AdiS
Well-known member
Introduction
One of the most commonly suggested OEM+ modifications for the E46 330i manual is to swap the standard 2.93 rear differential with the 3.38 ratio rear differential that is fitted as standard to the E46 330i Automatic. Known as the ‘poor man’s supercharger’, the purported benefits are improved acceleration, and a more ‘lively’ character to the car.
Here is a video by Engineering Explained which analyses the impact of installing a shorter ratio rear diff:
[video=youtube]
Why change the Diff?
The demeanor of the E46 330i with the standard 2.93 ratio diff could be described as lethargic. This should not be interpreted as slow, the M54B30 is a lovely, torquey motor and the car is certainly brisk by anyones standards. But the M54B30 is not a very "free-revving" engine, so it’s character does feel somewhat lazy with its torquey power delivery.
I have always been curious about this mod, and was reluctant to to do it on my first E46 330i for fear of compromising the fuel efficiency of the car. With the 6 speed gearbox, highway cruising at 120km/h is at a relaxed 2600rpm, and the car can achieve roughly 6L/100km in ideal conditions. Recently my curiosity got the better of me and I sought to fit a 3.38 diff to my 330i.
How did it change the car?
The outcome was interesting. The first thing I noticed when pulling off in first gear, was that the gearing was noticeable shorter than before. The consequence of this that no one ever discusses is that in traffic situations, you find yourself changing through first, second and third gear a lot more quickly and a lot more often. This in itself, is a little more tiresome in daily driving situations. My normal driving style in daily commutes is relaxed, with no excessive revving through the gears. I usually change early and keep the revs relatively low. I actually had to change my driving style a little in order to achieve a smooth drive when changing from first to second. There’s always a subtle art to driving manual BMWs of this generation smoothly, and I found that the best way was to change out of first at around 3000rpm, as opposed to perhaps 2200-2500 that I was used to.
Performance Benefits
When it comes down to driving the car hard, this is where this mod shines. The long gearing of the standard diff always made the car seem lazy even under wide-open throttle and the acceleration seemed uneventful. Red line in third gear would see the other end of 150km/h, and that means you never really get the feeling of winding the car out fully. With the shorter diff, there is much more fun factor. The car accelerates through the gears quicker, and this adds a new level of excitement to the car that wasn’t present before. I feel that acceleration in 2nd and 3rd gear is now much more satisfying. I also have much more confidence now that when I mash the throttle from a low speed in second gear, the car will lurch forward with authority. This is useful for those low speed traffic maneuvers which need a short burst of quick acceleration.
I do feel that the ‘poor man’s supercharger’ moniker is an exaggeration. While the difference is noticeable and a lot more exciting when driven hard, the car is not significantly faster. When driven slowly around town, its actually a bit more tiresome as you have to change gears more often in traffic situations. One must not lose sight of the fact that changing the rear differential does not change the nature of the power delivery of the M54B30. It is still a relatively lazy engine compared to say the B25, and so it’s still not a ‘revvy’ engine with this change. But the shorter diff ratio does improve the feel.
Fuel Consumption
The fuel consumption is an obvious concern to anyone who might consider this mod. In town situations the fuel consumption is for all intents and purposes, the same. Obviously if you start driving the car harder in town because its more fun, then your fuel consumption will rise, but all things being equal I can’t really tell a difference. On the open road, I do feel there is a difference. Previously the best I could get on a certain stretch was 6.4L/100km. I repeated the same test and the best I can get now is 7.2L/100km. These are of course in ideal situations, overall I feel that highway consumption is compromised by about 1-1.5L/100km. It’s not a huge difference, but it is one that should be considered.
Final Thoughts
For me personally, the jury is still out on this mod. The benefits are clear, but it’s not without compromise. Because the car is my daily driver, and I prefer to drive in a relaxed manner day-to-day, I find that the extra gear changing at low speeds unnecessary and a little annoying. However, when I do choose to drive the car hard, I enjoy the car more than before. There is also a theoretical part of me that hates that the car is not as fuel efficient as it could be on the highway.
To some people, the compromises might be irrelevant, to others they might matter a great deal. I would evaluate how often you drive in a spirited manner and compare this with how often you drive in traffic or on the open road. If you have regular opportunities to push the car hard, then this mod is worthwhile. If however you are mostly driving in slow speed traffic or cruising on the highway, then it’s probably better to stick with the original 2.93.
