My X5d- A reliable daily driven tow rig

[RL18]

Originally Posted by wcs531

I was assuming the ratio may have been targeted towards rated fuel economy for advertising (not real world fuel economy). It could be to reduce excess strain, but since when does BMW care about longevity past the warranty period? 10k+ mile oil change intervals, "lifetime" transmission fluid, etc. I would guess the e70's towing limits are more chassis related than engine/transmission related - they both seem pretty stout.

Also for non towing situations, shaving a few hundred RPM while cruising at 80mph for hours on end would have to reduce engine wear a reasonable amount in addition to better mpg.

We’re talking about a stock x5d right? It would be a mistake for a stock x5d to change to 3.15 final ratio. It’s already slow as is stock. And I should correct myself, the drivetrain wouldn’t be as affected but the powertrain would be very affected by this. You’d be bogging this engine everytime you shifted gears casually driving, even WOT. A deleted and tuned x5d would probably fair better but it would still put strain on the powertrain.

It has nothing to do with economy. An X5d gets worse economy on the highway if you drive above 75mph, which most people do. It has to do with performance and strain on the engine/transmission. And towing would only exacerbate it. It would of course still do it, it has diesel torque, but that doesn’t mean it’s good for the powertrain.

The n57 got the 3.15 gearing because the 8spd gives you two more gears down low to accelerate and a better gear ratio spread up top for highway speeds. If they had the 6speed for the v8 models and i6 models they would probably use the same 3.64 final ratio or something in between, maybe not though because they have much more rpm to work with.

[jbash87]

Originally Posted by RL18

Don’t do it. If you’re going to do anything there’s a guy on the bmw North American diesel group on Facebook that’s selling a kit to swap our 6 spd to the newer 8spd trans, full integration. Only then would it make sense to swap to 3.15 gearing.
You’re putting unnecessary strain on the engine and drivetrain with the stock 6spd. There’s a reason bmw went with 3.64 gearing in these and it wasn’t because of towing.

I would love to do an 8HP swap but currently out of my budget (boat and M5 stuff). My future plans include that AND the 3.15's though. I searched the NABDOG group for towing with 3.15's and all I can find there is praise for it w/ my concerns noted as well. I was hoping for some more real world experience from Spyro235 for another data point.

I'm not worried much about strain on the drivetrain (if there is any considerable increase) because it's pretty stout as is. Worst case I decrease the life of my transmission and get forced into an 8HP swap... bummer

[RL18]

Originally Posted by jbash87

I would love to do an 8HP swap but currently out of my budget (boat and M5 stuff). My future plans include that AND the 3.15's though. I searched the NABDOG group for towing with 3.15's and all I can find there is praise for it w/ my concerns noted as well. I was hoping for some more real world experience from Spyro235 for another data point.

I'm not worried much about strain on the drivetrain (if there is any considerable increase) because it's pretty stout as is. Worst case I decrease the life of my transmission and get forced into an 8HP swap... bummer

Are you stock?

[jbash87]

Originally Posted by RL18

Are you stock?

Nope

[wcs531]

Originally Posted by RL18

It has nothing to do with economy. An X5d gets worse economy on the highway if you drive above 75mph, which most people do. It has to do with performance and strain on the engine/transmission. And towing would only exacerbate it. It would of course still do it, it has diesel torque, but that doesn’t mean it’s good for the powertrain.

I was just kind of thinking out loud (and still am), but definitely has nothing to do with real world economy. I was talking rated economy (meeting government standards and marketing purposes). US ratings top out at 80mph but the highway cycle only averages 48mph apparently. EU highway cycle maxes out at 120kmh or ~75 mph. So they are both in the sweet spot for a shorter final drive ratio.

Performance/drivability while towing makes more sense than strain/wear to me, especially since first gear is so damn short. A lot of people set xhp to start in 2nd on flat surfaces.

[RL18]

Originally Posted by wcs531

I was just kind of thinking out loud (and still am), but definitely has nothing to do with real world economy. I was talking rated economy (meeting government standards and marketing purposes). US ratings top out at 80mph but the highway cycle only averages 48mph apparently. EU highway cycle maxes out at 120kmh or ~75 mph. So they are both in the sweet spot for a shorter final drive ratio.

Performance/drivability while towing makes more sense than strain/wear to me, especially since first gear is so damn short. A lot of people set xhp to start in 2nd on flat surfaces.

