Rb26/30 With Super Responsive Twins Anyone Done It

[rockabilly]

hi guys, alot of you know my motor from my threads. i have been doing alot of track work recently and although its a complete monster i want to lower my boost threshold. currently the car makes 1.5 bar by 4500rpm and that 660 bhp @ all 4 on a hub dyno. i know i will have to drop to maybe 500 @ the hubs but gain responce. has any members fitted 2860-5 or similar twins and run them at 1.7 bar.... if yes what are they like coming out of a tight corner in say 2nd gear at 2500rpm..bernie

p.s i need to chase some evo,s lol.

Edited August 25, 2010 by rockabilly

[GTRNUR]

Those dam evo's do have a big advantage over the heavier GTR's in the tight corners. Particularly in braking and acceleration, and dam understeer.

Something to consider though is that if the power delivery of your current setup works and feels nice and smooth, and more importantly it is controlable adding more response at the engine may unsettle the car and make it very taily in the corners. Too much response may force you to drive on and off the throttle to control power oversteer.

GTS4 diff gears might be worth considering to prevent rpm's dropping too far in the corners and to give you better acceleration out of the corners. Im guessing your racing at the same track all the time, and that there are corners too fast for 1st gear, yet too slow for 2nd? I have the same issue with the sprints I race in... and the evo's dominate there as well.

Another option worth considering is a Vcam setup, to prop up low end torque without making boost response too savage.

Sorry that this isnt even close to the answer you were asking for, but since you mentioend the evo's I think this may be relivent.

[gt0311]

how about a changing the exhaust housing to a smaller 0.93

[R31Nismoid]

You'll easily make 500hp @ the hubs on 20psi with -5s, probably even less boost.

They will make 400-420rwkw if the motor is built right and be much more responsive

Not sure about them coming on hard @ 2500rpm though. You'd need to go smaller again IMO.

[James_03]

Yeah I am just about to drop in my new motor which is a 26/30 9:1 with -5's. I can't answer the question directly but.

I won't have any idea on response until I get it out to Lakeside for a run.

But as Ash has mentioned -5's would probably be your best bet, will net the power and response your chasing. That's why I chose them anyway, I am expecting them to be pretty strong at around 3000, maybe a bit earlier if I muck around with the cam gears.

The cheap alternative is to find a track with more straights.

Edited August 26, 2010 by James_03

[Marlin]

Berry's 3.0L in the 34 was awesome with -5's on it.

Add E85 and it'd be even better.

[N1GTR]

Rockabilly what cams do you have?

[rockabilly]

Rockabilly what cams do you have?

hi mate,

cams are hks step 2 270/in and 280/ex 10.2mm lift

motors all forged, cp,s spool rods etc.will support 1000bhp..lol

will be running shell v-poer pump fuel 98 ron uk

as for tracks, not one track in perticular. i have drive this year,

castle combe,silverstone, spa franchorchamps, the ring, zolder.. many different curcuits but usually the same issue, my friend runs a gtr with a rb26 on 2859r,s these are superb but not really available any more. he made 490 at the hubs on boost 3k..bernie

[N1GTR]

Well first up; I'm quite jealous of those tracks

Other than that, as everyone else has said dash5's seem to be the best suited to what you want but you're no doubt giving this a lot of thought so here's something to think about:

Why only have that power? Given that you've got capacity on your side you could get away with slightly bigger turbos and gts4 diff gears. Check my last dyno sheet in the results thread, that's all standard gearing and diffs. If I had a set of 260 cams I'd LOVE to do a back to back comparison of the 270's. Id be willing to bet the 260's would make the curve even more desirable. Now remembering that thedash5's will be a drop in power compared to what you're used to, I'd suggest the dash10's as the perfect setup with 260's and gts4 gears.

Yes I'm biased as a GTRS owner, but they're about to be swapped for dash5's and I am NOT looking forward to less power

Hope that helps in some way

[Scooby]

Yes I'm biased as a GTRS owner, but they're about to be swapped for dash5's and I am NOT looking forward to less power

Hey Stevo why are you going to -5s?

[N1GTR]

Hey Stevo why are you going to -5s?

