -5 turbos install to my R34 Gtr, it now has alot of lag which make street driving a bit "slow". My car before with the stock turbo had a very flat curve, full boost at 3500 rpm, max power 244awkw, very responsive with hardly any lag, but turbo looses puff after 7000 rpm.

So I decided to get bigger turbos to fix the top end, was expecting some lag but now the car hits full boost at 5000 rpm! It takes at least second or two for the turbo to hit full boost. New turbos now make 292awkw limited by stock injectors and pump etc (will be done at a later stage). Now before you guys say I should have got the -7 or -9 turbos, my goal eventually is to get above 350kw on 98 or 400kw on e85.

So my question is can someone tell me how to lower the lag down to 4500 rpm or even 4000 rpm if possible. Tuner says intake hard piping, bigger inter-cooler, exhaust shops says twin 3 inch into 4 inch exhaust, internet says cams, don't know what to do. Just want to lower the lag before I chase for more top end power, any advise or help from you guys would be much appreciated.

My set up is

Standard: motor, inter-cooler, injectors, dumps, cams, pumps etc

Mods:

Apexi pods

dual 2.5 inch to 3 inch nismo exhaust

Tomei cam gears

Splitfire coil packs

Greddy ebc

Haltech platinum pro ecu

Alloy radiator

[XGTRX]

You need to upgrade

inter-cooler,

injectors,

dumps,

pumps

and at least a 3.5 inch exhaust from front pipe collector into good hi flowing system

especially for e85

you have too much restriction currently for good response out of -5s

at 3500rpm you should be close to 50-70% of full boost

Also check your cams are dialed in for response.

Its a shame you didnt do the dumps with the turbo change. If you dont want to spend the coin just do the 3.5 inch exhaust from front pipe collector into good hi flowing system..... you should get improved response just from this.

Edited February 17, 2015 by XGTRX

[baicai]

Thanks xgtrx, i will be doing all the supporting mods later, just saving up for the build. Was told cam gears was dialed in a bit. So you think for now just changing the exhaust will improve response in the lower rpm? My nismo exhaust is from turbo back with twin cats, i'll have to change the entire exhaust system, would twin 3 inch into 3.5 inch be enough for the future as well? Thanks for your input on this.

[hypergear]

-5s are very laggy turbos for RB26. and in lot of cases, the standard "T1.5" turbine manifold gets bored out, which adds more lag. if you are using adjustable cam gears, dial +5 on the inlet and leave 0 on exhaust. That will advance response by roughly 300RPM. Or get HKS V cams with active VCT cam set, that knocks out about 700RPM of lag.

Alternatively get -9s or check out our latest single development on our thread.

[XGTRX]

No worries mate. Yeah the 3.5inch exhaust will make a noticeable difference just get the exhaust place to cut out the 3 inch restriction near the down pipe flange and put a 3.5 inch flange. Also don't worry what people say, -5s are perfect for the rb26, they come on nicely from 3500ish.

[discopotato03]

IMO the Dash 9s are purpose built to do a good job on a fairly std GTR . I don't think anything is going to boost like standard R34 turbos and pull well over 7000 revs . 2568ccs isn't a whole lot for 1500 kilos of GTR and the roads to big power is breathing better at higher revs . The cost is boost lag because bigger is generally heavier and needs greater gas speed to overcome the inertia .

Everyones idea of adequate performance is different , usable performance probably doesn't involve 7000 plus revs in a street car . The killer of adequate imo is numbers because everyone seems to think if you haven't got 400 at the bags you haven't got a life . V8ers with longer arms than legs think like this . Voy oight .

A .

[XGTRX]

Beauty is in the eye of the beholder.

I find -9s boring, but that's just me. -5s are very good in-between turbo, yes, a bit more lag, and come on nice and strong. I have driven Laggy -5 set ups and more responsive -5 setups like mine and you can improve the response significantly with the correct breathing support to optimise the turbine spool. But anyway it's what ever floats people's boat. When my turbos have had enough I will be going TO4Z or similar because that's what I like. Obviously the op has made his decision with turbo choice and ask a specific question, and the answer to his question is YES, based on his current setup he can improve response by 500 rpm or more with certain changes without emptying his bank account, it would have been nice if he installed bigger dumps when he installed the turbos though. My 2 cents take it as you will.

[GTRPSI]

Get it on the dyno, get it tuned, advance the cams for earlier response.

Also make sure the wategates are shutting properly.

Dyno tuner should be able to pull much more bottom end into it if the wategates are OK.

Ive seen GTR's change dramatically in the way they drive from tuner to tuner, some tunes have more lag but plenty of top end, some come on hard but start running out of puff up top, some are a good balance.

[Stixbnr32]

Ok I am also speaking from my experience.

Things you do not need to waste money on.

Intercooler - I run 400kw with standard R32 intercooler although i have a hard pipe kit.

