Hks Gt-rs - Rb25det

[Beeble]

The 230 sheet was NOT in shootut mode and done in January which is summer so if it was a hot day it would of read higher in shootout mode.

34 degrees, to be precise

I like to think i didn't care what power figure i got, but to be honest i was not too happy with the weatherman's prediction that day

and yes... Nengun/Greenline - look at their prices before you start worrying about the lack of 2nd hand GTRS's

[discopotato03]

I would be asking Brett at GCG to build me a GT30R but with the 52 trim 76mm GT37 compressor and .50 A/R TO4E comp cover . This is essentially a GT3037 52T and with one of the soon to be available GT30 T3 flanged integral gate housings would be a good package for an RB25DET . The smaller trim comp makes a 3037 spool 500 rpm lower on an SR20 and still makes nearly 400 at the wheels .

Cheers A .

[Abo Bob]

As usual I will point out that there are two different GT-RS's. The one for SR20's and RB26's in pairs is smaller than the one for RB25's.

I think the GT-RS is a slightly bigger possibly better turbo than the GCG highflow with R34 or VG exhaust housing but the 2535 is on a par with it.

[Cake]

Anyone running their GT-RS on an RB25DET with the standard AFM? If so, what power are you making and has it maxed out yet?

[justin911]

wouldnt the AFM max out at the same point regardless of the turbo ?

Anyone running their GT-RS on an RB25DET with the standard AFM? If so, what power are you making and has it maxed out yet?

[Cake]

Yes, but The GT-RS seems to be making anywhere from 310rwhp - 370rwhp on similar setups. Seen a few dyno graph's of GT-RS's on RB25's but the AFM wasn't stated. Anyway I won't go offtopic and made a new thread regarding the AFM question.

[paulr33]

all the guys using the gt-rs would be using

z32

larger injectors

cold air intake

at least 3" turbo back system

[paulr33]

the afm also wont max out at the same spot

it depends on the compressor wheel and where its effiency zone is

ie a t88 on an rb25 may max out the afm like 6400rpm

whereas a gt-rs may do it at 3800rpm as it sucks a crapload more air in its effiency zone

[discopotato03]

Abo Bob I had a look around to be sure of the facts . I only found two versions of the HKS spec GT-RS .

The first is the SR20 version which has the S14 style comp cover on the std GT-RS cartridge .

The second is the RB20/25 version which has the straight snout version of the TO4B cover with a kind of port shrouding . It also has HKS's own custom .64 a/r T3 flanged GT28 exhaust housing specifically for RB's .

Interestingly Garrett is just about to release a version of the GT2871R in 52 compressor trim and the pic is identical to HKS's GT-RS for SR20's . The turbo no is 472560-15 and its cartridge no is 446179-67 . Its turbine and compressor spec is identical to the GT-RS . Because I'm a kluts and don't know how to copy links its at turbobygarrett/products/turbos and see 2871R 472560-15 . The turbine map is woeful as you would expect from the 71mm comp 53.85mm turbine mismatch .

Because I'm away with work (foreign computer) I cant post pics of the RB specific GT-RS but they are available at - Unique Autosports Online Catalogue - Skyline GTS-T Turbo , third item down .

I think this turbo in any version is a POS and you can do better . Sure the compressor may push enough air for ~ 400 Hp but the 53.85mm turbine in a .64 GT28 housing - very sceptical . HKS claim 300 wheel PS out of their own demo Silvia - they would claim more if they could ....

If you played around enough with some sort of GT30 turbine based CHRA with VERY careful compressor and housings selection you could do better . The real GT3071R with the right compressor or as I said small trim GT30R/3037 52 trim could do it and be reliable .

Cheers A .

[Al]

I think the GT-RS is a slightly bigger possibly better turbo than the GCG highflow with R34 or VG exhaust housing but the 2535 is on a par with it.

I totally disagree with this statement...

I currently have an rb25 hi-flow turbo, with the VG30 ext. housing. Although I am very happy with the end power (274rwkw @ 15psi on a 33deg day, non shoot-out), I am far from happy with the lag, hence the reason why I am now looking at purchasing a HKS GT-RS. Also I am having problems with compressor surge at light throttle/heavy load. This fault does not happen to all high flows, mainly the ones with the roller-bearing cores and the biggest sierra-sierra wheels. Basically at certain rpm and throttle position, the turbo is producing too much compressed air for the engine to digest, so it bounces back into the turbine.

In conclusion; HKS spend soooo much $$$$'s in R&D and produce a complete turbo that is engineered for a specific purpose. When it comes to hi-flows, wheels are taken from another turbo, placed in a foreign housing that have been machined/modified to allow clearances for fitment and "slapped" together. There is no way near the R&D as a specifically designed turbo, thus things like response, efficiency, etc are compromised.

