The S54 and S65 are two off the best motors BMW has ever produced. There is a reason why the BMW Motorsport name is associated with both of of these powerplants. They are the best 6 cylinder and 8 cylinder motors in BMW M production car history in my estimation. The S54 is the last true 6 cylinder to follow the M philosophy and the S65 is the last true 8 cylinder to do the same. We will never see motors like them again from BMW. They are the pure, undiluted, true interpretation of the ideals M once placed above politics. Sadly, economic and political pressure forced BMW M to abandon these types of motors which once were the pride and joy of BMW. Real joy, not the BS marketing campaign.
Ultimately, we as enthusiasts love these motors. For myself, I was drawn to BMW because of their motors in particular. Not to mention the incredible chassis and transmissions they are mated to, but these motors were the heart and soul of the M experience. This leads inevitably to us as enthusiasts sitting around and arguing for years on end as to which is better. Some of these enthusiasts have even suggested that BMW should have not abandoned the I6 for the M3 and the V8 was a mistake. Basically, it boils down to, which is better?
History and Accolades
The S54 is considered the final and most powerful evolution of the M50 I6 engine line. The block was made out of iron which allowed for extremely close cylinder spacing of four milimeters in order to keep it compact. Iron does not distort easily and with the high revs and stress this motor would be subjected to with thin cylinder walls, Iron was necessary instead of aluminum. It would debut in the USA in the E46 M3 in 2001. This same year, it won the "best new engine" category in the International Engine of the Year competition as well as "Engine of the Year" 2001. It would end up dominating the 3-4 liter category for 6 straight years and its entire production run, a feat no other motor has achieved.
Why a V8?
If the S54 was such a spectacular 6 cylinder motor, why the change to a V8? Couldn't they just keep tweaking the 6 cylinder? Well no, they couldn't. The 6 began to be a liability in racing. Porsche was steadily pulling away from the M3's in the ALMS series with their GT3's and rubbing it in BMW's face. There was no room to increase the bore and the stroke was already incredibly long. As a matter of fact, the S54 has a stroke exceeding the bore (bore 87 mm x stroke 91 mm) which is very odd to see in a high revving motor. Traditionally, stroke is shorter than bore in a high revving motor to keep piston speeds at levels where the motor won't fly apart. The S54 ditches convention to reach its 3.2 liter displacement and also has great torque due to the long stroke design. It also makes for a motor pushed to the limit and one that is a testament to BMW's engineering.
BMW fights back against Porsche
While the S54 was still in production and sweeping engine award categories across the board, Porsche was working with more displacement in flat-6's that were less stressed in racing. BMW ran out of room with the 6, they maxed it out. Their answer was the P60B40 V8 which bitch slapped the smug look right off Porsche's face. With the switch to the V8, BMW started setting new records in the ALMS series in '01. Porsche, being the good sports they are (translation: bunch of weenies who want to protect the 911's image), complained that the M3 GTR with the V8 was not for sale. The ALMS rules stated cars must be for sale on two continents within 12 months of the rules being issued. This is exactly what BMW did, producing 10 road going GTR's with 4.0 liter V8's for sale in Europe and Asia after the '01 season.
Porsche, being the good sports they are, said this was not good enough even though it followed the rules to the letter. Porsche executives walked into the ALMS executives offices and started crying. The sight of grown men crying about losing in their precious 911's prompted ALMS to change the rules in Porsche's favor for the 2002 season to state 100 cars and 1000 engines must be built to race without penalty. Since this was impossible to do in the short time period before the season and extremely cost prohibitive, rather than cave in to Porsche's lobbying which would make BMW race with neutered/restricted cars, BMW chose to pull out of the ALMS series. BMW did not return until last year leaving the field wide open for the Porsche GT3 for 7 years. The first race of the 2010 season saw the M3 with the V8 set new lap records and Porsche unable to do anything about it.
What did we get out of all this? Well, BMW was already thinking M3 with V8 in 2001. The P60B40 V8 was 3,997 cc's with a bore and stroke of 94 x 72. The S65 which followed is 3,999 cc's and has a bore and stroke 92 x 75.2. The racing V8 would influence BMW motor development which would translate into the S85 V10 and the S65 V8. It set the stage for us getting a V8 M3.