Well it’s already obvious that the economy would be better with 3.15s highway. But the issue still is that you’re stretching out the gearing too much for the 6 spd transmission causing unwanted stress

I start in 2nd all the time. I also drive in manual and usually rev out to between 2,200-2,500 rpm, maybe even 3,000rpm going up a hill in 2nd gear. High load, low rpm situations are terrible for a small displacement diesel, just ask first gen ram ecodiesel owners. The problem is you’re lugging this engine if you drive in D mode. And you better have every boost leak fixed and a healthy vcg. If you’re gonna do this kind of mod you should also be driving in either M or sport mode to prevent lugging the engine in low rpm. Peak torque in these engines is 2,400rpm, it’s not making torque down low in the rpm like larger displacement diesel pickups.

Once again, it’ll do it. But it will increase stress on the engine. The rpm difference is hardly a difference, especially on a diesel.

[jbash87]

Originally Posted by RL18

Well it’s already obvious that the economy would be better with 3.15s highway.

Yup. That's the idea. I drive 75-80% highway miles and only 1/4-1/3 of the year towing. It's worth it to me.

Originally Posted by RL18

Peak torque in these engines is 2,400rpm, it’s not making torque down low in the rpm like larger displacement diesel pickups.

Ok. But they make almost 90% of that around 1800 and if you're tuned you'd be making similar torque closer to 1500.

Originally Posted by RL18

If you’re gonna do this kind of mod you should also be driving in either M or sport mode to prevent lugging the engine in low rpm.

Why was it so hard for you to just say that?

I forgot to ask. Do you have any experience towing over 4000lbs with your X5?

[RL18]

[QUOTE=jbash87;29762952]Why was it so hard for you to just say that?

I forgot to ask. Do you have any experience towing over 4000lbs with your X5?

Because I still don’t think it’s a good idea lol. The transmission gearing just isn’t optimized for that final gear ratio. I’ve already mapped out the powerband/shift points based on mph of each final ratio with both 6 spd and 8 spd and you can clearly see that the 6spd with the 3.64 and 8spd with the 3.15 have similar characteristics (1st is identical actually). 3.15 with 6spd is too “tall” in 4th gear and below and would need more revving to prevent lugging the engine… yes fine in 5th and 6th, but you also don’t get that extremely useful 6th gear like you do in the 8spd to accelerate up to those higher gears. 3.64 with 8spd would be revvy, first would be useless but probably really fun/fast and a tank towing otherwise, and also still better on the highway in 8th with about a 100rpm drop, which you could get more with 31.5” oversized tires. That’s why I would lean towards doing the 8spd swap before the 3.15 swap.

But yeah 1750 rpm is when turbos would be spooled up you want to be at or above that rpm ideally so your exhaust bypass stays open. With 3.64 gearing at around 2,500 rpm in second, it drops you pretty much at that rpm actually which is perfect. 3rd, 4th and 5th can be shifted lower than 2,500rpm. I’ve also noticed that shifting at that rpm range in 2nd gets rid of that sloppy 2->3 shift bump which I think might be from the exhaust bypass shutting then reopening really fast. With 3.15s it drops you just below that and that gear is stretched out a bit longer too. So you want to be revving a bit over 2,500rpm, like 2,700rpm, atleast in second. Then atleast 2,500rpm in third and fourth to prevent lugging the engine. And since you’ll likely be using 1st now, because 2nd will be sluggish, revving up 2,700-3,000rpm would be better too. Btw this is casual driving, spirited or WOT is worse, which is why I think this is counterproductive.

I wouldn’t mess with sport mode, I hate sport mode, it would likely only be useful for something like towing, even then too sensitive. M-mode would be ideal, that’s what I always drive in. Gives you full control. You could possibly do the customization license in xhp and tune the D-mode shift points to happen later in those gears. Please for the love of God do not get a sutphin tune though.

And no I haven’t towed with my x5 yet. I have the hitch, factory wiring and trailerbrake controller but haven’t installed it yet. Will likely do it this summer when I rewire my audio system.

[Spyro235]

Originally Posted by jbash87

I'd love to hear your thoughts on towing with the 3.15 diffs. I really want to drop my final drive ratios for daily driving but I tow my surf boat around all summer. The boat weighs a bit more than your trailer depending on how much gear I have stashed in it.

My initial thoughts are that it won't matter much, maybe I'd lose 6th gear unless I'm really getting after it on the highway. Any insight would be much appreciated.

My thoughts are- it's wonderful. My name is Aaron on the BMW group, I'm one of the loud praising ones there for the 3.15. I believe it's really how the car should've come from the factory. my 5th gear is 5% shorter than your 6th gear. If the engine needs to gear down while towing, I let it. I try to stay in D while towing so it shifts based on load, not based on how much I want to hear the turbos. The car does completely fine with the 3.15's.

The boat weight a bit more than 7k? My trailer fully loaded is 7k. I wouldnt recommend regularly, or even not regularly with any distance and speed, towing more than 7k. That's where I've "drawn the line in the sand"(based on math) for myself and the safety of others around me.

