Rexbo

The last time F1 was turbo was 1988... running single turbos. The Le Mans cars now run twin turbos due to packaging constraints and rule mandates. As to the rotating inertia, that is a very good valid point, which is why i say twins have better response at already high rpm, because they do have less rotating inertia. However there is a critical key missing from this, and its not pulsematching or inertia, its the pressure differential and efficiency on the turbine side of the turbo. A single turbo will have a larger pressure differential across the turbine wheel than twins, causing faster spoolup than equivalent twins. The spoolup capability due to the pressure differential is also largely due to turbine efficiency. Larger wheels will always have higher efficiency than smaller wheels for the same reason that large combustion chambers have higher burning efficiency in and engine. There's less internal loss due to heat transfer and friction. Twin small turbos create lots of drag on the exhaust gas from the turbine housing walls and the turbine wheel blades. Also, more of the heat from the engine is transferred to the metal in the turbo, taking away from the energy of the exhaust gas. Now when i talk about this, im talking about terms of 3-5% less efficient than a single turbo. Its not much but everything helps, thats why extrude honing your exhaust housing is beneficial. Something else that someone brought up at work is that the advantage of a single turbo dissipates as the number of cylinders of the engine goes up. If you look at the combustion cycles of engines, a 4 cylinder engine takes 2 rotations of the crank to fire all 4 cylinders, and the subsequent exhaust gas pulses are easily tuneable to hit the turbo efficiently, more so than tuning for 3 cylinders that don't fire evenly. Also when dealing with V-engines, a single turbo setup requires long exhaust manifold runners and a lot of space, which would be beneficial on a V6, but on a V8, V10 or V12, the story would be different. Its all a tradeoff between cost and benefit, as is all racing. Cost not being money, but performance, packaging, weight, and in the end, its all speed in a race car. This is a really good thread, I like it!

yeah rally cars are an interesting example... take the group B era for instance. Thats where I think most of the good research came from. There were cars that were super-turbo'd (supercharged and turbo charged), twin-turbo'd, single turbo'd and just about everything else you can do. What came out of it all at the end? A single turbo and a restrictor. The 30mm restrictor within a certain distance of the turbo is specific for the WRC class of cars which was created in 1998, before that, the Group A cars were allowed any number of turbos that passed through a single restrictor that had no distance limit behind it. Same goes for champ cars, they used to not have to run a spec turbo, but now the weenies who make the rules say that everyone has to run a single Garrett TR30R turbo. How lame. Now i like the twin turbo idea where they're sequential sequence turbos. You have one large turbo spool into another smaller turbo. Say your "large" turbo is a GT28 on an RB25. That would spool up plenty fast for everyone, agreed? Now have that compressed air, say 5psi, flow into a little GT22 or GT25 that was also being spun by the exhaust. Say that's also set at 5psi of boost. its not just 5+5 is 10 psi, you would have a total of 5+5+14.7 = 24.7psi of boost goin into the engine! A ridiculous setup and far less efficient than just getting a gt3071r or something and doing the same thing, but still it would be a trick little setup hahah.