Summary
Pros
One of the most commonly suggested OEM+ modifications for the E46 330i manual is to swap the standard 2.93 rear differential with the 3.38 ratio rear differential that is fitted as standard to the E46 330i Automatic. Known as the ‘poor man’s supercharger’, the purported benefits are improved acceleration, and a more ‘lively’ character to the car.
Here is a video by Engineering Explained which analyses the impact of installing a shorter ratio rear diff:
[video=youtube]
Why change the Diff?
The demeanor of the E46 330i with the standard 2.93 ratio diff could be described as lethargic. This should not be interpreted as slow, the M54B30 is a lovely, torquey motor and the car is certainly brisk by anyones standards. But the M54B30 is not a very "free-revving" engine, so it’s character does feel somewhat lazy with its torquey power delivery.
I have always been curious about this mod, and was reluctant to to do it on my first E46 330i for fear of compromising the fuel efficiency of the car. With the 6 speed gearbox, highway cruising at 120km/h is at a relaxed 2600rpm, and the car can achieve roughly 6L/100km in ideal conditions. Recently my curiosity got the better of me and I sought to fit a 3.38 diff to my 330i.
How did it change the car?
The outcome was interesting. The first thing I noticed when pulling off in first gear, was that the gearing was noticeable shorter than before. The consequence of this that no one ever discusses is that in traffic situations, you find yourself changing through first, second and third gear a lot more quickly and a lot more often. This in itself, is a little more tiresome in daily driving situations. My normal driving style in daily commutes is relaxed, with no excessive revving through the gears. I usually change early and keep the revs relatively low. I actually had to change my driving style a little in order to achieve a smooth drive when changing from first to second. There’s always a subtle art to driving manual BMWs of this generation smoothly, and I found that the best way was to change out of first at around 3000rpm, as opposed to perhaps 2200-2500 that I was used to.
Performance Benefits
When it comes down to driving the car hard, this is where this mod shines. The long gearing of the standard diff always made the car seem lazy even under wide-open throttle and the acceleration seemed uneventful. Red line in third gear would see the other end of 150km/h, and that means you never really get the feeling of winding the car out fully. With the shorter diff, there is much more fun factor. The car accelerates through the gears quicker, and this adds a new level of excitement to the car that wasn’t present before. I feel that acceleration in 2nd and 3rd gear is now much more satisfying. I also have much more confidence now that when I mash the throttle from a low speed in second gear, the car will lurch forward with authority. This is useful for those low speed traffic maneuvers which need a short burst of quick acceleration.
I do feel that the ‘poor man’s supercharger’ moniker is an exaggeration. While the difference is noticeable and a lot more exciting when driven hard, the car is not significantly faster. When driven slowly around town, its actually a bit more tiresome as you have to change gears more often in traffic situations. One must not lose sight of the fact that changing the rear differential does not change the nature of the power delivery of the M54B30. It is still a relatively lazy engine compared to say the B25, and so it’s still not a ‘revvy’ engine with this change. But the shorter diff ratio does improve the feel.
Fuel Consumption
The fuel consumption is an obvious concern to anyone who might consider this mod. In town situations the fuel consumption is for all intents and purposes, the same. Obviously if you start driving the car harder in town because its more fun, then your fuel consumption will rise, but all things being equal I can’t really tell a difference. On the open road, I do feel there is a difference. Previously the best I could get on a certain stretch was 6.4L/100km. I repeated the same test and the best I can get now is 7.2L/100km. These are of course in ideal situations, overall I feel that highway consumption is compromised by about 1-1.5L/100km. It’s not a huge difference, but it is one that should be considered.
Final Thoughts
For me personally, the jury is still out on this mod. The benefits are clear, but it’s not without compromise. Because the car is my daily driver, and I prefer to drive in a relaxed manner day-to-day, I find that the extra gear changing at low speeds unnecessary and a little annoying. However, when I do choose to drive the car hard, I enjoy the car more than before. There is also a theoretical part of me that hates that the car is not as fuel efficient as it could be on the highway.
To some people, the compromises might be irrelevant, to others they might matter a great deal. I would evaluate how often you drive in a spirited manner and compare this with how often you drive in traffic or on the open road. If you have regular opportunities to push the car hard, then this mod is worthwhile. If however you are mostly driving in slow speed traffic or cruising on the highway, then it’s probably better to stick with the original 2.93.
Summary
Pros
- Added fun factor and excitement during spirited driving,
- More satisfying in-gear acceleration - car is less lethargic at low speeds
- Need to change gears more often in slow speed traffic
- Decrease in highway fuel consumption