Originally Posted by RL18

Don’t do it. If you’re going to do anything there’s a guy on the bmw North American diesel group on Facebook that’s selling a kit to swap our 6 spd to the newer 8spd trans, full integration. Only then would it make sense to swap to 3.15 gearing.
You’re putting unnecessary strain on the engine and drivetrain with the stock 6spd. There’s a reason bmw went with 3.64 gearing in these and it wasn’t because of towing.

Very interested in your reasonings here, because I VERY much disagree. the 8 speed swap does very little for anything, as 8th is nearly the same as our 6th, and it essentially just makes a shorter 1st, and adds a gear (tightens up the ratios) from there until the "same" top gear. Don't get me wrong, I love the 8hp and wish I had the cash to do it to my car, but it just didnt make any financial sense for me to be putting 4-5k total into putting the 8hp in when all it gives is much better and smoother shift behavior. Now that I have a nearly brand new transmission in my X5, it turns out the 6hp is actually quite smooth when not damaged by hundreds of thousands of miles of negligent abuse. My new 6hp (got with 33k miles on it) will have fluid changes every 30k and seals every 60. It'll stay healthy for a long, long time. It's never going to be as fast or as smooth as the 8hp, but it's not lacking for the vehicle that it's in.
The reason bmw went for 3.64 gearing imo was because they wanted it to feel peppy with stock emissions. Taller ratio with stock power and you definitely notice it being slower. Taller ratio with delete and tune, and it runs fine and is certainly not "taxed" at all. How do I know? The EGT's, I monitor them a LOT. a diesel running 450-550f EGT's down the highway at 85+ is NOT taxed. Around town and beating on it, the temps barely get higher than 600, and that's 3/4 tilt off the line in city traffic. This engine when properly operating isn't taxed whatsoever with this drivetrain. Adding 15% more load with the 15% taller diffs adds 15%, but when it's +15% on top of completely untaxed... who cares?

Originally Posted by wcs531

I was assuming the ratio may have been targeted towards rated fuel economy for advertising (not real world fuel economy). It could be to reduce excess strain, but since when does BMW care about longevity past the warranty period? 10k+ mile oil change intervals, "lifetime" transmission fluid, etc. I would guess the e70's towing limits are more chassis related than engine/transmission related - they both seem pretty stout.

Also for non towing situations, shaving a few hundred RPM while cruising at 80mph for hours on end would have to reduce engine wear a reasonable amount in addition to better mpg.

Shaving a few hundred rpm off 80 not only saves some mpg (not as much as you'd think, aero penalty above 70 really starts to limit potential gains) but also makes the x5 significantly more comfortable form a NVH standpoint. The motor doesn't feel like it's revving unnecessarily, it's much quieter, and it just FEELS completely appropriate for the vehicle.

MPG gains under 75 are in the order of 3mpg. Under 70 they can really stack up, as myself and Evan have shown.


Overall, I encourage anyone to do the 3.15 swap to their 35d. It's great around town, it's even better on road trips. It's a wonderful mod that changes the feel of the car from "I'm geared short because i want to feel peppy and revvy" to "I'm big truck, i spool and get up and go" while at the same time feeling more relaxed.

[Spyro235]

[QUOTE=RL18;29764237]

Originally Posted by jbash87

Why was it so hard for you to just say that?

I forgot to ask. Do you have any experience towing over 4000lbs with your X5?

Because I still don’t think it’s a good idea lol. The transmission gearing just isn’t optimized for that final gear ratio. I’ve already mapped out the powerband/shift points based on mph of each final ratio with both 6 spd and 8 spd and you can clearly see that the 6spd with the 3.64 and 8spd with the 3.15 have similar characteristics (1st is identical actually). 3.15 with 6spd is too “tall” in 4th gear and below and would need more revving to prevent lugging the engine… yes fine in 5th and 6th, but you also don’t get that extremely useful 6th gear like you do in the 8spd to accelerate up to those higher gears. 3.64 with 8spd would be revvy, first would be useless but probably really fun/fast and a tank towing otherwise, and also still better on the highway in 8th with about a 100rpm drop, which you could get more with 31.5” oversized tires. That’s why I would lean towards doing the 8spd swap before the 3.15 swap.

