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  #31  
Old 05-01-2020, 01:05 AM
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Quote:
Originally Posted by RocketyMan View Post
Not true. Very broad understatement. By your logic, everyone should never shift out of first gear then. Which obviously doesn't make sense. You neglect the frictional losses of the engine that are inherent to speed as well as characteristics of a NA engine.
Ok, l am not going to respond to the shifting, because my logic is not suggesting one drive around in first gear.

But, I will follow up on the second portion of your response. The higher diff ratios allow the lower horsepower, lower torque M54 get to speed and carry its weight more efficiently. It’s the reason BMW engineered M54 powered E53’s with 4.10 gearing.

The M62/N62 powered E53’s have more horsepower and torque. It’s the reason BMW engineered with 3.64 gearing. The V8 has a specific power band that’s is most efficient, and the I6 has a specific power band that is most efficient.

When you put 4.10 gearing on a M62/N62 powered E53 you are increasing torque. It will increase acceleration and it is going to overdrive the V8. When you put 3.64 gearing on a M54 powered E53 you are decreasing torque. It will decrease acceleration and underdrive the I6.

When you re-engineer an M54 powered E53 with 3.64 gearing you are going to lose acceleration, and your 0 to 60 is going to take a hit. My guess is you are going to need more throttle to compensate.

My question to you is, where are you going to get that extra power?

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  #32  
Old 05-01-2020, 01:30 AM
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Originally Posted by Clavurion View Post
This not that simple. You would have to know the engine's nominal consumption curve and it usually has a sweet spot RPM/load though on naturally aspirated petrol engine anything other than max revs is more or less restricted with pumping losses.

I am willing to bet that is why BMW put 4.10’s on the M54 powered E53.
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  #33  
Old 05-01-2020, 01:48 AM
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Originally Posted by RocketyMan View Post
That's why Clavurion said there's a "sweet-spot" with this. Because conversely you can't get performance out of an engine by "lugging" it everywhere you go. At the same rate, you can't get efficiency near-redlining the engine everywhere you go.
With the loss of torque, you are going to be “lugging”. The M54 is in my opinion underpowered as it is. That may be why BMW wanted the RPM’s higher, to hit that sweet spot to keep it from lugging.

I am interested in reviewing your results.
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  #34  
Old 05-01-2020, 12:58 PM
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True, there are ton more variables that could be considered. Intended to keep it simple and mentioned there are other factors that could cause the opposite to be true later in post.

Adding any variable ya'll think important will the mileage increase or decrease if you change from a 3.36 to 4.10 ratio then accelerate from a full stop normally down a freeway on ramp to cruise speed of 70 MPH. Will you burn more fuel or less fuel after one mile?

I will answer first. Yes, with that wide of a ratio change I think you will burn more fuel.
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  #35  
Old 05-01-2020, 01:22 PM
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Quote:
Originally Posted by Happy View Post
Ok, l am not going to respond to the shifting, because my logic is not suggesting one drive around in first gear.

But, I will follow up on the second portion of your response. The higher diff ratios allow the lower horsepower, lower torque M54 get to speed and carry its weight more efficiently. It’s the reason BMW engineered M54 powered E53’s with 4.10 gearing.

The M62/N62 powered E53’s have more horsepower and torque. It’s the reason BMW engineered with 3.64 gearing. The V8 has a specific power band that’s is most efficient, and the I6 has a specific power band that is most efficient.

When you put 4.10 gearing on a M62/N62 powered E53 you are increasing torque. It will increase acceleration and it is going to overdrive the V8. When you put 3.64 gearing on a M54 powered E53 you are decreasing torque. It will decrease acceleration and underdrive the I6.

When you re-engineer an M54 powered E53 with 3.64 gearing you are going to lose acceleration, and your 0 to 60 is going to take a hit. My guess is you are going to need more throttle to compensate.

My question to you is, where are you going to get that extra power?