Naturally Aspirated Power Comparison
So how do the S54 and S65 compare in naturally aspirated form? Take a look at this dyno here, the V8 having an x-pipe and pulley (thank you to DLSJ5 for the graph):
273 vs 366 whp and 226 vs. 266 rwtq. This S65 is modified so take my dyno results when stock (can't find the graphs) from my own cars on a dynojet, having had and dyno'd both an S54 and S65: 275 rwhp vs. 349 rwhp. You may notice both motors follow the 15% drivetrain loss rule almost exactly. We will say the difference in hp is ultimately around 70 wheel, pretty good for what is supposed to be 81 horsepower on paper (414-333).
The torque is extremely interesting, as the S54 makes more per CC than the S65. Why is this? It is due to the bore stroke ratio of .945 and being undersquare for the S54 vs. 1.223 and oversquare for the S65. The torque for the S54 is 12.39 cc/ft.lb. while the S65's number is 13.56 cc/ft.lb. This oversquare design also makes the S54 extremely stressed necessitating the iron block and strong internals. Not only is the block stressed, but the crank, pistons, rods, everything.
Here is a list of the top 5 highest production piston speeds:
1. Honda S2000:
Engine Code: F20C1
Bore/Stroke: 3.43" X 3.31"
Piston Speed: 4965 Ft/min
2. Lamborghini Gallardo
Engine Code: N/A
Bore/Stroke: 3.25" X 3.65"
Piston Speed: 4866.67 Ft/min
3. Acura Integra Type R
Engine Code: B18C5
Bore/Stroke: 3.19" X 3.43"
Piston Speed: 4802 Ft/min
4. BMW M3 (Germany)
Engine Code: S54
Bore/Stroke: 3.43" X 3.58"
Piston Speed: 4773.33 Ft/min
5. Honda S2000 2004
Engine Code: F22C
Bore/Stroke: 3.43" X 3.57"
Piston Speed: 4760 Ft/min
The S54 is fourth on the all time list with 4773.33 ft/minute. Compare this to the S65 which has 4070.86 ft/minute at redline. The 75.2 mm stroke can rev to 8250 rpm, 250 rpm higher than the S54, and reach that RPM with far less stress to the block and internals than the S54 at redline. Not to mention, the stroke can be increased, significantly.
How far can the S65 be taken? Well, Dinan for example increases the bore 2 mm and the stroke 7.8 mm to hit 4.6 liters in the S65. This raises the stress on the crank and raises the piston speed to 4493 ft/minute which is still rather conservative. Even BMW themselves raises the S65 stroke 7-8 mm to hit 4.4 liters in the GTS. Why did BMW leave this displacement on the table? For one, the S65 shares the bore and stroke of the S85 V10. The pistons and rods are the same thing, it literally is the v10 with 2 cylinders missing. This is where BMW started cutting costs. BMW also gave themselves room for a CSL (which ended up being cancelled). Unlike the S54, which is as good as it could be and took some unique work to gain power on with the CSL, the S65 was just a lopped off V10. A very good V10 mind you, but this motor is not even close to maxed nor did the BMW engineers push it as hard as they pushed the S54. This gives the S65 far more room in the afrermarket but does not display the engineers skill as well as the S54 did.
So what advantages did the V8 present?
- Lower cost, shared development with the V10 and development learned from the racing V8 in 2001.
- Lower weight, the S65 is 33 pounds lighter than the S54
- Higer rev limit due to shorter stroke and oversquare design
- Advantageous for racing
- Larger displacement and more room to increase displacement
- Less stress on the crank, block, and rods
- Shorter block
- Better engine bay placement
- Aluminum dissipates heat better than iron
Forced Induction Power Comparison
What is ironic about BMW pushing the S54 to the limit? Well, the iron block and the strength of the motor made for an excellent aftermarket forced induction platform. The S54 is the closest thing to a German 2JZ-GTE in existence. The rods are forged as well as the crank. The pistons are cast but lined with graphite. The motor itself, even at the high stock compression of 11.5:1 has taken double digit boost. The S54 routinely is taken to this level now with companies such as Active Autowerke delivering 12.0 psi on the stock internals and HPF has hit 16 PSI with their turbos. Over 600 horsepower at the wheels has been hit on the stock internals:
When building the motor with aftermarket internals and dropping the compression, the sky is really the limit on the S54:
1000 wheel can realistically be hit and the only thing holding it back from further gains is the turbo placement. Perhaps once we see different manifolds or even maybe a top mount the S54 will hit levels people would have once thought were impossible.