But yeah 1750 rpm is when turbos would be spooled up you want to be at or above that rpm ideally so your exhaust bypass stays open. With 3.64 gearing at around 2,500 rpm in second, it drops you pretty much at that rpm actually which is perfect. 3rd, 4th and 5th can be shifted lower than 2,500rpm. I’ve also noticed that shifting at that rpm range in 2nd gets rid of that sloppy 2->3 shift bump which I think might be from the exhaust bypass shutting then reopening really fast. With 3.15s it drops you just below that and that gear is stretched out a bit longer too. So you want to be revving a bit over 2,500rpm, like 2,700rpm, atleast in second. Then atleast 2,500rpm in third and fourth to prevent lugging the engine. And since you’ll likely be using 1st now, because 2nd will be sluggish, revving up 2,700-3,000rpm would be better too. Btw this is casual driving, spirited or WOT is worse, which is why I think this is counterproductive.

I wouldn’t mess with sport mode, I hate sport mode, it would likely only be useful for something like towing, even then too sensitive. M-mode would be ideal, that’s what I always drive in. Gives you full control. You could possibly do the customization license in xhp and tune the D-mode shift points to happen later in those gears. Please for the love of God do not get a sutphin tune though.

And no I haven’t towed with my x5 yet. I have the hitch, factory wiring and trailerbrake controller but haven’t installed it yet. Will likely do it this summer when I rewire my audio system.

Want to say- first of all, I run a sutphin trans tune. It's wonderful, before and after the 3.15 swap.

I'm very curious why you think the shift points will have the X5 bogging. Mine is smooth linear power over all throttle/ load requests. Like, REALLY smooth. I'm the kind of person that LOATHES shitty trans behavior, and would absolutely not be able to tolerate ever for a day my x5 falling out of boost or falling on it's face between shifts. This ABSOLUTELY is not how my X5 performs. Once my X5 gets back up and running, I'm happy to post dash videos if you'd like to see visually how my X5 drives, it's shift points, etc. High throttle, low throttle, I can't give you towing because I moved across the country from my trailer, but that's also not a worry at all.

[Spyro235]

Feb 2023 update time:

The X5 has been doing great. Dash is at 326k miles, which means the new powertrain has 11.5k miles on it in my X5. It's running awesome, except that I recently notices my boost is only spooling to 28psi. I thought my tune should be running 32-33, and asked my tuner- it's true! So I'm going to reflash my tune and see if that fixes the issue. 0 drivability problems, was just logging randomly and noticed.

Also, I moved to the greater Seattle area. After many long road trips from the denver area, (I drove to Vegas for SEMA

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, Zion NP for tday+ engagement, camping on the way there,

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a few big weekend trips around the CO area,

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Seattle for 3 weeks for work) We ended up actually moving to seattle, and those weekend miles really added up. Through october-december I was working all week in seattle, so all of the miles were weekend ones!
Through all of those trips I hit some CRAZY snow, and continued to love my Nokian Hakkapelita R3's. They got us everywhere safely, and completely in control. SO impressive.


That brings me to now: X5's been down for a week. Should be able to fix it this coming weekend: My front drivers wheelbearing, was a dead on arrival unit a few months ago when I changed it. It made some noise but was smooth, so I rode it out. It's dangerously bad as of last week, and was vibrating like crazy and sounding like a bucket of ground marbles. My front calipers were also starting to go wonky, and rear needed pads, so I decided to go for the 50i caliper upgrade all around. Have the calipers and am just waiting on FCP rotors and pads and bimmerworld steel braided soft lines. I'm going with textar oe(m?) pads all around. Now that I have my own garage and driveway, I'm shameless about washing my cars whenever needed, so I don't really care about dust. I want good bite! If I don't get it with the brake 2 piston front+ oem pads, I'll go for Hawk HPS 5.0's and see how I like those.

[RL18]

Originally Posted by RL18

Don’t do it. If you’re going to do anything there’s a guy on the bmw North American diesel group on Facebook that’s selling a kit to swap our 6 spd to the newer 8spd trans, full integration. Only then would it make sense to swap to 3.15 gearing.
You’re putting unnecessary strain on the engine and drivetrain with the stock 6spd. There’s a reason bmw went with 3.64 gearing in these and it wasn’t because of towing.

“Very interested in your reasonings here, because I VERY much disagree. the 8 speed swap does very little for anything, as 8th is nearly the same as our 6th, and it essentially just makes a shorter 1st, and adds a gear (tightens up the ratios) from there until the "same" top gear. Don't get me wrong, I love the 8hp and wish I had the cash to do it to my car, but it just didnt make any financial sense for me to be putting 4-5k total into putting the 8hp in when all it gives is much better and smoother shift behavior. Now that I have a nearly brand new transmission in my X5, it turns out the 6hp is actually quite smooth when not damaged by hundreds of thousands of miles of negligent abuse. My new 6hp (got with 33k miles on it) will have fluid changes every 30k and seals every 60. It'll stay healthy for a long, long time. It's never going to be as fast or as smooth as the 8hp, but it's not lacking for the vehicle that it's in.
The reason bmw went for 3.64 gearing imo was because they wanted it to feel peppy with stock emissions. Taller ratio with stock power and you definitely notice it being slower. Taller ratio with delete and tune, and it runs fine and is certainly not "taxed" at all. How do I know? The EGT's, I monitor them a LOT. a diesel running 450-550f EGT's down the highway at 85+ is NOT taxed. Around town and beating on it, the temps barely get higher than 600, and that's 3/4 tilt off the line in city traffic. This engine when properly operating isn't taxed whatsoever with this drivetrain. Adding 15% more load with the 15% taller diffs adds 15%, but when it's +15% on top of completely untaxed... who cares?”