If your read closely, a single has two VERY important things over twins: overall power and faster low-end spoolup time. 1) Overall power. What can I say, every race team needs more power unless you're traction limited. Look a champ cars, look at Le Mans cars, look at JGTC cars, Formula Atlantic, and many many others. All single turbo for that single reason. Time attack cars are race cars, but very very specialized for a certain type of racing, i.e. they are the exception to the rule. 2) Low-end spoolup time. If twin turbos were the most efficient way of making boost, WRC cars would have them. But they dont. Why is that? Its because single turbos provide the fastest spoolup from low rpm that rally cars sometimes see. To compensate for the "recovery spool-up" as you call it, they have an anti-lag system installed. I'm not saying that all those race teams are wrong, I'm saying that they have different motivations for going twin turbo. Porsche: have you ever looked at the engine bay of a mid-engine flat-6 engine? Draw me a diagram of where a large single turbo will go. Nissan and Toyota: I dont know where they use twin turbos on any race cars, only in factory cars and again, its for driveability or packaging. The supra came with twin parallel sequential turbos so that it had a big broad driveable powerband, as did the RX-7. The 300zx came with twins for packaging, and the skyline for marketing reasons really... you can't expect your top of the line car to have less turbos than the Z do you? HKS, Tomei and Apex'i are driven by something else: profit. They build time attack cars, which are a relatively low-budget race car (in comparison to the big boys). But more importantly they build those cars to sell their product. Now everyone knows that the higher volume of a product you sell, the more money you make. I can't THINK of an easier way to sell your product than to make your car twin turbo, so everyone else out there wants to now buy two of your turbos instead of one. You've doubled your volume! Its almost genius. I'm not bashing on Time Attack cars, but they aren't in the top level of motorsports, where you do whatever you can, regardless of money, to go as fast as you possibly can, and that is the job of the team. Time Attack cars are not those cars. F1, WRC, Le Mans, Touring Cars, JGTC, those are top level teams. Those teams are built to beat the other team, not sell products. If you look in the top level of motorsports, you'll have a hard time finding twin turbos that are there for a performance advantage over packaging cionstraints or rule mandates. We can argue around forever about how I said twins are almost as good as a single, but the original statement stands: A correctly set up single turbo will always outperform twins. Call or email any Turbo engineer you know. Call Holset, call Garrett, call Borg-Warner, call Mitsubishi, call IHI. I'd be interested in hearing a response contrary to what has been said already. http://www.holset.co.uk/files/ http://www.turbobygarrett.com/ http://www.bwauto.com/menu01.html http://www.ihi-turbo.com/

slow13... almost always. A co-worker brought up a good point though. There are really two types of spool times (transient response) that we're talking about here. The first is low RPM response where the turbo is spooling up as the engine is going from low to high rpm, and the second is instant response while the engine is at high rpm but the throttle goes from full closed (no boost) to full open, as happens on road courses frequently. A single turbo setup will always be more efficient, you can't argue that, so you'll get higher HP at a certain boost level with a single turbo than with twins. Singles will always also have better response from low rpm to high rpm revving conditions, which usually happens on the street and on the drag strip. Twins however, do have an advantage in one situation, and this is really only an advantage depending on the driver, car, and conditions. This is when you're already at high rpm, and are going from no throttle and no boost to full throttle and full boost, an example being coming out of a low-speed corner that the driver has had to brake hard and downshift a couple times then accelerates out of. The turbo has spooled down, but the engine is still at high rpm because of the downshifts. In this situation, the lower rotating inertia of the twin turbos will cause them to spool faster than a similar single. This can be circumvented though. Anti-lag systems that may not work on street cars or many racing series can keep the turbo spooled up, allowing you to keep the efficient single turbo. Driver technique can be altered to account for the spool time of the turbo, such as getting on the gas earlier in the turn or even left foot braking in the case of rally cars. Sometimes it can even be ignored, because the benefit of higher horsepower at the expensive of driveability is acceptable. I put this under the "tuning" catergory of a single turbo system. Whether it be the fuel map, the driver, or the vehicle, its harder to "get perfect" a single turbo system. So in the case of the Nismo Z-tune, the JUN cars, the Mines cars, the HKS cars, those are primarily built for time attack and tuner battles, which would favor twin turbos over a single slightly laggier turbo at high rpm, because traction is a limiting factor so increased power wouldnt necessarily cause faster lap times. Really... its up to you.

Twin turbos are put on cars for many reasons: - Packaging. Notice that all the large single turbo setups require expensive manifolds and piping to get it to fit in the engine bay? Why not just cast simple small collectors and put two small turbos without packaging problems. - Marketing. Two turbos MUST be faster than one... because there are TWO of them, right? - Cost. Cast manifolds are cheap and easy to make. Tubular ones with reinforced flanges and pulse-matched length runners arent. - PROFIT! You can sell two turbos instead of just one, so you make more money! - Driveability. Single turbos have a habit of "hitting" harder than twins even if they make full boost at the same RPM. Not good in the eyes of tuning companies or OEM companies. - Other... sometimes there are reasons you can't even think of off hand for why there are twin turbos on a car. Take the 2jz supra for example, toyota wanted two turbos so they could cast their own turbine and compressor housings especially for the car, and call them "toyota turbos". Dont ask me why! 180b is right, a single well matched ball bearing turbo will always outperform ball bearing twins for equivalent HP levels. There's a good reason for this, and its called "twin scroll" or "divided turbine housing". A well designed exhaust manifold will coordinate the exhaust pulses from the cylinders to hit the turbine wheel all sequentially, creating a steady and constant stream of exhaust to spool the turbo. Now think about that... which will spool more efficiently, a turbo that will get 6 tightly packed pulses of energy in addition to the normal flow volume, or two rotating masses with proportionally similar volume but 3 longer spaced pulses. Years of research have gone into this. Thing is... thats usually fairly hard to do unless you do a lot of design work, which most companies don't want to do, especially aftermarket ones, so they slap two on that work well and call it a day. Believe me, twin turbos work, just singles work better when done correctly. This is the key word: correctly. More often than not, its not done right, so it doesnt work right. If you don't believe me, feel free to contact me with questions, I can find any answer you want here at the office where we make turbos for a living... EDIT: Think of this argument as similar to the difference between a 300hp SR20DET or a 300hp RB20DET... that should raise someone's blood pressure!

