Volumetric Efficiency

[discopotato03]

The "GT2560R" part number 707160-9 is the real GT-SS from what I can find . Too many people in the US quoted the same numbers as that Garrett unit from their purpose bought HKS RB26 specific GT-SS turbos to assume anything different .

If you pay attention to the Garrett specs at the link I posted you'll notice that its compressor wheels major diameter is 59.4mm not 60.1mm like most GT28 BB compressor wheels . I really would like to see a pic of one of these turbos with the compressor housing removed but the only contact I had here never got around to pulling the cover and posting some pics .

For mild street RB26 nuts it's a godsend that you can buy HKS spec turbos at a Garrett price off the shelf . If you throw HKS spec actuators at them I reckon thats what ya get if you order them through HKS .

For a pure street std capacity early GTR they would be the pick to have better turbine response and probably a little more top end that factory dryers .

A .

[Lithium]

I am a little confused. The -7 has been tagged as the GTSS equivalent but now a few people have moved over to the -9 as being more closely aligned.

I've always taken the -7 to be more like an N1 equivalent... it seems the first person to be heard to say something about a topic (ie, -7s = GT-SS) is the one thats right and it takes a lot to get it set right if they weren't.

[The Dan]

I've always taken the -7 to be more like an N1 equivalent... it seems the first person to be heard to say something about a topic (ie, -7s = GT-SS) is the one thats right and it takes a lot to get it set right if they weren't.

-5 is R33 N1

-7 is R34 N1

Well this is what Garrett tell me anyway

[rev210]

I've been looking at the -9's and they almost look like they are a newer design.

They seem to enjoy the best of the -7 early spool action and yet have the efficiency in the bigger airflow regions akin to the -5's.

For a road car I reckon the -9 is the new black.

[discopotato03]

I think they were a bit of a special HKS got Garrett to cobble together based on parts Garrett already had .

The turbine is the more OEM style GT25/28 and I'm not real sure about the compressor wheels except that the major diameter is a tad smaller than usual for A GT28BB turbo .

They sound real good to me because I believe they want to get going in the 3000-3500 engine speed range , the bit where most non originally GTR people feel a bit short changed in an expensive performance car . I get the feeling that people who progress from single turbo Skylines to GTR's find this tiresome when driving around town in the 2-3000 rpm range , they feel they have to buzz the things around everywhere in the 3500-4000 range so they get some squirt when they want it .

If that were me and I had the chance to pull the effective power range down 500 revs I'd leap at it because its far easier to do it with bolt on turbos than say a capacity increase .

I think there was a long thread here ages ago by someone who called himself (I think) WilliamsF1 that went to a lot of trouble to turn his street GTR into something more acceptable than the factory had R32's (I think his was a 32) .

From memory he did head work / Poncams /GT-SS's and the results were really good as in pulled pretty hard everywhere and didn't have to rev it to do it . One would imagine that it would not be as free reving or have the very top end that say HKS GT2530's would have but for a street car who needs that ?

I you want to burn off the coke tin LS V8's and XR6T's your better off with something that pulls from a bit lower down , the "innertia rush" is more pronounced and your get you jollies without exceeding the speed limit by a factor of 2 .

Lets face it big capacity engines feel soooo strong because they make bulk torque at lowish revs . Where you should be able to annihilate the 2WD V8's is from standing starts because they can't get all that power to the ground so by the time you're running out of second they should be history - thats the time to back off and watch them hurtle past into the next speed trap ....

A .