Actually we agree on more things than you think. I agree that it’s fine 5th and 6th are completely fine. It’s probably great on the highway. I don’t like the trade off in town and I like the peppy characteristics because it feels like a diesel truck (not sure what “trucks” you’re talking about it driving like… gas jobs?). Another thing is a heavy duty diesel truck has much more grunt down low. You can’t compare our diesel engine with a heavy duty diesel engine with twice as much displacement. A ram eco diesel is the best comparison of ours to a pickup truck and they had an 8spd trans with 3.23 and 3.55 rear ends. The first gen had a ton of issues with engines blowing up in low rpm high load situations. Could that be another issue? Sure. Could also be because people were driving them like a heavy duty diesel? Yeah. Apparently the second gen fixed this issue though but is probably just trans tuning. But still, while our diesels are extremely impressive they rev higher to achieve it. Our diesels stock rev about 1000rpm higher then the newer heavy duty diesels, 1800rpm if you compare it to a 7.3, the ecodiesel is limited at 4,800 like ours (stock) but I’d be willing to bet it can’t rev as high as our diesels reliably with tuning. Not to mention none of those have twin turbos, they’re all vgts. Does it have a ton of torque? Yes but it’s not a direct comparison at all.

The problem I’m pointing out is all gears before it to accelerate up to 5th. You’re having to rev higher in those gears to put similar amounts of load on the engine as with the stock gearing. And if your not, you are most definitely putting on more strain on it. +15% more load is not nothing. 1st is probably usuable now and probably very helpful for gaining momentum. But also 1st is useful with the stock gearing, the fastest 1/4 mile times are done using first gear. You’re egts are not going to be that affected by the gearing but egts aren’t necessarily THE indicator of how much strain is being put on your powertrain anyways. And btw My egts highway and city are 375-475F. If I’m beating on it, it doesn’t go over 600 or much over depending how long I stay on. That’s with 31.5” tires too which are oversized. Its was even lower on stock tires. Our egts are low because of the turbos. If it wasn’t for being deleted too, stock would be much worse. Driving in D mode might be smart for the reason it will shift load based, but I just drive in manual because I like the control and it’s much smoother.

With all that being said, it’s a fair assumption to be made that the 8spd is fully optimized for the 3.15 gearing and the 6spd is fully optimized for the 3.64 gearing. Bmw definitely knew what they were doing with the gearing. The fuel mileage is still incredible for a full size suv. You really can’t say the 3.15 swap is “ideal” for the 6spd. It “can” be a good option. You’d probably see a benefit if you drive mostly highway. If you drive city mostly it’ll obviously going to lack the “pickup” the 3.64 gearing has, it’s adding more strain and overall it’s slower. Will it be detrimental? Possibly long term. Short term it probably won’t make much of a difference. I would still do an 8spd first then 3.15s, but that’s just me, do whatever you’d like to yours. I’m not trying to directly oppose you at all. But this is a public forum so people should be able to hear all the benefits as well as the all downfalls before they make a decision like this.

[Spyro235]

Originally Posted by RL18

The problem I’m pointing out is all gears before it to accelerate up to 5th. You’re having to rev higher in those gears to put similar amounts of load on the engine as with the stock gearing. And if your not, you are most definitely putting on more strain on it. +15% more load is not nothing. 1st is probably usuable now and probably very helpful for gaining momentum. But also 1st is useful with the stock gearing, the fastest 1/4 mile times are done using first gear. You’re egts are not going to be that affected by the gearing but egts aren’t necessarily THE indicator of how much strain is being put on your powertrain anyways. And btw My egts highway and city are 375-475F. If I’m beating on it, it doesn’t go over 600 or much over depending how long I stay on. That’s with 31.5” tires too which are oversized. Its was even lower on stock tires. Our egts are low because of the turbos. If it wasn’t for being deleted too, stock would be much worse. Driving in D mode might be smart for the reason it will shift load based, but I just drive in manual because I like the control and it’s much smoother.