A HKS 2530, 2535, 2540, GT-RS will shit all over a hi-flow, under any condition. Peak power really doesn't mean shit (unless your goal is to be dyno king); it's all about a broad range of usable power. If you can't afford a new HKS turbo than a hi-flow is a great option, just accept that it is purely a compromise.

Below is a dyno graph of my rb25 hi-flow with a VG30 ext. housing.

Note at what rpm full boost is achieved.

[GtstCoupe]

slightly off topic does the bos split pulse dump and front pipe fit the back or a gtrs as i have seen a pic

of the back of one and it look like it has no room for the tounge to go in and looks to have its own as opposed to stock turbo.

thanks lee

[180bfj20det]

I think this turbo in any version is a POS

Funny you say that...didnt you once mention youd go the 48 trim GT2871r if you could go back and turbocharge your fj????

But like you, I find it hard to believe the 53mm turbine could drive the 71mm compressor. But it does and very well so. You frequent the NS forums...have you seen the 2871r thread there?? Srs and CAs making 230-250rwkw, full boost from 4k rpm. It flows, may seem small like I said in my previous post but there is more than enough proof isnt there (check it out on NS for yourself). And remember this is for the 56 trim. The 52 trim will be less laggy albeit make less power (gtrs equivalent).

HKS know what theyre doing and so do garrett by having brought out the 52 trim 2871r. May seem bad on paper, but the 52T in 0.6 compressor housing works well.

[Abo Bob]

I totally disagree with this statement...

I currently have an rb25 hi-flow turbo, with the VG30 ext. housing. Although I am very happy with the end power (274rwkw @ 15psi on a 33deg day, non shoot-out), I am far from happy with the lag, hence the reason why I am now looking at purchasing a HKS GT-RS. Also I am having problems with compressor surge at light throttle/heavy load. This fault does not happen to all high flows, mainly the ones with the roller-bearing cores and the biggest sierra-sierra wheels. Basically at certain rpm and throttle position, the turbo is producing too much compressed air for the engine to digest, so it bounces back into the turbine.

In conclusion; HKS spend soooo much $$$$'s in R&D and produce a complete turbo that is engineered for a specific purpose. When it comes to hi-flows, wheels are taken from another turbo, placed in a foreign housing that have been machined/modified to allow clearances for fitment and "slapped" together. There is no way near the R&D as a specifically designed turbo, thus things like response, efficiency, etc are compromised.

A HKS 2530, 2535, 2540, GT-RS will shit all over a hi-flow, under any condition. Peak power really doesn't mean shit (unless your goal is to be dyno king); it's all about a broad range of usable power. If you can't afford a new HKS turbo than a hi-flow is a great option, just accept that it is purely a compromise.

Below is a dyno graph of my rb25 hi-flow with a VG30 ext. housing.

Note at what rpm full boost is achieved.

So ya wanna fight?!!!! hehe.

You certainly do have some serious lag there and I'm wondering whether you have cams or not. Your engine or associated hardware may have a restriction on the inlet side causing the compressor surge. Perhaps some cams or adjustment of the cam gears would bring the boost on earlier if you can get some more overlap.

By way of comparison here is my dyno sheet from the SAU Dyno Day last saturday.

I can get 1 bar by 3200. Also my car hasn't been tuned for this setup. My AFR's a very rich and all over the shop so more power to be had without requiring more boost.

BTW Disco - Did you realise you were agreeing with me there? :confused:

[R31Nismoid]

I totally disagree with this statement...

I currently have an rb25 hi-flow turbo, with the VG30 ext. housing. Although I am very happy with the end power (274rwkw @ 15psi on a 33deg day, non shoot-out), I am far from happy with the lag, hence the reason why I am now looking at purchasing a HKS GT-RS. Also I am having problems with compressor surge at light throttle/heavy load.

Now now... you arent using a GCG hi-flow, that why you are having problems in the first place.

Its something that "TBA PLACE" have come up with, and is not the same an a GCG item which does

1) Not suffer from Surge

2) Have shocking response

Here is the GCG from Bass Junky's car

He has cams as you do, but no head porting

http://image-cache.skylinesaustralia.com/f...-1132188138.jpg

Thats brilliant power, and response. I wouldnt call that a turbo made without any R&D.

IMO its spot on the money

The "TBA PLACE" one is the one thats showing how little R&D has been done on its design

[discopotato03]

This topic is about the GT-RS and my opinion is for it , have less time for the 56T version .

What I said about the 48T version I stand behind for these reasons .

Everyone at the time (me included) wanted to know what was the next small step up from the GT28RS (GT2860RS) in Garretts GTBB range . The GT28RS is good for ~ 35-36lbs compressor flow and the 48T GT2871R is good for ~ 39 . From memory the 52 and 56T versions do about 44lbs - the energy required to power a 44lb capacity air pump is significantly greater than a 39 or 35 lb one . ALL of these turbos use THE same 53.85mm 76T turbine . Because the GT28RS's compressor is a very good match for this turbine it works very well - in a .86 a/r turbine housing - on a 2L four .

