[Jelle458]

I see people asking and asking, so here's my take on it.

Mostly for people who might just search the internet to find out stuff.

I bought my car almost 2 years now, and since I came from M52B25 the N52B30A had a lot of extra power, but as with all things you get used to it, and the same goes for the power.

It started to feel like I needed at least a bit more. Not knowing this engine at all, I took my Delphi tester to the car and it gave me an error on the DISA. I deleted the error and it didn't come back for months. I did however crave a bit more.

It wasn't until I asked around that I got pointed to some people who tune and knows the engine pretty well.

I got the HP output measured for very cheap, just to see. Most people I talked to say that these cars NEVER have 258 HP, they usually settle in at 240 HP, so I needed to know.

The outcome was 254 HP, but at 3000 to 4500 RPM the engine had almost the same power output, and then it spiked up.

No issues with idle, or with low or high end power, it was all in the middle.

When driving home from the tune shop I swear I started actually feeling and hearing when the engine hit 3000 RPM. It was like the car was breaking. Of course now that I know, I also feel it.

I purchased some RIDEX DISA valves, and when time seemed alright I got to work.

I took away the air filter box, and the throttlebody, so I had the bare manifold in the car.
I read somewhere (I think on these forums) that you need to be careful with some hoses as they can break and a replacement isn't easy. So I started out thinking if I let the manifold just sit in the engine bay, I could do it.
I am happy to report that it is possible. You need to seperate the manifold from the engine though, to get the small DISA off, and you need to feel where the bolts go. Definitely took longer than taking off the manifold, but with time saved from removing and refitting the manifold I think I'm in plus time-wise.

The small valve was completely broken, I could flip it with my finger. The big one was still working, but the rubber seal was torn up.

I didn't even bother with the new rubber gaskets I purchased for the manifold, the whole intake looked and felt pretty new, and I found no carbon build up in the engine part. The intake ports were very smooth and clean, so I just slapped the manifold back on as-is.

After changing I did feel a difference. Not crazy but definitely a difference.

I see the ESP going off on a dry road for the first time since I had the car, only by pushing the accelerator. That's on Michilin Alpin 6 tires that's 255 wide, brand new.

I went to get the power measured again:







I think it's pretty obvious which lines are the old and the new, especially at 3000 - 4500 RPM.

I've heard many people dismiss that it was DISA, because if DISA is broken it can cause bad idle, or stuttering in power delivery that you feel. In this case there was none of that, just a little dip of power.

I was told that they of course only measure full throttle, but at half throttle there might be a bigger difference.

With this done, engine-wise I'm looking at the ESS kompressor kit V3. The guys who measured the engine could definitely make it deliver some crazy power with that on.

[Suvorovo]

Nice results. Good to know broken DISAs don't always produce codes. I bought Genuine BMW ones on sale for around $630 @130k miles. Good preventative maintenance last thing you want is broken pieces ending up in the engine. Port injected engines don't have carbon buildup on the valves. Gasoline is a good cleaner.

[The Nightman]

Thanks for sharing, especially the dyno graphs

[Jelle458]

So I went to fill up fuel today. I live in Denmark where octan 100 is the best I can get from OK. We also have vpower but not in the area I live. I was told the octan 100 from OK was a bit better though.

Anyway been driving on this octan 100 for many kilometers before I got the DISA job done. I was always around 9.8 to 10.1 kilometers per liter.
After first fill up after this job was done I noticed I put in less than usual, so I did the math...

I ended up with 11.1 kilometers per liter, and that's with the dyno session included.
I did not hold back on trying my new power either. I honestly expected this first fuel tank to be way worse than normal, yet the result is the other way around.

So yeah... It doesn't always throw a fault apparently, and if you do have a fault you can save on fuel by doing the repair job.

Now you can probably buy a lot of fuel for the price of two new disa valves, but that also leaves performance on the table.

Overall pretty happy, and it seems like the disa valve is a pretty common failure, could be worth checking out if you aren't getting good fuel mileage, or something just seems off.