With all that being said, it’s a fair assumption to be made that the 8spd is fully optimized for the 3.15 gearing and the 6spd is fully optimized for the 3.64 gearing. Bmw definitely knew what they were doing with the gearing. The fuel mileage is still incredible for a full size suv. You really can’t say the 3.15 swap is “ideal” for the 6spd. It “can” be a good option. You’d probably see a benefit if you drive mostly highway. If you drive city mostly it’ll obviously going to lack the “pickup” the 3.64 gearing has, it’s adding more strain and overall it’s slower. Will it be detrimental? Possibly long term. Short term it probably won’t make much of a difference. I would still do an 8spd first then 3.15s, but that’s just me, do whatever you’d like to yours. I’m not trying to directly oppose you at all. But this is a public forum so people should be able to hear all the benefits as well as the all downfalls before they make a decision like this.

Hey, no hate here. Love the conversation.

First off- what size are are your tires? I'm oversized as well, at 30.6" IIRC, 265/60-18.


I do completely modify my X5 in mind for it's long trips, so there's that. Deleted and tuned, back to back to a normal geared X5, I don't find myself driving any differently, hitting the pedal harder, etc. I genuinely don't notice it unless I focus on the fact that gears last a bit longer. I'm not the type to be beating on my X5 from stoplight to stoplight, I'm more of the "keep the dog and fiance comfortable" mindset when I'm in the X5.

And sure, when towing that 15% definitely makes a difference, but nearly none of my towing time is done around town, so I'm not personally worried much about that.

As far as the trucks I have experience with- I only have a lot of experience driving trucks when actually towing. Only 6.7's and 7.3's with 10k+ pounds behind them, so I was referring to the spoolin' and boolin' feel of letting the diesel eat some boost.

[RL18]

Originally Posted by Spyro235

Hey, no hate here. Love the conversation.

First off- what size are are your tires? I'm oversized as well, at 30.6" IIRC, 265/60-18.


I do completely modify my X5 in mind for it's long trips, so there's that. Deleted and tuned, back to back to a normal geared X5, I don't find myself driving any differently, hitting the pedal harder, etc. I genuinely don't notice it unless I focus on the fact that gears last a bit longer. I'm not the type to be beating on my X5 from stoplight to stoplight, I'm more of the "keep the dog and fiance comfortable" mindset when I'm in the X5.

And sure, when towing that 15% definitely makes a difference, but nearly none of my towing time is done around town, so I'm not personally worried much about that.

As far as the trucks I have experience with- I only have a lot of experience driving trucks when actually towing. Only 6.7's and 7.3's with 10k+ pounds behind them, so I was referring to the spoolin' and boolin' feel of letting the diesel eat some boost.

Sorry mine are 30.6” like yours. I do wanna lift my x5 though so maybe someday I’ll get close to 32” tires.


I get where you’re coming from. But where I am. I love the gearing characteristics because it’s very hilly where I am so I’m constantly going up or down. I don’t necessarily drive aggressively, but I do let it get up in rpms quite a bit before shifting, atleast in lower gears. I find that atleast in second shifting around 2500rpm completely gets rid of that bump shift that these trans are notorious for. My 335d can be bad sometimes with it.

My concerns would mostly be towing and city driving. But like I’ve said you can still do it. You just are going to be revving higher than you would with 3.64 gearing for similar load. And on flat ground it may not cause any problems.

That’s funny because those are two engines I’m very familiar with too. Have driven some durmaxs but those are city trucks lol. Had an old 7.3 and my dad has the new 6.7 that we use to tow all the time for our business. You can do that with those because they are more than twice the displacement, so they can handle much more load. They also have single turbos, the 6.7 being vgt and my 7.3 had the garret ball bearing turbo (which sounded amazing). Very different from our turbo system though. Ours was specifically designed for our tiny displacement too give us pep down low, but even then, our turbo’s don’t really get spool up until the exhaust bypass opens at 1750rpm. The turbos down low is great for our displacement to create more torque, but it still isn’t a 7.3 or 6.7.

[Spyro235]

Originally Posted by RL18

Sorry mine are 30.6” like yours. I do wanna lift my x5 though so maybe someday I’ll get close to 32” tires.


I get where you’re coming from. But where I am. I love the gearing characteristics because it’s very hilly where I am so I’m constantly going up or down. I don’t necessarily drive aggressively, but I do let it get up in rpms quite a bit before shifting, atleast in lower gears. I find that atleast in second shifting around 2500rpm completely gets rid of that bump shift that these trans are notorious for. My 335d can be bad sometimes with it.

My concerns would mostly be towing and city driving. But like I’ve said you can still do it. You just are going to be revving higher than you would with 3.64 gearing for similar load. And on flat ground it may not cause any problems.

