What are they?
The BMW N63 and S63 are both twin turbo and direct injected V8's. They are different from traditional turbo V8's in the sense that the intake and exhaust systems are reversed. By designing the intake and exhaust this way BMW is able to put the turbos in the V, or valley, of the motor on top instead of the traditional location which would have turbos at the bottom off the exhaust manifold. The advantage is that the exhaust gas leaves the head traveling a very short distance to reach the turbo. BMW engineers have often prided themselves on the response of their motors and with this type of design even when going to turbo motors they are able to provide very little lag and strong response from low RPM. Not to mention, top mount turbos are just flat out cool.
How are they different?
The S63 is based on the N63 but there are some very significant differences between the two motors. The main difference being that the S63 uses a pulse tuned, cross engine exhaust manifold. That sounds cool, but what does it mean? It means that each turbo gets its exhaust flow from 4 exhaust pulses but also from opposite cylinder banks. This exhaust gas is fed into twin-scroll turbos which means there are two passages for the exhaust gases in the turbos. The N63 on the other hand uses single scroll turbos which means one passage for the exhaust gases. It is this pulse tuned exhaust manifold as well as the twin-scroll turbos that is major difference in the architecture of the S63 vs. the N63.
BMW released the graphics above to illustrate what is taking place. By using this manifold with the twin scroll setup BMW is able to keep constant exhaust pulses flowing to the turbos at every 180 degree rotation. The N63 on the hand will have uneven exhaust pulses as it is fed by only one bank of cylinders instead of a cross-engine setup. This is a significant difference that shows BMW innovation in turbo development.
Any other differences?
Yes. The exhaust camshafts on the S63 are different, designed for higher lift. The S63 has a different cooling system using a belt-driven mechanical pump. An additional oil cooler is used in it that is mounted below the radiator as well as a larger engine oil cooler. The water to air intercoolers on the S63 are larger than those on the N63. The transmission fluid cooler used is also larger. The turbo bearings receive a separate cooling circuit on the S63. The intake setup is slightly different as well but this is more to meet pedestrian crash regulations than a design difference for performance.
The redline on the two motors is slightly different with the N63 set at 6500 whereas the S63 revs to 6800 rpm. In the upcoming F10 M5, it is likely the cam profiles in the S63 will be slightly different from the X5 and X6 M as the photos of the tachometer have shown a redline in the low 7000 range. The final major difference is that the compression ratios between the two are not the same also leading to speculation that the the S63 pistons may be stronger. The N63 compression is at 10.0:1 while the S63 is at 9.3:1. Why the compression difference? The S63 runs more boost with 17.4 psi peak vs. the N63 hitting 11.6 psi of maximum boost pressure. Other than these differences, the motors are the same with identical bore/stroke, valve sizes, and engine blocks.
Can I just add the S63 turbos, manifold, and other parts to my N63?
Maybe. Wish I had a better answer but that is where we are currently at with these platforms. Sure, you can order the parts as they are available from dealers but it is not quite so simple as just bolting them on. Yes, physically, you will have no issues matching them up. The problem would be the tuning. I can tell you there currently are tuners trying to do exactly this. Have they been successful? Well, the jury is still out on that as the hurdle seems to be the tuning. What is more likely is that upgrades that are currently in the works will apply to both the S63 and the N63. Since these upgrades will be more efficient than the factory parts anyway it will make the most sense to simply skip trying to mimic an S63 and go big. One of the reasons these motors will be so much fun to tune and will get so much attention is that with having the same basic architecture most if not all of the hardware will apply. The wildcard as always is the tuning but we expect that to be figured out especially with how much competition there will be in this sector.
What is the power difference between the two?
Well, in stock form the N63 is rated at 400 horsepower and the S63 is rated at 555 horsepower. The reality of it is that the motors are fairly close to one another in stock form, at least closer than the crank ratings from BMW would have you believe. The N63's higher compression likely plays a role in that allowing more horsepower per psi. Below you will see a dyno of a stock X6 M vs. a stock X6 50i. The cars actually belong to the same owner and the fuel is 91 octane and as luck would have it are from the same gas station. You will notice the peak horsepower difference is only 60 all wheel hp and the torque difference is just under 30 pound feet. The torque curves from 2750 to about 5000 rpm mirror each other pretty closely.
What happens at 5000 rpm though is the N63 falls off a cliff. The S63 does not look pretty either but the turbos show greater sustainability up top not only due to their size but also due to being fed with more exhaust pulses. Look at the large area under the curve from about 5000 to 6500 rpm for the S63. The N63 really stands to benefit up top from some larger turbos and that higher lift exhaust cam. To be perfectly honest, compared to the table top flat torque curves across the range of BMW naturally aspirated jewels like the S65 or S85, these curves look embarassing for a company like BMW that set such a high standard previously. Are turbos letting them be lazy? Clearly, these are all about the down low torque and not the top end although the S63 is able to shift its peak power to the right considerably compared to the N63. We have heard some preliminary details on the S63 in the M5 and it should have a powerband slightly more conducive to the top end we have grown accustomed to in M5's previously although it will not be anything like an S85.