The S65 conversely is at an early point in its aftermarket forced induction lifespan. No one has done turbos thus far and space for turbos is the main issue. There are limitations on space not to mention the complexities of having split manifolds due to being a V8. The internals are extremely strong with a forged crank, piston, and rods. I have seen 9.5 psi personally with a supercharger on this motor and feel that double digit boost is possible even on the stock 12.0:1 compression. The question mark is the block strength being aluminum silicon alloy. The same factory that produces this block produced the F1 blocks (see what we lose by BMW leaving F1?). The cylinders are lined with silicon crystals and not iron, which leads me to believe the block is not as strong as that of the S54. For high boost applications, the block will no doubt need iron sleeves.
Which is more efficient per pound of boost? This is tough to say, as both are extremely efficient due to being such good NA powerplants to begin with. Boost goes a long way with these motors and they both have very high flowing heads. Turbos also tend to be a bit more efficient so we can't really compare the S54 turbo numbers to S65 SC numbers. If we do compare S54 SC numbers to S65 SC numbers, the S54 makes around 19 wheel per psi of boost whereas the S65 is at around 22 wheel per psi of boost. That is very general and there simply is too much variance between dynos and suppelmentary mods to say it is 100% accurate. Regardless, they are both very efficient.
In the Forced Induction Realm, the S54 is the better motor right now with these advantages:
- Longer development time
- Turbos available
- Iron Block
- More power
- Proven track record
- More tuning options
- Still room for improvement
Down the line things may change once the S65 gets turbos, and the power potential for both is extreme when built. As of today though, I favor the S54 for pure power, I may not in the future.
What are the drawbacks of these motors? Well, fuel consumption is one and that is also why the party is over. They are also expensive to build, from the factory and in the aftermarket. These motors require strong parts, great engineering, and excellent tuning. The S54 received a reputation as being fragile early on due to bearing failures. The engine is not fragile, as this was proven over the years, but this stigma followed it for some time as the bearing mess was played up by everyone. The S65 is not without its faults, I personally experienced a valve spring failure. Others have experienced this as well and BMW has quietly kept it under wraps. It clearly is not as big of an issue as the bearing failures were, but still either BMW skimped on the valve springs or a bad batch went out leading to the impression that high revs may hurt the S65.
Which is better?
This leads us to the main question, which motor is better? Well, it depends. There is no clear cut answer to the question. Frankly, both motors are spectacular. The S54 is the most awarded motor in BMW history. The S65 also has its share of awards winning the 3.0 liter to 4.0 liter category in the International Engine of the Year awards since its inception just like the S54 . There are also numerous technological advances that naturally came with the newer V8, the ECU for example is capable of 200 million calculations per second, exceeeding the S54's ecu 8 times. There is also a newer, more sophisticated knock control system, and other natural technological evolutions. It is more advanced in several key areas.
Clearly, for racing, the S65 is the better motor. It was a necessary change and has its share of advantages. The S54, however, is a great motor for the aftermarket enthusiast and has its own share of advantages. I don't think BMW seeks to cater to the aftermarket but as enthusiasts we certainly do care and the S54 has done some pretty remarkable things power wise, as well as holding the overall BMW 60-130 record. The answer to the question is simply that both motors are incredible and any true enthusiast will appreciate both. The S54 was the last motor which really showed the M engineers pushing the boundaries. The S65 will never see this type of push or evolution as the move has been made to cancel these types of motors in favor of "efficient dynamics." We will never see high revving motors pushed far like this from BMW ever again, and that my friends is not joy, it's sad.