That’s funny because those are two engines I’m very familiar with too. Have driven some durmaxs but those are city trucks lol. Had an old 7.3 and my dad has the new 6.7 that we use to tow all the time for our business. You can do that with those because they are more than twice the displacement, so they can handle much more load. They also have single turbos, the 6.7 being vgt and my 7.3 had the garret ball bearing turbo (which sounded amazing). Very different from our turbo system though. Ours was specifically designed for our tiny displacement too give us pep down low, but even then, our turbo’s don’t really get spool up until the exhaust bypass opens at 1750rpm. The turbos down low is great for our displacement to create more torque, but it still isn’t a 7.3 or 6.7.

With my new trans- I've found out that that bump shift is entirely the fault of worn trans/valve body internals. Never would've known otherwise, but my new trans is smooth as glass!

Listen, I totally agree about the displacement. Towing 10, even 15k pounds behind a 6.7 is working it less than ours is working with my 7k trailer behind it. Doesnt mean it wont last nearly, if not just as long as one not towing. These engines are meant to, and happy to sit in boost. I have no doubt my original motor wouldve still been going past 315k miles, had I not diluted the oil/ washed the bearings with diesel. It was over 25k miles of towing 4k-7k pounds of weight from 200k-315k miles when it let go. This new(ish)motor better keep up!

[jbash87]

Originally Posted by Spyro235

My thoughts are- it's wonderful. My name is Aaron on the BMW group, I'm one of the loud praising ones there for the 3.15. I believe it's really how the car should've come from the factory. my 5th gear is 5% shorter than your 6th gear. If the engine needs to gear down while towing, I let it. I try to stay in D while towing so it shifts based on load, not based on how much I want to hear the turbos. The car does completely fine with the 3.15's.

The boat weight a bit more than 7k? My trailer fully loaded is 7k. I wouldnt recommend regularly, or even not regularly with any distance and speed, towing more than 7k. That's where I've "drawn the line in the sand"(based on math) for myself and the safety of others around me.

Thanks for the reply! I actually bit the bullet and did the swap over a few days last weekend/week. It was way more faffing about than I was hoping it would be and I ended up tearing a front CV boot in the process although it didn't let go until after driving around a bit. Good lord what a mess that made... I'm running in 2wd mode now as I have 3 axles in the car debating on what to do about the 4th. Genuine axles are $$$$

I absolutely love the 3.15s so far. I would echo your opinion that the diesels should have come with them from the factory. Driveability is much better all around.
The Sutphin tune does quite nicely with it as well. I've had the tranny tune since my delete. Initially the 1st to 2nd shifts were pretty bad, but I've received 2 updated from Rod and the first one helped a ton. I haven't tried the 2nd yet as I just got it and the 3.15s have made that shift smoother.

My boat does NOT weigh more than 7k. I have no idea where I misread your post but its 4500lbs dry so probably closer to 5k on any given day. The X5 handles it just fine although you DEFINITELY know it's there . I'm excited to see how it tows this summer. Hope ATM gets some upper hoses shipped before then...

Originally Posted by Spyro235

Seattle for 3 weeks for work) We ended up actually moving to seattle, and those weekend miles really added up. Through october-december I was working all week in seattle, so all of the miles were weekend ones!

Hey!! Welcome to Seattle! Where abouts are you? I'm in West Seattle. Always good to know local BMW nuts.

Congrats on the engagement, too!

[RL18]

jbash87

Oh god not the sutphin tune. Highly recommend dropping that and just using the xhp tunes.

[RL18]

Originally Posted by Spyro235

With my new trans- I've found out that that bump shift is entirely the fault of worn trans/valve body internals. Never would've known otherwise, but my new trans is smooth as glass!

Listen, I totally agree about the displacement. Towing 10, even 15k pounds behind a 6.7 is working it less than ours is working with my 7k trailer behind it. Doesnt mean it wont last nearly, if not just as long as one not towing. These engines are meant to, and happy to sit in boost. I have no doubt my original motor wouldve still been going past 315k miles, had I not diluted the oil/ washed the bearings with diesel. It was over 25k miles of towing 4k-7k pounds of weight from 200k-315k miles when it let go. This new(ish)motor better keep up!

You could be totally right just better to be said than not said. One day I’ll make the switch too, but I’m gonna do both the 8 spd and 3.15s. Will make a world of difference, especially since I plan on doing hybrids, valve springs, and dual pumps in the near future.

Glad that you’re up and running again though. Must feel good!

