JBD tuner for MB
03-21-2014, 03:28 PM
#51
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GLK250
Increasing rail pressure works, and I'll even admit fairly well. Proper injector sizing is a WAY more expensive option for getting more fuel into the motor. My concern with these mods is primarily the cost in life to the injectors themselves, the pumps seem more than happy to make 23,000 or 26,000 or even 30,000 psi. I recently reflashed and bumped rail pressure only slightly from approx 23,000 to 23,650 psi along with longer duration/higher duty cycle on injectors. I am still VERY safe on EGT as EGR was killed at the same time and I have straight pipe exhaust. I've considered a Kleeman box for play days but would hesitate to use 2000 Bar injection pressure daily.
Am I wrong in thinking such a large jump in rail pressure is a bad idea? For those of you with rail pressure mods what downsides have you seen? I'm already at tranny torque limit until a bit over 3,000 rpm so future mods are aimed more squarely at keeping lower and middle rpm ranges where they are at now but increasing 3500-4500 rpm power. Thoughts?
Am I wrong in thinking such a large jump in rail pressure is a bad idea? For those of you with rail pressure mods what downsides have you seen? I'm already at tranny torque limit until a bit over 3,000 rpm so future mods are aimed more squarely at keeping lower and middle rpm ranges where they are at now but increasing 3500-4500 rpm power. Thoughts?
I've been fiddling around with it, trying to find the optimal setting. Plus the weather has been really back and forth between sub-zero and spring thaw, so the testing conditions haven't been ideal.
At any rate, I'm finding that the 85% setting seems to work best in cold weather, providing the spirited driving without tripping the CEL. At 90% or 100% in cold weather, the CEL definitely comes on and I suspect that power is dialed back a bit (though not at all like a limp mode would be). However now that it's a bit warmer out, I've been leaving the JBD at around 90% to 95% setting and all seems well, though I need to keep an eye on it.
Net result at 90%+ is pretty impressive. I've not had the GLK dyno'd but I have owned some pretty buff cars in the past (APR Stage 2 GTI, Dinan Stage 1 BMW 135i, SRT Dodge Challenger, etc.) and I know what big power feels like.
I think it's fair to say that at 90% setting I'm putting down 450 lb-ft at minimum, likely more. Horsepower is harder to tell with a 4,200 rpm redline but 240 to 250 hp is completely in the realm of possibility. No sign of the ECU adapting and dialing back fuel pressure, either. On the E350 BT, power gains are quite a bit less. My guess is that's because the E350 is a single turbo V6 while the OM651 is a twin turbo.
Power delivery is much more linear than before. Off-the-line it just lunges forward effortlessly, making the GLK feel very very light on its feet (a sure sign that torque is probably within shouting distance of 500 lb-ft crank). Power at the 'high' end of the range (if 4,000 rpm can be considered high) is also greatly improved. All in all, the thrust is such that the tranny in Sport mode is shifting pow-pow-pow every few tenths of a second. No fuss. No drama. Just lots of go.
As for fuel economy, it's hard to say since I haven't burned off a full tank. However, highway mpg seems to be up by one or two, same goes for city mpg
All in all, well worth the $300 that I spent on the JBD.
Last edited by roscoe108; 03-21-2014 at 03:31 PM.
