Originally Posted by e39_touring (Post 1227572)

I'll throw my two cents in here since I've kind of been thinking of doing the same thing as you are. I've concluded that the M54 engine will be fine with boost provided you don't become addicted to it and overdo it and also provided that your tune is good (never lean). The N54 has basically the same bottom end and runs 8 psi of boost for ~300 chp from the factory. An M54 with 8 psi of boost properly tuned will do just fine under the rigors of towing.

A small-ish turbo or positive displacement supercharger will be a better match for a heavy SUV like the E53 compared to a centrifugal blower like others have already mentioned. The centrifugal blower won't 'feel stronger everywhere' but will rather come on stronger and stronger as RPM's build with little difference being felt coming off a stop and at lower RPM's. Not really ideal for towing.

Upgrading the cooling and drivetrain is not a necessity, but making sure it they are in tip top shape is. IIRC, the auto 3.0 is rated to 5 or 5.5k lbs while the manual is 6k. Keep your loads within those limits, and don't do extended full throttle pulls at max load, and you'll be fine.

However, if your trans is already heating, it's already slipping, and adding power will make its failure that much quicker. The E53 GM trans is electronically controlled and has a series of clutches and solenoids to actuate gear changes. Once a gear is locked, there should be no slippage, and the heat generated should be minimal (i.e. towing or not, your ATF should roughly maintain engine coolant temps since it is cooled & heated by the engine radiator). If it's heating, it means that you trans is slipping excessively during gear changes, which can be more frequent with towing.

I've also decided that if I go the V8 route, it won't be in a BMW but something domestic with a more robust drive train like a Trailblazer SS or Jeep Grand Cherokee SRT or the like. A little less refined than the bimmer, but they sure can take a beating in the drivetrain dept.

Keep us posted on what you decide to do!

Originally Posted by X5chemist (Post 1227583)

How does Sport mode on a 3.0i work with towing? When I need to accelerate aggressively, I throw it in Sport mode.

Originally Posted by nick325xit 5spd (Post 1227582)

It seems like OP's real issue is that his transmission can't handle the load already. I really don't see how adding more power fixes that.

The GM transmission is configured for extreme sloppiness. BMW uses that torque converter to give the X5 way more oomph than it rightfully should seem like it has. The result is that of *course* it's going to struggle under load.

Edit: That and if you're going to tow with an automatic E53, it's kind of nuts to engineer your own FI kit vs. just pick up an N62 with the ZF6 that will have the power, torque, and transmission to handle it.

Originally Posted by e39_touring (Post 1227586)

Adding power won't fix a bad transmission, and I noted that in my post where I said the transmission and cooling need to be in top shape before considering boost.

However, I think you misunderstand how auto transmissions and torque converters work. By 'extreme sloppiness', I assume you mean that the torque converter is loose/high stall speed. Yes, this slippage allows the engine to get into its RPM power range before transmitting power to the transmission, but that is VERY different than a transmission that's slipping due to bad clutches, seals, or solenoids. Once at highway speed, with the torque converter locked and the transmission in gear, there should be no slippage and minimal heat.

In the OP's case, there isn't enough information to tell exactly what's going on since I don't know how and what he's measuring with his temps. It could be the engine is heating from load and since the ATF shares the engine radiator, the ATF will heat, too. The temp gauge will still stay in the center with quite a wide range of coolant temperature change. My point is, you can look at your gauge and see that it's centered but monitor engine or trans temps with an OBD reader and see something different than you expect.

No need to engineer a power adder for the M54 as there are a couple of positive-displacement blowers out there that will do the trick. A V8 will certainly work as well, but the OP sounds like he's experienced the typical unreliability and high cost of maintenance associated with the BMW V8 (and probably the reason the resale value of them is so low). Oh yeah, and everything that we've both said about towing and the driveline applies to the 4.4/4.6/4.8 as well. It's not like those don't eat their share of transmissions, too, towing or not.

Anyway, different strokes for different folks - do what makes you happy :thumbup:

Originally Posted by nick325xit 5spd (Post 1227591)

As for transmission reliability, well, the ZF6 is by FAR the best and toughest and most reliable auto transmission that you can get in an E53. It is only in the N62 X5s in the US. The N62 has quirks that can be managed.

Originally Posted by nick325xit 5spd (Post 1227591)

Also, you say that there positive displacement blower kits out there, but are there any actually still in production? Because I did check that and none of the ones that I recall are still available.

Originally Posted by EODguy (Post 1227611)

I'm heading to a pool party...

Originally Posted by e39_touring (Post 1227616)

No, I think only centrifugal blowers can still be bought new for the m54 - now or of production for what, 17 years? You'd have find a pd blower used. But, no way I'd spend $5-7k on a blower for an e53 x5 3.0 these days when the truck is only worth $3-4k at best.

P.s. - ironically, I've never had a problem with the gm transmission in our old x5 3.0 even with a bit of towing (waaay over max rating, but only around town), but the zf auto in our old e46 3 series took a dump at 40k miles. However, the zf6 manual in my old corvette IS a brute!