I would not take this turbine past the 48T GT35 71mm compressor because I don't believe it can drive it properly read efficiently . The GT2835R starts to look much better than the 2871R because it has more turbine to drive the 71mm or GT35 compressors with . The modified turbine in the GT2835R is larger at ~ 56.6mm in 84 or 90 trim and developes more shaft torque for the same exhaust gas energy .

The GT-RS was the answer to the ultra lag HKS GT2540R , that doesn't make it perfect just less of a compromise . You people really should be testing the turbine inlet pressure and comparing it to boost pressure downstream of the throttle/s . You also should go to the maps for compressors AND turbines to get an idea how efficient the turbines are or are not . A turbine with an appropriate compressor is always going to be more efficient than the same turbine with a bad ie huge comp hanging off its shaft . Don't believe me ? Go back to turbobygarrett and have a look at the turbine map for the GT2860RS . Now flick over to the turbine map for the 52T GT2871R . This is the exact same turbine but its efficiency is pathetic don't you think ? The reason for this is 1) the diametre mismatch 2) its lack of gas flow capacity particularly in a .64 a/r turbine housing .

It is critical when specing turbochargers to compare the turbine/housing combinations corrected flow capacity and compare it to the compressor/housing's choke flow capacity . Now somewhere in the 55- 65% region of turbine to compressor flow seems to be ok , its a hell of a juggle with wheel trims and housing's a/r's but that's as broad a generalisation as I can work out . The best compromises seem to be 60%+ but you start to trade boost threshold for efficiency under full load full boost .

If I was going to work with FJ20's again (not) I would use a GT30 turbine or better still the 60mm NS111 turbine from Champ Car type turbos . In a perfect world my GT30 turbine would be 76 or 78 trim not the Diesel 84 trim and the compressor a GT35 71mm 48 or 52 trim . With a bit of stuffing around it would have more grunt than mine did with the GT28RS and no more chance of choking on its exhaust and melting down .

Custom GT BB turbos can be had if you know where to look but they are expensive and the success of them depends on your understanding of what makes a good one tick .

Out of time cheers A .

[mokompri]

heres a dyno sheet of the 52 trim version on an SR, just for comparison, stolen from silviansw.com, its TMB's chart..

the overly large compressor on the small turbine, doesnt allow boost to be held up top as the turbine starts choking, but even so its pretty impressive, with whats reported to be an awesome midrange

Edited March 14, 2006 by mokompri

[Al]

Now now... you arent using a GCG hi-flow, that why you are having problems in the first place.

Its something that "TBA PLACE" have come up with, and is not the same an a GCG item which does

1) Not suffer from Surge

2) Have shocking response

Here is the GCG from Bass Junky's car

He has cams as you do, but no head porting

http://image-cache.skylinesaustralia.com/f...-1132188138.jpg

Thats brilliant power, and response. I wouldnt call that a turbo made without any R&D.

IMO its spot on the money

The "TBA PLACE" one is the one thats showing how little R&D has been done on its design

In the past GCG did have various power options for rb25 hi-flows, they have since changed their options as some where surging. So please do not ASSUME without knowing all the info.

There are quite a few differances between Pete's set-up and my own, admitantly i have no strong idea on how they affect response and power.

1/ Pete has larger cams with longer duration; Pete D=260 / L=9.15 =/= Al D=252 / L=8.5

2/ Pete has higher compression which generally brings on boost sooner

3/ My combo is producing as self imposed (std bottom end) 270rwkw, Pete's started knocking when more psi was added (ie: 250rwkw is his limit). This suggests that mine is an older hi-flow that uses the larger sierra wheel (ie: my hi-flow has been rated at 500hp, by ATP).

4/ Pete's AFR are hovering at about 12:1, mine are hovering at 11.2:1

5/ My heads have been race ported, which i have now correctly been informed does cause slightly more lag.

6/ As pete's graph does not show boost, i can only estimate that he reaches full boost by 4k, which for me is still pretty laggy.

The 800 (or so) rpm differance is probably justified by the differance in set-up, as stated above.

[R31Nismoid]

So who did it then?

[Sass]

Would the 0.84 a/r version perform slightly better given we've seen the compressor wheel is too larger, or at least larger than it needs to be or is it just as bad?

I was under the impression the gt-rs was the bee's knees for the rb25. I think there are more suitable turbo's for the sr20 as they run (from what ive seen) split pulse and can generally bring on a slightly larger turbo earlier, in fact that gt-rs on the sr20 graph looks laggy, i wouldnt even expect the rb25 version to perform like that.

a gt30 on an rb25 has that sorta response. also 24psi? that doesnt sound right, it would be way off its effiency i would have thought?

[paulr33]

crap, i posted that