For our long rides, and riding style, we've wanted to tame the high RPMs of the 825i for a long time now. Especially when climbing the long, tall mountains of WV(constant +4500 screaming RPMs while going only 10-12 mph)! But also while cruising at speeds of 15-25 mph. After reading several members on here discussing the diesel weights/spring setup, we decided those running characteristics would be more aligned to what we use our gator for.
If you like constant ripping and roaring... slinging mud and rocks everywhere all the time... the crazy high rpms and loud noise levels(even when barely moving)... and extracting every last ounce of horsepower out of your ride, then this modification isn't for you! But if you're looking for lower rpms, less noise, better fuel economy, and still have plenty power to use it on the farm/around your property, then you might just wanna do this.
I admit that this modification is more suited for people who live in non-mountainous terrains, but it seems to do just fine and is still more than we need for our driving/riding style!
M161228 - $20 - 855D Primary clutch "compression spring"
AM140452 - $6 - 855D Primary clutch "weight kit"(1/4" needs cut off the end of weights with a cutoff wheel or grinder. Then balanced to the gram.) I used the "mower blade/nail in the wall" method to get it close, and will be going back and adjusting them with a gram scale
Combination: Stock/Diesel Parts
WOT shiftpoint RPMs 5500/4000
Engagement RPMs 1500/1200-1300(hard to tell, it's so low)
Disengagement RPMs 2300-2400/1200-1300
Lower RPMs at all speeds(except top speed)
Less throttle to go faster speeds(less fuel consumption)
Knocks 600-1000 RPMs off of cruise speeds
Quieter(can carry on a conversation now with passenger)
Deeper sound(almost like a v-twin now) no more raspiness
Better fuel economy(27.1 MPG in the mountains, not even being conservative)
Engine wear reduced because of lower RPMs
Loses some acceleration at wide open throttle, off the line(due to lower RPM upshift point) Typical driving accelerates faster from a start, though
No more wide open throttle, high-rpm shenanigans
We got 27.1 mpg on a 4 hour ride with elevation changes ranging from 1800-3000ft the entire time. I feel like someone who lives in a relatively flat part of the country could attain 35 mpg with this setup.
If you're worried about less pulling power for work/farming duty, dont be! As you can see in this graph, it still has 44 ft/lbs of torque @ a measly 1700 rpms. Looks like the peak pulling power of 47 ft/lbs occurs at ~3200 rpms, which is still attainable with this setup.(Will rev to 3900-4000 when floored) And in case you don't know, the 825i has more torque at EVERY rpm than the 855d does! The diesel does NOT have more "low-end grunt".
And now the results!!!
Speed/rpm comparison on level ground(diesel parts - red/stock - blue)
As you can see, the diesel setup goes a lot faster at every rpm. 12 mph faster @ 3500 rpm!
Speed/rpm comparison on a steep WV gravel road(diesel parts - red/stock - blue)
You can see that the stock setup has to rev to around 3500 rpms before the light weights overcome the spring and start making it upshift. Sooooo much quieter now, especially going up hills!
Thanks to [MENTION=407]arzdog[/MENTION] for the picture, and info of what to modify on the weights(cut 1/4" off the end). And the part number!
Part throttle cruising at different rpms... at ~26 seconds, I start going up a hill and you see it slowing down. Throttle position is held the same and RPMs only drop ~100 rpms. Backshifting still works good!
Full throttle test from a start, showing the new ~4000 rpm shift point of the clutches. Watching and listening closely, it appears to be fully shifted out at 4275. At that point you see the tach start making larger jumps in rpm and you can also hear the engine start to speed up. I let off the throttle because I was approaching a curve.