The 4.6is and 4.8is both use 3.91 rear end ratios--which is closer to 4.10 than it is to 3.64 I would say. A better comparison would be an e46 in my opinion because those mostly came with M54. Looking at those they use much lower ratios for final drive but ALSO have smaller curb weight and smaller tires. Maybe a better comparison would be an e83 which actually use 3.64 final drive ratio and have less drastic differences in curb weight.

Yes, the higher final drive ratio will give better acceleration--but my goal isn't with acceleration nor towing capability/off-roading. It's with crusing ability. I don't anticipate ever towing with my X5 nor do I anticipate doing offroading/rock-crawling.

With cruising ability lower engine speed will give better mileage. Now again, this would be within reason (again with either lugging or overspeeding an engine). "Then cruising rpm should be at max torque engine speed." This is also a misconception in terms of best cruising-mileage OTR. All max torque tells you is the maximum volumetric efficiency engine speed. Just because you can more efficiently use more fuel at a given engine speed does NOT directly translate to most efficient cruising engine speed. This is characteristical because there are cases where you can exceed 100% VE, e.g. when an engine has an excessive "cam" or even when the intake pressures are super charged (from either supercharger or turbo). Both of which use more fuel.

Again, just like what was said before with a "sweet-spot" and using that. This is data I've seen empirically. It's a simple fact that faster engine speed is not directly proportional to the fuel per stroke required to overcome frictional parasitic losses. These losses are exponential with speed. This is why I gave the example of not driving around everywhere in first gear. Clavurion said it best, "You would have to know the engine's nominal consumption curve and it usually has a sweet spot RPM/load." Meaning...non-linear fashion.

An interesting website to check out would be: BMW E46 Differential Info
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  #36  
Old 05-01-2020, 01:32 PM
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Quote:
Originally Posted by e39_touring View Post
The 4.10 gears are quite zippy around town but involve a lot of shifting as there isn't as much range in each gear. It's very strung out at highway speeds of over 70mph.

To me, the 3.64 gears are just about right for everything except maybe that 6500lb trailer. I've towed about 3-3500lbs since doing the gear swap and had no problem getting going at all.
E39_touring, I overlooked your post stating that you had already done the swap.

What were your results regarding acceleration and fuel consumption with the lower diff ratio?

Also, did you go with a lightweight flywheel, and what type of clutch did you go with? And if memory serves me, you have an intake, headers, exhaust, and a tune?
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  #37  
Old 05-01-2020, 01:35 PM
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Originally Posted by Happy View Post
With the loss of torque, you are going to be “lugging”. The M54 is in my opinion underpowered as it is. That may be why BMW wanted the RPM’s higher, to hit that sweet spot to keep it from lugging.

I am interested in reviewing your results.
I'm interested too! So last time I got 21 mpg going to the tri-cities. It was about 200 miles one way for me of about 85/15 highway to city driving.

Granted...this was with:
* Snow tires on @255/60R18
* Winter pump fuel (I'm not sure when this changes at gas stations)
* Going 70-75 mph with somewhere around 3500 ish-rpms
* Colder ambient temperature 40-50F...?

I will make another trip to the tri cities again soonish:
* 20" Dubs on (with 315s in rear)
* Maybe summer fuel (this has more energy per mass than winter)
* Still anticipate 70-75 mph but with around 3000 ish-rpms
* Warmer ambient temps 60-75ishF maybe??
* Lowered car with H&R springs about 1.5"

The variables above I think might be too much to skew and get good, fair results. In reality I only anticipate getting maybe .5 to 1 mpg better at most!
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  #38  
Old 05-01-2020, 01:36 PM
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What is cruising ability to you?
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  #39  
Old 05-01-2020, 02:06 PM
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Originally Posted by RocketyMan View Post
The 4.6is and 4.8is both use 3.91 rear end ratios--which is closer to 4.10 than it is to 3.64 I would say. A better comparison would be an e46 in my opinion because those mostly came with M54. Looking at those they use much lower ratios for final drive but ALSO have smaller curb weight and smaller tires. Maybe a better comparison would be an e83 which actually use 3.64 final drive ratio and have less drastic differences in curb weight.