Way too much to into in someone elses thread, basically I want to try out a different setup and see how it goes. End of the day if dash5's don't make the right power, it's back to GTRS's but I'm looking for low end power as opposed to bucketloads of top end power and no low/midrange. It makes 400rwkw by 5250rpm now but I think I can get it at lower rpm which is the same thing rockabilly is chasing but he's built his motor and I'm fairly certain doesn't want to have to build another one (and who would blame him, no one has a money tree) whereas I'm happy to build another one with some changes to see if it makes a difference

I'll probably make a thread on it once it's done

[Lithium]

Why did you change from the GT3582R to a GT4094R? Would that have not been responsive/powerful enough for what you describe? As I mentioned on another forum, I'd have thought a T4 twin scroll GT3582R would be far easier, cheaper and generally better than going to -5s from your current position

[Marko R1]

bernie - i wouldnt go any smaller than -5s & im sure that yout tuner can pick the lower revs with his tuning as well as smaller cams.

if u went with the above mentioned gts4 diff gears...i think u will eat those little evo's

[rockabilly]

cheers guys, to answer some questions, here in the uk gts4 diff are very rare. also when i fitted the gt35 r with a 1.06 rear and t3 that was about 3 years ago it wasn,t as responsive as i would like. the gt4094r spools as fast as my old gt35r did back then. so at the time it was a no brainer. i like the idea of fast reponding twins, maybe go 2860-5 and alter the cam timing, as for mapping marko i do that on the road with a friend of mine.....lol

Edited August 27, 2010 by rockabilly

[rockabilly]

just come across an intersting turbo i may try. its a 2871r.. but it has a 48 trim so smaller than a -10 but bigger than 2860-5 rated at 400bhp each. i have spoken to a guy in the uk who has an os giken 3.0 with -5,s,spool is instant but he has massive surge problems that he cant get rid off. he runs them at 1.65 bar.. maybe the 48 t will help this. i have only found apt that do this turbo in the gtr fitment internal wastegate.. will dig deeper.

http://www.atpturbo.com/mm5/merchant.mvc?S...tegory_Code=GRT

thats a 56t but i am sure they can there hand on a 48 t

this is the baby but with the wrong housings

http://www.turbobygarrett.com/turbobygarre...1R_743347_3.htm

Edited August 27, 2010 by rockabilly

[rockabilly]

copied from the fiat forum, seems they are good in single form even on a 2.0 ltr 4 pot

I use a GT2871R 0.64 and it gives positive boost pressure soon after 2,000rpm. It give 1 bar just before 3,000rpm and it is boosting fully by about 3,500 - 3,750rpm (depending on gear)

It has a 76 trim turbine wheel and a 48 trim compressor wheel

[GTScotT]

The 2871 with a 52 trim compressor is AKA the HKS GTRS. Going the 48T version IMO would be a miss match (as otherwise would have been used by HKS themselves) and is likely to be less responsive than the -5s.

I do however see a theory forming... Essentially the exhaust side on the 2871 to the 2860 is the same... Perhaps this could help resolve the surge issue.

I am a firm believer in pursuing what works though, this could be an odd mismatch.. There is someone on this site that could provide a better opinion though.

[rockabilly]

The 2871 with a 52 trim compressor is AKA the HKS GTRS. Going the 48T version IMO would be a miss match (as otherwise would have been used by HKS themselves) and is likely to be less responsive than the -5s.

I do however see a theory forming... Essentially the exhaust side on the 2871 to the 2860 is the same... Perhaps this could help resolve the surge issue.

I am a firm believer in pursuing what works though, this could be an odd mismatch.. There is someone on this site that could provide a better opinion though.

true mate. the os giken 3.0 ltr here with 2860-5 is an animal, but from 5800 onwards on light throttle shuffle is horrendous, it wont evn map out. under load alls well, but the guy lives in cumbria where there are lots of twisty country roads, he is a rally driver by day and wanted power and immediate responce, he is happy with the set up bar the shuffle, you have to come completely of throttle and then back on hard to remove it.. the 48t version may help this. not sure but io think hks 25/30,s ran a 48 t..will check lol

[GTRNUR]

I just had a thought...

Is your turbo a twin scroll housing? If it is you could use one of the quick spool valves that are becoming popular with the supra guys.

http://www.supramania.com/forums/showthrea...ick-Spool-Valve

And the link where there are some pictures of the valve...

http://www.spracingonline.com/store/Sound_...pool_Valve/3643

Edited August 28, 2010 by GTRNUR

[rockabilly]

managed to find this.the hks 2835 uses a 48t but cant work out the housing sizes, i think they are in inches?.

http://sites.google.com/site/tyndago/gt-rturbos

hks GT2835

ps 380

comp trim 48

inducer 49.3

comp major 71.1

comp inlet 70

comp outlet 50

a/r 0.50

turbine trim 84

turbine major 56.5

turbine exducer 51.8

GT25 Internal - GT28 84 trim

0.64

0.86

garrett Turbo CHRA

743347-1 446179-31

Wh Dia Trim A/R

Ind Exd

49.2mm 71.0mm 48 0.60

Wh Dia Trim A/R Type

53.8mm 76 0.86 Wastegated

TURBINE HOUSING OPTION

Part Number

430609-230

Wh Dia Trim A/R Type

- - 0.64 Wastegated

Oil & Water-cooled Bearing System

Edited August 28, 2010 by rockabilly