[mrvedit]

The issue of walnut shell blasting of the intake valves has been mentioned many times, such as in this recent thread:
http://www.e90post.com/forums/showthread.php?t=1029521

To determine how much difference it makes, if any, I decided to document performances run before and after walnut shell blasting on my 2008 335xi with 75,000 miles. I used the iPhone app Dynolicious for this. The runs were made on the same stretch of level road at about the same temperature (34F and 30F) and from idle with no brake-torquing.

The "before" values were:
0-30mph 2.25
0-60mph 6.00
0-90mph 11.56
60ft 2.45
1/8 mile 9.52 sec 78.8 mph

After a very thorough job of walnut shell blasting the intake valves and ports, and giving the car a few days to "retune" itself, the values are:
0-30mph 2.07
0-60mph 5.34
0-90mph 10.33
60ft 2.07
1/8 mile 8.81 sec 81.9 mph

I am very pleased with the improvement, which was already obvious to my "butt dyno".

According to a commonly used drag racing calculator, and using a weight of 3850 lbs, power improved by 38HP from from 307 to 345. I know that is more than the advertised 300HP, but you can play with the calculator yourself:
http://www.wallaceracing.com/hpcalculatoreigth.php
I have confirmed at the drag strip that Dynolicious is reasonably accurate.

While I have JB4 installed, these runs were made with the stock setting (Level 0). The "after" performance without JB4 is very close to the "before" performance with JB4 enabled. That should give you some idea how much difference it made.

Comparing the condition of my valves with the pictures in the aforementioned thread, I would say mine were "average" as the condition of some engines was much worse.

I'm sorry not to have 1/4 mile or 0-100mph times, but I didn't have that opportunity for the "before" run.
(I also had to promise to the State Police to stop using the local highway for 120+mph drag strip runs.)

Since walnut shell blasting is not a trivial procedure, I also installed Burger Tuning's "Oil Catch Can" which hopefully will help keep the valves cleaner in the future. I do wonder if all direct-injection cars, now becoming commonplace, will have this problem.

[IN54NITY]

MrVedit. Thanks. I believe manufactures (including BMW) are aware of the problem, from what I have heard, the N55 motor doesn't have this problem as bad as the N54, but I can't remember why. (Slightly different crankcase design so that air has to move around a wall - and the oil collects on thls and falls off - or something like that.)

[adidoman]

I had a N55 with my last 135 and it still had problems and had a good amount of gunk at 50k miles

[HazChem]

Thanks for sharing. I'm at 86,000 miles and am finally doing it during my next oil change.

[Laurus_CEO]

Thanks for sharing this is great info, if anyone in the SF Bay area needs blasting feel free to contact me.