Turbos in 2020 : Nissan Skyline GT-R : Twins Are Better Than Singles : Garrett Bolt on Turbos

During this test, the small runner manifold increased spool by 160-220rpm over the large runner manifold. This was also accompanied by a large increase in VE/fueling requirements, particularly during spool up, that resulted in more power/torque at the same boost level nearly everywhere with the smaller runner manifold. Torque was augmented from 40ft/lbs to as high as 125ft/lbs during spool up and as much as 42ft/lbs in peak torque numbers. Horsepower was augmented as much as 50whp at some points in the curve and ranged between 19-25 higher peak horsepower numbers.

We run a pair of turbochargers on our RB26 in our Project RH8 R33 GT-R. Cylinders #1, #2 and #3 feed the front turbo while cylinders #4, #5 and #6 feed the rear turbo. Because there are no cylinders that fire in sequence paired to the same turbine, the amount of time between exhaust valve events that will happen on cylinders feeding the same turbine has doubled. Instead of having only 120 degrees, there is now 240 degrees.

Tomei cast exhaust manifolds vs stock exhaust manifolds

OEM RB26 vs N1 Exhaust manifolds  Thanks Brook

All this talk about exhaust manifolds and no talk about turbos yet.   The OEM R32, R33, and R34 GT-R turbos, on the “normal, and Vspec” cars are all ceramic exhaust wheels. There are some cars that have metal turbine wheels, the Nismos, the later N1 cars, a few others, but generally they are ceramic. Being ceramic is awesome for weight.  The lighter the wheel, the easier it is for the exhaust energy to act on the exhaust wheel. The exhaust wheel is mechanically coupled to the compressor wheel, so the easier it is to push that, the sooner that the compressor wheel, starts compressing, the sooner the magic happens. However, ceramic wheels are somewhat fragile. Or, really just not as durable as a metal wheel would be a better statement.  

On the exhaust side, you can 100% have too small an exhaust housing. There is a point, when no matter what you do, you have so much backpressure across the turbo, turning it up anymore, doesn’t gain anywhere near the amount you think you should.  It is something that isn’t talked about a lot in the turbo world.  Some people assume the smallest exhaust housing will give them the best spool, minimize lag, and still be able to make power. However once you get above the 1:1 ratio of boost to backpressure, you are done.  In the video below, Gale Banks explains boost to backpressure ratio. He knows his way around turbochargers, you should listen to what he has to say. You will probably learn something. 

•  A Billet Compressor Wheel compared to a Cast Compressor Wheel offers NO GAIN in performance by its material alone. Some have argued that they can be made lighter for better spool, or that they can be made with more aggressive fin designed due to there better sheer strength. While that MIGHT be true, we have seen no conclusive evidence or study that has proven this so we have to rule it out for now and say it’s NOT FACTUAL even though it MIGHT be true.

Billet wheels CAN, again that is CAN, perform better. Because they can be a low production run of wheels, there flow and performance can be tailored to running a specific pressure ratio (PR) or to have a certain amount of peak flow, or surge line capability, or be able to jump on new blade design technology faster since there is no need to delay the technology getting to market because of setting up machining and tooling.

ATP Turbo sells a number of bolt on Garrett choices for the RB26dett.  The horsepower ratings are at the engine, and in the best most perfect world that unicorns live in.  In the real world, on 91 octane fuel, and 1 bar of boost, your output will vary greatly.   As a general idea, the Nismos will do about 400 wheel in a pair, the N1 about 425 wheel in a pair, 2530 about 500 wheel in a pair, and -10 about 550 wheel in a pair. E85, wound up, magic dyno correction will all vary your numbers. 

GTX2971R turbocharger from Garrett and ATP

Garrett GTX2971R dual ball bearing turbo for the Nissan Skyline RB26DETT platform. Direct drop-in upgrade turbo for the stock Nissan Skyline RB26DETT twin turbochargers.
The GTX2971R features an ultra high flow compressor wheel and Garrett 11-Blade technology. 560HP potential flow.

These are pretty huge. 54.1 mm inducer. 71.4 exducer on the compressor side.  56.5 mm inducer and 53.6 mm exducer on the turbine side. In the meat of the efficiency they flow about 40 lb/min airflow at 2.5 pressure ratio on the compressor. Exhaust side with the 0.64 trim maxes out at about 19 lb/min at 2.5 pressure ratio. In theory these should do about 100 horsepower over the GT-RS at the same boost levels.  But wait, there is more.  The next step up in the GTX bolt on RB26 lineup.

GTX2976R turbocharger from Garrett and ATP

Garrett GTX2976R dual ball bearing turbo for the Nissan Skyline RB26DETT platform. Direct drop-in upgrade turbo for the stock Nissan Skyline RB26DETT twin turbochargers.The GTX2976R features an ultra high flow compressor wheel and Garrett 11-Blade technology. +600HP potential flow.

If the last ones were big, well these are more bigger. 58 mm inducer, 76.6 mm exducer. However the exhaust side is the same.  We have run into issues in the past when, even stepping up the compressor side, we saw no more power as the turbine was just tapped out.  We think this could be a possibility here with this turbo. In the meat of the efficiency they flow about 45 lb/min airflow at 2.5 pressure ratio on the compressor. Exhaust side with the 0.64 trim maxes out at about 19 lb/min at 2.5 pressure ratio. Again in theory another 100 horsepower over the GTX2971, 200 horsepower over the GT-RS turbos.

Gen II GX 2876R bolt on RB26dett turbos

One other potential option is the Gen II GTX 2867R

Garrett GEN2 GTX2867R dual ball bearing Twin Turbochargers for the Nissan Skyline GT-R RB26DETT. Supports 1,000HP+ in twin turbo configuration.

50mm inducer, 67 mm exducer on the compressor side. 54 mm inducer and 47 mm exducer on the turbine side. Right around 35 lbs/min on the compressor, and about 17 lbs/min on the exhaust side.  Even if the compressor side is better, if the exhaust won’t let the flow, it will not make any more horsepower.  They say the new GenII wheel can produce up to 20% more than the previous version.

Where theories and realities meet are on the dyno. When working on another vehicle, we did several hotswaps of a single turbo setup with different turbocharger setups. The exhaust housing stayed the same, and even with three different turbos, we saw almost the same amount of power. Until we swapped exhaust housings did we see more power. Everything shifted right about 300 rpm, but we gained the power we were expecting.  We were not logging exhaust backpressure pre turbo, but it is something you should think of logging if you are serious.

Then there are some other options now, that this car has the JGTC manifolds. Those include the new G series turbos.  Those will not be exact bolt on, and they won’t work for most, so using them may not really gather much real data.  

G25-660.  54 mm inducer 67 mm exducer on the compressor side. 54 mm inducer and 49 mm exducer on the turbine side. That turbine side, could be an issue with making power on a T25 footprint.  Compressor flows about 42 lbs/min at 2.5 pressure ratio, the exhaust is still about 15 lbs/min at 2.5 pressure ratio.

Buy USA Legal R32 and R33 Skylines at Importavehicle.com!
Index and Start Page