Twin Garrett Gt3071r Vs Twin Garrett Gt2860r On 26/30

[shanef]

As topic states guys and girls i'm after some input on turbo's set-up for my build in progress rb26/30 in my 32 gtr.

Twin high mount Garrett GT3071R or Twin lowmount Garrett GT2860R (GT-RS equivalent)

Quick rundown on engine specs

rb30 bottom end

head ported, inlet port re-profiled

Forged pistons standard bore

Argo Rods

ARP rod bolts

Tomei headgasket

JUN 264 in 272 ex 10.5mm lift cams

JUN springs

Tomei cam gears

800cc or 1000cc injectors (dependant on turbo pick)

SX external fuel pump

CR of 8.5:1

The car will be set-up for track work BUT i want to run a 10 sec 1/4 pass. I aslo dont want to run anymore than 2bar boost (hit me here with advice also please) to obtain a power figure of 700awhp. I dont want it to be a lag monster, as for the track it'll need to be responsive as possible.

So can i get some for and against on these turbo's and maybe other turbo's i could perhaps go for. Any input would be very helpful and general discussion welcome.

Once again i'll say thanks in advance

cheers

Shane

[paulr33]

boost is irrelvant, choose a suitable compressor based off compressor maps to get you the airflow you need. have you chosen largeish twins for reason? why not a big single, it could simplify stuff a bit and make it a nicer package possibly

[shanef]

first thing is i cant 100% read compressor maps confidently enough to go yep that ones for me

i was thinking keeping the twins for the responsiveness and also the larger twins for the higher power output, rather the big single being laggy and not being able to produce as much power up top as 'larger' twins. hit me on your thoughts of this

[paulr33]

howstuff works or google on how to read compressor maps. work out how much airflow you need to make your power target and then simply pick a compressor wheel combo that suits that output and its efficency should be spot on. takes out the guess work.

well you can get a big single, one amount of rotating mass, interia, friction

also oil, water, ball bearing

or

two smaller twins, two amonuts of rotating mass, twice the interia needed, twice as much friction and heat loss. you wouldnt want plain bearing twins as it would preform worse than a ball bearing single

i dont see how a large single vs twins would vary much in terms of lag.

as long as you did your homework on the compressor maps and made sure it was spot on, i dont see how it would be more or less laggy, if anything i could only see big single as being better

[shanef]

alrite, i did a search on google and found a site about maps and how to read them.

1 question. in working out the cfm, the formula i use is (enginecapacity in cubic inch/1728) X (RPM/2) ?

so in my case its (91.536/1728) X (8000/2) = 211.89 cfm

as per this site http://www.automotivearticles.com/Turbo_Selection.shtml

[discopotato03]

In my inexperienced opinion single and a TO4Z can do the gas flow numbers . GT3071R's will only fit with HKS exhaust housings as these are the only T28 flanged GT30 housings I know of available . The "WG" version of the GT3071R is a dog so fit at your own risk .

TO4Z's are handy because there are so many exhaust housings options out there ie T3 and T4 flange and single or split entry . I've seen a huge range of AR ratios ie from .32 up to I think 1.6x so very tunable . Its TO4R compressor is said to be very resistant to surge which is good if you need small AR turbine housings . You can buy HKS exhaust housings for them in T4/TA45 flange and probably fair to assume these are the most highly developed housings for the old P trim turbine in a performance petrol application . They are more compact than Garretts agricultural T4 truck type housings .

I believe Cruiseliner has the HKS version so his opinion would tell the story .

Cheers A .

[paulr33]

im for big single

[shanef]

There is no way in the world im going to pay the HKS tag price for a turbo, so its Garrett for me.

I was up til 1 this morning trying to figure out which turbo/turbos would be for me lol

Paul, do you know how to read the maps and work out flow rates? If you do can i grab an email or msn caus i have a few more questions.

[discopotato03]

Thats not what I said , I mean you can buy a Garrett TO4Z without the Garrett turbine housing and fit a HKS turbine housing to it . Far cheaper than the High Kost Spec unit complete .

[paulr33]

have a search on discopotato03's posts he has explained it a few times im pretty sure on how to read compressor maps and choose ideal flow for a given engine and turbo setup. make sure you set the search to his username only and you should find what you need. i can pm you my msn login but i dont know how to read compressor maps nor do i understand the full merits behind all the info, i just know if you read them you can basically pick what compressor combo you need make the power

[BU5TER]

Go with the twin high mounts you should get full boost by 6000