What is the power potential?
The majority of tuning that will take place for these motors will be bolt on's and basic tuning. This means exhaust and ecu modifications for the most part. The N63 has more room to gain from stock vs. the S63 since it is not in as high of a state of tune also running less boost. Dinan is a notoriously conservative (for street applications) but solid tuner and their gains illustrate this point well. For the N63 Dinan gains about 100 horsepower and 100 pound-feet of torque from the base. On the S63 the gain is only 56 horsepower and 74 pound-feet of torque. This makes sense as boost can not be raised as much with the S63.
Here is an X6 M graph of a before and after tune by OE Tuning. You will see the gains primarily come under the curve down low and the peak HP is not affected all that much. That does not mean the car will not be much faster, area gained is huge but up top at peak there is not as much room to gain as there is with the N63.
What about upgraded turbos?
Yes, oh yes, these will come. Some claim to already have them but we remain skeptical. A tuner named ALSA for example claimed to have upgraded turbos capable of over 700 horsepower for the X6 M. We asked for a dyno graph to substantiate this but never received it. More than one tuner claims such a package but there have not been any real world details to substantiate the claims.
So nobody has done upgraded turbos?
No, Alpina has. The Alpina B7 uses larger turbos on the N63 so clearly it can be done. The thing is, Alpina doing upgraded turbos on an N63 is almost like BMW doing it themselves. The relationship between the two is so close that Alpina can get whatever software support it needs to make the hardware work. This type of work trickles down to other tuners over time but that is the thing, it takes time. So do we believe anyone has a working turbo upgrade package out there yet? Other than Alpina, no, but they will come.
How much power will these motors hit?
I wrote an article in January of last year where I said 700 horsepower will be common place. It will be, as 700 horsepower will not be a number that opens too many eyes on this motor after a while when tuners start hitting it routinely. Even early last year tuners such as Noelle were claiming 650 horsepower out of the N63, let alone the S63. ALSA already is claiming over 700. On the stock internals and fuel system, this is going to be about the limit for the S63. The N63 internals may be hindered slightly by the compression but with big enough turbos even it should approach the 700 mark on the stock internals. There have been no complaints about the fuel system not having enough headroom for this level.
These motors are going to hit big numbers fairly quickly as that is the advantage of having a forced induction motor from the factory. With the S63 being in four M vehicles (X5M, X6M, M5, and M6) at no other time has an M motor been in so many different models at once. Not to mention the number of N63's out there which will benefit from development of the S63. With the proclivity of M owners to seek higher and higher performance and the ease at which forced induction motors are tuned, the tuner competition is going to be intense. Wise tuners would already be working on their offering as hitting quickly to gain control will be vital.
The N63 will be capable of hitting anything the S63 can. With the stock hardware the N63 will not be able to go as far, similar to the difference between a 996 K16 turbo and an X50 K24 996 turbo, but with built internals and larger turbos they both will be able to hit the same eventual peak. One does not have to buy an M motor any longer to be able to have the same type of headroom as an M motor. There is something about that which is bittersweet but it opens BMW tuning to a greater range of people while keeping BMW's own costs down. Not to mention the fuel efficiency gains but we could also argue 555 horsepower 5300 pound SUV's and efficiency are oxymorons.
Well, not from BMW's perspective. They can take a motor and give it bigger turbos while changing the tuning and call it an M motor. Lowers costs, improves fuel economy, the marketing and accounting departments are happy. For some cars they don't even have to bother with doing anything other than minor software changes (1M coupe). We feel these motors no longer show off the M engineers skill in the same way. They allow them to be lazier as they no longer need to strive for squeezing out every last NA horse. It also allows them to muscle out parts of the tuning market by offering their own software upgrades providing a secondary cash grab. This might force out some of the weaker tuning houses as you all know how BMW owners are weenies when it comes to preserving their warranty. More power and a warranty? For the more restrained/timid crowd it will be an easy choice.
There still is great innovation as the top mount turbos in the V show but the motors are not quite as impressive of an engineering feat or as unique as the naturally aspirated M motors were. These also have a completely different character with a curve that is very unlike what we have grown to expect out of M. Then again, these motors need a ton of torque to move heavy 5300 pound SUV's quickly. Tuning will be different than what we are used to such as trying to add aftermarket forced induction but it looks like there will be more of it and faster. So, there are only downsides depending on your perspective. Many welcome increased torque and easier tuning along with MPG gains, I just wish BMW still gave the customer the choice.