A single turbo will almost always spool faster than a set of twins if it is matched correctly.

i dropped by Stoptech on friday and asked that exact same question and the engineer there said that performancewise, there really isnt any difference which direction they face. They DO increase performance of the rotors, but the direction they face is dependant on the orientation of the vanes inside the rotor. If you orient the slots the wrong way, you can significantly weaken the rotor by creating stress risers on the outside of the rotor that will combine with the weaker spaces on the interior of the rotor to cause flexing and eventually cracking from metal fatigue.

most people weld brackets to the top and bottom of the intercooler and just bolt it on. It works but transmits lots of vibration to the intercooler which could lead to weld fatigue. If you do bolt it straight to the body, try to at least put a rubber washer in between to help isolate the intercooler. Ideally it would be mounted to the body in the same way that the radiator is from the factory. Take a look at that and try to get close to it.

Common symptoms and conditions: - Turbine Seal Leak: White smoke in exhaust, bad O2 sensor readings, Oily exhaust pipe, black oil due to excessive blowby. - Compressor Seal Leak: Oil in intercooler piping and Throttle Body, also white smoke out the tailpipe. - Damaged compressor or turbine wheels: loud sounds, vibrations and chunks of metal coming from the turbo. - Damaged bearings or bearing failure: Decreased boost levels, increased noise and vibrations, usually accompanied by more smoke. Those are all the major problems that turbos have.

Who is doing this stuff for you? The whole 270 degree vs 360 degree thrust bearing durability argument is kinda pointless if the shop that's doing it for you doesn't low-speed and high-speed balance the rotating assemblies for you, and you're going to be spinning it past its efficiency range anyways. Especially with the ceramic wheels, overspinning will lead do very premature failure. I'd say, save your money and get a real ball bearing turbo (not a single ball bearing unit with a thrust bearing), that is properly matched to the engine. You know we DO make turbos smaller than a GT40R... And it seems that for the prices you are saying, you could be coming close to just buying a new gt28R or gt25R with the t25 flange that will bolt right up anyways. I'd say unless the shop you're doing this at is VERY reputable with turbos, you're only buying a temporary solution.

you'll probably also need to get a new thrust bearing... might as well get a new turbo because all that stuff adds up especially from shops that do it for you. I dont know of any shops that do balancing of the rotating assembly outside of the states, be sure to ask specifically how they balance the parts if you do decide to rebuild.

What kind of horsepower level are you looking for? 250-300 hp: Garrett gt28rs (0.64 a/r) 280-350 hp: gt28rs (0.86 a/r) 320-400 hp: gt2871r (0.86 a/r) 350-450 hp: gt3071r 380-500 hp: gt30r

if you have the part number from the little tag on the center housing... i can tell you all about it. PM me with it if you want.

As the title says, I REALLY want a set of r32 gtr or r33/34 front calipers for sure, but I am willing to buy all 4 corners as well (calipers and rotors). Have money burning a hole in my pocket! Must be willing to ship to Los Angeles though... Email me at [email protected]

why get HKS turbos when you can order garrett units straight for cheaper? We make the exact same turbos, just differently named...

most of the time the stock clutches give up over about 250hp or so...

Crower is awesome stuff! they've been around a long time and definitely know their stuff. I've seen many engines fail... but never their rods!

Most people in the states go with a 300zx (z32) throttle body or a 90mm Q45 throttle body. Personally i'm trying to adapt the pulsar GTi-R individual throttle bodies to my rwd SR... Also some use the J30 throttle body i think...

are they GTR wheels or GTS wheels?