Things that are needed to make it more responsive.

1) Dump pipes - your tuner should have recommended when doing the turbos.

2) Exhaust - I run 3.5inch (as i said 400kw)

3) Decent tune

4) set of cams to bring those turbos alive 500rpm earlier. I use Tomei Type B poncams but there are others.

5) Lighter forged internals. Brought my turbos on 300ish rpm quicker.

You should see a good increase in response.

Do not forget a decent oil pump if you do a build with all the supporting mods (as you say).

Oh E85 for 400kw.......your tuner is not very good haha.

I run that on 98 and that is with 600cc injectors. If I had 700cc's it would be 430 odd.

Edited February 18, 2015 by Stixbnr32

[Roy]

If you are chasing response then leave std intercooler, leave std injectors, std fuel pumps etc. They are all fine if youa re just looking for a more responsive 300-310rwkws

As others have said spend the time on the good quality dump pipes that have 76mm outlet. Get matching front pipes and then get a good 3.5" exhaust that matches the merge of the 76mm front pipe.

From there check cams are set as per others comments...check the Apexi pods dont need a clean and away you go. Then just make sure your tuner knows what he is doing and isnt sitting on the fence with regards to ignition etc

My 2c..if he is telling you that you need a bigger intercooler, hard piping kit etc to cure the lag then either there is more to the story or is trying to milk money from the situation.

If you are trying to improve respnse and up the power to 400rwkws that the turbos are easily capable of then the story changes

[Stixbnr32]

agree with the above.

[XGTRX]

Roy is spot on with what he said right here: quote 'As others have said spend the time on the good quality dump pipes that have 76mm outlet. Get matching front pipes and then get a good 3.5" exhaust that matches the merge of the 76mm front pipe.' get rid of the 3inch collector collar and flange and full 3.5 inch exhaust. Like this

[r32-25t]

As everyone here has said for response exhaust does 75% of the job, cam timing does at lot as well. There are other ways of increasing response but most require a lot of commitment and money.

Leave the standard cams in there as longer duration camshafts will actually be detrimental to response

[GTRPSI]

I agree, a shorter duration camshaft comes on quicker so leave the stock one in there.

Pretty much sort out any exhaust side restrictions, play with cam gear timing and if the car is mechanically OK its down to the tune only.

[baicai]

Thanks every one for the advise so far, looks like dumps and exhaust will be my first to do list.

Reason for selecting the -5 turbos is that the car is a weekend car and i plan taking it to the track. Will be going to wakefield in a few weeks time

As the car is not driven on the streets all time so didn't mind a bit of lag as long as theres mid range and top end. Happy to put up with some lag just not 5000 rpm which i think is too laggy even for a track car.

Car was tuned by Adam from JEM and he said that he tune it with a balance between top end power and response, if he reduced lag would also lose top end. I will attach a dyno sheet when i get home tonight so you guys can have a look for me.

[Blackkers]

considering you've maxed out the injectors and must still be at low boost I'd say it would be a better idea to tune for best response as you can just push boost until you run out of injector flow...

[mr skidz]

Ok I am also speaking from my experience.

Things you do not need to waste money on.

Intercooler - I run 400kw with standard R32 intercooler although i have a hard pipe kit.

Things that are needed to make it more responsive.

1) Dump pipes - your tuner should have recommended when doing the turbos.

2) Exhaust - I run 3.5inch (as i said 400kw)

3) Decent tune

4) set of cams to bring those turbos alive 500rpm earlier. I use Tomei Type B poncams but there are others.

5) Lighter forged internals. Brought my turbos on 300ish rpm quicker.

You should see a good increase in response.

Do not forget a decent oil pump if you do a build with all the supporting mods (as you say).

Oh E85 for 400kw.......your tuner is not very good haha.

I run that on 98 and that is with 600cc injectors. If I had 700cc's it would be 430 odd.

hey stix

im doing identical setup except im keeping stock cooler pipes for the "its bog stock" look. did you need to change to hard pipe or just wanted to for obvious reasons.

what boost did you use for that power on 98

[paulr33]

i think most have covered it

intercooler wont change lag profile

1) displacement will change lag profile (stroker kit)

2) vvt kit will change lag profile (VCT or HKS kit)

3) tune tune tune (more timing in boost build)

4) cams, cam gear adjustment

5) explore exhaust manifold setup / split pulse etc - anything to get the turbocharger exhaust wheel moving quicker

6) downgrade the turbochargers to smaller exhaust wheel or different turbocharger profile

obviously they range form cheap, to outright mega expensive

[baicai]

Here is the dyno run overlapped with my previous set up on stock turbos 15psi, only thing that's changed is upgrade to -5 turbos.

[baicai]

Dyno run with over lap, also noticed a bit unstable at top rpm, unsure why.