Yes, the higher final drive ratio will give better acceleration--but my goal isn't with acceleration nor towing capability/off-roading. It's with crusing ability. I don't anticipate ever towing with my X5 nor do I anticipate doing offroading/rock-crawling.

With cruising ability lower engine speed will give better mileage. Now again, this would be within reason (again with either lugging or overspeeding an engine). "Then cruising rpm should be at max torque engine speed." This is also a misconception in terms of best cruising-mileage OTR. All max torque tells you is the maximum volumetric efficiency engine speed. Just because you can more efficiently use more fuel at a given engine speed does NOT directly translate to most efficient cruising engine speed. This is characteristical because there are cases where you can exceed 100% VE, e.g. when an engine has an excessive "cam" or even when the intake pressures are super charged (from either supercharger or turbo). Both of which use more fuel.

Again, just like what was said before with a "sweet-spot" and using that. This is data I've seen empirically. It's a simple fact that faster engine speed is not directly proportional to the fuel per stroke required to overcome frictional parasitic losses. These losses are exponential with speed. This is why I gave the example of not driving around everywhere in first gear. Clavurion said it best, "You would have to know the engine's nominal consumption curve and it usually has a sweet spot RPM/load." Meaning...non-linear fashion.

An interesting website to check out would be: BMW E46 Differential Info

Yes, I’ll agree with the cruising theory. If you are constantly on the freeway with speeds above 60 mph, then yes a decrease of 400 rpm’s will save fuel due to less rotation.

But, I am curious about in town driving. There may be a need for more torque to get the E53 up to speed, requiring more throttle.

With supercharging, I actually got better gas mileage. And, when I went from 6 lbs of boost to 10 lbs of boost it got even better. This applies to the cruising theory as well, but not only freeway, city driving also.

The additional energy produced by the supercharger aids the underpowered M54 to more efficiency accelerate to a desired speed. The extra torque aids with the “lugging” as you call it, requiring less throttle. The E53 is indeed heavy. On the freeway, even though the rpm’s are at levels earlier mention in previous posts on this thread. The supercharger is constantly producing boost because it’s belt driven, and therefore leaves power on tap, again requiring less throttle to cruise or accelerate.

Now, if you “punch it” with the supercharger! You are going to drink fuel!
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  #40  
Old 05-01-2020, 02:15 PM
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Quote:
Originally Posted by Happy View Post
Yes, I’ll agree with the cruising theory. If you are constantly on the freeway with speeds above 60 mph, then yes a decrease of 400 rpm’s will save fuel due to less rotation.

But, I am curious about in town driving. There may be a need for more torque to get the E53 up to speed, requiring more throttle.

With supercharging, I actually got better gas mileage. And, when I went from 6 lbs of boost to 10 lbs of boost it got even better. This applies to the cruising theory as well, but not only freeway, city driving also.

The additional energy produced by the supercharger aids the underpowered M54 to more efficiency accelerate to a desired speed. The extra torque aids with the “lugging” as you call it, requiring less throttle. The E53 is indeed heavy. On the freeway, even though the rpm’s are at levels earlier mention in previous posts on this thread. The supercharger is constantly producing boost because it’s belt driven, and therefore leaves power on tap, again requiring less throttle to cruise or accelerate.

Now, if you “punch it” with the supercharger! You are going to drink fuel!
I cannot find it...but there's an article I read where it compared a Prius and a Corvette fuel economy first to 100mph. At full throttle for both Prius and Corvette, the Corvette got better mileage first to 100 mph than the Prius!

Both vehicles have very similar drag coefficients...I think like .29 and .28 respectively. And it talked about how the Prius took more fuel because it was constantly trying to accelerate at full throttle and took FOREVER to get to 100 mph. Versus the Corvette got there in like 8 seconds or something? Very interesting even tho the vette engine was like a 6.2L I think.

I cannot find the article!
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