Sport Compact Car was a great magazine. Lots of interesting tech information. Over the years, had a chance to compete in the USCC several times, and have cars featured in the magazine a number of times. The death of SCC was sad, but just an example of creative destruction. In this test, SCC takes a R33 Skyline GT-R, WRX, Evo, and Audi TT and run them in an all wheel drive battle to the death. If you see the main image, you will notice that in fact this yellow Cobb WRX did die. This cover is a composite image, or in other words it wasn't shot like this. Each car was slid like this individually. During one of the drifts, the WRX hooked up, and hit a water truck. It did some damage, and killed the car. Two Evo, two WRX, one TT, and one R33. HPA has a PDF of the article up here.
I think this car was a customers car, I can't say I 100% remember for sure, so some of the modifications I liked, others I would have done different. For sure I would have run different coil overs. The GAB are pretty awful. However we don't always get what we want.
This magazine test was done at least partially under wet conditions, to try and show some of the advantages of different types of all wheel drive cars. The yellow Cobb WRX was a weapon. That car was super fast, and was going to be the one to beat, until it hit the water truck. The R33 should have been better with better suspension, but 3rd just barely behind the Evo VII wasn't bad.
Onto the skidpad. Drive around in a circle in both directions. The fastest skidpad run in the world, looks nearly exactly the same as the slowest. The R33 pulled 0.98g not too bad for the 265mm BFG KD's which were real street tires in 2002. The Cobb WRX was higher, but also on 285mm Kumho Victorracers all around. At the One Lap of America in 2016, we pulled 1g average on Bridgestone RE71R street tires, in a Toyota Sienna minivan. Still 2nd is just fine for "the boat."
Acceleration. Here is how it works in the real world, with magazine testing. They give you/will take a certain number of runs, maybe 1,2,3 runs. Take that number, they may average the two, they may take the best number, and then that is published. So while you may have a better number on your perfect pass, the real world, every day, this day number will be different. These are the results from this day, with these cars, and the magazine tester driving it. 0-60 in 4.1 seconds. This could have probably been even better on a good surface. 11.9 @121 mph. The thing had decent mph. Was probably making near 500 hp. 0-60 in 5.9 in the wet, isn't bad either.
Slalom speeds. 66.6 mph. Nearly last. Just the rally car was worse. Even though the car pulled 0.98 on the skidpad, it didn't want to transition much. Probably that GAB suspension. Either way not last.
The last test was braking. I forget what brake pads we had in the car, but it was nothing crazy from what I remember. The car had stock Brembo calipers, some stock rotors, pads, and fluid from what I remember. Even though it was the heaviest car, it stopped the best.
As you can see, even though some people give the R33 GT-R a hard time, it actually does pretty well against the smaller and lighter cars.
If you shift with the stock tach you are shifting at 7600 rpm
If you shift at the limiter then that is most likely 8000 rpm
If you shift at a different point, the links are below to figure that out
Gear
1
2
3
4
5
6
R32/R33
3.214
1.925
1.302
1.000
0.752
R34
3.827
2.360
1.685
1.312
1.000
0.793
One example, my bluecar. It has a 275/35/18 tire on it, which is 25.58 inches tall. It has a stock 5 speed transmission. Overall/Final gear ratios are 4.111. It is shifted at 8500 rpm.
So about if we swapped to a Getrag? Well actually the bluecar used to have a Getrag in it, but we sold it to a friend, that needed one. So add a 6th gear, keep the 4.111 gear vs the 3.545 gear of the R34. Then we get:
Now onto a sequential. My Nismo has(had, till I stole it out for Big Bird 2) OS88 sequential transmission, and 4.375 gears. 255/50/16 tires are 26.04" tall. The shift points are higher at 9000 rpm, as this car has a lot of cam in it. The OS ratios are:
Unpopular and scientifically proven to be untrue. However, proof and science will not change my point of view when it comes to twin turbos for a street car. While things may be different in the last 10 years, my experience in the 10 years prior to that, with single turbo manifolds was nothing but frustration. Between them not fitting correctly, leaking at the head, warping, cracking, and melting things, I got my fill. We endurance raced a car with a thick flange, thick tube, basic log exhaust manifold, and we still cracked it when racing. Turbo technology has improved in the last 10 years, but honestly nothing I would call amazing, or magic, unless you include not available to the public electrically assisted turbos.
Cast exhaust manifolds on an RB26 do not fail. I have never seen them fail. Tubular exhaust manifolds, even stock replacement on an RB26 fail. I have tried them all, had them all leak and fail. The R34 race car N1 cast manifolds had a few interesting mods done to them, but nothing that cars not running an endurance race will need.
Other than a big hole in the block, this Greddy manifold was braced and rewelded several times.