[Spyro235]

Originally Posted by jbash87

Thanks for the reply! I actually bit the bullet and did the swap over a few days last weekend/week. It was way more faffing about than I was hoping it would be and I ended up tearing a front CV boot in the process although it didn't let go until after driving around a bit. Good lord what a mess that made... I'm running in 2wd mode now as I have 3 axles in the car debating on what to do about the 4th. Genuine axles are $$$$

I absolutely love the 3.15s so far. I would echo your opinion that the diesels should have come with them from the factory. Driveability is much better all around.
The Sutphin tune does quite nicely with it as well. I've had the tranny tune since my delete. Initially the 1st to 2nd shifts were pretty bad, but I've received 2 updated from Rod and the first one helped a ton. I haven't tried the 2nd yet as I just got it and the 3.15s have made that shift smoother.

My boat does NOT weigh more than 7k. I have no idea where I misread your post but its 4500lbs dry so probably closer to 5k on any given day. The X5 handles it just fine although you DEFINITELY know it's there . I'm excited to see how it tows this summer. Hope ATM gets some upper hoses shipped before then...



Hey!! Welcome to Seattle! Where abouts are you? I'm in West Seattle. Always good to know local BMW nuts.

Congrats on the engagement, too!

Glad you're liking in. Also, glad you're liking the sutphin tune. I've tried the XHP ones and couldnt stand them, personally. Sutphin is sooooo much more refined in my experience

Originally Posted by RL18

jbash87

Oh god not the sutphin tune. Highly recommend dropping that and just using the xhp tunes.

You're the only person who feels that way around these parts lol. Nothing against you- maybe you just had a revision/ adaptation issue. My sutphin tune drives my transmission nearly exactly as I would drive my X5 if it was manual transmissioned. Imo it's automatic perfection, this side of an 8hp. Especially this last revision with lockup on shift to second, which sounds crazy but is actually done so smoothly and well.

[Spyro235]

Originally Posted by RL18

You could be totally right just better to be said than not said. One day I’ll make the switch too, but I’m gonna do both the 8 spd and 3.15s. Will make a world of difference, especially since I plan on doing hybrids, valve springs, and dual pumps in the near future.

Glad that you’re up and running again though. Must feel good!

The ultimate combo. I'd love to do this, and with a new motor there's no better time to go hybrid+ duals but I don't want anyyyyy more spool lag than I have right now, and this thing just needs to be my reliable workhorse. I'm selling off all my other toys in order to buy something fun, to focus all my 'fun' energy on. My X5 needs to stay deleted, stock, and happy....

[RL18]

Originally Posted by Spyro235

The ultimate combo. I'd love to do this, and with a new motor there's no better time to go hybrid+ duals but I don't want anyyyyy more spool lag than I have right now, and this thing just needs to be my reliable workhorse. I'm selling off all my other toys in order to buy something fun, to focus all my 'fun' energy on. My X5 needs to stay deleted, stock, and happy....

There’s no spool lag. It’s only the Lp turbo that’s upgraded and the dual pumps spool it up quicker than stock pump and turbos. And it’s reliable with the right tune

Btw been watching my egt more lately and basically cruising speed starting at 25mph I see about 315F, then going up in speed to 45mph I’ll see about 440F cruising. Any up hills will bring egts up, it’s hard to put a number on it because there’s so many variables but a large up hill might spike egts 100F, sometimes a bit more or less. A normal acceleration up to 45mph on flat ground peaks about 450F. Uphill acceleration to 45mph is about 100F higher, depends on the uphill and duration. Highway driving at 80mph on flat ground is pretty steady at 550F. 75mph is around 520F. Normal passing will bring it above 600F. Uphills highway can peak around 650F. Then WOT from a stop 2nd->3rd might peak at 585ish. WOT accelerating on the on ramp 3rd to 4th will peak around 800F.

[Spyro235]

Originally Posted by RL18

There’s no spool lag. It’s only the Lp turbo that’s upgraded and the dual pumps spool it up quicker than stock pump and turbos. And it’s reliable with the right tune

Btw been watching my egt more lately and basically cruising speed starting at 25mph I see about 315F, then going up in speed to 45mph I’ll see about 440F cruising. Any up hills will bring egts up, it’s hard to put a number on it because there’s so many variables but a large up hill might spike egts 100F, sometimes a bit more or less. A normal acceleration up to 45mph on flat ground peaks about 450F. Uphill acceleration to 45mph is about 100F higher, depends on the uphill and duration. Highway driving at 80mph on flat ground is pretty steady at 550F. 75mph is around 520F. Normal passing will bring it above 600F. Uphills highway can peak around 650F. Then WOT from a stop 2nd->3rd might peak at 585ish. WOT accelerating on the on ramp 3rd to 4th will peak around 800F.

Mine runs exactly the same EGT's as yours does. Cool!