This is an interesting test on a 4G63, as a twin turbo setup, undermanifold on an RB26 has a relatively small tube diameter, and is fairly short. Most single turbo setup manifolds have a lot of volume to fill before they start to push on the exhaust wheel. This effects response and power production, up to a point.
Large runner vs small runner testing on a Mitsubishi Lancer Evolution from Morrison Fabrications. In this test of two different exhaust manifolds on a 4G63, they tested a Borg Warner S362SX-E with a 76mm turbine, and .91 divided T4 exhaust housing. The large runner had 1.68" ID, or 1.75" tube, and 1.42" ID, or 1.5" tube.
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.
Twin scroll vs single scroll. Not every exhaust manifold, not every exhaust housing is setup for twin scroll. The advantage of a twin scroll is that it takes advantage of exhaust pulses to add time between exhaust events. Dsport Magazine has a great explanation here. A twin turbo exhaust manifold on an inline 6 cylinder engine, like an RB26, does this naturally.
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.
So if your exhaust housing, and exhaust manifold for your single turbo are not twin scroll, you are giving up some response as shown in the Dsport Magazine article.
Tomei cast exhaust manifolds vs stock exhaust manifolds
Tomei cast exhaust manifold
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.
Time Markers :
0:00 - Intro
3:08 - 912 horsepower
6:58 - Exhaust system backpressure
12:10 - Turbocharger Boost to Backpressure Ratio
17:22 - Engine Scavenge Ratio
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.
So that all is just some notes about why and what may or may not work. You need to have knowledge of that in order to make some good choices for your twin turbocharger setup.
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.
The first, most basic, and cheapest starts off with a Nismo turbo equivalent. They come in at $800 each, have a 0.64 exhaust housing, and in theory will do about 300 hp per turbo. It has a 60 mm compressor wheel, and a 53 mm exhaust wheel. It has a journal bearing, aka not ball bearing center section. We have used these turbos.
The next turbo worth talking about in a twin turbo setup, would be a -7 or N1. They are just over $1000 each, have a 0.64 exhaust housing, and in theory will do up to 310 hp per turbo. 60mm compressor wheel, and a 53.85 mm exhaust wheel. It is a ball bearing center section. We have used these turbos.
The next turbo you have heard of. You must have heard of. It's the 2530, at least when HKS was selling it. The turbos that Mines ran on their R34. The 2860-5. They are under $1000 each, probably because of popularity. They have a .64 exhaust housing, and will do up to 350 hp per turbo in theory. 60mm compressor wheel, and a 53.85 mm exhaust wheel. It has a ball bearing center section. We have used these turbos.
The next turbos we have not used, but have seen results from testing. $3200 for a pair of Gen2 GTX2860R. They have a .64 exhaust housing, and they say they will do 450 hp per turbo. 60mm compressor wheel, and a 54mm exhaust wheel. They have a ball bearing center section. Next up in the Gen2 lineup, are the GTX2867. Also $3200 for a pair. They have a .64 exhaust housing, and say they will do 500 hp per turbo. 67mm compressor wheel, and a 54 mm exhaust wheel. They have a ball bearing center section.
After those turbos, we have posted about some other turbo options for Big Bird 2. That information is below.
To make the kind of power we want, the minimum sized turbo we would be looking at is something like the HKS GT-RS or the 2871-R. AKA a 2871-10 707160-10. We have done over 600 wheel horsepower on a 2.8 with these turbos. Response was good, when cam timing was tuned correctly. These are bolt on RB26 turbos. 53 mm inducer, 71 mm exducer on the compressor side, 54 mm inducer and 47 mm on the turbine side. 76 trim, with a 0.64 A/R. In the meat of the efficiency they flow about 35 lb/min airflow at 2.5 pressure ratio on the compressor. Exhaust side with the 0.64 trim maxes out at about 17 lb/min at 2.5 pressure ratio. These are older turbos, but they work, are proven, and easy.
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.
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.
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.
The G25-550 - 48 mm inducer, 60 mm exducer compressor side, 54 mm inducer 49 mm exducer on the turbine side. Compressor flows about 32 lbs/min at 2.5 pressure ratio. The T25 flanged exhaust side is a 0.49 trim, and flows about 15 lbs/min at 2.5 pressure ratio.
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.
R34 GT-R brake deflectors these are made of rubber and flexible
The R32 GT-R N1, R32 GT-R Vspec, R33 GT-R, and R34 GT-R all had brake deflectors to direct airflow to the brake rotors. They also sported Brembo brake calipers. In an ideal world, the Skyline GT-R would have had a trailing caliper, so that air could easier get to the center of the rotor, to be pumped out through the vanes, cooling the rotor itself. On the street, this part, probably isn't important for you . The the track, very important.
R34 front lower control arm. It is cast aluminum and one piece in the R34 vs two piece in the R32/R33
R34 GT-R brake deflectors
You can set that air deflector is doing its best to direct some air at the center of the rotor. However we have a caliper, a axle all in the way.
